Changes In Soil Carbon Pools Research Articles

Growing season average temperature range is the optimal choice for Q10 incubation experiments of SOM decomposition

Temperature sensitivity (Q10) of soil organic matter (SOM) decomposition is an essential parameter that reflects the feedback relationship between climate warming and atmospheric CO2 concentration and plays a key role in accurately estimating changes in soil carbon pools and their feedback to climate change. Setting the incubation temperature range (ITR) scenario is essential to accurately estimate the temperature sensitivity of SOM decomposition; however, this has been widely ignored. To address this issue, we conducted a systematic incubation experiment using 54 soils covering the most typical ecosystems in China and nine ITR scenarios. The results showed that ITR scenarios had a significant effect on Q10 in different ecosystems and soil types. Combining the results of fitting mean annual temperature (MAT) to the Q10 of different ITR and the interpretation rate of factors (including climate, soil, and microbial community composition) to the Q10 of different ITR, the results indicate that the growing season average temperature range (GSA) scenario had better performance than the other ITR scenarios and should be the optimum ITR scenario. Furthermore, the variation of main influence factors of Q10 across different ecosystems should be accounted for to accurately predict the feedback between soil C cycle and climate change. Overall, our findings highlight the importance of the ITR for the estimates of Q10 using widespread experimental data, providing a reference for subsequent experiments accurately measure Q10, as well as compare and compile global data to better predict the feedback between the global carbon cycle and climate change.

Impact of Land-Use Changes on Soil Properties and Carbon Pools in India: A Meta-analysis

Land-use changes (LUC), primarily due to deforestation and soil disturbance, are one of the major causes of soil quality degradation and greenhouse gas emissions. Effects of LUC on soil physicochemical properties and changes in soil quality and land use management strategies that can effectively restore soil carbon and microbial biomass levels have been reported from all over the world, but the impact analysis of such practices in the Indian context is limited. In this study, over 1,786 paired datasets (for meta-analysis) on land uses (LUs) were collected from Indian literature (1990–2019) to determine the magnitude of the influence of LUC on soil carbon, microbial biomass, and other physical and chemical properties at three soil depths. Meta-analysis results showed that grasslands (36.1%) lost the most soil organic carbon (SOC) compared to native forest lands, followed by plantation lands (35.5%), cultivated lands (31.1%), barren lands (27.3%), and horticulture lands (11.5%). Our findings also revealed that, when compared to forest land, the microbial quotient was lower in other LUs. Due to the depletion of SOC stock, carbon dioxide equivalent (CO2 eq) emissions were significantly higher in all LUs than in forest land. Results also showed that due to the conversion of forest land to cultivated land, total carbon, labile carbon, non-labile carbon, microbial biomass carbon, and SOC stocks were lost by 21%, 25%, 32%, 26%, and 41.2%, respectively. Changes in soil carbon pools and properties were more pronounced in surface (0–15 cm) soils than in subsurface soils (15–30 cm and 30–45 cm). Restoration of the SOC stocks from different LUs ranged from a minimum of 2% (grasslands) to a maximum of 48% (plantation lands). Overall, this study showed that soil carbon pools decreased as LUC transitioned from native forestland to other LUs, and it is suggested that adopting crop-production systems that can reduce CO2 emissions from the intensive LUs such as the ones evaluated here could contribute to improvements in soil quality and mitigation of climate change impacts, particularly under Indian agro-climatic conditions.

Soil organic and inorganic carbon pools as affected by straw return modes under a wheat-maize rotation system in the Guanzhong Plain, Northwest China

To understand the effects of straw return modes on soil carbon pools, we investigated total soil organic carbon (SOC), labile organic carbon fractions, and inorganic carbon (SIC) in different straw return modes at a depth of 0-40 cm under a maize-wheat cropping system in the Guanzhong Plain, Shaanxi, based on an 11-year field experiment. There were five straw return modes, i.e., no return of straw of both wheat and maize (CK), the retention of high wheat stubble plus the return of chopped maize straw (WH-MC), the return of both chopped wheat and maize straw (WC-MC), the retention of high wheat stubble and no return of maize straw (WH-MN), and the return of chopped wheat straw and no return of maize straw (WC-MN). The proportions of SOC storage were significantly higher under the WH-MC and WC-MC treatments than that under the CK by 28.1% and 22.2%, respectively. The proportions of SIC storage were increased by 20.4% and 17.3%, respectively. Compared with the initial value, the increases of sequestered SOC and SIC ranged from -0.84 t·hm-2 to 6.55 t·hm-2, respectively, and from -0.26 t·hm-2 to 8.61 t·hm-2, respectively. The efficiency of sequestration of SOC was 7.5%. To maintain the basic SOC level, the minimum carbon input from straw was 4.65 t·hm-2·a-1. The contents of labile carbon fractions at the 0-20 cm layer increased significantly under the WH-MC and WC-MC treatments compared with those of the control. Results of principal component analysis showed that the changes in soil carbon pools were primarily affected by the amount of straw return. Additionally, the increases in SIC storage could be ascribed to the Ca2+ and Mg2+ ions derived from irrigation water and plant residues that could coprecipitate with the CO2 from SOC mineralization to form CaCO3. In conclusion, our results indicated that the straw return mode that utilized the retention of high wheat stubble and chopped maize straw was sufficient to maintain soil carbon storage and would be the optimal straw-returning strategy for the region.

Vertical and seasonal changes in soil carbon pools to vegetation degradation in a wet meadow on the Qinghai-Tibet Plateau

Wet meadows provide opportunities to decrease carbon dioxide (CO2) and methane (CH4) released into the atmosphere by increasing the soil organic carbon (SOC) stored in wetland systems. Although wet meadows serve as the most important and stable C sinks, there has been very few investigations on the seasonal distributions of SOC fractions in high-altitude wet meadows. Here, we studied the effects of four vegetation degradation levels, non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD), on the measured vertical and seasonal changes of SOC and its different fractions. Among these vegetation degradation levels, 0–10 and 10–20 cm soil depths in ND plots had significantly higher SOC contents than the other degradation levels had throughout the year. This is attributed to the relatively greater inputs of aboveground plant litter and richer fine-root biomass in ND plots. Particulate organic carbon (POC) and light fraction organic carbon (LFOC) showed similar vertical and seasonal variations in autumn, reaching a minimum. Moreover, microbial biomass (MBC) and easily oxidizable organic carbon (EOC) contents were highest in summer and the smallest in winter, while dissolved organic carbon (DOC) content was highest in spring and lowest in summer, and were mainly concentrated in the 0–20 cm layer. Pearson correlation analysis indicated that soil properties and aboveground biomass were significantly related to different SOC fractions. The results indicate that vegetation degradation reduces the accumulation of total SOC and its different fractions, which may reduce carbon sink capacity and soil quality of alpine wet meadows, and increase atmospheric environmental pressure. In addition, vegetation biomass and soil characteristics play a key role in the formation and transformation of soil carbon. These results strengthen our understanding of soil C dynamics, specifically related to the different C fractions as affected by vegetation degradation levels and soil depth, in wet meadow systems.

Plateau pika offsets the positive effects of warming on soil organic carbon in an alpine swamp meadow on the Tibetan Plateau

Both climate warming and plateau pika (Ochotona curzoniae) exert considerable impacts on carbon cycling in alpine ecosystems on the Tibetan Plateau. However, the interaction of warming and pika disturbance on soil organic carbon (SOC) dynamics in alpine ecosystems remains largely unknown. Here, we measured plant, soil and microbial properties after four-year warming in a swamp meadow (with or without pika disturbance) on the Tibetan Plateau. Our results showed that in non-pika plots, warming not only increased plant belowground biomass (48%), but also enhanced microbial biomass, hydrolytic enzyme activities, and bacterial functional genes (41–46%). More plant inputs likely outweighed faster microbial decomposition, leading to the accumulation of fast-cycling particulate organic carbon (POC, 49%) and bulk SOC (22%), but not slow-cycling mineral-associated organic carbon (MAOC). In pika-disturbed plots, however, warming did not significantly change plant belowground biomass (which dominates total plant biomass), microbial biomass and hydrolytic enzyme activities. Although bacterial functional genes were suppressed (−40%) and plant aboveground biomass was increased (118%), oxidative enzymes were significantly stimulated (17%), which likely counteracted the higher aboveground plant inputs and led to minor changes in soil carbon pools (SOC, POC and MAOC) with warming. Moreover, bacterial and fungal community structure were significantly altered by pika disturbance, but not warming. Overall, these findings demonstrated that pika disturbance could offset the short-term positive effect of warming on soil organic carbon in the alpine swamp meadow ecosystem.

Changes in soil carbon pools and components induced by replacing secondary evergreen broadleaf forest with Moso bamboo plantations in subtropical China

Moso bamboo (Phyllostachys edulis) is widely distributed in southern China, and is one of the fastest growing plants worldwide; however, information remains limited on the impact of converting secondary broad-leaved evergreen forests to Moso bamboo plantations, and how the soil organic carbon (SOC) pool and its chemical composition should be managed subsequently. To elucidate these effects, three representative areas were chosen, all with very similar site conditions. In each area, four comparable stands were selected; namely, undisturbed (M0), extensively managed (M1), and intensively managed (M2) stands in each Moso bamboo plantation, and a secondary broad-leaved evergreen forest (CK). Soil samples were collected and examined from depths of 0–20 and 20–40 cm in all 12 stands. The results showed that, SOC and mineral-associated organic matter C (MOM-C) stocks in 0–40 cm soil depths were significantly higher in M0 and M1 than in CK; however, these two parameters were significantly lower in M2. M0 and M1 showed a significant decline in the ratio of microbial biomass C (MBC) to total organic C (TOC), hot-water-extractable organic C (DOC) to TOC, and the C mineralization rate. However, M2 showed a significant increase compared to CK for all of these parameters. Fourier-transform infrared spectroscopy (FTIR) showed that land-use conversion also changed SOC chemical composition. Compared with CK and M2, M0 and M1 showed lower relative content of polysaccharides and higher content of recalcitrant compounds and soil hydrophobicity. Aliphatic and aromatic compounds were positively correlated with accumulated C sequestration in all fractions but negatively correlated with microbial activity in both soil layers; thus, chemical protection mechanism was important for stabilizing the soil in M0 and M1. Overall, Moso bamboo plantations with management strategies M0 and M1 could stabilize more C through promoting the formation of stable organic-mineral complexes and the accumulation of resistant organic components, showing much higher potential in terms of soil C sequestration than M2.

Impacts of invasive plants on carbon pools depend on both species' traits and local climate.

Invasive plants can alter ecosystem properties, leading to changes in the ecosystem services on which humans depend. However, generalizing about these effects is difficult because invasive plants represent a wide range of life forms, and invaded ecosystems differ in their plant communities and abiotic conditions. We hypothesize that differences in traits between the invader and native species can be used to predict impacts and so aid generalization. We further hypothesize that environmental conditions at invaded sites modify the effect of trait differences and so combine with traits to predict invasion impacts. To test these hypotheses, we used systematic review to compile data on changes in aboveground and soil carbon pools following non-native plant invasion from studies across the World. Maximum potential height (Hmax ) of each species was drawn from trait databases and other sources. We used meta-regression to assess which of invasive species' Hmax , differences in this height trait between native and invasive plants, and climatic water deficit, a measure of water stress, were good predictors of changes in carbon pools following invasion. We found that aboveground biomass in invaded ecosystems relative to uninvaded ones increased as the value of Hmax of invasive relative to native species increased, but that this effect was reduced in more water stressed ecosystems. Changes in soil carbon pools were also positively correlated with the relative Hmax of invasive species, but were not altered by water stress. This study is one of the first to show quantitatively that the impact of invasive species on an ecosystem may depend on differences in invasive and native species' traits, rather than solely the traits of invasive species. Our study is also the first to show that the influence of trait differences can be altered by climate. Further developing our understanding of the impacts of invasive species using this framework could help researchers to identify not only potentially dangerous invasive species, but also the ecosystems where impacts are likely to be greatest.

An experience in regional estimates of changes in soil carbon pools of the southern taiga and forest-steppe during the historical period

Regional estimates of changes in soil organic carbon (SOC) pools during the historical period were obtained according to a unified approach for Kostroma (southern taiga) and Kursk (forest-steppe) oblasts. The potential pools of soil carbon were calculated with due account for the classification position of particular soils, their texture, and the character of natural vegetation. In the estimates of actual SOC pools, land use patterns and the age structure of forest stands were taken into account. It was shown that modern pools of organic carbon in the soils of Kostroma oblast are only 1–2% smaller than the potential pools; for the soils of Kursk oblast, this difference reaches 23–27%. Mean weighted values of the actual SOC contents in these oblasts decreased by 0.1–0.2 and 6.5–7.6 kg C/m2 in comparison with the potential SOC contents, respectively, which is related to their environmental specificity and to different types of land use at present and in the historical past.

Changes in soil carbon pools and microbial biomass from urban land development and subsequent post-development soil rehabilitation

Urbanization degrades soil by surface soil removal and subsoil compaction. Subsoiling and organic matter incorporation offer potential to increase soil carbon (C) storage over time. We evaluated the effects of urban land development practices and post-development soil rehabilitation on soil C pools and microbial biomass carbon (MBC). In 2007, four treatments [typical development practice (A horizon removed, subsoil compacted, and A horizon soil partially replaced), enhanced topsoil (same as typical practice plus tillage), profile rebuilding (compost incorporation to 60-cm depth in subsoil; A horizon soil partially replaced plus tillage), and undisturbed soil] were applied to 24 plots in Virginia, USA. In 2011, soil C pools and MBC were measured at 0–5, 5–10 and 15–30 cm depths. In surface soils, undisturbed soils had greater total soil C (12.10 and 7.73 Mg C ha−1 at 0–5 and 5–10 cm depths, respectively) than the three practices where A horizon soils were disturbed. However, profile rebuilding had higher total soil C (6.12 Mg C ha−1) and larger available and aggregate-protected C pools (1.59 and 2.04 Mg C ha−1, respectively) at 15–30 cm depth than other treatments, including undisturbed. In surface soils, MBC ranged from 185.3 to 287.3 mg C kg−1 soil among all practices. At the 15–30 cm soil depth, profile rebuilding had the greatest MBC (149.5 mg C kg−1 soil). Total soil C, available, aggregate-protected and mineral-bound C pools had positive relationships with MBC at the 15–30 cm depth (r = 0.85, 0.71, 0.77, and 0.69, respectively). We found typical land development practices led to soil C loss during construction processes even when topsoil is replaced. Soil rehabilitation that includes compost additions and subsoiling has potential to increase soil C storage below the surface horizons.

Modelling the sensitivity of soil mercury storage to climate-induced changes in soil carbon pools

Abstract. Substantial amounts of mercury (Hg) in the terrestrial environment reside in soils and are associated with soil organic carbon (C) pools, where they accumulated due to increased atmospheric deposition resulting from anthropogenic activities. The purpose of this study was to examine potential sensitivity of surface soil Hg pools to global change variables, particularly affected by predicted changes in soil C pools, in the contiguous US. To investigate, we included a soil Hg component in the Community Land Model based on empirical statistical relationships between soil Hg / C ratios and precipitation, latitude, and clay; and subsequently explored the sensitivity of soil C and soil Hg densities (i.e., areal-mass) to climate scenarios in which we altered annual precipitation, carbon dioxide (CO2) concentrations and temperature. Our model simulations showed that current sequestration of Hg in the contiguous US accounted for 15 230 metric tons of Hg in the top 0–40 cm of soils, or for over 300 000 metric tons when extrapolated globally. In the simulations, US soil Hg pools were most sensitive to changes in precipitation because of strong effects on soil C pools, plus a direct effect of precipitation on soil Hg / C ratios. Soil Hg pools were predicted to increase beyond present-day values following an increase in precipitation amounts and decrease following a reduction in precipitation. We found pronounced regional differences in sensitivity of soil Hg to precipitation, which were particularly high along high-precipitation areas along the West and East Coasts. Modelled increases in CO2 concentrations to 700 ppm stimulated soil C and Hg accrual, while increased air temperatures had small negative effects on soil C and Hg densities. The combined effects of increased CO2, increased temperature and increased or decreased precipitation were strongly governed by precipitation and CO2 showing pronounced regional patterns. Based on these results, we conclude that the combination of precipitation and CO2 should be emphasised when assessing how climate-induced changes in soil C may affect sequestration of Hg in soils.

Soil organic matter dynamics in grassland soils under elevated CO 2: Insights from long-term incubations and stable isotopes

Elevated atmospheric carbon dioxide (CO 2) levels generally stimulate carbon (C) uptake by plants, but the fate of this additional C largely remains unknown. This uncertainty is due in part to the difficulty in detecting small changes in soil carbon pools. We conducted a series of long-term (170–330 days) laboratory incubation experiments to examine changes in soil organic matter pool sizes and turnover rates in soil collected from an open-top chamber (OTC) elevated CO 2 study in Colorado shortgrass steppe. We measured concentration and isotopic composition of respired CO 2 and applied a two-pool exponential decay model to estimate pool sizes and turnover rates of active and slow C pools. The active and slow C pools of surface soils (5–10 cm depth) were increased by elevated CO 2, but turnover rates of these pools were not consistently altered. These findings indicate a potential for C accumulation in near-surface soil C pools under elevated CO 2. Stable isotopes provided evidence that elevated CO 2 did not alter the decomposition rate of new C inputs. Temporal variations in measured δ 13C of respired CO 2 during incubation probably resulted mainly from the decomposition of changing mixtures of fresh residue and older organic matter. Lignin decomposition may have contributed to declining δ 13C values late in the experiments. Isotopic dynamics during decomposition should be taken into account when interpreting δ 13C measurements of soil respiration. Our study provides new understanding of soil C dynamics under elevated CO 2 through the use of stable C isotope measurements during microbial organic matter mineralization.