Soil Organic C Stocks Research Articles

Soil Organic Carbon Stock Assessment for Volunteer Carbon Removal Benefit: Methodological Approach in Chestnut Orchard for Fruit Production

The implementation of a protocol for supporting a reliable soil C market is needed. This paper aims to propose a methodology for evaluating soil organic C (SOC) stock changes for the C credit market. A 15-year-old chestnut orchard (CO) and a chestnut coppice (CC) as reference land were selected in the northern part of the Apennine chain (Italy). The CO is the result of the CC conversion carried out in 2005. The soil sampling by pedogenetic horizons till parent material was carried out in 2005, 2010, 2015 and 2020 in CO and in 2005 and 2020 in CC. For each sample, the concentration and stock of the total SOC and of the most recalcitrant SOC form were estimated. Unlike the CC, in CO, an increase over time of SOC stocks was observed throughout the entire soil profile indicating the suitability of CO for C credit gaining. Most of the SOC was stored within the deepest soil horizon. The methodology can be considered eligible for the C credit market because, replicable, the CO was intentionally realized by humans after 1990, and the additionality was evaluated. Moreover, soil functionality was considered through the evaluation of SOC forms and of the pedogenetic horizons.

Storage and Stability of Soil Organic Carbon in Two Temperate Forests in Northeastern China

Forests worldwide store large quantities of carbon (C), particularly in soils as soil organic C (SOC). In northeastern China, two dominant forest types, secondary mixed forest (MF) and larch plantation forest (LF), cover extensive areas. However, we lack an understanding of the patterns and the mechanisms of SOC storage and stabilization in MF and LF, especially in deep soil layers. This research aims to illustrate the vertical distribution and mineral protection of SOC over soil depth; we also used δ13C values of soil fractions to evaluate SOC stability. Samples from the surface litter (Oi), organic layer (Oa+e), and 0–40 cm mineral soils were collected from both MF and LF plots. We used two different methods to separate bulk soils into distinguished fractions: (1) macro- and micro-aggregates and the non-aggregated fraction, and (2) particulate organic matter (POM) and mineral-associated organic matter (MAOM). The C concentrations, C stocks, and δ13C of all soil fractions were determined. Our findings were as follows: (1) SOC was mainly stored in mineral soils and was 13.6% lower in LF (8609 ± 1180 g C m−2) than MF (9969 ± 2084 g C m−2). (2) In both MF and LF, the SOC stock was mainly stored in aggregates (averaged 92.7%); macroaggregates dominated in the surface layers (Oa+e layer and 0–10 cm) but microaggregates dominated in the deep layers (10–20 cm and 20–40 cm). In mineral soils, MAOM was the dominant fraction of the C stock (averaged 81.6%). (3) The proportion of C distributed in microaggregates and MAOM increased from Oa+e to the 20–40 cm layer. (4) The C/N ratios and δ13C values of MAOM were smaller and heavier compared to those of POM. Our study demonstrated that in both forests, aggregate formation and mineral association predominantly contributed to SOC storage, and large stocks of SOC were distributed in the deep soil. The increasing proportion of SOC in microaggregates and MAOM along the soil depth, most likely derived from microbial turnover and microbial necromass, influenced SOC stability in both forest types.

Near-Term Effects of Perennial Grasses on Soil Carbon and Nitrogen in Eastern Nebraska

Incorporating native perennial grasses adjacent to annual row crop systems managed on marginal lands can increase system resiliency by diversifying food and energy production. This study evaluated (1) soil organic C (SOC) and total N stocks (TN) under warm-season grass (WSG) monocultures and a low diversity mixture compared to an adjacent no-till continuous-corn system, and (2) WSG total above-ground biomass (AGB) in response to two levels of N fertilization from 2012 to 2017 in eastern Nebraska, USA. The WSG treatments consisted of (1) switchgrass (SWG), (2) big bluestem (BGB), and (3) low-diversity grass mixture (LDM; big bluestem, Indiangrass, and sideoat grama). Soils were sampled at fixed depth increments (0–120 cm) in the WSG plots and in the adjacent corn experiment in 2012 and 2017. Soil stocks (Mg ha−1) of SOC and TN were calculated on an equivalent soil mass (ESM) basis and compared within the three WSG treatments as well as between experiments (corn compared to the mean of all WSGs). Soil organic C and TN stocks within soil layers and cumulative stocks responded to the main effect of WSG (PWSG < 0.05) but were no different when comparing the WSGs to corn (Pexpt = NS). Both SOC/TN stocks and cumulative stocks were generally greater in the LDM compared to the BGB. Neither SOC nor TN changed over time under either the WSGs or corn. Warm-season grass AGB responded to a three-way interaction of year, N rate, and WSG (p = 0.0007). Decreases in AGB over time were significant across WSGs and N levels except for SWG at 56 kg N ha−1 and LDM at 112 kg N ha−1. Above-ground biomass was generally greater in the LDM after the first harvest year (2013). Results suggest that incorporating WSGs into marginal cropland can maintain SOC and TN stocks while providing a significant source of biomass to be used in energy production or in integrated livestock systems.

No-till is more of sustaining the soil than a climate change mitigation option

No-till is often referred to as a climate change mitigation option, possibly with a stronger conviction, than as a practice to manage soil organic C (SOC) content. We conducted a global meta-analysis to evaluate the effect of no-till (NT) on SOC concentration (SOCc, g C kg−1 soil) and stock (SOCs, Mg C ha−1 land) across climate, soil texture, cropping systems, and no-till duration to appraise the priority-setting. Compared to conventional tillage, NT favoured a significant rise (ΔSOCc) of 38% in the 0–5 cm soil layer and a much lesser 6% increase in the 5–10 cm layer and no change beyond 10 cm. The temperate climate had nearly twice ΔSOCc in the 0–5 cm layer compared to other climates, while the tropical climate favoured sub-surface accumulation. Coarse- and medium-textured soils and the inclusion of legumes in crop rotation facilitated larger positive ΔSOCs under NT. The microbial biomass C was the most abundant C pool, with 61% and 23% increases under NT in 0–5 and 5–10 cm layers. A large ΔSOCc in aggregates also characterized the top 0–5 cm layer. The difference in SOCs was realized to a maximum 30 cm depth (5.4 Mg ha−1 or 14%) in favour of NT, although varying with the duration of its adoption. The contribution of NT in mitigating global anthropogenic greenhouse gas emissions is meagre, although it can substantially offset emissions from agriculture (17–58%). The benefit of NT in improving SOC is primarily restricted to the surface layer, which is potentially exposed, and therefore an increase could be short-lived. Nevertheless, a short-term gain in SOC is likely to enhance soil quality and crop productivity. Thus, NT may be promoted as a sustainable agricultural management practice rather than emphasizing its role as a potential climate change mitigation option.

Aridity shifts the difference in carbon uptake and storage between wooded and pure grasslands from positive to negative

Woody plant encroachment in arid grasslands may reduce plant uptake and soil storage of carbon (C) with consequences for the global C cycle, yet multi-site comparative studies have not been done so far and experiments are not feasible due to the long time needed for soil organic C (SOC) to accumulate. We selected multiple grassland sites with ≥50 % or 0 % woody plant aboveground biomass in each of six vegetation types representing a gradient of increasing aridity, resulting in a comparative study design with a total of 178 pure and 106 wooded grasslands distributed over the large geographic area of Xinjiang, China. Differences between wooded and pure grasslands in SOC stocks in the top 100 cm of the soil changed from positive to negative with increasing aridity. This effect was strongest in the upper soil layers, suggesting that woody plants had perhaps not been present for long enough to leave a signal in the lower soil layers. The differences in SOC stocks were related to differences in plant belowground standing C (BGC) and these to differences in yearly plant aboveground C uptake (ANPP) between wooded and pure grasslands. At more arid sites, wooded grasslands had lower ANPP and BGC because of reduced contributions of herbaceous plants that were not fully compensated by woody plants. Considering predicted increases in aridity in the study region, our results suggest that to avoid future losses of grassland SOC stocks — which are several ten times higher than the C stored in plant organs — management should try to prevent or reduce woody plant encroachment.

Variability of carbon stored in inland freshwater wetland in Northeast India

Inland freshwater wetland ecosystems are among the largest sink of carbon (C) in the biosphere. However, improved scientific understanding of the C stability and sequestration potential is required to predict response of C pool under environmental change and to identify priorities for lacustrine C sink management. This study analyses the concentration of organic C fractions based on their stability and estimates C stock along with depth and eco-zones of the Rudrasagar lake in Northeast India. Sediment samples up to 100 cm depth were collected from littoral, sub-littoral and deep layers, and analysed for organic C concentrations. Results showed that C concentration decreases with depth in the littoral layer but increases with depth in sub-littoral and deep layers. Two-way analysis of variance showed that concentrations of soil organic C (SOC) fractions were significantly different among the eco-zones but not between the soil depth. Average SOC stock was significantly higher in the deep layer (334.9 Mg C ha−1) followed by sub-littoral (248.4 Mg C ha−1) and littoral layer (106.1 Mg C ha−1). Overall, we show that substantial spatial variability in SOC stock exists among the eco-zones and depth that may be driven by water inundation in deep layer and fluctuating hydrological conditions at the edges of the lacustrine ecosystem. Our study demonstrates that inland freshwater wetland is a major sink of organic C and if disturbed it can act as a carbon dioxide source.

How Much Organic Carbon Could Be Stored in Rainfed Olive Grove Soil? A Case Study in Mediterranean Areas

Agricultural activities generate CO2, CH4, and N2O, affecting the global climate and the sustainability of agricultural production systems. This topic is essential in those areas where agriculture has caused soil decarbonization. The soil can regenerate by implementing sustainable soil management (SSM), and this regeneration is finite. Therefore, it is necessary to determine the maximum carbon (C) storage capacity to establish the most SSM for soil recarbonization. This research analyzes the C storage capacity in soils with rainfed olive groves and traditional tillage in the largest olive-oil-producing area in the world (Jaén, Andalusia, Spain). The results show that these soils had low soil organic C (SOC) content, ranging from 5.16 g kg−1 (topsoil) to 1.60 g kg−1 (subsoil) and low SOC stock (SOC-S) (43.12 Mg ha−1; 0–120 cm depth). In addition, the SOC fractionation showed that the highest SOC concentrations were in the particulate organic C form. The SOC-S linked to the fine mineral fraction (<20 µm) in topsoil was 21.93 Mg C ha−1, and the SOC-S saturated ranged between 50.69 and 33.11 Mg C ha−1. Therefore, on the soil surface (0–32.7 cm depth), these soils have a C storage maximum capacity of 28.76 Mg C ha−1, with a net C sink capacity of 105.55 Mg ha−1 of CO2-eq. All this suggests that these soils could have a high recarbonization capacity, and applying SSM (in the coming years) could be an essential C sink.

A Comparison of Soil C, N, and P Stoichiometry Characteristics under Different Thinning Intensities in a Subtropical Moso bamboo (Phyllostachys edulis) Forest of China

Land management using suitable thinning intensities can promote the yield of Moso bamboo (Phyllostachys edulis) forests and alter the nutrient content and stoichiometric characteristics within the soil. However, the effects of different thinning intensities on soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry of P. edulis forests have not been comprehensively studied. Here, we evaluated the effects of three thinning intensities—no thinning control (NT), moderate thinning (annual removal of 15% of mature bamboo, MT), and heavy thinning (annual removal of 33% of mature bamboo, IT)—on the soil organic C (SOC), total N (TN), and total P (TP) stocks and their stoichiometry characteristics of a P. edulis forest located in the subtropical zone. The results showed that SOC, TN, and TP stocks decreased with increasing soil depth after three years of thinning. The SOC, TN, and TP stocks and the ecological stoichiometry ratios were varied with the change of thinning intensity and SOC stocks declining with the increased thinning intensity, but TN and TP stocks for the MT treatment were enhanced. The order of TN and TP stocks was MT > NT > IT. In comparison to CK, TN and TP stocks for MT increased significantly by 18.8 and 37.3%, while SOC, TN, and TP stocks for IT decreased by 31.0%, 7.2%, and 21.4%, respectively. The C:N and C:P ratios of MT decreased by 32.8% and 39.0%, and those of IT decreased by 26.5% and 15.6%, respectively. In summary, we conclude that the MT is an effective management strategy to promote soil nutrient cycling and provides a reference for formulating management strategies in subtropical Moso bamboo forests.

Carbon storage in an arable soil combining field measurements, aggregate turnover modeling and climate scenarios

Quantifying soil structural dynamics and aggregate turnover is important in understanding soil organic carbon (SOC) stocks, particularly over decadal and larger time scales. Until now it has remained unclear clear how soil aggregate size and its associated carbon respond to both long-term soil fertility and climate change. Here, we explore changes in soil structure and aggregate organic C (OC) stocks under different fertilization practices by combining field chronosequence SOC measurements with dynamic and process modeling in a long-term wheat-maize field experiment on the North China Plain. The fertilization practices comprise no fertilization (CK), chemical fertilization (NPK), and combined manure and NPK treatments (MNPK). The experimental measurements included the mass of OC stocks in different soil aggregate size classes. We used this information to calibrate parameters of the Carbon, Aggregation, and Structure Turnover (CAST) model and to predict future changes in aggregate structure and the resulting OC stocks using the RCP2.6 scenarios that were defined by the outputs of five future climate models from IPCC projection. With trends towards a wetter climate and increasing soil moisture under the RCP2.6 scenarios for the region, soil OC stocks will increase in all three treatments, with the strongest increase under MNPK due to exogenous C inputs. The CAST model output further suggests that changes in microaggregate (250–53 μm) OC stocks in the NPK and MNPK treatments accounted for 78.6 % and 75.3 % of the calculated change in total SOC stocks between the early and late 21st century. In conclusion, our combined data and modeling approach describes changes in soil aggregate C, identifies the primary soil aggregate size class of microaggregates involved in C sequestration in an agricultural soil, and predicts the role of Fluvaquent soils on the North China Plain as a future C sink.

Experimental Precipitation Reduction Slows Down Litter Decomposition but Exhibits Weak to No Effect on Soil Organic Carbon and Nitrogen Stocks in Three Mediterranean Forests of Southern France

Forest ecosystems are some of the largest carbon (C) reservoirs on earth. Pinus halepensis Mill., Quercus ilex L. and Quercus pubescens Willd. represent the dominant tree cover in the Mediterranean forests of southern France. However, their contributions to the French and global forest C and nitrogen (N) stocks are frequently overlooked and inaccurately quantified and little is known about to what extent the ongoing climate change can alter these stocks. We quantified the soil organic C (SOC) and N (SN) stocks in Mediterranean forests dominated by these tree species and evaluated to what extent an experimental precipitation reduction (about −30% yearly) affects these stocks and the litter decomposition efficiency. Litter mass losses were 55.7, 49.8 and 45.7% after 24 months of decomposition in Q. ilex, Q. pubescens and P. halepensis forests, respectively, and were 19% lower under drier climatic conditions. The SOC stocks were 14.0, 16.7 and 18.5 Mg ha−1 and the SN stocks were 0.70, 0.93 and 0.88 Mg ha−1 in Q. ilex, Q. pubescens and P. halepensis forests, respectively. The shallowness and stoniness of these Mediterranean forests could explain these limited stocks. By distinguishing the organic from the organo–mineral layer, we showed 74% less SOC in the organic layer of the P. halepensis forest under drier conditions, while no difference was detected in the organo–mineral layer or in the two oak forests. This last finding deserves further investigation and points out the necessity to distinguish the organic from the organo–mineral layer to detect the first impacts of climate change on SOC stocks.

The climate change mitigation potential of annual grasslands under future climates.

Composted manure and green waste amendments have been shown to increase net carbon (C) sequestration in rangeland soils and have been proposed as a means to help lower atmospheric CO2 concentrations. However, the effect of climate change on soil organic C (SOC) stocks and greenhouse gas emissions in rangelands is not well understood, and the viability of climate change mitigation strategies under future conditions is even less certain. We used a process-based biogeochemical model (DayCent) at a daily time step to explore the long-term effects of potential future climate changes on C and greenhouse gas dynamics in annual grassland ecosystems. We then used the model to explore how the same ecosystems might respond to climate change following compost amendments to soils and determined the long-term viability of net SOC sequestration under changing climates. We simulated net primary productivity (NPP), SOC, and greenhouse gas fluxes across seven California annual grasslands with and without compost amendments. We drove the DayCent simulations with field data and with site-specific daily climate data from two Earth system models (CanESM2 and HadGEM-ES) and two representative concentration pathways (RCP4.5 and RCP8.5) through 2100. NPP and SOC stocks in unamended and amended ecosystems were surprisingly insensitive to projected climate changes. A one-time amendment of compost to rangeland acted as a slow-release organic fertilizer and increased NPP by up to 390-814 kg C ha-1 year-1 across sites. The amendment effect on NPP was not sensitive to Earth system model or emissions scenario and endured through the end of the century. Net SOC sequestration amounted to 1.96 ± 0.02 Mg C ha-1 relative to unamended soils at the maximum amendment effect. Averaged across sites and scenarios, SOC sequestration peaked 22 ± 1 years after amendment and declined but remained positive throughout the century. Though compost stimulated nitrous oxide (N2 O) emissions, the cumulative net emissions (in CO2 equivalents) due to compost were far less than the amount of SOC sequestered. Compost amendments resulted in a net climate benefit of 69.6 ± 0.5 Tg CO2 e 20 ± 1 years after amendment if applied to similar ecosystems across the state, amounting to 39% of California's rangeland. These results suggest that the biogeochemical benefits of a single amendment of compost to rangelands in California are insensitive to climate change and could contribute to decadal-scale climate change mitigation goals alongside emissions reductions.

Exclusion of plant input affects the temperature sensitivity of soil organic carbon decomposition

Plant residue input plays a vital role in cropland carbon (C) balance, which can be greatly affected by climate change. Our knowledge of the effect of plant residue on soil respiration is crucial for evaluating C exchange between the atmosphere and terrestrial ecosystems, but large uncertainties remain in the effect of plant input on the temperature sensitivity (Q10) of soil organic C (SOC) decomposition in cropland ecosystems. Here, soils were sampled from two bare fallow plots (including a Mollisol and an Alfisol with different climate and land-use history) and their adjacent old field plots, and were incubated at 10 °C and 20 °C for 815 days. The ‘equal-time’, ‘equal-C’, ‘one-pool model’ and ‘two-pool model’ methods were used to evaluate the Q10 of SOC decomposition. Results indicated that in the early stage of incubation, exclusion of plant input increased the Q10 (Alfisol) or had minor effect on the Q10 (Mollisol), which may be related to the interactions between substrate quality decrease (increase of chemical stability) and clay mineral suppression on microbial decomposition. However, in the later stage of incubation, plant residue removal decreased the Q10 values in both soils possibly due to the limitation of substrate availability on microbial decomposition. Overall, the role of plant input in the temperature sensitivity of SOC decomposition should be considered when predicting SOC stocks in a future warmer world.

Altered microbial resource limitation regulates soil organic carbon sequestration based on ecoenzyme stoichiometry under long‐term tillage systems

AbstractSoil microbial metabolism is critically important for regulating soil carbon (C) sequestration. However, how soil organic C (SOC) stock responds to the changes in microbial resource limitation and microbial C use efficiency (CUE) under long‐term tillage system remains uncertain. Soil samples were randomly collected from a long‐term (19 years) tillage experiment growing winter wheat with three treatments [i.e., moldboard‐plough without straw retention (MPN), no‐tillage with straw retention (NTS), and subsoiling with straw retention (SSS)] and an adjacent natural grassland (GRL) in 2018. We analyzed microbial resource limitation and CUE based on ecoenzyme stoichiometry. Results revealed that the reduction of soil bulk density and total dissolved nitrogen (N) resulted in an increased vector angle. Higher total dissolved N and lower vector length jointly led to higher CUE under long‐term conservation tillage practices (i.e., NTS and SSS). Notably, the higher CUE and soil available phosphorus as well as the lower N limitation both directly contributed explaining the increase in SOC stock under conservation tillage practices. Overall, long‐term conservation tillage practices could alleviate microbial resource limitation by enhancing available nutrients to promote SOC sequestration. Our study provides new knowledge to enhance the understanding of SOC stock regulated by microbial resource limitations and microbial C use efficiency.

Fungal biomass and microbial necromass facilitate soil carbon sequestration and aggregate stability under different soil tillage intensities

The aim of global carbon (C) neutrality brings soils and their potential for C storage into the spotlight. Improved agricultural management techniques such as minimum or no-tillage are thought to foster soil C sequestration. However, the underlying mechanisms are still not well understood. In this study, we investigated the inter-relations of soil organic C (SOC), fungal biomass, microbial necromass biomarkers, and aggregate stability in rhizosphere and bulk soil after thirteen years of reduced tillage intensities (reduced, minimum, and no-tillage). Overall, rhizosphere and bulk soil were indifferent in their response to reduced tillage. Reducing tillage intensity increased SOC and nitrogen stocks and dissolved organic C contents in the following order: minimum > no-tillage > reduced > conventional. Aggregate stability showed the strongest increase under no-tillage. Interestingly, ergosterol contents were highest under reduced and minimum tillage followed by no-tillage. The amino sugars muramic acid, galactosamine, and glucosamine – proxies for soil microbial-derived necromass – showed similar increases under all three tillage reduction systems. Structural equation modelling revealed that increased dissolved organic C contents under reduced tillage intensity facilitated SOC sequestration and aggregate stability through enhanced fungal biomass to necromass turnover. Thus, reducing soil tillage intensity is a valuable tool to facilitate microbial growth and hence to increase SOC sequestration in agricultural soils.

Combined slag and biochar amendments to subtropical paddy soils lead to a short-term change of bacteria community structure and rise of soil organic carbon

Applying industrial waste amendments, such as steel slag and biochar, to soils is an increasingly common practice to improve soil fertility, crop yield, and soil carbon (C) pool storage and stability. However, the effects of separate and combined applications of slag and biochar on total and active soil organic C (SOC) pools and the associated relationships between soil microorganisms and C cycling are unclear. Therefore, this study examined the effects of steel slag, rice straw biochar, and slag+biochar amendments to subtropical early and late rice paddy soils on total and active SOC concentrations and microbial abundance and diversity. The results showed that slag+biochar increased SOC content in early and late rice, with increases in dissolved organic C of 28.7 and 52.6 % in the early and late rice jointing stages, respectively. Soil organic C was positively correlated with soil C:N ratios in the two crop seasons. Applications of slag and biochar alone increased the diversity of soil bacteria in early rice but decreased in late rice. Meanwhile, the combined application of slag and biochar decreased diversity of soil bacterial community diversity and increased the relative abundance of some beneficial bacterial taxa, such as Pseudomonas, Bacillus, Flavisolibacter, and Ferruginibacte which are related to SOC cycling and sequestration. The results highlight that the combined slag and biochar amendments can improve soil specific properties, such as pH and SOC stocks, which elicit alterations in soil bacterial composition, especially of some keystone genera, altogether resulting in enhanced soil C sequestration and C pool stability.

Recovery of soil carbon and nitrogen stocks following afforestation with xerophytic shrubs in the Tengger Desert, North China

Afforestation, as a key measure to curb land degradation and to drive the changes in soil C and N stocks and cycles, has been increasingly implemented in drylands worldwide. However, the long-term effects of this restoration practice on C accumulation in soil are still uncertain, especially because C-N interactions are poorly understood, which constrains the accurate assessment of potential soil C sequestration. In this study, we investigated the soil organic C (SOC) and soil total N (STN) storage in artificial shrublands in chronosequences in the Tengger Desert to address the hypothesis that afforestation with xerophytic shrubs significantly enhanced SOC and STN stocks in desert regions and that SOC and STN stocks would be positively correlated during the restoration processes. Our results showed that afforestation significantly enhanced SOC and STN accumulation. The SOC and STN stocks in 17-, 52- and 60-year-old artificial shrublands were 1.22, 2.67, 2.80 and 1.21, 2.33, 2.47 times greater than those in mobile sand dunes, respectively, with increased rates of 5.61 g C m−2 yr−1, 14.25 g C m−2 yr−1 and 13.30 g C m−2 yr−1 and 1.27 g N m−2 yr−1, 2.61 g N m−2 yr−1 and 2.50 g N m−2 yr−1, respectively. The significant enhancement of SOC and STN stocks primarily occurred in the upper 0–20 cm soil layer. SOC stocks were positively correlated with STN stocks and the C:N ratio, and the regression slopes increased with vegetation age, indicating a coupling relationship between SOC and STN stocks. Additionally, this finding suggests that the increase in STN stocks was slower than that of SOC during restoration, leading to an asynchrony in N supply and the demand and subsequent N limitations on SOC accumulation. It would take approximately 139 and 177 years to fully recover SOC and STN stocks in the 100 cm soil profile, respectively, in mobile sand dunes through afforestation with xerophytic shrubs in the Tengger Desert, which implied that afforestation-induced soil quality improvements were a long-term process and that soil conservation was a key issue in water-limited ecosystems; therefore, optimized management strategies are urgently needed.

Spatially explicit estimation of soil organic carbon stock of an estuarine mangrove wetland of eastern India using elemental analysis and very-fine resolution satellite data

BackgroundThis study estimated the total soil organic C (SOC) stock of the wetland influence zone of Bichitrapur mangroves in eastern India in a spatially explicit manner. Both spatial and vertical distribution of SOC densities with respect to land use/land cover (LULC) pattern were assessed. Subsequently, some site-specific management strategies were forwarded towards enhancement of C sequestration potential.MethodsThe changing patterns of LULC within the wetland influence zone of the site were analyzed using Landsat TM (30 m) and Pleiades-1A (2 m) imageries from 1988 to 2018. Point-specific SOC measurement was done using samples taken from four core-depth intervals (viz. D1: 0–20 cm, D2: 20–40 cm, D3: 40–70 cm, D4: 70–100 cm) at 89 locations belonging to different LULC categories. Spatial interpolation was applied on this point-based data to produce SOC density and stock models as a whole and at all core-depths. Relationships between SOC density, core-depth and present LULC were evaluated through multivariate statistical analyses.ResultsThe LULC transformations during last three decades suggested the gradual growth of mangrove plantations as well as agricultural and aquacultural activities. Most amount of SOC was concentrated in D1 (37.17%) followed by D3 (26.51%), while D4 had the lowest (10.87%). The highest mean SOC density was observed in the dense mangrove patches (248.92 Mg ha−1) and the lowest mean was in the Casuarina plantations (2.78 Mg ha−1). Here, Spline method emerged as the best-fit interpolation technique to model SOC data (R2 = 0.74) and estimated total SOC stock of the entire wetland influence zone as 169,569.40 Mg and the grand mean as 125.56 Mg ha−1. Overall, LULC was inferred as a major determinant of SOC dynamics with a statistically significant effect (p < 0.001), whereas no such inference could be drawn for soil core-depth.ConclusionsThe C sequestration potential of sites such as the present one could be increased with appropriate zone-wise plantation strategies, restriction on the land conversion to aquaculture and promotion of ecotourism. Periodic monitoring through integration of geospatial techniques and elemental analyses would be immensely beneficial in this regard.Graphic

Warming offsets the beneficial effect of elevated CO2 on maize plant-carbon accumulation in particulate organic carbon pools in a Mollisol

Investigating the interactive effect of elevated CO2 and warming on photosynthetic carbon (C) detained in soil organic C (SOC) fractions is pivotal to predict the SOC stability in farming soils in response to climate change, especially in a major maize-grown Mollisol, one of most fertile farming soil in the world. Using open top growth chamber (OTC) to mimic the rises of atmospheric CO2 concentration up to 550 ppm and temperature 2 °C above surroundings, one set of maize plants were labelled with 13CO2 across the first growth season, and the other set of plants were grown in OTCs for four seasons. We found that elevated CO2 increased plant-C in the fine particulate organic C fraction from 0.53 mg kg−1 under the control to 0.89 mg kg−1, while warming plus elevated CO2 did not alter plant-C allocation into this fraction. Elevated CO2 increased plant-C accumulated in the mineral-associated C (MOC) fraction, but not C content in this fraction. There was no change of C content in the MOC fraction with plant grown under climatic conditions over time. Climate change may not alter SOC stock but accelerate the fresh-old-C exchange in maize-grown Mollisols as warming may accelerate turnover of plant-derived C.

Responses of Above- and Belowground Carbon Stocks to Degraded and Recovering Wetlands in the Yellow River Delta

Wetlands reserve a large amount of organic carbon (C), playing a key role in contributing global C stocks. It is still uncertain to evaluate wetland C stocks due to wetland disturbance or degradation. In this study, we performed the degraded and recovering wetlands to estimate aboveground C stocks and soil organic C (SOC) stocks at the depth of 1 m in the Yellow River Delta. Our results showed that the recovering wetland sequestered 1.67 Mg C ha–1 aboveground, approximately three times higher than those (0.56 Mg C ha–1) of degraded wetland, and recovering wetland stored more SOC of 51.86 Mg C ha–1 in the top 1 m soils, approximately two times higher than those (26.94 Mg C ha–1) of degraded wetland. These findings indicate that the transformation between degraded and recovering wetlands is associated with the conversion of wetland C sources and sinks. The shifts in aboveground C stocks and SOC stocks were mainly attributed to changed biotic (i.e., aboveground biomass and photosynthetic C) and abiotic (i.e., soil water, salinity, SOC and N contents, and SOC compounds) factors. The improved soil water, salinity, and nutrient enhance C reservoir, sequestering more C in aboveground vegetation and storing more SOC via photosynthetic C input of plant litter and root exudates in recovering wetland than in degraded wetland with poor soil conditions. The relationships among wetland C stocks, plant, and soil properties indicate plant-soil interaction driving wetland ecosystem C stocks in degraded and recovering wetlands. Our research suggests that wetland restoration highlights a positive response to “carbon neutrality” by efficiently sequestering C above- and belowground.

Grassland rehabilitation significantly increases soil carbon stocks by reducing net soil CO2 emissions

AbstractRestoration of degraded grasslands through improved management is among the possible sustainable solutions to compensate for anthropogenic soil carbon (C) emissions. While several studies have shown a positive effect of rehabilitation on soil C, the impact on soil CO2 emissions is still uncertain. Therefore, this study aimed at quantifying the impact of grassland rehabilitation on soil CO2 emissions in a degraded grassland, South Africa. Commonly used rehabilitation practices were considered, that is rotational grazing (RG), livestock exclosure with fertilizer application (EF) and annual burning (AB), all being compared with traditional free grazing (FG). A total of 2880 in situ measurements of CO2 emissions were performed over 2.5 years under field conditions simultaneously with aboveground biomass, soil temperature, water content and soil organic C (SOC) to understand the changes in C fluxes. The RG performed the best under degraded grasslands by decreasing net CO2 emissions (per g of C) by 17% compared to FG, while EF increased emissions by 76% and AB had similar emissions to FG. The lower net emission under RG is associated with an increase in SOC stocks by 50% and aboveground biomass by 93%, after three years of implementation. Soil CO2 emissions were correlated positively to aboveground biomass and topsoil temperature (r = 0.91 and 0.60, respectively), implying a high effect of grass cover on soil microclimate and microbial activity. These results suggested RG as a potential cost‐effective nature‐based soil management strategy to increase SOC stocks into degraded grassland. However, long‐term trials replicated in different environments are still required.