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Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is well known that aboveground productivity usually increases with precipitation. However, how belowground carbon (C) processes respond to changes in precipitation remains elusive, although belowground net primary productivity (BNPP) represents more than one-half of NPP and soil stores the largest terrestrial C in the biosphere. This paper reviews the patterns of belowground C processes (BNPP and soil C) in response to changes in precipitation from transect studies, manipulative experiments, modeling and data integration and synthesis. The results suggest the possible existence of nonlinear patterns of BNPP and soil C in response to changes in precipitation, which is largely different from linear response for aboveground productivity. C allocation, root turnover time and species composition may be three key processes underlying mechanisms of the nonlinear responses to changes in precipitation for belowground C processes. In addition, microbial community structure and long-term ecosystem processes (e.g. mineral assemblage, soil texture, aggregate stability) may also affect patterns of belowground C processes in response to changes in precipitation. At last, we discuss implications and future perspectives for potential nonlinear responses of belowground C processes to changes in precipitation. [ABSTRACT FROM AUTHOR]

The reclamation of degraded pastures has a prominent role in the Brazilian climate policy and is one of the main strategies of Brazil's Low-Carbon Agriculture Plan (ABC Plan). Here, we aimed to evaluate the changes in soil C and N stocks in livestock areas under pasture reclamation and contribute to the empirical basis for evaluating the ABC Plan. Based on the assessment of six chronosequences across Brazilian Cerrado, we observed that the effects of management practices for pasture reclamation on soil C and N stocks in livestock areas were quite variable. Any general tendencies depend on the depth evaluated. At the 0–30 cm soil layer, pasture areas under reclamation in Brazilian Cerrado showed an average soil C change rate of 0.47 Mg C ha−1 yr−1. However, for the more in-depth assessment (0–100 cm), the adoption of management practices for pasture reclamation did not affect the average rate of soil C changes for these areas. In this sense, we suggest that an up-scaling from single case studies may lead to overestimations of soil C inventories. Thefore, ABC Plan must review some of its approaches based on general values and extrapolations regarding C sequestration in pasture areas.

Increasing levels of atmospheric CO2 may change C and N dynamics in pasture ecosystems. The present study was conducted to examine the impact of four years of CO2 enrichment on soil and root composition and soil N transformation in natural pastureland. Plots of open-top growth chambers were continuously injected with ambient CO2 (350 µL L–1) and elevated CO2 (625 µL L–1). Soil cores exposed to ambient and elevated CO2 treatment were incubated and collected each year. Net N-mineralization rates in soil (NH4+-N plus NO3ˉ–-N), in addition to total C and N content (%) of soil and root tissues were measured. Results revealed that elevated CO2 caused a significant reduction in soil NO3 (P < 0.05), however, no significant CO2 effect was found on total soil C and N content (%). Roots of plants grown under elevated CO2 treatment had higher C/N ratios. Changes in root C/N ratios were driven by changes in root N concentrations as total root N content (%) was significantly reduced by 30% (P < 0.05). Overall, findings suggest that the effects of CO2 enrichment was more noticeable on N content (%) than C content (%) of soil and roots; elevated CO2 significantly affected soil N-mineralization and total N content (%) in roots, however, no substantial change was found in C inputs in CO2-enriched soil.

Community density of grassland has obvious impacts on the absorption, sequestration, and accumulation of soil carbon (C). However, few studies have examined the effect of community density on soil C dynamics and their internal driving forces after cropland abandonment. Here, we synthesized the responses of soil C to community density of grassland over a 45‐year time‐sequence along a natural restoration time sequence. The results showed that the soil C content during the late‐successional period was greater than that during the early‐successional period, that is, annual C storage rates for the first sequence (1–15 years) for the 0–60 cm depth profiles were −0.34, −0.27, −0.15 to 0.02 Mg‐C ha−1 yr−1, in the ≤10, 11–20, 21–30, and >30 community densities. And the third sequence (31–45 years) presented values that were 79.28% and 44.60% greater than those of the initial stage of vegetation restoration (CK) for the 0–20 and 0–60 cm profiles, respectively. The increased soil C storage rates of the late‐successional sequence were associated with both increased aboveground production and root biomass for this sequence and the presence of multiple species, especially Leguminosae and Gramineae species, with developed roots. Overall, the effects of community density on soil C were regulated by the recovery time, root mass, and species genera. Furthermore, our results suggest that soil may still be a carbon source even after 15 years of the abandonment restoring, and high community density may greatly increase C capture and storage rates in abandoned lands. The findings enhance the understanding of soil C sequestration and accumulation responses to community density following long‐term natural vegetation succession, providing support for estimating and predicting the regional C budget and global C cycle. [ABSTRACT FROM AUTHOR]

The reclamation of degraded pastures has a prominent role in the Brazilian climate policy and is one of the main strategies of Brazil's Low-Carbon Agriculture Plan (ABC Plan). Here, we aimed to evaluate the changes in soil C and N stocks in livestock areas under pasture reclamation and contribute to the empirical basis for evaluating the ABC Plan. Based on the assessment of six chronosequences across Brazilian Cerrado, we observed that the effects of management practices for pasture reclamation on soil C and N stocks in livestock areas were quite variable. Any general tendencies depend on the depth evaluated. At the 0–30 cm soil layer, pasture areas under reclamation in Brazilian Cerrado showed an average soil C change rate of 0.47 Mg C ha−1 yr−1. However, for the more in-depth assessment (0–100 cm), the adoption of management practices for pasture reclamation did not affect the average rate of soil C changes for these areas. In this sense, we suggest that an up-scaling from single case studies may lead to overestimations of soil C inventories. Thefore, ABC Plan must review some of its approaches based on general values and extrapolations regarding C sequestration in pasture areas. [ABSTRACT FROM AUTHOR]

Increasing levels of atmospheric CO2 may change C and N dynamics in pasture ecosystems. The present study was conducted to examine the impact of four years of CO2 enrichment on soil and root composition and soil N transformation in natural pastureland. Plots of open-top growth chambers were continuously injected with ambient CO2 (350 µL L–1) and elevated CO2 (625 µL L–1). Soil cores exposed to ambient and elevated CO2 treatment were incubated and collected each year. Net N-mineralization rates in soil (NH4+-N plus NO3ˉ–-N), in addition to total C and N content (%) of soil and root tissues were measured. Results revealed that elevated CO2 caused a significant reduction in soil NO3 (P < 0.05), however, no significant CO2 effect was found on total soil C and N content (%). Roots of plants grown under elevated CO2 treatment had higher C/N ratios. Changes in root C/N ratios were driven by changes in root N concentrations as total root N content (%) was significantly reduced by 30% (P < 0.05). Overall, findings suggest that the effects of CO2 enrichment was more noticeable on N content (%) than C content (%) of soil and roots; elevated CO2 significantly affected soil N-mineralization and total N content (%) in roots, however, no substantial change was found in C inputs in CO2-enriched soil. [ABSTRACT FROM AUTHOR]

Secondary forests comprise an increasing area of the tropics and play an important role in global carbon cycling. We compare above-ground biomass accumulation of both planted and naturally regenerating trees, as well as C in the top soil layer, in three restoration treatments replicated at 14, six to eight year old restoration sites in southern Costa Rica. Restoration strategies include: control (no planting), planting tree islands, and conventional, mixed-species tree plantations. We evaluate the importance of past land-use, soil nutrients, understory cover, and surrounding forest cover in explaining variation in above-ground biomass accumulation (ABA) rate across sites. Total ABA and planted tree ABA rate were highest in plantations, intermediate in islands, and lowest in control treatments, whereas ABA rate of naturally regenerating trees did not differ across treatments. Most ABA in plantations (89%) and islands (70%) was due to growth of planted trees. Soil carbon did not change significantly over the time period of the study in any treatment. The majority of across-site variation in both total and planted tree ABA rate was explained by duration of prior pasture use. Tree growth in the first two years after planting explained approximately two-thirds of the variation in ABA rate after 6-8. years. Soil nutrient concentrations explained relatively little of the variation in planted or naturally recruiting ABA rate. Our results show that planting trees substantially increases biomass accumulation during the first several years of forest recovery in former agricultural lands and that past-land use has a strong effect on the rate of biomass accumulation. Planting tree islands is a cost-effective strategy for increasing ABA and creating more heterogeneous habitat conditions than tree plantations. We recommend small scale planting trials to quickly assess potential biomass accumulation and prioritize sites for ecosystem service payments for carbon sequestration. © 2014 Elsevier B.V.

Secondary forests comprise an increasing area of the tropics and play an important role in global carbon cycling. We compare above-ground biomass accumulation of both planted and naturally regenerating trees, as well as C in the top soil layer, in three restoration treatments replicated at 14, six to eight year old restoration sites in southern Costa Rica. Restoration strategies include: control (no planting), planting tree islands, and conventional, mixed-species tree plantations. We evaluate the importance of past land-use, soil nutrients, understory cover, and surrounding forest cover in explaining variation in above-ground biomass accumulation (ABA) rate across sites. Total ABA and planted tree ABA rate were highest in plantations, intermediate in islands, and lowest in control treatments, whereas ABA rate of naturally regenerating trees did not differ across treatments. Most ABA in plantations (89%) and islands (70%) was due to growth of planted trees. Soil carbon did not change significantly over the time period of the study in any treatment. The majority of across-site variation in both total and planted tree ABA rate was explained by duration of prior pasture use. Tree growth in the first two years after planting explained approximately two-thirds of the variation in ABA rate after 6-8. years. Soil nutrient concentrations explained relatively little of the variation in planted or naturally recruiting ABA rate. Our results show that planting trees substantially increases biomass accumulation during the first several years of forest recovery in former agricultural lands and that past-land use has a strong effect on the rate of biomass accumulation. Planting tree islands is a cost-effective strategy for increasing ABA and creating more heterogeneous habitat conditions than tree plantations. We recommend small scale planting trials to quickly assess potential biomass accumulation and prioritize sites for ecosystem service payments for carbon sequestration. © 2014 Elsevier B.V.

Copyright of Tropical Grasslands / Forrajes Tropicales is the property of International Centre for Tropical Agriculture - CIAT and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Globally, excessive grazing is identified as one of the key disturbances leading to grassland degradation and soil carbon (C) loss. Grazing exclusion has been proposed as an effective practice to restore degraded grasslands and to promote C sequestration. However, there is still little knowledge about how soil C changes with grazing exclusion in high-altitude alpine ecosystems with very cold climates. We synthesized data from 63 sites in the literature and 15 sites in a field sampling and investigated the dynamics of soil C stocks following grazing exclusion in alpine grasslands of the Tibetan Plateau. The results showed that the soil C stock increased with grazing exclusion at most sites, with average C sequestration rates of 0.84, 0.58, and 0.49 Mg ha−1 yr−1 in the soil layers of 0–10, 10–20, and 20–30 cm, respectively. Based on these results, if 60 million ha of the grasslands on Tibetan Plateau were excluded from grazing livestock by 2020 according to the national plan, then approximately 0.11 Pg C yr−1 would be sequestered in the soil which equates to about 4.4% of fossil fuel and cement CO 2 emissions in China in 2013. Generally, the rates of soil C increase exhibited a declining pattern with increasing years of grazing exclusion, with a significant decrease occurring after ten years of grazing exclusion. Of the factors examined, the rates of absolute and relative soil C change were both positively related to mean annual precipitation but negatively related to the year of grazing exclusion and initial soil C stock, respectively. The rates of soil C changes increased linearly with those of N change, and no matter how soil C changed (whether it increased or decreased), soil C:N ratios remained stable over the years of grazing exclusion. Our results implied that grazing exclusion is beneficial for soil C sequestration in degraded alpine grassland, especially in humid areas. Moreover, the intrinsic increase in N could keep up with the pace of soil C changes and would sustain soil C sequestration during the recovery process. • Grazing exclusion increased soil carbon in alpine grasslands of the Tibetan Plateau. • Grazing exclusion can sequester 1.91 Mg C ha−1 yr−1 at soil depth of 0–30 cm. • Carbon sequestration rate declined significantly after ten years of grazing exclusion. • Grazing exclusion is more beneficial for soil carbon sequestration in humid regions. • Nitrogen increase could keep up with the pace of soil carbon changes. [ABSTRACT FROM AUTHOR]

Aims: Trade-offs between slow and fast nutrient turnover rates among plants may affect soil properties and biomass production. We examined how plant traits interact with abiotic variables to modulate ecosystem properties (soil C, soil C/N ratio, aboveground biomass) in peatlands. Methods: We determined the interacting effects of abiotic variables (vegetation management, water table height) and leaf traits (specific leaf area, leaf dry-matter content, leaf C/N ratio) on ecosystem properties in two lowland fens in East Anglia, UK using structural equation modelling. Results: Our models explained between 21% and 95% of the variability in ecosystem properties. Leaf traits directly influenced soil nutrient content and plant biomass and mediated the effects of abiotic variables on ecosystem properties. Abiotic variables exerted larger effects on ecosystem properties among herbaceous communities, but leaf traits were equally important when modelling all communities in combination. Conclusions: The expected trade-offs between exploitative and conservative life strategies among species scaled-up to changes in soil properties and biomass production, even in fen habitats where abiotic variables play an important role through marked seasonal variations. Our findings suggest an important role of leaf economics in the functioning of fens, but their effects on ecosystems may be highly dependent on local conditions. [ABSTRACT FROM AUTHOR]

Abstract Nitrogen (N) and phosphorus (P) availabilities can affect soil C cycling by altering both plants and microbial activity. It remains unclear how the changes in plant and microbial processes could regulate C dynamics of different soil fractions, thereby affecting soil C sequestration. Based on a field fertilization experiment in a subalpine spruce plantation, we examined the effects of N, P and combined N and P addition (NP) treatments on plant C inputs, soil C contents and enzyme activities of bulk soil and different aggregate fractions. We aimed to explore the mechanisms by which N and P addition affected soil C sequestration. After 4-year fertilization, the N treatment increased soil C content by 21%, accompanied by suppressed polyphenol oxidase activity (−43%). However, the P and NP treatments decreased soil C content by 14% and 7%, respectively, accompanied by reduction in fine root biomass (−51% and −50%, respectively). Fertilization also affected soil aggregate C pools, with decreased C content in the macroaggregates (5000–250 μm; MaA) under the P and NP treatments, and increased C content in the silt and clay fraction (<53 μm; S&C) under all fertilization treatments. The step-AIC analysis showed that the effects of fertilization on bulk soil C content were best explained by changes in soil polyphenol oxidase activity and fine root biomass. Overall, our results indicate that N-induced soil C accrual, mainly accumulating in the S&C, could be largely driven by the suppressed oxidase activity, and that decreases in soil C content under the P and NP treatments, mostly occurring in the MaA, was likely associated with the reduced C inputs by fine roots. Highlights • N and P addition showed opposing effects on soil C sequestration. • N-induced soil C accumulation was associated with the reduced oxidase activity. • N-induced soil C accrual mainly accumulated in silt and clay fractions. • P-induced reduction in soil C was associated with the reduced fine root biomass. • P-induced decreases in soil C mostly occurred in macroaggregate fractions. [ABSTRACT FROM AUTHOR]

To avoid competition with food crops, biofuel feedstocks may need to be produced on economically marginal lands where yields are limited and replacement of existing vegetation will reduce soil C, foregoing some CO2 emission savings. Therefore, our first goal was to determine whether biochar application to marginal lands could improve switchgrass yield while sequestering sufficient soil C to eliminate the negative impact of cultivation. Because it may be difficult to obtain large quantities of biochar, our second goal was to compare small, incremental and large, all-at-once biochar applications. Our third goal was to determine whether biochar had any negative effects on earthworms, mycorrhizal fungi, soil bacteria, soil fungi, and soil enzyme activity. We grew switchgrass at two sites with poorly drained soils and two sites with excessively drained soils. Irrespective of site, biochar significantly increased yield when we rototilled in the entire amount before planting but not when we applied it incrementally between crop rows using a chisel plow. Biochar increased soil C stocks, in some cases increasing it beyond that found in soils of intact marginal land vegetation. Nevertheless, mixing biochar with soil had little or no impact on earthworm activity, mycorrhizal colonization, soil bacterial and fungal communities, and soil enzyme activities. We conclude that biochar may be part of an effective strategy for producing switchgrass on marginal lands, but the choice of application method depends on the relative importance of several considerations including biochar availability, switchgrass yield, C sequestration, soil erosion, and ease of application. [ABSTRACT FROM AUTHOR]

• Dwarf bamboo overabundance simplified vegetation structure and caused giant panda habitat degradation. • Soil organic carbon, N and P stocks decreased with increasing degradation intensity. • Dwarf bamboo overabundance initiated a decrease in soil organic carbon, N and P stocks by influencing the litter quality. Although forest degradation caused by dwarf bamboo overabundance has a significant effect on the survival of wild giant pandas, the degradation process and its impact on soil C, N and P stocks remain unclear. By investigating the vegetation structure and physicochemical analysis of litter and soil, we explored the changes in soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP) and available phosphorus (AP) stocks and the driving forces at three degradation levels triggered by dwarf bamboo overabundance in an important giant panda habitat—the subalpine coniferous forest. Dwarf bamboo overabundance following forest logging prevented tree regeneration, resulting in simplified a vegetation structure; even after 23 years of natural recovery, the clear-cut forestlands remained in the shrub stage, and the tree density and basal area were only 1.6% and 38%, respectively, of those in primary subalpine coniferous forest. With increasing degradation intensity, the litter stock and litter quality showed a decreasing trend, as did the SOC, N and P stocks in the litter layer and topsoil. The vegetation structure and litter quality together explained more than 90% of the variance in the C, N and P stocks (SOC: 97.3%, TN soil : 93.5%, AN soil : 96.2%, TP soil : 97.2% and AP soil : 97.0%), and litter quality had greater explanatory power than the vegetation structure. The SEM analysis results showed that the increase in dwarf bamboo density caused by the reduction in tree basal area affected the litter C/N and C/P ratios, and ultimately reduced the SOC, N soil and P soil stocks. This study highlights that dwarf bamboo overabundance not only causes forest degradation but also reduces the carbon sequestration function of giant panda habitat, leading to the loss of soil N and P. We suggest that reducing bamboo abundance can promote the recovery of the soil carbon, nitrogen and phosphorus stocks in degraded giant panda habitats. [ABSTRACT FROM AUTHOR]

Most experimental studies measuring the effects of climate change on terrestrial C cycling have focused on processes that occur at relatively short time scales (up to a few years). However, climate-soil C interactions are influenced over much longer time scales by bioturbation and soil weathering affecting soil fertility, ecosystem productivity, and C storage. Elevated CO2can increase belowground C inputs and stimulate soil biota, potentially affecting bioturbation, and can decrease soil pH which could accelerate soil weathering rates. To determine whether we could resolve any changes in bioturbation or C storage, we investigated soil profiles collected from ambient and elevated-CO2plots at the Free-Air Carbon-Dioxide Enrichment (FACE) forest site at Oak Ridge National Laboratory after 11 years of 13C-depleted CO2 release. Profiles of organic carbon concentration, δ13C values, and activities of 137Cs, 210Pb, and 226Ra were measured to ∼30 cm depth in replicated soil cores to evaluate the effects of elevated CO2 on these parameters. Bioturbation models based on fitting advection-diffusion equations to 137Cs and 210Pb profiles showed that ambient and elevated-CO2 plots had indistinguishable ranges of apparent biodiffusion constants, advection rates, and soil mixing times, although apparent biodiffusion constants and advection rates were larger for 137Cs than for 210Pb as is generally observed in soils. Temporal changes in profiles of δ13C values of soil organic carbon (SOC) suggest that addition of new SOC at depth was occurring at a faster rate than that implied by the net advection term of the bioturbation model. Ratios of (210Pb/226Ra) may indicate apparent soil mixing cells that are consistent with biological mechanisms, possibly earthworms and root proliferation, driving C addition and the mixing of soil between ∼4 cm and ∼18 cm depth. Burial of SOC by soil mixing processes could substantially increase the net long-term storage of soil C and should be incorporated in soil-atmosphere interaction models.

Nitrogen (N) and phosphorus (P) have a critical role in soil carbon (C) cycling, but the mechanisms underlying the responses of soil C dynamics to N and P availability remain unclear because both N and P addition have divergent effects on different soil C pools. Here, we studied enzyme activities and C dynamics in bulk soil and three aggregate fractions, i.e. macroaggregates (5000-250 μm; MaA), microaggregates (250-53 μm; MiA) and silt and clay (< 53 μm; S&C), following two growing seasons of N addition (0, 5 and 20 g N m−2 y−1) fully crossed with P addition (15 g P m−2 y−1) in a subalpine spruce plantation. We found increased activities of two oxidases (catalase and polyphenol oxidase) in bulk soil following N and P addition. β-glucosidase activity was suppressed by N in MiA (− 34%) and S&C (− 23%) but increased by P in MaA (+ 35%). P addition increased catalase activity of S&C (+ 20%). Bulk soil C content showed no significant response to N or P addition, whereas C distribution in soil aggregates was affected, with increased relative C content of S&C in N-only addition plots (+ 53%) and increased relative C content of MaA after P addition (+ 11%). Our results demonstrated divergent sensitivities of both C pools and enzyme activities in different soil aggregates to fertilization, which can enhance our understanding of the responses of bulk soil C pool and enzyme activities to fertilization. [ABSTRACT FROM AUTHOR]

Most experimental studies measuring the effects of climate change on terrestrial C cycling have focused on processes that occur at relatively short time scales (up to a few years). However, climate-soil C interactions are influenced over much longer time scales by bioturbation and soil weathering affecting soil fertility, ecosystem productivity, and C storage. Elevated CO2 can increase belowground C inputs and stimulate soil biota, potentially affecting bioturbation, and can decrease soil pH which could accelerate soil weathering rates. To determine whether we could resolve any changes in bioturbation or C storage, we investigated soil profiles collected from ambient and elevated-CO2 plots at the Free-Air Carbon-Dioxide Enrichment (FACE) forest site at Oak Ridge National Laboratory after 11 years of 13C-depleted CO2 release. Profiles of organic carbon concentration, δ13C values, and activities of 137Cs, 210Pb, and 226Ra were measured to ~30 cm depth in replicated soil cores to evaluate the effects of elevated CO2 on these parameters. Bioturbation models based on fitting advectiondiffusion equations to 137Cs and 210Pb profiles showed that ambient and elevated-CO2 plots had indistinguishable ranges of apparent biodiffusion constants, advection rates, and soil mixing times, although apparent biodiffusion constants and advection rates were larger for 137Cs than for 210Pb as is generally observed in soils. Temporal changes in profiles of δ13C values of soil organic carbon (SOC) suggest that addition of new SOC at depth was occurring at a faster rate than that implied by the net advection term of the bioturbation model. Ratios of (210Pb/226Ra) may indicate apparent soil mixing cells that are consistent with biological mechanisms, possibly earthworms and root proliferation, driving C addition and the mixing of soil between ~4 cm and 18 cm depth. Burial of SOC by soil mixing processes could substantially increase the net long-term storage of soil C and should be incorporated in soil-atmosphere interaction models. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric nitrogen (N) deposition has increased dramatically since preindustrial times and continues to increase across many regions of the Earth. In temperate forests, this agent of global change has increased soil carbon (C) storage, but the mechanisms underlying this response are not understood. One long‐standing hypothesis proposed to explain the accumulation of soil C proposes that higher inorganic N availability may suppress both the activity and abundance of fungi that decay lignin and other polyphenols in soil. In field studies, elevated rates of N deposition have reduced the activity of enzymes mediating lignin decay, but a decline in the abundance of lignolytic fungi has not been definitively documented to date. Here, we tested the hypothesis that elevated rates of anthropogenic N deposition reduce the abundance of lignolytic fungi. We conducted a field experiment in which we compared fungal communities colonizing low‐lignin, high‐lignin, and wood substrates in a northern hardwood forest that is part of a long‐term N deposition experiment. We reasoned that if lignolytic fungi decline under experimental N deposition, this effect should be most evident among fungi colonizing high‐lignin and wood substrates. Using molecular approaches, we provide evidence that anthropogenic N deposition reduces the relative abundance of lignolytic fungi on both wood and a high‐lignin substrate. Furthermore, experimental N deposition increased total fungal abundance on a low‐lignin substrate, reduced fungal abundance on wood, and had no significant effect on fungal abundance on a high‐lignin substrate. We simultaneously examined these responses in the surrounding soil and forest floor, in which we did not observe significant reductions in the relative abundance of lignolytic fungi or in the size of the fungal community; however, we did detect a change in community composition in the forest floor that appears to be driven by a shift away from lignolytic fungi and towards cellulolytic fungi. Our results provide direct evidence that reductions in the abundance of lignolytic fungi are part of the mechanism by which anthropogenic N deposition increases soil C storage. [ABSTRACT FROM AUTHOR]

Carbonates constitute a significant proportion of the soil mass in many semi-arid soils. Due to their solubility, they can be affected by changes in the soil water regime. This needs to be taken into account when assessing the environmental and agronomical impacts of the adoption of irrigation. To gain knowledge on the importance of the effect of irrigation on carbonates dynamics in the tilled layer (0–20 cm) of agricultural soils, we conducted a two-step study embracing field observations and numerical simulation. First, carbonates storage and their size distribution were quantified for two different situations (irrigation and non-irrigation) in three irrigation districts with different time under irrigation (Valtierra (19 years), Miranda (5 years) and Funes (12 years)) in Navarre (Spain). Soil sampling was designed to ensure homogeneous comparisons in the most characteristic soil types at each site ( Xeric Haplocalcid , Typic Calcixerept and Xeric Haplocalcid , respectively). Carbonates concentration was systematically lower with irrigation in the finest (< 50 μm) soil fraction: 22.2 ± 1.4 g carbonates 100 g − 1 fraction without irrigation for 16.1 ± 0.9 with irrigation in Valtierra, 26.7 ± 1.1 for 19.1 ± 3.8 in Miranda and 27.8 ± 2.9 for 22.7 ± 1.5 at Funes1. However, the net annual balance of total carbonates-C between irrigated and non-irrigated condition was neutral at the three sites. This can be explained by agricultural management affecting carbonates in the sand-size fraction, including the addition of carbonates with fertilizers, and coarse carbonate particles brought to the surface by tillage. In a second step, a simplified model was developed for use with easily available data in most irrigation districts, and numerical simulations of the geochemical interactions between the soil, the soil solution and irrigation water were run using actual soil and soil solution data from the tilled layer of another pair of plots in Funes (Funes2). Sensitive analysis was also conducted to investigate the potential impact of water quality and crop types as sources of variability on the model outputs. The modelling results showed annual values of carbonates-C loss in the range between 13.52 and 12.06 g m − 2 year − 1 in the studied depth under irrigation, depending on the quality of irrigation water, for 0.46 g m − 2 without irrigation. These data were within the range of carbonates budgets found in the literature but one order of magnitude lower than the observed results in the fine fraction in the field. Overall, our results showed that irrigation can significantly alter carbonates dynamics in semi-arid Mediterranean land, which implies that human use can significantly alter the mineral phase of these soils in a relatively short time lapse. Simple geochemical models can be a useful approach to evaluate changes in the carbonates balance at the local and regional scale when irrigation is applied, although they have to be improved to account for other factors related to agricultural management and local geochemical conditions. [ABSTRACT FROM AUTHOR]

Understanding the response of soil respiration to climate variability is critical to formulate realistic predictions of future carbon (C) fluxes under different climate change scenarios. There is growing evidence that the influence of long-term climate variability in C fluxes from terrestrial ecosystems is modulated by adjustments in the aboveground-belowground links. Here, we studied the inter-annual variability in soil respiration from a wet shrubland going through successional change in North Wales (UK) during 13 years. We hypothesised that the decline in plant productivity observed over a decade would result in a decrease in the apparent sensitivity of soil respiration to soil temperature, and that rainfall variability would explain a significant fraction of the inter-annual variability in plant productivity, and consequently, in soil respiration, due to excess-water constraining nutrient availability for plants. As hypothesised, there were parallel decreases between plant productivity and annual and summer CO emissions over the 13-year period. Soil temperatures did not follow a similar trend, which resulted in a decline in the apparent sensitivity of soil respiration to soil temperature (apparent Q values decreased from 9.4 to 2.8). Contrary to our second hypothesis, summer maximum air temperature rather than rainfall was the climate variable with the greatest influence on aboveground biomass and annual cumulative respiration. Since summer air temperature and rainfall were positively associated, the greatest annual respiration values were recorded during years of high rainfall. The results suggest that adjustments in plant productivity might have a critical role in determining the long-term-sensitivity of soil respiration to changing climate conditions. [ABSTRACT FROM AUTHOR]

Reforestation of agricultural lands is an important means of restoring land and sequestering carbon (C). At large scales, the labour and costs of direct measurement of ecosystem responses can be prohibitive, making the development of models valuable. Here, we develop a new sampling scenario-based modelling approach coupled with Bayesian model averaging to build predictive models for absolute values in mixed-species woody plantings and differences from their adjacent pasture, for litter stocks, soil C stocks and soil C:N ratios. Modelling scenarios of increasing data availability and effort were tested. These included variables that could be derived without a site visit (e.g. location, climate and management) that were sampled in the adjacent pasture (e.g. soil C and nutrients) or were sampled in the environmental planting (e.g. vegetation, litter properties, soil C and nutrients). The predictive power of models varied considerably among C variables (litter stocks, soil C stocks and soil C:N ratios in tree plantings and their differences to their adjacent pastures) and the model scenarios used. The use of a sampling scenario-based approach to building predictive models shows promise for monitoring changes in tree plantings, following reforestation. The approach could also be readily adapted to other contexts where sampling effort for predictor variables in models is a major potential limitation to model utilization. This study demonstrates the benefit of exploring scenarios of data availability during modelling and will be especially valuable where the sampling effort differs greatly among variables. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The carbon (C) dynamics of a bioenergy system are key to correctly defining its viability as a sustainable alternative to conventional fossil fuel energy sources. Recent studies have quantified the greenhouse gas mitigation potential of these bioenergy crops, often concluding that C sequestration in soils plays a primary role in offsetting emissions through energy generation. Miscanthus is a particularly promising bioenergy crop and research has shown that soil C stocks can increase by more than 2 t C ha yr. In this study, we use a stable isotope (C) technique to trace the inputs and outputs from soils below a commercial Miscanthus plantation in Lincolnshire, UK, over the first 7 years of growth after conversion from a conventional arable crop. Results suggest that an unchanging total topsoil (0-30 cm) C stock is caused by Miscanthus additions displacing older soil organic matter. Further, using a comparison between bare soil plots (no new Miscanthus inputs) and undisturbed Miscanthus controls, soil respiration was seen to be unaffected through priming by fresh inputs or rhizosphere. The temperature sensitivity of old soil C was also seen to be very similar with and without the presence of live root biomass. Total soil respiration from control plots was dominated by Miscanthus-derived emissions with autotrophic respiration alone accounting for ∼50 % of CO. Although total soil C stocks did not change significantly over time, the Miscanthus-derived soil C accumulated at a rate of 860 kg C ha yr over the top 30 cm. Ultimately, the results from this study indicate that soil C stocks below Miscanthus plantations do not necessarily increase during the first 7 years. [ABSTRACT FROM AUTHOR]

National governments and international organizations perceive bioenergy, from crops such as Miscanthus, to have an important role in mitigating greenhouse gas ( GHG) emissions and combating climate change. In this research, we address three objectives aimed at reducing uncertainty regarding the climate change mitigation potential of commercial Miscanthus plantations in the United Kingdom: (i) to examine soil temperature and moisture as potential drivers of soil GHG emissions through four years of parallel measurements, (ii) to quantify carbon (C) dynamics associated with soil sequestration using regular measurements of topsoil (0-30 cm) C and the surface litter layer and (iii) to calculate a life cycle GHG budget using site-specific measurements, enabling the GHG intensity of Miscanthus used for electricity generation to be compared against coal and natural gas. Our results show that methane ( CH4) and nitrous oxide (N2O) emissions contributed little to the overall GHG budget of Miscanthus, while soil respiration offset 30% of the crop's net aboveground C uptake. Temperature sensitivity of soil respiration was highest during crop growth and lowest during winter months. We observed no significant change in topsoil C or nitrogen stocks following 7 years of Miscanthus cultivation. The depth of litter did, however, increase significantly, stabilizing at approximately 7 tonnes dry biomass per hectare after 6 years. The cradle-to-farm gate GHG budget of this crop indicated a net removal of 24.5 t CO2-eq ha−1 yr−1 from the atmosphere despite no detectable C sequestration in soils. When scaled up to consider the full life cycle, Miscanthus fared very well in comparison with coal and natural gas, suggesting considerable CO2 offsetting per kWh generated. Although the comparison does not account for the land area requirements of the energy generated, Miscanthus used for electricity generation can make a significant contribution to climate change mitigation even when combusted in conventional steam turbine power plants. [ABSTRACT FROM AUTHOR]

Evaluating the response of soil organic matter decomposition to warming and changes in rainfall is critical to assess the likelihood of proposed positive feedbacks from the terrestrial to the atmospheric system. The response of soil respiration and extracellular activities (EEAs) to long-term warming and recurrent summer drought was studied in a wet shrubland ecosystem in Wales (UK), after 13 years of climate change simulation in a whole-ecosystem experiment. Over a year soil respiration, temperature and moisture was monitored in the field. During the summer season, coinciding with maximum soil respiration rates, soil inorganic N and P, microbial biomass and the extracellular activities (EEAs) of a selection of enzymes involved in C, N and P cycling were analysed. Based on previous field measurements of C and N mineralization, we expected a stronger response of C-cycling EEAs, in comparison to N-cycling EEAs, to drought and warming, and a greater sensitivity of C-cycling EEAs to drought than to warming. Drought had a clear impact on soil respiration during the summer season. However, the availability of inorganic N or P was not significantly affected by the treatments. Microbial biomass and C:N ratio also remained unchanged. In contrast to one of our hypothesis, C-cycling EEAs measured under non-optimal conditions that simulated soil environment in the field (pH of 4.1 and with a temperature incubation of 10 °C) showed no significant differences due to long-term warming and recurring drought treatments. Possibly, this assay approach may have obscured treatment effects on the soil enzyme pool. Our results highlight the need for developing methods for the in-situ analysis of EEAs to determine rates of reactions. [ABSTRACT FROM AUTHOR]

Soil respiration (Rs) is the second largest carbon flux in terrestrial ecosystems and therefore plays a crucial role in global carbon (C) cycling. This biogeochemical process is closely related to ecosystem productivity and soil fertility and is considered as a key indicator of soil health and quality reflecting the level of microbial activity. Wildfires can have a significant effect on Rs rates and the magnitude of the impacts will depend on environmental factors such as climate and vegetation, fire severity and meteorological conditions post-fire. In this research, we aimed to assess the impacts of a wildfire on the soil CO 2 fluxes and soil respiration in a semi-arid ecosystem of Western Australia, and to understand the main edaphic and environmental drivers controlling these fluxes for different vegetation types. Our results demonstrated increased rates of Rs in the burnt areas compared to the unburnt control sites, although these differences were highly dependent on the type of vegetation cover and time since fire. The sensitivity of Rs to temperature ( Q 10) was also larger in the burnt site compared to the control. Both Rs and soil organic C were consistently higher under Eucalyptus trees, followed by Acacia shrubs. Triodia grasses had the lowest Rs rates and C contents, which were similar to those found under bare soil patches. Regardless of the site condition (unburnt or burnt), Rs was triggered during periods of higher temperatures and water availability and environmental factors (temperature and moisture) could explain a large fraction of Rs variability, improving the relationship of moisture or temperature as single factors with Rs. This study demonstrates the importance of assessing CO 2 fluxes considering both abiotic factors and vegetation types after disturbances such as fire which is particularly important in heterogeneous semi-arid areas with patchy vegetation distribution where CO 2 fluxes can be largely underestimated. [ABSTRACT FROM AUTHOR]

We assessed the impact of a single application of wood biochar on soil chemical and physical properties and aerobic rice grain yield on an irrigated kaolinitic clay Ferralsol in a tropical Savannah. We used linear mixed models to analyse the response of soil and plant variables to application rates of biochar (0, 8, 16 and 32 t ha − 1 ) and mineral N fertilization (0, 30, 60 and 90 kg N ha − 1 ), and their interaction. The response was analysed within three aerobic rice-growing seasons (S), equivalent to 1.5, 2.5 and 3.5 years after biochar application (S1.5, S2.5 and S3.5). The fraction of oxidisable C in soil increased with biochar application rate, irrespective of N fertilization, at S2.5 and S3.5, whereas the rice stress-free available water (soil water retention between − 6 and − 100 kPa) decreased with biochar application rate at S1.5 and S2.5. Rice grain yield and yield components varied with the seasons according to the changes in soil properties and weather conditions. A single application rate up to 32 t ha − 1 of the wood biochar type used in this study had no impact on aerobic rice yield increase on a kaolinitic clay Ferralsol under the climatic conditions of the Brazilian Savannah prone to dry spells. Most likely, the beneficial effects of wood biochar on soil chemical properties on rice production were offset by a decrease in soil water retention capacity and N uptake by the crop. [ABSTRACT FROM AUTHOR]

Primary succession is limited by both ecosystem development and plant dispersal, but the extent to which dispersal constrains succession over the long-term is unknown. We compared primary succession along two co-occurring arctic chronosequences with contrasting spatial scales: sorted circles that span a few meters and may have few dispersal constraints and glacial forelands that span several kilometers and may have greater dispersal constraints. Dispersal constraints slowed primary succession by centuries: plots were dominated by cryptogams after 20 years on circles but after 270 years on forelands; plots supported deciduous plants after 100 years on circles but after >400 years on forelands. Our study provides century-scale evidence suggesting that dispersal limitations constrain the rate of primary succession in glacial forelands. [ABSTRACT FROM AUTHOR]

The removal of perennial bioenergy crops, such as Miscanthus, has rarely been studied although it is an important form of land use change. Miscanthus is a C4 plant, and the carbon (C) it deposits during its growth has a different isotopic signature (12/13C) compared to a C3 plant. Identifying the proportion of C stored and released to the atmosphere is important information for ecosystem models and life cycle analyses. During a removal experiment in June 2011 of a 20-year old Miscanthus field (Grignon, France), vegetation was removed mechanically and chemically. Two replicate plots were converted into a rotation of annual crops, two plots had Miscanthus removed with no soil disturbance, followed by bare soil (set-aside), one control plot was left with continued Miscanthus cultivation, and an adjacent field was used as annual arable crops control. There was a significant difference in the isotopic composition of the total soil C under Miscanthus compared with adjacent annual arable crops in all three measured soil layers (0-5, 5-10 and 10-20 cm). Before Miscanthus removal, total C in the soil under Miscanthus ranged from 4.9% in the top layer to 3.9% in the lower layers with δ13C values of −16.3 to −17.8 while soil C under the adjacent arable crop was significantly lower and ranged from 1.6 to 2% with δ13C values of −23.2. This did not change much in 2012, suggesting the accumulation of soil C under Miscanthus persists for at least the first year. In contrast, the isotopic signals of soil respiration 1 year after Miscanthus removal from recultivated and set-aside plots were similar to that of the annual arable control, while just after removal the signals were similar to that of the Miscanthus control. This suggests a rapid change in the form of soil C pools that are respired. [ABSTRACT FROM AUTHOR]

Decisions to use crop residues as soil cover for conservation agriculture create trade-offs for farmers who own cattle in crop-livestock systems. Trade-offs among soil C, crop and animal and crop productivity were analysed using the NUANCES-FARMSIM (FArm-scale Resource Management SIMulator) dynamic model. Retention on the soil surface of 0, 25, 50, 75 and 100% of the maize stover yield produced per farm, and the use of the remainder as animal feed was quantified over a 12 year period for four farm types in Murehwa, Zimbabwe. Retaining 100% maize residues in the field led to an annual loss of on average 68 and 93 kg body weight per animal for cattle on farms of the relatively wealthiest farmers (Resource Group, RG1) who had most land and cattle and RG2 respectively), and is therefore unsustainable for livestock production. There was an increase in grain yield of 1.6 t farm −1 and 0.7 t farm −1 for RG1 and RG2 respectively. Farmers without cattle (RG3 and RG4) may have a greater incentive for retaining their crop residues but they have to invest labour to keep the residues during the dry season. However, improved crop productivity for these farmers is limited by lack of access to fertiliser. The current practice of allocating all crop residues to animals results in average gross margin of US$7429 and US$4037 for RG1 and RG2 farmers respectively. Our results showed that from an economic perspective, it is logical that farmers prioritise the sustenance of cattle with crop residues over soil fertility management. We conclude that at current productivity levels, farmers who own cattle have limited scope to allocate crop residues for soil cover as it leads to significant loss in animal production and economic value. [ABSTRACT FROM AUTHOR]

• The farmland soil in Jiangxi Province is facing a serious threat of acidification. • parental materials and soil group greatly affect soil C, N and P stoichiometry. • The MAT and MAP is significantly related to soil C, N and P stoichiometry. • The cropping system has essential effect on soil C, N and P stoichiometry. • Straw return could clearly increase the soil N:P ratio. Soil carbon (C), nitrogen (N), and phosphorus (P) contents and its stoichiometry are important indicators of the elemental balance in ecological interactions and processes. Farmland usually is featured by extensive anthropogenic actions which profoundly alters the soil C, N, P contents and its stoichiometry. However, it remains largely unknown how the soil C, N and P stoichiometry in farmlands is comprehensively affected by natural factors including parental material, soil types, annual mean temperature, annual precipitation, and soil management measures such as crop rotation and straw return at large spatial scale. The main aim of this study is to analyze the summary statistics, spatial variability, as well as main controls of soil C, N and P stoichiometry in farmland of the whole Jiangxi Province, which is one of the most important food production base. Our results found that the average concentration of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) is 17.91, 1.58 and 0.52 g kg−1 in farmland soil of Jiangxi Province, respectively. The averaged value of the soil C:N, the soil C:P ratio, and the soil N:P ratio is 11.73, 38.31 and 3.38, correspondingly. Great differences were detected for C, N and P stoichiometry in farmland soil derived from different parental materials or different soil groups. The mean annual temperature (MAT) is significantly and negatively related to soil C:N ratio, soil C:P ratio as well as soil N:P ratio while the annual precipitation (MAP) is significantly and positively related to soil C:P ratio, soil N:P ratio but significantly and negatively related to soil C:N ratio. The structural equation model analysis showed that soil properties and soil management have greater influences on soil C, N and P stoichiometry than climate and lithology. Our results could provide important implications for soil management and agricultural production. [ABSTRACT FROM AUTHOR]

Background and aims: A strategy to increase soil C under pasture-based systems is to increase the root mass inputs or increase rooting depth of plants. Our objective in this study was to measure the seasonal dynamics of root mass and C inputs under two different pasture types (ryegrass-clover vs moderately diverse) that differ in plant diversity and which are commonly used in New Zealand agriculture. Methods: This study was carried out on an existing plant diversity field trial containing six replicate paddocks of both moderately-diverse and ryegrass-clover pastures. Soil cores (0-100-200-300 mm sections) were collected seasonally across 1 year and individual root traits assessed from all species. Results: The moderately diverse pasture had greater root mass (5320-9350 kg ha) than the ryegrass-clover pasture (3810-5700 kg ha) for all seasons and had greater root mass lower in the soil profile. A secondary objective demostrated no significant difference in root mass between high and low sugar ryegrass cultivar. Increased root mass results in an estimated increase of C input to the soil of about 1203 kg C ha (0-300 mm depth) under the moderately diverse pasture, excluding root exudates. Root trait measurements demonstrated a greater diversity of root traits in the moderately diverse sward compared to the ryegrass-clover pasture. Conclusions: Moderately diverse pasture systems offer scope to increase soil C under grazed pastures through increased root mass inputs and rooting depth. [ABSTRACT FROM AUTHOR]

Reforestation has large potential for mitigating climate change through carbon sequestration. Native mixed-species plantings have a higher potential to reverse biodiversity loss than do plantations of production species, but there are few data on their capacity to store carbon. A chronosequence (5-45 years) of 36 native mixed-species plantings, paired with adjacent pastures, was measured to investigate changes to stocks among C pools following reforestation of agricultural land in the medium rainfall zone (400-800 mm yr−1) of temperate Australia. These mixed-species plantings accumulated 3.09 ± 0.85 t C ha−1 yr−1 in aboveground biomass and 0.18 ± 0.05 t C ha−1 yr−1 in plant litter, reaching amounts comparable to those measured in remnant woodlands by 20 years and 36 years after reforestation respectively. Soil C was slower to increase, with increases seen only after 45 years, at which time stocks had not reached the amounts found in remnant woodlands. The amount of trees (tree density and basal area) was positively associated with the accumulation of carbon in aboveground biomass and litter. In contrast, changes to soil C were most strongly related to the productivity of the location (a forest productivity index and soil N content in the adjacent pasture). At 30 years, native mixed-species plantings had increased the stability of soil C stocks, with higher amounts of recalcitrant C and higher C : N ratios than their adjacent pastures. Reforestation with native mixed-species plantings did not significantly change the availability of macronutrients (N, K, Ca, Mg, P, and S) or micronutrients (Fe, B, Mn, Zn, and Cu), content of plant toxins (Al, Si), acidity, or salinity (Na, electrical conductivity) in the soil. In this medium rainfall area, native mixed-species plantings provided comparable rates of C sequestration to local production species, with the probable additional benefit of providing better quality habitat for native biota. These results demonstrate that reforestation using native mixed-species plantings is an effective alternative for carbon sequestration to standard monocultures of production species in medium rainfall areas of temperate continental climates, where they can effectively store C, convert C into stable pools and provide greater benefits for biodiversity. [ABSTRACT FROM AUTHOR]

'Blue Carbon' initiatives have highlighted the significant role of seagrasses in organic carbon ( C) burial and sequestration. However, global databases on the extent of C stocks in seagrass ecosystems are largely comprised of studies conducted in monospecific beds from a limited number of regions, thus potentially biasing global estimates. To better characterize carbon stocks in seagrass beds of varying structure and composition, and to further expand the current 'Blue Carbon' database to under-represented regions, we evaluate the extent of C stocks in the relatively undocumented seagrass meadows of the Arabian Gulf. Surveys were conducted along the coast of Abu Dhabi (UAE) and encompassed sites ranging from sheltered embayments to offshore islands. Seagrass beds consisted of Halodule uninervis, Halophila ovalis and Halophila stipulacea. While seagrasses were widely distributed along the coast, both living and soil C stores were relatively modest on an areal basis. Total seagrass biomass ranged from 0.03 to 1.13 Mg C ha, with a mean of 0.4 ± 0.1 (±SEM), and soil C stocks (as estimated over the top meter) ranged from 1.9 to 109 Mg C ha, with a mean of 49.1 ± 7.0 (±SEM). However, owing to the expansive distribution of seagrasses in the Arabian Gulf, seagrass 'Blue Carbon' stocks were large, with 400 Gg C stored in living seagrass biomass and 49.1 Tg C stored in soils. Thus, despite low C stores for any given location, the overall contribution of seagrass beds to carbon storage are relatively large given their extensive coverage. This research adds to a growing global dataset on carbon stocks and further demonstrates that even seagrass beds dominated by small-bodied species function to store carbon in coastal environments. [ABSTRACT FROM AUTHOR]

Conservative site management practices such as harvest residue retention can potentially convey long term benefits for site sustainability, but they are only practiced to a limited extent in many Eucalyptus plantations in the tropical regions. Burning and/or removal of harvest residues can remove substantial quantities of nutrients, but it is still common practice in many parts of India. We explored the effect of harvest residue retention or removal on soil properties at 4 multi-rotation Eucalyptus plantations in Kerala, India. Soil carbon, N and P content were little influenced by differing harvest residue treatments. Interestingly, soil N mineralization rates were affected only minimally by harvest residue retention at individual sites, however, laboratory incubations demonstrated a significant increase in soil N-mineralization potential with increasing harvest residue additions. Soil microbial biomass was influenced to a lesser extent by harvest residue retention. We conclude that harvest residue retention can help to sustain the soil fertility in subsequent rotations and minimize the loss of nutrients from the sites, but fertilizers are still likely to be an important part of the nutrient management regime for productive plantations. [ABSTRACT FROM AUTHOR]

Background and aims: Growth and distribution of fine roots closely depend on soil resource availability and affect soil C distribution in return. Understanding of relationships between fine root distribution and soil C can help to predict the contribution of fine root turnover to soil C accumulation. Methods: A study was conducted in a subtropical Cunninghamia lanceolata plantation to assess the fine root mass density (FRMD), fine root C density (FRCD) of different fine root groups as well as their relations with soil C. Results: The FRMD and FRCD of short-lived roots, dead roots and herb roots peaked in the 0-10 cm soil layer and decreased with soil depth, while FRMD, FRCD of long-lived roots peaked in the 10-20 cm soil layer. Soil C was positively related to FRMD and FRCD of total fine roots (across all three soil layers), dead roots (0-10 cm) and herb roots (10-20 cm) as well as FRCD of short-lived roots (20-40 cm) (P <0.05). Conclusions: Soil C was mainly affected by herb roots in upper soil layers and by woody plant roots in deeper soil layers. [ABSTRACT FROM AUTHOR]

Highlights: [•] We compared above-ground biomass accumulation (ABA) in tropical forest restoration. [•] ABA rates were plantations>island tree plantings>control treatments. [•] Duration of prior pasture use best explained differences in planted tree ABA rate. [•] Tree height after two years was a strong predictor of planted tree ABA rate. [•] Soil nutrient concentrations explained minimal differences in ABA rate. [Copyright &y& Elsevier]

Simulation models are useful tools for assessment of the impacts of agriculture on nutrient and soil organic C (SOC) dynamics. Results of simulation studies can be applied to develop sustainable agricultural systems. This study simulated SOC in clayey Humic Hapludox with Century model (version 4.0) in a subtropical climate, with support from historical soil and land-use surveys; GIS and remote sensing techniques. Major reductions in SOC stocks were observed after land under native vegetation was converted to agricultural use, especially under annual crops managed under conventional tillage. Simulations of these soils under current management to the year 2058 showed that soils under conservation systems (especially no tillage) can recover and in some cases even exceed the original SOC stocks under native vegetation. [ABSTRACT FROM AUTHOR]