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Soil microorganisms help transform plant inputs into mineral-associated soil organic carbon (SOC) – the largest and slowest-cycling pool of organic carbon on land. However, the microbial traits that influence this process are widely debated. While current theory and biogeochemical models have settled on carbon-use efficiency (CUE) and growth rate as positive predictors of mineral-associated SOC, empirical tests are sparse, with contradictory observations. Using 13C-labeling of an annual grass (Avena barbata) under two moisture regimes, we found that microbial traits associated with formation of 13C-mineral-associated SOC varied by soil habitat, as did active microbial taxa and SOC chemical composition. In the rhizosphere, bacterial-dominated communities with fast growth, high biomass, and high extracellular polymeric substance (EPS) production were positively associated with 13C-mineral-associated SOC. In contrast, the detritusphere held communities dominated by fungi and more filamentous bacteria, and with greater exoenzyme activity; there, 13C-mineral-associated SOC was associated with slower microbial growth and lower microbial biomass. CUE was a negative predictor of 13C-mineral-associated SOC in both habitats. Using 13C-quantitative stable isotope probing, we found that the majority of 13C assimilation in the rhizosphere and detritusphere at week 12 of the experiment was performed by very few bacterial and fungal taxa (3–5% of the total taxa that assimilated 13C). Several complementary chemical analyses (13C-NMR, FTICR-MS, and STXM-NEXAFS) suggested that SOC in the rhizosphere had a more oxidized chemical signature, while SOC in the detritusphere had a less oxidized, more lignin-like chemical signature. Our findings challenge current theory by demonstrating that microbial traits linked with mineral-associated SOC are not universal, but vary with soil habitat and moisture conditions, and are shaped by a small number of active taxa. Emerging SOC models that explicitly reflect these interactions may better predict SOC storage, since climate change causes shifts in soil moisture regimes and the ratio of living versus decaying roots.

Stabilizing climate requires reducing greenhouse gas (GHG) emissions and storing atmospheric carbon dioxide (CO2) in land or ocean systems. Soil management practices can reduce GHG emissions or sequester atmospheric CO2 into inorganic and organic forms. However, whether soil carbon strategies represent a viable and impactful climate mitigation pathway is uncertain. A specific question concerns the role that land-management practices and soil amendments can play in realizing California’s ambition for carbon neutrality by 2045. Here we examine the carbon flux impacts of soil conservation (i.e., compost, reduced tillage, cover crop) and enhanced silicate rock weathering (EW) practices at different areal extents of implementation in cropland, grassland, and savanna in California under two climate change cases. We show that with implementation areas of 15% or 50% of private cultivated land, grassland, and savanna in California, soil conservation practices alone can contribute 1.4 0.7 2.1 % ( − 1.8 − 0.9 − 2.7 Mt CO2eq y−1) and 4.6 2.3 6.9 % ( − 6.0 − 3.0 − 8.9 Mt CO2eq y−1) of the additional emissions reduction needed (beyond previous targets) to meet the 2045 net neutrality goal (−129.3 Mt CO2eq y−1), respectively, on an average annual basis, including climate uncertainty. Including EW in these scenarios increases the total contributions of management practices to 4.1 2.5 5.6 % ( − 5.2 − 3.2 − 7.3 Mt CO2eq y−1) and 13.5 8.2 18.6 % ( − 17.5 − 10.7 − 24.2 Mt CO2eq y−1), respectively, of this reduction. This highlights that the extent of implementation area is a major factor in determining benefits and that EW has the potential to make a real contribution to net reduction targets. Results are similar across climate cases, indicating that contemporary field data can be used to make future projections. With EW there remains mechanistic uncertainties, however, such as rock dissolution rate and environmental controls on weathering products, which require additional field research to improve understanding of the technological efficacy of this approach for California’s 2045 carbon neutrality goal.

Arbuscular mycorrhizal fungi (AMF) transport substantial plant carbon (C) that serves as a substrate for soil organisms, a precursor of soil organic matter (SOM), and a driver of soil microbial dynamics. Using two-chamber microcosms where an air gap isolated AMF from roots, we 13CO2-labeled Avena barbata for 6 wk and measured the C Rhizophagus intraradices transferred to SOM and hyphosphere microorganisms. NanoSIMS imaging revealed hyphae and roots had similar 13C enrichment. SOM density fractionation, 13C NMR, and IRMS showed AMF transferred 0.77 mg C g-1 of soil (increasing total C by 2% relative to non-mycorrhizal controls); 33% was found in occluded or mineral-associated pools. In the AMF hyphosphere, there was no overall change in community diversity but 36 bacterial ASVs significantly changed in relative abundance. With stable isotope probing (SIP)-enabled shotgun sequencing, we found taxa from the Solibacterales, Sphingobacteriales, Myxococcales, and Nitrososphaerales (ammonium oxidizing archaea) were highly enriched in AMF-imported 13C (> 20 atom%). Mapping sequences from 13C-SIP metagenomes to total ASVs showed at least 92 bacteria and archaea were significantly 13C-enriched. Our results illustrate the quantitative and ecological impact of hyphal C transport on the formation of potentially protective SOM pools and microbial roles in the AMF hyphosphere soil food web.

In the Sacramento–San Joaquin Delta (Delta), widespread drainage of historical wetlands has led to extensive subsidence and peat carbon losses, as well as high ongoing greenhouse gas (GHG) emissions. Large-scale wetland restoration and conversion to rice fields has the potential to mitigate these effects while conferring flood protection and creating habitat for wetland species. To explore the scale of these potential benefits, this study evaluated the effects of seven Delta-wide land-use scenarios on carbon stocks, land-surface elevation, GHG emissions, and habitat. Peat mapping and data from peat cores indicate that soil carbon stocks have decreased between the early 1800s and 2010s from 288 ± 15 to 145 ± 14 million metric tons (Mt) of carbon (C). If existing land uses continue, the Delta could lose an additional 8.3 Mt C during the coming 40 years, equal to average GHG emissions of 1.2 Mt CO2 equivalents (CO2e) yr-1. Future restoration and rice-farming scenarios indicate that wetland restoration could theoretically halt GHG emissions, converting the Delta from a large GHG source to a weak net source or sink. Across three future scenarios based on existing restoration targets, wetland creation and conversion to rice fields reduced GHG emissions by 0.39 to 0.67 Mt CO2e yr-1, with per-area benefits of 16 to 28 t CO2e per hectare (ha) yr-1. Differences among scenarios in extents of wetland types influenced their relative benefits for different management goals. Tidal restoration and conversion to rice fields enhanced habitat benefits and offered a source of agricultural income, but with reduced GHG mitigation compared with conversion to peat-building wetlands. This highlights the importance of clear objectives when developing land-use plans. A strategic land-management portfolio that includes rice fields and both impounded and tidal wetlands could be designed to provide GHG and subsidence mitigation while offering a diverse suite of benefits for ecosystems and people.

The long-standing assumption that aboveground plant litter inputs have a substantial influence on soil organic carbon storage (SOC) and dynamics has been challenged by a new paradigm for SOC formation and persistence. We tested the importance of plant litter chemistry on SOC storage, distribution, composition, and age by comparing two highly contrasting ecosystems: an old-growth coast redwood (Sequoia sempervirens) forest, with highly aromatic litter, and an adjacent coastal prairie, with more easily decomposed litter. We hypothesized that if plant litter chemistry was the primary driver, redwood would store more and older SOC that was less microbially processed than prairie. Total soil carbon stocks to 110 cm depth were higher in prairie (35 kg C m-2) than redwood (28 kg C m-2). Radiocarbon values indicated shorter SOC residence times in redwood than prairie throughout the profile. Higher amounts of pyrogenic carbon and a higher degree of microbial processing of SOC appear to be instrumental for soil carbon storage and persistence in prairie, while differences in fine-root carbon inputs likely contribute to younger SOC in redwood. We conclude that at these sites fire residues, root inputs, and soil properties influence soil carbon dynamics to a greater degree than the properties of aboveground litter.

Models project that climate change is increasing the frequency of severe storm events such as hurricanes. Hurricanes are an important driver of ecosystem structure and function in tropical coastal and island regions and thus impact tropical forest carbon (C) cycling. We used the DayCent model to explore the effects of increased hurricane frequency on humid tropical forest C stocks and fluxes at decadal and centennial timescales. The model was parameterized with empirical data from the Luquillo Experimental Forest (LEF), Puerto Rico. The DayCent model replicated the well-documented cyclical pattern of forest biomass fluctuations in hurricane-impacted forests such as the LEF. At the historical hurricane frequency (60 years), the dynamic steady state mean forest biomass was 80.9 ± 0.8 Mg C/ha during the 500-year study period. Increasing hurricane frequency to 30 and 10 years did not significantly affect net primary productivity but resulted in a significant decrease in mean forest biomass to 61.1 ± 0.6 and 33.2 ± 0.2 Mg C/ha, respectively (p < 0.001). Hurricane events at all intervals had a positive effect on soil C stocks, although the magnitude and rate of change of soil C varied with hurricane frequency. However, the gain in soil C stocks was insufficient to offset the larger losses from aboveground biomass C over the time period. Heterotrophic respiration increased with hurricane frequency by 1.6 to 4.8%. Overall, we found that an increasing frequency of tropical hurricanes led to a decrease in net ecosystem production by − 0.2 ± 0.08 Mg C/ha/y to − 0.4 ± 0.04 Mg C/ha/y for 30–10-year hurricane intervals, respectively, significantly increasing the C source strength of this forest. These results demonstrate how changes in hurricane frequency can have major implications for the tropical forest C cycle and limit the potential for this ecosystem to serve as a net C sink. [ABSTRACT FROM AUTHOR]

There are major gaps in our understanding of how Mediterranean ecosystems will respond to anticipated changes in precipitation. In particular, limited data exists on the response of deep soil carbon dynamics to changes in climate. In this study we wanted to examine carbon and nitrogen dynamics between topsoils and subsoils along a precipitation gradient of California grasslands. We focused on organic matter composition across three California grassland sites, from a dry and hot regime (~ 300 mm precipitation; MAT: 14.6 ∘ C ) to a wet, cool regime (~ 2160 mm precipitation/year; MAT: 11.7 ∘ C ). We determined changes in total elemental concentrations of soil carbon and nitrogen, stable isotope composition (δ13C, δ15N), and composition of soil organic matter (SOM) as measured through Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS) to 1 m soil depth. We measured carbon persistence in soil organic matter (SOM) based on beta ( β ), a parameter based on the slope of carbon isotope composition across depth and proxy for turnover. Further, we examined the relationship between δ15N and C:N values to infer SOM's degree of microbial processing. As expected, we measured the greatest carbon stock at the surface of our wettest site, but carbon stocks in subsoils converged at Angelo and Sedgwick, the wettest and driest sites, respectively. Soils at depth (> 30 cm) at the wettest site, Angelo, had the lowest C:N and highest δ15N values with the greatest proportion of simple plant-derived organic matter according to DRIFTS. These results suggest differing stabilization mechanisms of organic matter at depth across our study sites. We infer that the greatest stability was conferred by associations with reactive minerals at depth in our wettest site. In contrast, organic matter at our driest site, Sedgwick, was subject to the most microbial processing. Results from this study demonstrate that precipitation patterns have important implications for deep soil carbon storage, composition, and stability. [ABSTRACT FROM AUTHOR]

Aim: Mycorrhizal fungi play key roles in the functioning of terrestrial ecosystems. The main types of mycorrhizal associations are arbuscular mycorrhizae, ectomycorrhizae, ericoid mycorrhizae and orchid mycorrhizae. Previous studies have shown that the abundance of plants with different types of mycorrhizal associations change gradually along latitudinal and altitudinal gradients driven by the effects of climate and soil nutrients. We aimed to understand how altitude and climatic and soil variables shape the distribution patterns of tropical plant mycorrhizal types and nitrogen‐fixing plants along altitudinal gradients in the Andes. Location: Colombian Andean mountain range. Time Period: Present day. Major Taxa Studied: Plants (vascular and non‐vascular). Methods: We used a herbarium plant records database and assigned mycorrhizal type to each plant species based on the available literature. Bioclimatic and soil variables were also compiled at a resolution of 10 km. We calculated the proportion of each mycorrhizal association type per grid cell and created a diversity index to explore their spatial distribution and association with abiotic factors based on LMs. Results: The diversity of mycorrhizal associations increased with altitude and peaked around 3000 m, in an ecotone belt known as the subpáramo recognised by the high abundance of Ericaceae species. Soil carbon stock and soil total nitrogen were also positively correlated with the diversity of mycorrhizal types. Moreover, the abundance of arbuscular mycorrhizal plants was highest at low elevations and increased with the proportion of nitrogen‐fixing plants per cell. Main Conclusions: Our results indicate that mycorrhizal associations gradually change along altitudinal gradients in the tropical Andes. Climatic factors and the interactions between climatic and edaphic factors have the greatest explanatory power to predict the distribution of types of mycorrhizal associations along the altitudinal gradient. Based on these results we expect that climate change could potentially alter the distribution of mycorrhizal types in tropical mountains with unknown consequences for ecosystem functions. [ABSTRACT FROM AUTHOR]

Enhancing terrestrial carbon (C) stock through ecological restoration, one of the prominent approaches for natural climate solutions, is conventionally considered to be achieved through an ecological pathway, i.e., increased plant C uptake. By conducting a comprehensive regional survey of 4279 1 × 1 m² plots at 517 sites across China's drylands and a 13-y manipulative experiment in a semiarid grassland within the same region, we show that greater soil and ecosystem C stocks in restored than degraded lands result predominantly from decreased surface soil C loss via suppressed wind erosion. This biophysical pathway is always overlooked in model evaluation of land-based C mitigation strategies. Surprisingly, stimulated plant growth plays a minor role in regulating C stocks under ecological restoration. In addition, the overall enhancement of C stocks in the restored lands increases with both initial degradation intensity and restoration duration. At the national scale, the rate of soil C accumulation (7.87 Tg C y-1) due to reduced wind erosion and surface soil C loss under dryland restoration is equal to 38.8% of afforestation and 56.2% of forest protection in China. Incorporating this unique but largely missed biophysical C-conserving mechanism into land surface models will greatly improve global assessments of the potential of land restoration for mitigating climate change. [ABSTRACT FROM AUTHOR]

Plants typically interact with multiple, co‐occurring symbionts, including arbuscular mycorrhizal (AM) fungi which can form networks, connecting neighbouring plants. A characteristic aspect of the mycorrhizal symbiosis is the bidirectional exchange of nutrients between host plants and fungal partners. Concurrent interactions with competing organisms such as aphids or potato cyst nematodes (PCN) can disrupt the carbon‐for‐nutrient exchange between plants and AM fungi. However, the role of mycorrhizal networks (MNs) in mediating these interactions remains unclear. Using isotope tracing in multi‐plant experimental systems, we investigated the movement of plant photosynthates and fungal‐acquired soil phosphorus through MNs and the interactive effects of PCN infection on this. We found evidence of preferential allocation of fungal‐acquired phosphorus to plants that were not infected by PCN compared with infected neighbours. Contrary to previous findings using single plants, we did not detect a PCN‐induced reduction in the amounts of plant carbon delivered to AM fungi in multi‐plant systems. However, the MN(s) moved plant‐fixed carbon away from PCN‐infected host plants, regardless of the PCN infection status of the neighbouring plant host. Our work highlights the responsiveness of MNs to interactions with below‐ground organisms. It also strengthens the argument for a more mycocentric view of AM–plant symbioses. Experimental designs of increasing ecological complexity are needed for a more comprehensive understanding of the carbon‐for‐nutrient dynamics in AM fungi–plant networks. This will, in turn, elucidate the role of AM fungi in terrestrial carbon cycling and their function in agricultural systems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Introduction: Plastic film mulching has been widely used to enhance soil hydrothermal conditions and increase crop yields in cool, semi-arid areas. However, its impact on soil microbial carbon metabolic activity and functional diversity during plant growth remains unclear despite their important roles in nutrient cycling and soil quality evaluation. Methods: This study used the Biolog EcoPlate technique to investigate the dynamics and driving factors of soil microbial carbon metabolic activity and functional diversity at different maize growth stages following plastic film mulching. Results and discussion: The results revealed that film mulching significantly increased microbial carbon metabolic activities [represented by average well color development (AWCD)] by 300% at the seedling stage and by 26.8% at maturity but decreased it by 47.4% at the flowering stage compared to the control (without mulching). A similar trend was observed for the microbial functional diversity index. Redundancy analysis identified soil moisture (SM), soil temperature (ST), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria amounts as the primary factors influencing changes in soil microbial carbon source utilization. The mulch treatment significantly increased SM at all growth stages, while its warming effect disappeared at the flowering stage. Soil DOC, MBC, and bacterial populations were notably higher under mulching at the seedling and maturity stages but lower at the flowering stage. Pearson correlation analysis showed that changes in SM, ST, DOC, MBC, and bacterial populations positively correlated with the utilization of all carbon source classes, AWCD, and functional diversity indexes after film mulching. Furthermore, maize grain yield and water use efficiency increased by 142 and 129%, respectively, following film mulching. In conclusion, plastic film mulching enhanced soil microbial carbon metabolic activity and functional diversity at the seedling and maturity stages, improving crop yields in cool, semi-arid areas. Furthermore, the decrease in soil carbon metabolic capacity at flowering stage highlights that supplementing soil carbon sources should be considered after continuous film mulching to sustain or enhance farmland productivity and soil quality. [ABSTRACT FROM AUTHOR]

Fibrous and pioneer roots are essential in the uptake and transport of water and nutrients from the soil. Their dynamic may be influenced by the changing of soil physicochemical properties due to the addition of biochar, which, in turn, has been shown to improve plant growth and productivity in the short term. However, the long-term effects of biochar application on root dynamics are still widely unknown. In this study, we aimed to investigate the long-term effects of biochar application on grapevine fibrous and pioneer root dynamics and morphological traits in relation to soil characteristics. To this aim, grapevine plants amended in 2009 and 2010 respectively with one and two doses of biochar, were analyzed in their fibrous and pioneer root production and turnover rate, standing biomass, length, and specific root length, over two growing seasons. Our findings demonstrate that in the long term, biochar application significantly increased soil pH, nutrient availability, and water-holding capacity causing a decrease in the production of fibrous and pioneer roots which is reflected in a reduction of the root web characterized though by a higher turnover rate. Furthermore, we observed that these root morpho-dynamical changes were of higher magnitude in the upper soil layers (0-20 cm) and, at least in the long term, with no significant difference between the two doses. These results suggest that in the long term, biochar can be a powerful tool for improving soil quality, which in turn lowers carbon-cost investment toward the root production and maintenance of a reduced root web that might be directed into grapevine growth and productivity. Such effects shed some light on the root plastic and functional adaptation to modified soil conditions facilitated by the long-term application of biochar, which can be used for implementing adaptive agricultural practices to face the current climate change in a frame of sustainable agricultural policies. [ABSTRACT FROM AUTHOR]

The importance of woody detritus as a source of soil organic matter is not well constrained. We quantified the recovery of 13C derived from isotopic-enriched sugar maple wood in various C fractions of two temperate forest soils in central New York, USA. Decay rates of small woody debris were quite rapid (k = 0.362 to 0.477 per year) and after 10 years less than 1% of the original wood mass remained in incubation bags. After six years we recovered only 0.26% (± 0.025) of the added 13C in the upper 5 cm of underlying soil. After 10 years this recovery declined to 0.11% (± 0.020) indicating substantial lability of retained SOC; most of this decline occurred from year 6 to 8 in the 1–5 cm depth increment, suggesting that the residue was quite stable at 10 years. The largest fraction of 13C was recovered in microaggregates (45%), especially those occluded within macroaggregates (30%), with a smaller proportion associated with the silt + clay fraction (20%). These proportions did not change significantly from year 6 to 10. Faster decay and higher 13C recovery were coincident with abundant saproxylic invertebrates from Scarabaeidae at one of the sites. We conclude that small woody debris is a minor source of stable SOC in these temperate forests (that is, less than 1% of annual SOC accumulation). [ABSTRACT FROM AUTHOR]

In the Northern Hemisphere, anthropogenic nitrogen (N) deposition contributed to the enhancement of the global terrestrial carbon (C) sink, partially offsetting CO2 emissions. Across several long‐term field experiments, this ecosystem‐level response was determined to be driven, in part, by the suppression of microbial activity associated with the breakdown of soil organic matter. However, since the implementation of emission abatement policies in the 1970s, atmospheric N deposition has declined globally, and the consequences of this decline are unknown. Here, we assessed the response of soil C storage and associated microbial activities, in a long‐term field study that experimentally increased N deposition for 24 years. We measured soil C and N, microbial activity, and compared effect sizes of soil C in response to, and in recovery from, the N deposition treatment across the history of our experiment (1994–2022). Our results demonstrate that the accumulated C in the organic horizon has been lost and exhibits additional deficits 5 years post‐termination of the N deposition treatment. These findings, in part, arise from mechanistic changes in microbial activity. Soil C in the mineral soil was less responsive thus far in recovery. If these organic horizon C dynamics are similar in other temperate forests, the Northern Hemisphere C sink will be reduced and climate warming will be enhanced. [ABSTRACT FROM AUTHOR]

The efficient use of vinasse, the primary byproduct of sugarcane ethanol production, is important for the economic and environmental sustainability of the industry. Few studies have quantified the soil health response to long‐term vinasse application, even though this byproduct is generally applied as a potassium (K) source in sugarcane fields. The Soil Management Assessment Framework (SMAF) was used to assess the integrated soil health response in soils with contrasting textures. Chemical, physical, and biological indicators were selected, measured, and integrated into a soil health index for clay‐ and sandy‐textured soils in Brazil. Overall, the application of vinasse improved soil health components in both soils. The results showed that the benefits of vinasse go beyond increasing the K content. Vinasse application showed increased soil organic carbon content, nutrient recycling, and soil physical quality. The long‐term application of vinasse increased the soil health from 49% to 62% in the clayey soil and from 43% to 61% in the sandy clay soil. The findings therefore revealed the potential of vinasse application to reduce the need for synthetic fertilizer and promote the circular economy and soil health regardless of soil type. This study verifies that the long‐term application of vinasse to sandy‐ and clay‐texture soils in Brazil has both economic and environmental benefits because it recycles an important ethanol byproduct and enhances soil health. [ABSTRACT FROM AUTHOR]

Organic manure amendments into the rainfed agricultural soil could change the carbon saturation deficit. This study was conducted in the central Himalayan region of India to assess the impact of varying quantities of farmyard manure (FYM) and vermicompost (VC) on changes of soil carbon saturation deficit in the rainfed agricultural system. The experimental plots with three replications and three different amendment rates, such as 15, 30, and 60 Mg ha−1 of FYM and VC were used on the traditional paddy-wheat-finger millet-fallow cropping system. The soil amended with FYM and VC showed significant (p <.05) variations in the soil carbon content, nitrogen content, total microbial activity, β-glucosidase activity, and acid phosphatase activity with an increasing rate of both the manures in each cropping season. The mean soil carbon saturation deficit values varied from 25 to 36% and 19 to 28% in the first year cropping and second year cropping seasons, respectively. Our results demonstrate that the VC amendment was better than FYM for the accumulation of more carbon content in the rainfed agricultural soils of Himalaya, whereas the organic manure amendment rates must be considered for climate change impact mitigation action policy in the future. [ABSTRACT FROM AUTHOR]

Soil carbon decomposition is primarily driven by microbial activities and is regulated by factors which stimulate or impede microbial functions. Deep podzolized carbon (DPC), found in the United States Southeastern Coastal Plain, is situated well below the soil surface in horizons isolated from active plant input. This carbon is characterized by high C:N ratios (>30) which could reflect nutrient limitation of microbial decomposition. To uncover the energy or nutrient limitation on DPC degradation, a 90‐day priming experiment was performed with soils from the surface horizon and DPC horizons (i.e., Bh1 and Bh2) received the additions of 13C‐labeled alanine and glucose. This resulted in prominent priming effects: addition of alanine increased basal decomposition of soil organic carbon by 918 ± 51% and 737 ± 7% in Bh2 and Bh1, respectively. Glucose relative priming was 505 ± 28% in Bh1 and 606 ± 77% of basal respiration in Bh2. These strong responses to substrate input highlight the susceptibility of DPC to loss when microbial carbon and nutrient constraints are alleviated. After 90 days, glucose addition increased the microbial biomass in DPC horizons relative to alanine addition, with the latter showing no difference from ultrapure‐water control. The response of the microbial biomass indicates constraint by a lack of energy sources both by the paucity of labile substrates and reduced availability of organic matter as a result of podzolization. Our study has important implications for predicting the response of DPC in Coastal Plain soils in the context of land management and global change. Plain Language Summary: In the United States Southeastern Coastal Plain deep podzolized carbon (DPC) is found well below the soil surface, this organic matter has a high ratio of carbon to nitrogen (C:N) and is highly associated with aluminum. This suggests that microbes struggle to decompose it due to a shortage of compounds which provide nutrients such as nitrogen to create enzymes, and energy‐providing compounds such as glucose. To understand how DPC breakdown can be affected by energy or nutrient availability, we conducted a 90‐day incubation experiment where we added specially labeled compounds (alanine and glucose) to soils taken from the surface (A) and DPC layers (Bh1 and Bh2). We found that adding these compounds caused a significant increase in microbial activity, especially in the DPC layers. We also observed a greater increase in microbial growth when glucose was added compared to alanine, which did not show much difference from the water‐addition control. This suggests that the lack of easily digestible nutrients and the protection from metal association restricts microbial growth and activity in these DPC layers. Understanding deep carbon response to changes in elemental flows is crucial for managing land and anticipating changes in response to global environmental shifts. Key Points: Glucose and alanine addition to deep podzolized carbon (DPC) soils resulted in relative priming effects greater than 500% basal respirationHigh priming response suggests DPC is vulnerable to destabilization when exposed to labile substratesMicrobial nutrient and energy limitations are key to the persistence of DPC [ABSTRACT FROM AUTHOR]

Forest management practices influence soil fertility and nutrient availability through different mechanisms. Despite the importance of soil fertility and nutrient availability in forest ecosystems, there is limited research on the effects of management practices on soil properties in mixed-species forests. This study investigates the impact of different management types (community forest area (CFA), Forest area (FR), and Sacred Grove (SG)) on soil physicochemical properties, organic matter, and organic carbon storage in Benue State, Nigeria. Soil samples from three forest management types were collected and analyzed using established laboratory standard procedures. Descriptive statistics, analysis of variance, and correlation analysis revealed significant differences (p<0.05) in soil texture, pH, organic carbon, and total nitrogen across the management types. CFA and FR were predominantly sandy loam soils, while SG had higher clay loam content. Soil pH ranged from 4.82 - 6.07 with SG having the highest pH value (6.07). The forest reserve has the highest sand content (75.0%) and SG has the highest clay content (34.6%). The highest soil organic matter content (3.13%) was recorded under CFA, while organic carbon of 1.83% was recorded under FR. The highest values of Mg (0.97 Cmol/kg), N (0.28%), P (3.77 ppm), K (0.20 Cmol/kg) Na (0.18 Cmol/kg), and Ca (1.24 Cmol/kg) were at their peak under the Sacred grove management types. Thus, the various types of forest management significantly impact soil properties and organic carbon content in the study area. It is recommended that SG or CFA management should be adopted for forest resource conservation in the study area. [ABSTRACT FROM AUTHOR]

Although regional soil mapping is commended, site-specific studies are required for mapping and quantifying soil organic carbon (SOC) stocks at a landscape scale for management and rehabilitation purposes. Site-specific studies are especially important in remote mountainous areas where soil data are largely absent. The aim of this study was to quantify and map the SOCs of an alpine region in the Maloti-Drakensberg. The samples collected in-field along with digital soil mapping techniques were used to map the SOCs. The models were SoLIM's rule based (RB) and sample based (SB), random forest (RF), least absolute shrinkage and selection operator (LASSO), regression kriging with cubist (RK-CB) and universal kriging. From the results, the mean SOC for the validation dataset of the study area was 12.44 kg organic carbon (OC) m−2. The best model was RK-CB (mean = 12.43 kg OC m−2), with R2 and root mean square error (RMSE) of 0.61 and 4.01 kg OC m−2, respectively. The underperforming model was SoLIM-RB (mean = 13.27 kg OC m−2), with R2 = 0.27 and RMSE = 5.75 kg OC m−2. The RK-CB model from this study significantly outperformed a region-scaled model, proving that site-specific studies in small catchments should be preferred to, especially if there are no soil data available for that area. [ABSTRACT FROM AUTHOR]

Research evaluating the impact of silvopastoral systems on physical and biological properties of Amazonian soils is scarce. Thus, this study aimed to compare the soil carbon storage potential and physical and chemical soil properties of silvopastoral systems (SPS) and conventional pastoral systems (CPS) in the San Martin region of Peru. Using the Walkley and Black method, we analyzed soil organic matter at two different depths (0–15 cm and 15–30 cm). In addition, bulk density, soil moisture, total porosity, and mechanical resistance were measured in both systems. The highest (P < 0.05) carbon stocks were reported at 0–15 cm of depth with values of 31.4 Mg ha−1 and 34.4 Mg ha−1 for CPS and SPS, respectively. At 15–30 cm depth, the total carbon stock was higher for SPS, with 29.12 Mg ha−1, than for CPS, which had 26.4 Mg ha−1. Despite the absence of statistically significant differences, soil carbon stocks were higher in SPS. No significant differences in soil moisture were found between systems, although soil moisture was slightly greater in SPS than CPS (28 and 25%, respectively). The CPS had 59% of the total porosity, which was higher than the SPS. Mechanical resistance was lower in SPS (2.15 kg/cm2) than in CPS (2.33 kg/cm2) at 10 cm of depth. These results indicated that the SPS has the potential to store more carbon and improve physical and chemical traits in the soil than the CPS. [ABSTRACT FROM AUTHOR]

Abstract There is growing interest in intercropping as a practice to increase productivity per unit area and ecosystem functioning in agricultural systems. Relay intercropping with soy and winter wheat may benefit soil health due to increased diversity and longer undisturbed soil cover, yet this remains largely unstudied. Using a field experiment in Eastern Germany, we studied the temporal dynamics of chemical, biological, and physical indicators of soil health in the topsoil over a year of cultivation to detect early effects of soy-wheat relay intercropping compared to sole cropping. Indicators included microbial abundance, permanganate-oxidizable carbon, carbon fractions, pH, and water infiltration. Relay intercropping showed no unique soil health benefits compared to sole cropping, likely affected by drought that stressed intercropped soy. Relay intercropping did, however, maintain several properties of both sole crops including an increased MAOM C:N ratio and higher soil water infiltration. The MAOM C:N ratio increased by 4.2 and 6.2% in intercropping and sole soy and decreased by 5% in sole wheat. Average near-saturated soil water infiltration rates were 12.6, 14.9, and 6.0 cm hr−1 for intercropping, sole wheat, and sole soy, respectively. Cropping system did not consistently affect other indicators but we found temporal patterns of these indicators, showing their sensitivity to external changes.

Societal Impact Statement As cities grow, it is essential to understand how landscape management decisions in urban spaces alter ecosystem function. This study demonstrates that the ubiquitous practice of long‐term leaf litter removal in suburbs, even in relatively small patches of a yard, reduces the soil's ability to cycle nutrients in plant litter and results in lower amounts of carbon stored in the soil. Even two years of retaining leaves where they previously were removed is insufficient to restore decomposition rates or carbon pools. This research is an important step in creating best practices for litter management to maintain essential ecosystem functions, like carbon sequestration, water holding capacity, and soil fertility. Summary Seasonal senesced leaf litter removal eliminates considerable organic material from suburban soils annually. We test if this disturbance alters decomposition and carbon cycles and depletes soils of organic matter over time, creating persistent legacy effects. We used a factorial experimental design to implement 1–2 years of current leaf litter manipulations (remove or retain fallen leaves) within historically raked and unraked areas in suburban Maryland yards. We then compared total organic soil carbon and decomposition using a standardized substrate decomposition methodology (Tea Bag Index) across treatment plots. Long‐term litter removal in suburban yards reduced decomposition rates by 17% and total soil organic carbon concentration by up to 24% compared to areas where leaf litter was retained in situ. In contrast, short‐term management changes (1–2 years) did not significantly impact decomposition rates or total organic soil carbon concentrations. Our findings suggest that long‐term suburban litter raking creates legacy effects that alter decomposition and carbon storage process trajectories that are not easily reversed. This is important in understanding urban ecosystem function and sustainable management.

The words we choose to describe our research ultimately directs its course. A dominant term in soil science now, is 'sequestration', referring to the removal of carbon (C) from air and its irreversible seclusion in soil, ideally as stable soil organic carbon (SOC). An emerging view, however, now sees SOC as an inherently dynamic assemblage of forms, all potentially vulnerable to decay, with no discrete, measurable fraction holding C in 'sequestered' form. Rather than speaking of C 'sequestration', then, we might refer instead to SOC 'stewardship'. This word, now, enfolds the entire spectrum of SOC, not merely some elusive 'persistent' or 'stable' fraction, perhaps redirecting inquiry; for example, does C need to be 'sequestered' in stable form for SOC to serve as effective repository of excess atmospheric CO2? 'Stewardship' explicitly accepts the relentless turnover of SOC, emphasizing the need to manage not only fixed stocks of C, but also the cyclical flows of C through ecosystems that drive their functions. Among other benefits, 'stewardship' might motivate us to consider all functions of SOC (not only climate mitigation), consider the entire C cycle (not only enhancing soil C), and preserve existing troves of SOC (not only augmenting them in selected places.) Perhaps most fundamentally, by its etymology, 'stewardship' poses a compelling, timeless question: for whom do we steward SOC? Asking why look after SOC, not only reflects our own underlying quest for resilience, but also expands our potential audience and entices the more creative minds that must succeed us. Although 'stewardship' may elicit new and fruitful inquiry, we may need to look for words even more evocative, more alluring, more true to our mandate of living well within the circling C that must always sustain us. [ABSTRACT FROM AUTHOR]

Land management practices that overlook soil limitations and potential have led to varying degrees of degradation. This study evaluates the carbon content in chemical and oxidisable soil fractions across different pasture recovery periods, comparing them to secondary forests. The management practices assessed include the following: secondary forest (SF), perennial pasture (PP), perennial pasture recovered five years ago (P5), and perennial pasture recovered eight years ago (P8), all on Plinthosols. We analysed carbon levels in oxidisable fractions and humic substances at depths of 0–0.10 m, 0.10–0.20 m, 0.20–0.30 m, and 0.30–0.40 m. The SF and P8 areas showed the highest organic matter content within the humic fractions, compared to the PP and P5 areas. Additionally, the P8 area demonstrated an increase in the labile and moderately recalcitrant fractions of organic matter, standing out among the different fractions evaluated. The multivariate principal component analysis indicated that P8 has the greatest impact on soil quality, followed by FS, P5, and PP. The pasture recovery over the past eight years has significantly improved soil carbon accumulation, highlighting the benefits of land restoration. [ABSTRACT FROM AUTHOR]

Composting organic matter can lower the global warming potential of food and agricultural waste and provide a nutrient-rich soil amendment. Compost applications generally increase net primary production (NPP) and soil water-holding capacity and may stimulate soil carbon (C) sequestration. Questions remain regarding the effects of compost nitrogen (N) concentrations and application rates on soil C and greenhouse gas dynamics. In this study, we explored the effects of compost with different initial N quality (food waste versus green waste compost) on soil greenhouse gas fluxes, aboveground biomass, and soil C and N pools in a fire-impacted annual grassland ecosystem. Composts were applied annually once, twice, or three times prior to the onset of the winter rainy season. A low-intensity fire event after the first growing season also allowed us to explore how compost-amended grasslands respond to burning events, which are expected to increase with climate change. After four growing seasons, all compost treatments significantly increased soil C pools from 9.5 ± 0.9 to 30.2 ± 0.7 Mg C ha−1 (0–40 cm) and 19.5 ± 0.9 to 40.1 ± 0.7 Mg C ha−1 (0–40 cm) relative to burned and unburned controls, respectively. Gains exceeded the compost-C applied, representing newly fixed C. The higher N food waste compost treatments yielded more cumulative soil C (5.2–10.9 Mg C ha−1) and aboveground biomass (0.19–0.66 Mg C ha−1) than the lower N green waste compost treatments, suggesting greater N inputs further increased soil stocks. The three-time green waste application increased soil C and N stocks relative to a single application of either compost. There was minimal impact on net ecosystem greenhouse gas emissions. Aboveground biomass accumulation was higher in all compost treatments relative to controls, likely due to increased water-holding capacity and N availability. Results show that higher N compost resulted in larger C gains with little offset from greenhouse gas emissions and that compost amendments may help mediate effects of low-intensity fire by increasing fertility and water-holding capacity. [ABSTRACT FROM AUTHOR]

Trees species-based carbon-stock estimates are rare in Nigeria. Therefore, we investigated individual trees’ abilities using non-destructive approach with systematic sampling technique. One hundred circular plots were laid, using pre-classified Landsat-OLI/TC image of Borgu Sector. Plot centres were located and marked with global positioning system receiver. The main plots with 12.61 m radius (500 m²) were subdivided into subplots of 5.64 m radius (100 m²). Trees with diameter at breast height (Dbh) ≥10 cm were measured in the main plots, while trees with ≥5 but <10 cm Dbh were considered in the subplots. Species identification and measurements were executed. Core samples were collected at breast height using 5 mm increment borer. Core samples were oven-dried at 70°C to constant weights. Wood densities were then calculated as oven-dried weights/fresh volumes. Above-ground carbon were determined as 50%-biomass. Soil samples were diagonally collected at three points within sample plots at two depths, using core sampler and soil auger for 600 samples. Samples were air-dried, ground and sieved through a 2 mm sieve. Core sampler and rings were used for measuring bulk density. Samples were oven-dried for 24 hours at 105°C. Soil organic matter was determined by Fe2SO4 titration of an acid-dichromate digestion, and organic carbon concentration was calculated. Tree carbon data were analyzed using allometric equations involving wood density, Dbh and tree-height and ANOVA. Thirty-five tree species in 16 families were encountered. Detarium microcarpum was the most frequently occurring (18.8%). Tree species richness, diversity and importance value indices were 2.852, 4.779, and 41.76 ± 35.41, respectively. Vitellaria paradoxa and Afzelia africana were the only vulnerable species identified. Trees with larger-Dbh sequestered more carbon. Consequently, Adansonia digitata with a mean Dbh of 111.4 ± 0.00 cm sequestered the highest amount (2.8 tons/ha), which were significantly different from others (p < .05). Securidaca longipendiculata had the least carbon stock (0.001 ton/ha). Meanwhile, soil carbon were higher in plots dominated by Acacia kosiensis, V. paradoxa, and Grewia mollis at 0.006758 ton/ha, averagely 0.073 ± 0.0021 ton/ha of carbon-stock and CO2 of 0.271 ± 0.010 ton/ha sequestered, respectively. [ABSTRACT FROM AUTHOR]

Background and aims: Several lines of evidence indicate that arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) associations can have different effects on soil nutrient dynamics. Some lineages of ECM fungi can extract N from organic matter, with varying impacts on decomposers, soil carbon pools, mineral N availability, and plants that lack ECM. However, these effects are not always observed, and it is not clear how they are mediated by environmental factors. Methods: We used Plant Root Simulator probes to compare soil availability of a wide range of nutrients beneath replicated 30-yr old plantations of Chilean Nothofagus (ECM) and Cupressaceae (Austrocedrus, Fitzroya: AM) on a lowland temperate site. Probes were buried for two 8-week periods in early spring and late summer. We also compared understorey composition beneath plantations, to test for evidence of different successional trajectories beneath Nothofagus and Cupressaceae. Results: Soil organic carbon, total N and total phosphorus did not differ significantly between Nothofagus and Cupressaceae stands. Redundancy analysis revealed significant effects of both plantation type (Nothofagus vs. Cupressaceae) and season on overall mineral nutrient availability. Mineral N availability did not differ significantly between Nothofagus and Cupressaceae plots, but pH and calcium availability were significantly lower beneath Nothofagus. Manganese (Mn) was much more available beneath Nothofagus stands, which might reflect abundant Mn-peroxidase, a key enzyme involved in breakdown of lignin by ECM fungi. Understorey composition varied considerably between individual plantations, but did not differ significantly between Nothofagus and Cupressaceae plantations. Conclusions: Despite an overall effect on the stoichiometry of nutrient availability, we found little evidence of modification of the local N cycle by ECM fungi, or of divergent regeneration patterns beneath AM and ECM plantations. This might reflect the relatively N-rich character of this site, and/or mycorrhizal effects being counteracted by leaf trait differences between Chilean Cupressaceae and Nothofagus species. [ABSTRACT FROM AUTHOR]

It is well known that long-term chemicalised agricultural practices harmfully affect soil health and prevent sustainable management of fertility in crop fields, including that of plantation crops. Accordingly, an investigation was carried out to check how soil fertility characteristics such as soil pH, soil mineral nutrient and organic carbon content are altered in long-term chemicalised rubber plantations of Kerala, located in the ecologically sensitive Western Ghats of South India. Soil fertility status concerning soil types in the Rubber fields (USDA soil orders - suborders) such as Inceptisols - Oxic Dystrudepts (IOD), Ultisols - Ustic Haplohumults (UUH), Ultisols - Typic Kandiustults (UTK) and Mollisols - Pachic Argiustolls (MPA) involving six soil series are critically analysed. A negative impact of long-term chemicalised agriculture was visible in low soil pH and nutrient levels. In general, rubber fields in the region, even in the generally alkaline Mollisols, showed a pH of 6.23. The soils showed reduced nutrient and carbon content and a comparatively poor soil fertility index specific to soil types. The soil available NPK and soil total cations were found to be comparatively low and soil specific. However, rubber fields in Mollisols were significantly higher in STK, STMg, STCa, and STNa while those in Ultisols were significantly higher in SAP and SAK than other soil orders. The Inceptisols were significantly higher in SAN, STP, and soil organic carbon than others. Therefore, balanced fertilizer application concerning soil types per proper soil fertility monitoring has become significant to sustainable soil productivity management in rubber plantations. [ABSTRACT FROM AUTHOR]

Cover crops between rows in orchards can improve the development of soil resources and increase agricultural productivity. However, there have been few reports of cover crops that can act as a "green manure" in apple orchards across arid and semiarid zones. This study investigated the effects of planting interrow vegetation on soil properties and apple tree performance during a 32-month experiment. There were six treatments: clean cultivation as a control; natural grass planting; planting with ryegrass; planting with alfalfa; planting with tall fescue; and planting with villous wild pea cover crops. The treatments primarily affected the 0- to 20-cm surface soil layer. Soil carbon, nitrogen, and enzyme levels initially decreased (during the first 12-24 months); then, they increased (24-32 months). The cover crops significantly increased nutrient contents (soluble organic carbon, microbial carbon and nitrogen, alkaline dissolved nitrogen, nitrate nitrogen, and ammonium nitrogen) in the 0- to 20-cm soil layer by more than 19.6% and increased the related enzyme activities by more than 25.2%. The alfalfa and wild pea alleys had a stronger effect on the soil environment than the control, natural grass, ryegrass, and tall fescue alley treatments; however, after 32 months, the alfalfa treatment inhibited fruit tree growth and development. This was unexpected because alfalfa seemed to have a positive effect on soil fertility characteristics. Under local ecological conditions, villous wild pea had the greatest effect on apple orchard productivity and significantly increased short branching by 15.9%, fruit weight per fruit by 12.6%, yield per plant by 8.6%, and soluble sugar content by 10.5% compared with clean cultivation. The correlation analysis showed that there were significant or highly significant positive correlations between fruit tree performance and soil carbon, nitrogen, and enzyme activity levels as the soil layer depth increased. Therefore, under local ecological conditions, cover crops have a greater effect on orchard surface soil fertility than on deeper soils, and intercropping with villous wild pea potentially produces the greatest improvement in apple orchard productivity. [ABSTRACT FROM AUTHOR]

Enhanced rock weathering (ERW), the application of crushed silicate rock to soil, can remove atmospheric carbon dioxide by converting it to (bi) carbonate ions or solid carbonate minerals. However, few studies have empirically evaluated ERW in field settings. A critical question remains as to whether additions of crushed rock might positively or negatively affect soil organic matter (SOM)—Earth's largest terrestrial organic carbon (C) pool and a massive reservoir of organic nitrogen (N). Here, in three irrigated cropland field trials in California, USA, we investigated the effect of crushed meta-basalt rock additions on different pools of soil organic carbon and nitrogen (i.e., mineral-associated organic matter, MAOM, and particulate organic matter, POM), active microbial biomass, and microbial community composition. After 2 years of crushed rock additions, MAOM stocks were lower in the upper surface soil (0–10 cm) of plots with crushed rock compared to unamended control plots. At the 2 sites where baseline pre-treatment data were available, neither total SOC nor SON decreased over the 2 years of study in plots with crushed rock or unamended control plots. However, the accrual rate of MAOM-C and MAOM-N at 0–10 cm was lower in plots with crushed rock vs. unamended controls. Before ERW is deployed at large scales, our results suggest that field trials should assess the effects of crushed rock on SOM pools, especially over multi-year time scales and in different environmental contexts, to accurately assess changes in net C and understand the mechanisms driving interactions between ERW and SOM cycling. [ABSTRACT FROM AUTHOR]

Decadal scale lake drying in interior Alaska results in lake margin colonization by willow shrub and graminoid vegetation, but the effects of these changes on plant production, biodiversity, soil properties, and soil microbial communities are not well known. We studied changes in soil organic carbon (SOC) and nitrogen (N) storage, plant and microbial community composition, and soil microbial activities in drying and non‐drying lakes in the Yukon Flats National Wildlife Refuge. Historic changes in lake area were determined using Landsat imagery. Results showed that SOC storage in drying lake margins declined by 0.13 kg C m−2 yr−1 over 30 years of exposure of lake sediments, with no significant change in soil N. Lake drying resulted in an increase in graminoid and shrub aboveground net primary production (ANPP, +3% yr−1) with little change in plant functional composition. Increases in ANPP were similar in magnitude (but opposite in sign) to losses in SOC over a 30‐year drying trend. Potential decomposition rates and soil enzyme activities were lower in drying lake margins compared to stable lake margins, possibly due to high salinities in drying lake margin soils. Microbial communities shifted in response to changing plant communities, although they still retained a legacy of the previous plant community. Understanding how changing lake hydrology impacts the ecology and biogeochemistry of lake margin terrestrial ecosystems is an underexamined phenomenon with large impacts to landscape processes. Plain Language Summary: Lake dominated ecosystems in Alaska have experienced periods of widespread lake drying in the past. We understand little of what occurs on these new nearshore habitats following lake drying, especially changes in soil properties and soil microbial communities. Using a combination of remote sensing and field sampling on hundreds of lakes in the Yukon Flats National Wildlife Refuge, we learned that lake margin soils lose significant quantities of soil C in the decades following lake drying, and at the same time soils become increasingly saline and soil microbial activites are reduced. Overall, lake drying has large impacts on the surrounding ecosystems and it is important to understand these changes for management. Key Points: Lake drying in the Yukon Flats National Wildlife Refuge triggers a succession of plant and microbial communities and losses of lake margin soil organic carbon (SOC)Lake drying also results in increases in the salinity of lake margin soils, slowing rates of microbial activitiesAlthough lake drying resulted in losses of SOC, increases in Aboveground Net Primary Production (ANPP) compensated for these losses [ABSTRACT FROM AUTHOR]

Background and aims: Root exudation is a key process for plant nutrient acquisition, but the controls on root exudation and its relationship to soil C and N processes in agroecosystems are unclear. We hypothesized that root exudation rates would be related to root morphological traits, N fertilization, and soil moisture. We also anticipated that root exudation would be correlated with bulk soil enzyme activity. Methods: Root exudation, root traits, and bulk soil extracellular enzyme activity were assessed in maize (Zea mays L.), soybean (Glycine max (L.) Merr.), biomass sorghum (Sorghum bicolor (L.) Moench), giant miscanthus (Miscanthus × giganteus), and switchgrass (Panicum virgatum L.). Measurements were taken in situ during two growing seasons with contrasting precipitation regimes, and N fertilization rate was varied in sorghum during one year. Results: Specific root exudation (per unit root surface area) was negatively related to root diameter and was generally higher in annuals than perennials. Sorghum N fertilization did not affect root exudation rates, and soil moisture regime had no effect on annual root exudation rates within maize, sorghum, and miscanthus. Specific root exudation was negatively related to bulk soil C- and N-degrading soil enzyme activities. Conclusion: Intrinsic plant characteristics appeared more important than environmental variables in controlling in situ root exudation rates. The relationships between root diameter, root exudation, and soil C and N processes link root morphological traits to soil functions and demonstrate the potential tradeoffs among plant nutrient acquisition strategies in agroecosystems. [ABSTRACT FROM AUTHOR]

Root exudation, the export of low-molecular weight organic carbon (C) from living plant roots to soil, influences microbial activity, nutrient availability, and ecosystem feedbacks to climate change, but the magnitude of this C flux at ecosystem and global scales is largely unknown. Here, we synthesize in situ measurements of root exudation rates and couple those to estimates of fine root biomass to estimate global and biome-level root exudate C fluxes. We estimate a global root exudate flux of 13.4 (10.1–20.2) Pg C y−1, or about 9% (7–14%) of global annual gross primary productivity. We did not find differences in root mass-specific exudation rates among biomes, though total exudate fluxes are estimated to be greatest in grasslands owing to their high density of absorptive root biomass. Our synthesis highlights the global importance of root exudates in the terrestrial C cycle and identifies regions where more in situ measurements are needed to improve future estimates of root exudate C fluxes. [ABSTRACT FROM AUTHOR]

Societal Impact Statement: As cities grow, it is essential to understand how landscape management decisions in urban spaces alter ecosystem function. This study demonstrates that the ubiquitous practice of long‐term leaf litter removal in suburbs, even in relatively small patches of a yard, reduces the soil's ability to cycle nutrients in plant litter and results in lower amounts of carbon stored in the soil. Even two years of retaining leaves where they previously were removed is insufficient to restore decomposition rates or carbon pools. This research is an important step in creating best practices for litter management to maintain essential ecosystem functions, like carbon sequestration, water holding capacity, and soil fertility. Summary: Seasonal senesced leaf litter removal eliminates considerable organic material from suburban soils annually. We test if this disturbance alters decomposition and carbon cycles and depletes soils of organic matter over time, creating persistent legacy effects.We used a factorial experimental design to implement 1–2 years of current leaf litter manipulations (remove or retain fallen leaves) within historically raked and unraked areas in suburban Maryland yards. We then compared total organic soil carbon and decomposition using a standardized substrate decomposition methodology (Tea Bag Index) across treatment plots.Long‐term litter removal in suburban yards reduced decomposition rates by 17% and total soil organic carbon concentration by up to 24% compared to areas where leaf litter was retained in situ. In contrast, short‐term management changes (1–2 years) did not significantly impact decomposition rates or total organic soil carbon concentrations.Our findings suggest that long‐term suburban litter raking creates legacy effects that alter decomposition and carbon storage process trajectories that are not easily reversed. This is important in understanding urban ecosystem function and sustainable management. [ABSTRACT FROM AUTHOR]

Tasmanian eucalypt forests are among the most carbon‐dense in the world, but projected climate change could destabilize this critical carbon sink. While the impact of abiotic factors on forest ecosystem carbon dynamics have received considerable attention, biotic factors such as the input of animal scat are less understood. Tasmanian devils (Sarcophilus harrisii)—an osteophageous scavenger that can ingest and solubilize nutrients locked in bone material—may subsidize plant and microbial productivity by concentrating bioavailable nutrients (e.g., nitrogen and phosphorus) in scat latrines. However, dramatic declines in devil population densities, driven by the spread of a transmissible cancer, may have underappreciated consequences for soil organic carbon (SOC) storage and forest productivity by altering nutrient cycling. Here, we fuse experimental data and modeling to quantify and predict future changes to forest productivity and SOC under various climate and scat‐quality futures. We find that devil scat significantly increases concentrations of nitrogen, ammonium, phosphorus, and phosphate in the soil and shifts soil microbial communities toward those dominated by r‐selected (e.g., fast‐growing) phyla. Further, under expected increases in temperature and changes in precipitation, devil scat inputs are projected to increase above‐ and below‐ground net primary productivity and microbial biomass carbon through 2100. In contrast, when devil scat is replaced by lower‐quality scat (e.g., from non‐osteophageous scavengers and herbivores), forest carbon pools are likely to increase more slowly, or in some cases, decline. Together, our results suggest often overlooked biotic factors will interact with climate change to drive current and future carbon pool dynamics in Tasmanian forests. [ABSTRACT FROM AUTHOR]

Agroforestry has the potential to support more resilient livelihoods, soil health, and biodiversity, when compared to monocropping. In Ecuador, the Union of Cacao Peasant Organizations (UNOCACE) has been working with producers since 2016 to transition cacao plots to a dynamic agroforestry system that includes timber and fruit species as well as ground cover in addition to cacao. This study evaluates the application of this model and its implications for agricultural production, livelihoods, and soil health through producer surveys and field-based sampling. The program is resulting in significantly more timber and fruit trees on the cacao plots. Despite this, cacao production and income have not decreased in a significant way, once accounting for the number of producing trees on the plots. In addition, while additional labor is utilized on the dynamic agroforestry plots, after utilizing a matching procedure, no significant difference is seen in total crop productivity for each day of labor utilized. Over time, total productivity could increase for the dynamic agroforestry plots as the companion crops and trees mature. As the program is relatively new and has undergone some changes, additional studies are needed to understand the benefits or challenges, especially for soil health, that might be realized further in the lifespan of the program. [ABSTRACT FROM AUTHOR]

Droughts are becoming more frequent and intense with climate change. As plants and microbes respond to drought, there may be consequences for the vast stocks of organic carbon stored in soils. If microbes sustain their activity under drought, soils could lose carbon, especially if inputs from plants decline. Empirical and theoretical studies reveal multiple mechanisms of microbial drought resistance, including tolerance and avoidance. Physiological responses allow microbes to acclimate to drought within minutes to days. Along with dispersal, shifts in community composition could allow microbiomes to maintain functioning despite drought. Microbes might also adapt to drier conditions through evolutionary processes. Together, these mechanisms could result in soil carbon losses larger than currently anticipated under climate change.

The Intergovernmental Panel on Climate Change (IPCC) established a methodology to estimate carbon sequestered from biochar additions to mineral soils in the 2019 Refinement Guideline, requiring a pyrolysis temperature exceeding 350 °C and three variables: organic carbon content in fraction (Fc), fraction of biochar carbon remaining after 100 years (Fperm), and biochar mass. Japan has reported biochar amendments in its national greenhouse gas inventory since 2020 using default IPCC values. However, Japan has traditionally evaluated biochar properties based on Japanese Industrial Standard (JIS) M 8812, which measures fixed carbon (FC), volatile matter (VM), and ash content. This study developed a protocol to convert the JIS parameters to the IPCC variables Fc and Fperm for woody and bamboo biochar. We established a VM/FC-based power approximation expression to estimate pyrolysis temperature, and derived a conversion equation from the liner relationship between JIS values, organic carbon content (Corg, %) and Fperm. Inventory country-specific values for woody and bamboo biochar were proposed, with Fc (Fc = Corg/100) and Fperm reflecting three pyrolysis temperature levels. This conversion protocol enables practical, cost-effective application to diverse biochar feedstocks, supporting country-specific variable development and broader biochar use for carbon dioxide removal.

Estimates of theoretical climate change mitigation potentials in agriculture need to be complemented with investigations of factors that influence deployment. This study introduces a framework for landscape-level assessment of climate change mitigation in agriculture that accounts for existing land uses, soil carbon stocks, and farmers’ preferences concerning specific mitigation options. The framework is used in an assessment of the deployment potentials for selected mitigation options in an agricultural landscape in Sweden, in which arable land covers approximately one-third of the land area. Three options were found to be preferable by farmers: biochar as soil amendment, cover crops, and (an increased) cultivation of ley crops in crop rotations. Cultivation of cover crops and leys was found to increase SOC stocks by 1.9 and 1.6 MgC ha−1 over three decades, respectively. About 10.2 MgC ha−1 is sequestered in soils over three decades when biochar is added as a soil amendment, if 50% of available residues are collected and utilized. This can be compared with GHG emissions from agriculture from the studied area, estimated at 1.6 Mg CO2-eq ha−1 yr−1 (GWP100). The framework was found useful for assessing mitigation options in the agriculture sector, underlining farmer involvement to identify actionable strategies.

In 2023, the Australian Government issued ∼250,000 soil carbon credits following a measurement period characterised by high rainfall (Decile 10). The inferred soil organic carbon (SOC) sequestration rates during this period, ranging from ∼2 to 8 t C ha−¹ yr−¹, significantly exceed rates reported in Australian scientific studies (∼0.1 to 1.2 t C ha−¹ yr−¹). Our analysis, incorporating SOC and biomass measurements alongside remote sensing of NDVI, reveals that these SOC gains were largely attributable to above-average rainfall rather than project interventions. Moreover, these gains were not sustained when rainfall returned to average levels, raising concerns about the durability of credited sequestration and its additionality beyond natural climatic variability. Our findings demonstrate that current safeguards within the Soil Carbon Method—such as withholding 25% of credits during the first measurement period—are likely insufficient to account for climatic variability. To strengthen the integrity of the carbon crediting system, we recommend extending the minimum measurement period for credit issuance to at least five years. Additionally, governments should establish science-based ‘reasonable bounds’ for expected long-term SOC gains from management practices to sense-check reported outcomes. These measures will ensure that credited SOC sequestration is more closely tied to management-driven outcomes rather than short-term climate-driven fluctuations.

Biochar is a recalcitrant carbon-rich solid produced by pyrolysis of organic residues, and its application to soil is considered a promising approach to mitigate climate change, as biochar resists decomposition to readily contributes to soil carbon (C) sequestration. The IPCC provides a basis for future national-scale accounting of the changes in soil C stocks following biochar application to cropland soils. The IPCC Tier 1 approach for biochar is based on fixed emission factors to estimate biochar C sequestration. In contrast, the Tier 2 approach allows countries to use local emission factors and climate data to calculate the contribution of biochar to soil C sequestration. Accurate accounting of biochar C sequestration is essential for ensuring the credibility of C offsetting projects, as well as providing incentives for implementing biochar in C credit schemes, calling for comparative analyses of the different biochar Tier approaches. Here we retrieved biochar samples from local producers and measured their H/Corg to estimate the persistence of biochar in Norwegian croplands post application. Various feedstocks were considered, including forest residues, woody wastes, manure, sludge, and straw. For all biochar samples, the 100-year stable C fraction was calculated at ≥ 0.945, thus exceeding the default Tier 1 value (0.8). Biochar sourced from woody- and forestry residues had a Corg content above the default Tier 1 value (0.77). Based on this and data about national feedstock supplies, we compared the theoretical potential of biochar soil C sequestration to mitigate climate change in Norway, using the IPCC Tier 1 and Tier 2 approaches. Biochar C sequestration in soil was calculated at 0.79 Tg CO2-eq yr−1 and 0.92 to 0.96 Tg CO2-eq yr−1, respectively for the Tier 1 and Tier 2 approaches, thus, underlining that the choice of IPCC Tier approach can have a large impact on the estimated mitigation potential of biochar.

The study aims to establish a correlation model between potential carbon and soil carbon storage. It examined soil carbon distribution, potential, and storage within a 0–100 cm soil profile across forest ecosystems and agricultural land in Aceh Besar, Indonesia. A total of 252 soil samples were collected from seven different depths, ranging from the surface to 100 cm1 , across 12 forest ecosystems and agricultural areas. These ecosystems included primary forests, secondary forests, pine woodlands, eucalyptus woodlands, teak woodlands, bush forests, shrublands, grasslands, mixed gardens, moorlands, rainfed rice fields, and barren lands. The Walkley & Black method was used to analyze soil carbon intensity. The results indicated that soil carbon intensity was highest at the surface level (0–30 cm) and decreased with increasing depth. The distribution pattern of soil carbon varied among the forest ecosystems, with primary forests showing the highest carbon storage and potential compared to other land uses. Potential and soil carbon storage have a significant positive linear relationship. The regression equation represents this: y = 2.1381X2 − 12.494X + 106.35, with an R2 value of 0.7608∗∗.

Despite the potential role of soil carbon offset schemes to reduce greenhouse gas emissions, there are concerns that the rules for assessment, monitoring, and operation are barriers to engagement. This may explain why there is low participation of Australian landholders in soil carbon projects. This study reviews the literature on three leading voluntary carbon standards and methods to assess their suitability for developing soil carbon projects in grazing systems in Australia. The soil carbon method of each standard was analysed based on several criteria: scope, eligibility/applicability, newness and additionality, permanency, baselines and quantification methodology, environmental sustainability, safeguard mechanism, and crediting period. A hypothetical grazing case study in Central Queensland, Australia’s premier beef cattle region, was used to model the cost-effectiveness and potential returns from establishing soil carbon projects under the three standards. Results show that credits created under the Emissions Reduction Fund in Australia generate higher returns for soil carbon projects compared to the Verified Carbon Standard and Gold Standard. This is largely due to a higher market price for soil carbon credits in the Emissions Reduction Fund, reflecting more robust standards of assessment and verification. While assessment costs for credits were higher in the international schemes, returns were lower because prices reflected less rigorous standards.

AbstractCarbon sequestration is defined as the process of capturing and storing atmospheric carbon dioxide. Fruit crops are indispensable both for climate change mitigation and ensuring food security. However, the impact of fruit trees is not adequately investigated. This review assesses the carbon sequestration potential of fruit trees and their implications for climate change mitigation. Fruit trees use photosynthesis to absorb CO2 from the atmosphere and assimilate it into their cellulose, lowering atmospheric buildup. Horn of Africa is the most vulnerable region for climate change, and Ethiopia is also facing unpredictable weather, which brings sporadic floods and droughts that harm the agricultural sectors. Dramatic rise of CO2 from 280 ppm in 1850 to 420.2 ± 0.5 ppm in 2023 is reported to link with human activity. In most Ethiopian farms, multipurpose fruit trees are rarely cultivated, and the only experience is planting trees in the homestead areas. Even though fruit trees have an enormous potential to store carbon, the destruction of those trees is also results greenhouse gas. Tree plants, including fruit trees, are thought to absorb 0.42 to 0.65 pentagrams of carbon per year. Above- and below-ground biomasses have been described to sink more than 40% of carbon. Agroforestry practices should adopt all fruit species on the basis of carbon sequestration and climate change mitigation in their growing stratum. Therefore, in order to oblige countries to adopt versatile fruit trees to meet food and nutrition security, carbon sequestration, and climate change mitigation efforts should have both political and economic sustainability.

Soil organic carbon (SOC) and soil inorganic carbon (SIC) are of longstanding interest due to their relationship with other key soil properties and indications for soil health and carbon storage. At the USDA-NRCS Kellogg Soil Survey Laboratory (KSSL), total carbon (SOC + SIC) is determined via dry combustion analysis, while calcium carbonate (CaCO3) equivalent is determined via manocalcimetry. For calcareous (carbonate bearing) samples, SIC is estimated as 12 % of CaCO3 equivalent, while SOC is estimated as the difference between measured total carbon and estimated SIC. An alternative dry combustion method for the measurement of SOC and SIC pools was evaluated with the goal of directly measuring – not estimating – inorganic and organic carbon on calcareous samples. The alternative temperature ramp dry combustion (TRDC) method comprises two variants that differ in ramp cycle and carrier gases used. One variant operates under continuous oxygen and has temperature ramp plateaus of 400, 600 and 900 °C; thus, it is referred to as the non-gas switching variant or TRDCNGS. The other variant operates under oxygen until 400 °C, then switches to nitrogen gas for a ramp to 900 °C, then reintroduces oxygen at 900 °C; thus, it is referred to as the gas switching variant or TRDCGS. Both variants were applied in duplicate to 110 diverse samples, including 32 calcareous samples, from across the USA that had been previously characterized by the KSSL. Samples were selected to capture wide variability in carbon contents. Comparing carbon data outcomes with data from the legacy KSSL methods revealed the TRDCGS variant as best for calcareous samples, whereas the TRDCNGS variant was preferred for non-calcareous samples. A combination of the two method variants offers an accurate and direct measurement of SOC and SIC. For calcareous samples, mid-infrared (MIR) spectral analysis demonstrated TRDC method as slightly more accurate than legacy KSSL methods for estimating SOC and SIC.

Background. Soil aggregates represent a major indicator of soil fertility as they are important components of soil C protection. However, in the Democratic Republic of Congo, the choice of tree species being integrated into crop farms influence the type of soil macrofauna beneath these agroforestry trees with effect on soil aggregates and carbon fractions. Objective. To assess the combined effect of diverse tree species alongside earthworms and termites on soil aggregation and soil organic C. Methodology. Soil samples were collected from five agroforestry systems comprising Eucalyptus saligna, Grevillea robusta and Ficus benghalensis (an indigenous tree) woodlots, an agricultural farm (beans) and a natural forest in four different locations. Soil aggregates and soil organic C were analysed in the laboratory following standard procedures. The analyses of variance and correlations were carried out using R programming software. Results. A significantly higher proportion of large macroaggregates was recorded in soil under natural forest (13.1 %) whereas microaggregates were significantly low in soils under natural forest. For all the categories of aggregate-associated C, natural forest recorded the highest values while beans had the lowest values. The same trends were observed for labile C with 22.9 g kg-1 in soil under natural forest and 9.7 g kg-1 in soil under beans. Implication. The high levels of soil aggregates as well as carbon fractions recovered from natural forest clearly show the significance of a well-diversified tree-based farm. Conclusion. Therefore, it is advisable to consider a large diversification of tree species on farms to sustain and maintain a better soil quality.

Purpose: This paper is aimed at the determination of digestate potential in a long-term carbon accumulation after its application as a biofertilizer. Method: Literature survey of > 1000 papers was conducted and resulted in a selection of 21 papers that involved data of soil C accumulation after digestate addition for at least a period of 12 months. Meta-analysis was used for data analysis and interpretation of a large database. The results of incorporation of total organic carbon in the soil after digestate biofertilization were measured by one-way analysis of variance (ANOVA). Results: A comprehensive literature review showed trends for carbon increase in the soil for different experiment periods up to 84 months and initial content of carbon in the soil. It was demonstrated that application of digestate, a byproduct of anaerobic digestion, to agricultural soils resulted in an increase of soil carbon content for a period of up to 8 years. Specifically, digestate derived from cow and pig manure had the highest potential to enhance soil carbon accumulation compared to digestate from other organic residues including food waste and sewage sludge, highlighting the need for a proper choice of the waste substrate used in anaerobic digestion. Soil carbon accumulation is notably more pronounced when digestate is applied to soils with low organic matter content, particularly sandy and loam soils. Conclusion: While digestate application to soils is typically used to substitute mineral fertilizers, it also leads to an overall increase in soil carbon content. Research Highlights • Among different types of manure cow and pig manure showed the highest results in the terms of long term (> 12 months) carbon accumulation in the soil after biofertilization. • A general tendency of lower carbon increase in the soil for the period of 12 months and maximum increase at 36 months of experiment was found. • Digestate can be very successfully used to help reforestation efforts, as they usually have lower soil C content than natural areas. • Obtained results for the period of more than 12 months showed the highest soil carbon increase (more than 2% per month) for sandy soil. • Wheat and maize were found to be the best crops in terms of the potential for carbon accumulation in the soil after digestate biofertilization.

IntroductionPlastic film mulching has been widely used to enhance soil hydrothermal conditions and increase crop yields in cool, semi-arid areas. However, its impact on soil microbial carbon metabolic activity and functional diversity during plant growth remains unclear despite their important roles in nutrient cycling and soil quality evaluation.MethodsThis study used the Biolog EcoPlate technique to investigate the dynamics and driving factors of soil microbial carbon metabolic activity and functional diversity at different maize growth stages following plastic film mulching.Results and discussionThe results revealed that film mulching significantly increased microbial carbon metabolic activities [represented by average well color development (AWCD)] by 300% at the seedling stage and by 26.8% at maturity but decreased it by 47.4% at the flowering stage compared to the control (without mulching). A similar trend was observed for the microbial functional diversity index. Redundancy analysis identified soil moisture (SM), soil temperature (ST), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and bacteria amounts as the primary factors influencing changes in soil microbial carbon source utilization. The mulch treatment significantly increased SM at all growth stages, while its warming effect disappeared at the flowering stage. Soil DOC, MBC, and bacterial populations were notably higher under mulching at the seedling and maturity stages but lower at the flowering stage. Pearson correlation analysis showed that changes in SM, ST, DOC, MBC, and bacterial populations positively correlated with the utilization of all carbon source classes, AWCD, and functional diversity indexes after film mulching. Furthermore, maize grain yield and water use efficiency increased by 142 and 129%, respectively, following film mulching. In conclusion, plastic film mulching enhanced soil microbial carbon metabolic activity and functional diversity at the seedling and maturity stages, improving crop yields in cool, semi-arid areas. Furthermore, the decrease in soil carbon metabolic capacity at flowering stage highlights that supplementing soil carbon sources should be considered after continuous film mulching to sustain or enhance farmland productivity and soil quality.

Fibrous and pioneer roots are essential in the uptake and transport of water and nutrients from the soil. Their dynamic may be influenced by the changing of soil physicochemical properties due to the addition of biochar, which, in turn, has been shown to improve plant growth and productivity in the short term. However, the long-term effects of biochar application on root dynamics are still widely unknown. In this study, we aimed to investigate the long-term effects of biochar application on grapevine fibrous and pioneer root dynamics and morphological traits in relation to soil characteristics. To this aim, grapevine plants amended in 2009 and 2010 respectively with one and two doses of biochar, were analyzed in their fibrous and pioneer root production and turnover rate, standing biomass, length, and specific root length, over two growing seasons. Our findings demonstrate that in the long term, biochar application significantly increased soil pH, nutrient availability, and water-holding capacity causing a decrease in the production of fibrous and pioneer roots which is reflected in a reduction of the root web characterized though by a higher turnover rate. Furthermore, we observed that these root morpho-dynamical changes were of higher magnitude in the upper soil layers (0-20 cm) and, at least in the long term, with no significant difference between the two doses. These results suggest that in the long term, biochar can be a powerful tool for improving soil quality, which in turn lowers carbon-cost investment toward the root production and maintenance of a reduced root web that might be directed into grapevine growth and productivity. Such effects shed some light on the root plastic and functional adaptation to modified soil conditions facilitated by the long-term application of biochar, which can be used for implementing adaptive agricultural practices to face the current climate change in a frame of sustainable agricultural policies.