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In drylands, where water scarcity limits vascular plant growth, much of the primary production occurs at the soil surface. This is where complex macro- and microbial communities, in an intricate bond with soil particles, form biological soil crusts (biocrusts). Despite their critical role in regulating C and N cycling in dryland ecosystems, there is limited understanding of the fate of biologically fixed C and N from biocrusts into the mineral soil, or how climate change will affect C and N fluxes between the atmosphere, biocrusts, and subsurface soils. To address these gaps, we subjected biocrust-soil systems to experimental warming and drought under controlled laboratory conditions, monitored CO 2 fluxes, and applied dual isotopic labeling pulses ( 13 CO 2 and 15 N 2 ). This allowed detailed quantification of elemental pathways into specific organic matter (OM) pools and microbial biomass via density fractionation and phospholipid fatty acid analyses. While biocrusts modulated CO 2 fluxes regardless of the temperature regime, drought severely limited their photosynthetic C uptake to the extent that the systems no longer sustained net C uptake. Furthermore, the effect of biocrusts extended into the underlying 1 cm of mineral soil, where C and N accumulated as mineral-associated OM (MAOM <63μm ). This was strongly associated with increased relative dominance of fungi, suggesting that fungal hyphae facilitate the downward C and N translocation and subsequent MAOM formation. Most strikingly, however, these pathways were disrupted in systems exposed to warming, where no effects of biocrusts on the elemental composition of the underlying soil nor on MAOM were determined. This was further associated with reduced net biological N fixation under combined warming and drought, highlighting how changing climatic conditions diminish some of the most fundamental ecosystem functions of biocrusts, with detrimental repercussions for C and N cycling and the persistence of soil organic matter pools in dryland ecosystems., (Global Change Biology© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Application of biochar has been demonstrated to be a successful strategy for boosting soil carbon sequestration and altering the agricultural soil carbon cycle. However, in the studies involving biochar worldwide, the effects of different types of biochar on the soil carbon component response direction and increase are not consistent. Therefore, to assess the effects of applying four types of biochar during the soil carbon cycle on carbon components on a farmland, we performed a meta-analysis of 1150 comparisons from 86 peer-reviewed publications. Generally speaking, the types of biochar raw materials have a significant impact on soil carbon cycle. The application of chaff biochar significantly inhibited (10.0 %) soil respiration, while the application of manure biochar (47.0 %), straw biochar (11.2 %) and wood biochar (8.7 %) showed a strong promotion effect on CO 2 emission. In addition, although the soil organic C, microbial biomass C and dissolved organic C all had positive responses to the application of the four biochar types, the degree and increase in their response varied greatly due to the differences in biomass raw materials. Moreover, by increasing the biochar rates applied to coarse-textured soils with low average annual rainfall and an average temperature under controlled circumstances, the relative increase in SOC was encouraged. Meanwhile, applying low temperature pyrolytic biochar (≤400 °C) at a lower rate (<25 t/ha) in the long-term experiment (>3 years) is more beneficial to soil C sequestration and emission reduction. Hence, climatic conditions, agricultural management practices, and initial soil properties jointly constrained and influenced the ability of biochar to alter the soil C cycle. Based on this, our research offers a fresh viewpoint for making a profound study biochar-enhanced soil C cycle., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Soil microorganisms determine the fate of soil organic matter (SOM), and their activities compose a major component of the global carbon (C) cycle. We employed a multisubstrate, DNA-stable isotope probing experiment to track bacterial assimilation of C derived from distinct sources that varied in bioavailability. This approach allowed us to measure microbial contributions to SOM processing by measuring the C assimilation dynamics of diverse microorganisms as they interacted within soil. We identified and tracked 1,286 bacterial taxa that assimilated 13 C in an agricultural soil over a period of 48 d. Overall 13 C-assimilation dynamics of bacterial taxa, defined by the source and timing of the 13 C they assimilated, exhibited low phylogenetic conservation. We identified bacterial guilds composed of taxa that had similar 13 C assimilation dynamics. We show that C-source bioavailability explained significant variation in both C mineralization dynamics and guild structure, and that the growth dynamics of bacterial guilds differed significantly in response to C addition. We also demonstrate that the guild structure explains significant variation in the biogeographical distribution of bacteria at continental and global scales. These results suggest that an understanding of in situ growth dynamics is essential for understanding microbial contributions to soil C cycling. We interpret these findings in the context of bacterial life history strategies and their relationship to terrestrial C cycling., Competing Interests: The authors declare no competing interest.

Forests are major sources of terrestrial CH4 and CO2 fluxes but not all surfaces within forests have been measured and accounted for. Stem respiration is a well-known source of CO2, but more recently tree stems have been shown to be sources of CH4 in wetlands and upland habitats. A study transect was established along a natural moisture gradient, with one end anchored in a forested wetland, the other in an upland forest and a transitional zone at the midpoint. Stem and soil fluxes of CH4 and CO2 were measured using static chambers during the 2013 and 2014 growing seasons, from May to October. Mean stem CH4 emissions were 68.8 ± 13.0 (mean ± standard error), 180.7 ± 55.2 and 567.9 ± 174.5 µg m−2 h−1 for the upland, transitional and wetland habitats, respectively. Mean soil methane fluxes in the upland, transitional and wetland were − 64.8 ± 6.2, 7.4 ± 25.0 and 190.0 ± 123.0 µg m−2 h−1, respectively. Measureable CH4 fluxes from tree stems were not always observed, but every individual tree in our experiment released measureable CH4 flux at some point during the study period. These results indicate that tree stems represent overlooked sources of CH4 in forested habitats and warrant investigation to further refine CH4 budgets and inventories. [ABSTRACT FROM AUTHOR]

Purpose: Climate-change impacts can be mitigated through greater use of bioenergy, but the extent to which specific options actually reduce overall impacts needs to be assessed. Most bioenergy assessments have used proxy measures for assessing its merits. Here, a new approach is presented, whereby the contribution of bioenergy use is assessed through quantifying marginal changes in climate-change impacts that result from the implementation of a bioenergy option. Methods: Marginal climate-change impacts were calculated for one specific example of a bioenergy option, conversion of an unutilised mature forest into a production forest harvested repeatedly for bioenergy over successive 25-year rotations. The overall benefit of the option was assessed by including stand-level carbon dynamics, global carbon-cycle feedback, progressively changing radiative efficiency and marginal impact sensitivity of warming. It also includes a differentiated assessment of three kinds of climatic impacts: direct-warming, rate-of-warming and cumulative-warming impacts. Marginal impacts were calculated and summed over 100 years to assess the overall marginal impact of this bioenergy option. Results and discussion: Bioenergy use in this specific example led to a large initial loss of biomass carbon followed by an ongoing and accumulating benefit through fossil-fuel substitution. This caused adverse climatic impacts over the first two rotations as the effects of the on-site carbon loss dominated the overall impact, but the option became increasingly beneficial over longer time frames as the benefit of fossil-fuel substitution accrued and eventually dominated. Summed over 100 years, the bioenergy option reduced direct-temperature and rate-of-warming impacts whilst increasing cumulative-warming impacts. The average of the three kinds of impacts showed a slight mitigation benefit by reducing overall impacts. In the particular example, bioenergy use was assessed to have a more beneficial effect if the analysis was carried out under the assumption of higher-emission concentrations pathways, or if it assumed a steeper relationship between climate perturbations and impacts. Conclusions: The usefulness of any climate-change mitigation option ultimately relates to the marginal climate-change impacts it can avert. It is shown here that marginal impacts can be calculated in routine operation and that they can provide an objective and methodologically consistent assessment of the mitigation potential of bioenergy use. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of NZVI on composting carbon cycle and carbon balance was investigated. • A NZVI-regulated composting C cycle was experimentally demonstrated. • NZVI addition increased CO 2 and CH 4 emissions by 51% and 128% respectively. • NZVI addition enhanced bacteria promoting hygiene of final product. The effectiveness of nano-zero-valent-iron (NZVI) addition during composting of pig manure (PM) was investigated. Different dosages of NZVI were mixed with PM substrate during a 50 days composting process. The results revealed that the higher share of NZVI addition, the higher OM degradation rate is. On contrary, it was observed that the higher share of NZVI addition, the lower the fulvic acid and the humin degradation rate is. Meanwhile, NZVI amendment increased the CO 2 and CH 4 emissions by 29–47 % and 53–57 %, respectively. The in-depth analysis showed that NZVI addition increased the activity of Sphaerobacter and Luteimonas , which eventually led to the degradation of hard-to-degrade OM faster. Additionally, NZVI was found to increase the filtration of microorganisms, reducing the toxicity and hygiene of compost products. No significant improvement in humic substance enhancement was observed during composting with NZVI addition but improved OM degradation. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are persistent organic pollutants globally, with a continuous increase in MP wastes near and away from the regions of human activities. Studies to date aimed to explore the impact of MPs on ecosystems, but the area of research could not go beyond environmental pollution caused by MPs. To address the menace of MPs, scientists need to pay enough attention to the biogeochemical cycles, microbial communities, and functional microorganisms. Hence, this study aimed to evaluate the impact of adding 0.3% (mass ratio) [low-concentration (LC) group] and 1% [high-concentration (HC) group] of polyamide (PA) MP to the soil microenvironment with regard to the aforementioned parameters. PA MP decreased the soil microbial diversity (Shannon and Simpson indices, P < 0.05). At the phylum level, PA MP increased the abundance of Acidobacteria, Firmicutes , and Crenarchaeota (P < 0.05); at the genus level, it enhanced that of Geobacter , Thiobacillus, Pseudomonas, and Bradyrhizobium (P < 0.01) while decreased that of Bacillus, Flavisolibacter, Geothrix , and Pseudarthrobacter (P < 0.05). PA MP affected the carbon (C) cycle. PA MP accelerated the soil C fixation by enhancing the abundance of the genes accA and pccA. The LC PA MP accelerated organic C degradation and methane metabolism by changing the abundance of mnp, chiA, mcrA, pmoA , and mmoX genes, while the HC PA MP inhibited them with increasing the experimental time. Regarding the effects of PA on the nitrogen (N) cycle, the PA MP promoted N assimilation and ammonification by increasing the abundance of the genes gdh and ureC , the impact of PA MP on N fixation and denitrification depended on its concentration and treating time. This study showed that PA MP impacted the microbial consortium, it also affected the C and N cycles and its effect depended on its concentration and the treating time. [Display omitted] • PA MP significantly impacted the diversity of soil bacterial community. • PA MP accelerated the soil carbon fixation. • PA MP promoted the soil nitrogen assimilation and ammonification. • The impact of PA MP on the C and N cycle depended on its concentration and treating time. [ABSTRACT FROM AUTHOR]

Climate change (i.e., high atmospheric carbon dioxide (CO2) concentrations (=400 ppm); increasing air temperatures (2-4 °C or greater); significant and/or abrupt changes in daily, seasonal, and interannual temperature; changes in the wet/dry cycles; intensive rainfall and/or heavy storms; extended periods of drought; extreme frost; heat waves and increased fire frequency) is and will significantly affect soil properties and fertility, water resources, food quantity and quality, and environmental quality. Biotic processes that consume atmospheric CO2 and create organic carbon (C) that is either reprocessed to CO2 or stored in soils, are the subject of active current investigations with great concern over the influence of climate change. In addition, abiotic C cycling and its influence on the inorganic C pool in soils is a fundamental global process in which acidic atmospheric CO2 participates in the weathering of carbonate and silicate minerals, ultimately delivering bicarbonate and Ca2+ or other cations that precipitate in the form of carbonates in soils or are transported to the rivers, lakes, and oceans. Soil responses to climate change will be complex, and there are many uncertainties and unresolved issues. The objective of the review is to initiate and further stimulate a discussion about some important and challenging aspects of climate-change effects on soils, such as accelerated weathering of soil minerals and resulting C and elemental fluxes in and out of soils, soil/geo-engineering methods used to increase C sequestration in soils, soil organic matter (SOM) protection, transformation and mineralization, and SOM temperature sensitivity. This review reports recent discoveries and identifies key research needs required to understand the effects of climate change on soils. [ABSTRACT FROM AUTHOR]

Currently, the global annual flux of methane (CH) to the atmosphere is fairly well constrained at ca. 645 Tg CH year. However, the relative magnitudes of the fluxes generated from different natural (e.g. wetlands, deep seepage, hydrates, ocean sediments) and anthropogenic sources remain poorly resolved. Of the identified natural sources, the contribution of vegetation to the global methane budget is arguably the least well understood. Historically, reviews of the contribution of vegetation to the global methane flux have focused on the role of plants as conduits for soil-borne methane emissions from wetlands, or the aerobic production of methane within plant tissues. Many recent global budgets only include the latter pathway (aerobic methane production) in estimating the importance of terrestrial vegetation to atmospheric CH flux. However, recent experimental evidence suggests several novel pathways through which vegetation can contribute to the flux of this globally important, trace greenhouse gas (GHG), such as plant cisterns that act as cryptic wetlands, heartwood rot in trees, the degradation of coarse woody debris and litter, or methane transport through herbaceous and woody plants. Herein, we synthesize the existing literature to provide a comprehensive estimate of the role of modern vegetation in the global methane budget. This first, albeit uncertain, estimate indicates that vegetation may represent up to 22 % of the annual flux of methane to the atmosphere, contributing ca. 32-143 Tg CH year to the global flux of this important trace GHG. Overall, our findings emphasize the need to better resolve the role of vegetation in the biogeochemical cycling of methane as an important component of closing the gap in the global methane budget. [ABSTRACT FROM AUTHOR]

Abstract: Microbial decay of emergent macrophyte litters in the standing-dead phase is an essential component of litter decomposition and thus carbon (C) cycle in wetland ecosystems. In this study, we examined the amount of microbial respiration from standing litter in a Deyeuxia angustifolia-dominated marsh in the Sanjiang Plain by integrating field studies with laboratory experiments. In the field, CO2 evolution from standing litter exhibited a pronounced diel pattern, with high evolution rates concurring with increasing litter water potential at night. Notably, significant CO2 evolution even existed at temperature of −4°C. Overall, rates of CO2 evolution showed strong positive correlations with relative humidity and litter water potential. In the laboratory, rates of CO2 evolution from wetted culms and leaves increased with increasing temperature, and the relationship between CO2 evolution rates and temperature could be well described with an exponential model. Based on extrapolation from temperature-adjusted mean CO2 evolution rates and standing litter mass, annual CO2 fluxes of culms (3.07gCm−2 yr−1) and leaves (6.81gCm−2 yr−1) accounted for 2.32% (culms, 132.30gCm−2 yr−1) and 6.94% (leaves, 98.20gCm−2 yr−1) of the corresponding annual net aboveground production, respectively. In total, microbial mineralization of standing litter only contributed to 1.12% of the ecosystem respiration (880gCm−2 yr−1). Our results highlight the importance of standing-dead phase in litter decomposition and C cycle in wetlands, and also suggest that CO2 flux from standing litter could even be neglected in assessing C budget in the D. angustifolia-dominated freshwater marshes in the Sanjiang Plain, Northeast China. [Copyright &y& Elsevier]

Abstract: Mitigation strategies for the reduction of carbon dioxide emissions are the central focus of the Kyoto Protocol and international scientific efforts. Agriculture plays a substantial role in the balance of the most significant greenhouse gases (CO2, N2O, CH4), mostly attributed to management practices. In this study, we present data on the effects of a conversion from a cropland (Zea mays L.) to N2-fixing grassland (Medicago sativa L.) on C cycle in an agricultural area of Northern Italy. Net ecosystem production (NEP) and net biome production (NBP) have been followed for 2 years by mesuring CO2 fluxes by paired eddy covariance stations (EC) and continuous soil respiration measurements (SR). Root exclusion subplot replicates were also used to estimate heterotrophic respiration (Rh). The comparison between the net primary production (NPP) inventory estimation and NPP based on measured CO2 fluxes (EC and Rh) showed excellent agreement for both land uses. An increase in NEP was observed 2 years after conversion from corn to alfalfa (+281gCm−2), however, in terms of NBP, maize was a lower source of C (−96gCm−2) than alfalfa (−354gCm−2). From the present study, it appears that this type of land conversion is not an effective measure of C sequestration in the short term (1–3 years). [Copyright &y& Elsevier]

Climatic variables have major effects on all components and processes of the global carbon (C) cycle, including soil C contents and dynamics, which in turn have significant feedback effects on the global climate. We have investigated the interactive effects between soil C and projected climatic changes using the Institute of Numerical Mathematics Climate Model (INMCM) climate–C cycle model coupled to three soil organic matter dynamics models [the Lund–Potsdam–Jena (LPJ) soil biogeochemistry, ROMUL and Q models] based on three markedly differing conceptual interpretations of soil organic matter transformation (biochemical, discrete succession and continuous quality, respectively). According to simulations using all these couplings the positive effect of CO2 fertilization on plant productivity outweighed the negative effects of increased soil temperature on soil C, consequently soils were projected to contain 10–104 Pg more C in 2100 than in the preindustrial period. However, the projected soil respiration rates tended to be higher and additional C storage lower when the LPJ soil biochemistry model was used rather than either the ROMUL or Q models. Global temperatures for 2100 predicted by the INMCM coupled to either the ROMUL or Q models were almost identical, but 0.4 °C lower than those predicted by the INMCM coupled to the LPJ soil biochemistry model. The differences in global predictions obtained with the ROMUL and Q models were smaller than expected given the fundamental difference in their formulations of the relationship between the quality and temperature sensitivity of soil organic matter decomposition. [ABSTRACT FROM AUTHOR]

It is uncertain whether elevated atmospheric CO2 will increase C storage in terrestrial ecosystems without concomitant increases in plant access to N. Elevated CO2 may alter microbial activities that regulate soil N availability by changing the amount or composition of organic substrates produced by roots. Our objective was to determine the potential for elevated CO2 to change N availability in an experimental plant-soil system by affecting the acquisition of root-derived C by soil microbes. We grew Populus tremuloides (trembling aspen) cuttings for 2 years under two levels of atmospheric CO2 (36.7 and 71.5 Pa) and at two levels of soil N (210 and 970 µg N g–1). Ambient and twice-ambient CO2 concentrations were applied using open-top chambers, and soil N availability was manipulated by mixing soils differing in organic N content. From June to October of the second growing season, we measured midday rates of soil respiration. In August, we pulse-labeled plants with 14CO2 and measured soil 14CO2 respiration and the 14C contents of plants, soils, and microorganisms after a 6-day chase period. In conjunction with the August radio-labeling and again in October, we used 15N pool dilution techniques to measure in situ rates of gross N mineralization, N immobilization by microbes, and plant N uptake. At both levels of soil N availability, elevated CO2 significantly increased whole-plant and root biomass, and marginally increased whole-plant N capital. Significant increases in soil respiration were closely linked to increases in root biomass under elevated CO2. CO2 enrichment had no significant effect on the allometric distribution of biomass or 14C among plant components, total 14C allocation belowground, or cumulative (6-day) 14CO2 soil respiration. Elevated CO2 significantly increased microbial 14C contents, indicating greater availability of microbial substrates derived from roots. The near doubling of microbial 14C contents at elevated CO2 was a relatively small quantitative change in the belowground C cycle of our experimental system, but represents an ecologically significant effect on the dynamics of microbial growth. Rates of plant N uptake during both 6-day periods in August and October were significantly greater at elevated CO2, and were closely related to fine-root biomass. Gross N mineralization was not affected by elevated CO2. Despite significantly greater rates of N immobilization under elevated CO2, standing pools of microbial N were not affected by elevated CO2, suggesting that N was cycling through microbes more rapidly. Our results contained elements of both positive and negative feedback hypotheses, and may be most relevant to young, aggrading ecosystems, where soil resources are not yet fully exploited by plant roots. If the turnover of microbial N increases, higher rates of N immobilization may not decrease N availability to plants under elevated CO2. [ABSTRACT FROM AUTHOR]