Soil Organic Carbon Turnover Rate Research Articles

Vertical Distribution and Mineralization Dynamics of Organic Carbon in Soil and Its Aggregates in the Chinese Loess Plateau Driven by Precipitation

The mineralization of soil organic carbon (SOC) is a critical process in the soil carbon cycle. This study aimed to investigate the vertical distribution characteristics and mineralization dynamics of SOC in soils and their aggregates across different steppe types in the Loess Plateau (LP). Soil profiles from three steppe types under varying precipitation gradients were selected: meadow steppe (MS), typical steppe (TS), and desert steppe (DS). A 60-day controlled laboratory incubation study was conducted for carbon mineralization and the influence of climatic and soil properties on SOC mineralization was analyzed. The results showed that the SOC content and cumulative mineralization (CM) in 1–2 mm aggregates were higher than in other particle sizes; SOC content and CM followed the order MS > TS > DS and both decreased significantly with increasing soil depth. Correlation analysis revealed that precipitation significantly affected aggregate mineralization (p < 0.001) and that mineralization in the 1–2 mm aggregates was more closely related to mean annual precipitation (MAP), SOC, and water-soluble organic carbon (SWOC). Precipitation primarily controlled SOC mineralization in the 0–50 cm soil layer, while SOC mineralization in the 50–100 cm layer was influenced by soil-related carbon content. Structural Equation Modeling indicated that precipitation influences the mineralization of organic carbon in topsoil indirectly through its direct impact on SOC. In the context of global warming, the SOC turnover rate in high-precipitation areas (MS) was faster than in low-precipitation areas (TS, DS), necessitating greater attention to soil carbon dynamics in these regions.

Effects of long-term application of inorganic fertilizers and organic amendments on the turnover rates of fractionated soil organic carbon and their determining factors in paddy fields

ABSTRACT To investigate how the long-term application of inorganic fertilizer and organic amendments affects the turnover rates of organic matter in physico-chemically fractionated components in paddy soils and how their rates are related to their amounts, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the ∆14C values of accumulated soil organic carbon (SOC) in fractionated components of 5 soil samples from three paddy fields. SOC was fractionated into four components based on their physico-chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The ∆14C values were determined by accelerator mass spectrometry using graphitized samples. The ∆14C values of SOC in NOxF (from −305‰ to − 90.5‰) were much lower than those of HF (from −123‰ to − 3.7‰) and OxF (from −215‰ to 21.0‰). Lowest values for NOxF suggested slowest turnover rates as expected, and higher and comparable values for OxF and HF implied much faster turnover rates of SOC in OxF compared with upland soils. This could be one of the characteristics of SOC dynamics in paddy soils, probably reflecting repeated puddling of plow layer soils. ∆14C values in all the fractions increased in response to the application of inorganic fertilizer and organic amendments, suggesting faster turnover rate. Soils with clayey and weathered characteristics had the lowest ∆14C values, or slowest turnover rates among the study fields. The relationship between the ∆14C value and the amount of accumulated C for HF, OxF and NOxF indicated that the more the SOC accumulated, the faster the turnover rate of the SOC was, regardless of the fractions, and the relationship of the HF was considerably different from those of OxF and NOxF. In conclusion, these results can be the basis for understanding the C dynamics and for improving soil fertility status and soil C sequestration in paddy soils.

Modelling Soil δ13C across the Tibetan Plateau Using Deep-Learning

Soil carbon isotopes (δ13C) provide reliable insights for studying soil carbon turnover at a long-term scale. The Tibetan Plateau (TP), often referred as “the third pole of the earth”, is highly sensitive to global climate change, and exhibits an early warning signal of global warming. Although many studies detected soil δ13C variability at site scales, there is still a knowledge gap existing in the spatial pattern of soil δ13C across the TP. In this study, we compiled a database of 198 topsoil δ13C observations from published literatures and used a modified multi-layer perceptron (MLP) neural network algorithm to predict the spatial pattern of topsoil δ13C and β (indicating the decomposition rate of soil organic carbon (SOC), calculated as δ13C divided by logarithmically converted SOC) at 500m resolution. Results showed that MLP model effectively predicted topsoil δ13C with a model efficiency of 0.72 and a root mean square error of 1.16‰. Topsoil δ13C varied significantly across different ecosystem types (p < 0.001) with a mean δ13C of –25.89 ± 1.15‰ (mean ± standard deviation) for forests, –24.91 ± 1.03‰ for shrublands, –22.95 ± 1.44‰ for grasslands, and –18.88 ± 2.37‰ for deserts. Furthermore, there was an increasing trend of predicted δ13C from the southeastern to the northwestern TP, likely linked to vegetation type and climatic conditions. β values were low in the eastern TP and higher in the northern and northwestern TP, indicating faster SOC turnover rate in the east TP compared to the north and northwest. This study represents the first effort to develop a fine resolution product of topsoil δ13C and β across the TP, which could provide an independent, data-driven benchmark for biogeochemical cycling models to study SOC turnover and terrestrial carbon-climate feedback over the TP under climate change.

Soil Organic Carbon Turnover Response to Nitrogen and Phosphorus Additions in Eastern China: Evidence from Stable Carbon Isotopes

Anthropogenic activities have drastically increased nitrogen (N) deposition, resulting in increased N availability. The continuous increase of N availability may exacerbate phosphorus (P) deficiency, which would limit forest productivity in subtropical forests. Effects of long-time N and N + P additions on SOC turnover in subtropical forests is therefore crucial for understanding the global carbon (C) cycle. The argument of whether N and N + P addition accelerates or slows SOC turnover has been under debate, particularly in P-limited subtropical forests. This study mainly aims to confirm this argument. A ten-year field experiment was conducted in a subtropical evergreen broad-leaved forest in southern Anhui, China. We measured the soil δ13CSOC contents and physicochemical properties under N (100 kg N·ha−1·a−1), N + P (100 kg N ha−1·a−1 + 50 kg P ha−1·a−1) additions, and the control (CK, no N and P additions). We also estimated the β value, which represents the soil organic carbon (SOC) turnover rate, from the slope of the regression between the log10-transformed SOC content and δ13CSOC in soil depth profiles. Our findings revealed that N addition significantly affected soil δ13CSOC compared to CK on both mid-slope and flat ridge sites. The β values responded differently to various treatments and sites. On the mid-slope, the β values did not show significant change with N and N + P additions. On the flat ridge, however, the β value decreased significantly in N and N + P additions, implying an increased SOC turnover rate. In addition, analysis of soil C–N–P stoichiometric ratios and physicochemical properties showed that N and N + P additions could affect β values by modifying soil nutrient content and composition. In general, our findings indicate that N and N + P additions could accelerate the SOC turnover in subtropical forest ecosystems, albeit with close dependence on site-specific factors.

Dynamics of litter decomposition rate and soil organic carbon sequestration following vegetation succession on the Loess Plateau, China

Litter quality determines the decomposability of litter and the proportion of recalcitrant residues, which in turn can affect the accumulation of soil organic carbon (SOC). However, the impact of litter decomposition on SOC turnover following vegetation succession has not been systematically studied. To clarify the dynamics and mechanisms of litter decomposition and SOC sequestration following vegetation succession, this study conducted a decomposition experiment across four successional stages: grassland (∼30 years), shrubland (∼60 years), pioneer forest (∼110 years), and climax forest (∼160 years). This study also analyzed the litter quality and the SOC turnover rate. The results showed that litter decomposition rates gradually decreased with vegetation succession. Litter lignin content (LC), and nitrogen content (LN) were the major factors controlling the change of litter decomposition rate. Litter with a high LC: LN ratio and lignin: LN ratio exhibited a lower decomposition rate, whereas the opposite was found for litter with a higher LN content. The increase in the SOC content mainly occurred in the early successional stage (<110 years), with a higher litter decomposition rate and SOC turnover rate. At the later stage (≥110 years), the SOC was close to saturation, together with low rates of litter decomposition and SOC turnover. The variation trend of the mineral-associated organic carbon (MAOC) content was the same as that of the SOC content, resulting from continuous litter inputs. Based on the above results, litter inputs can significantly increase the SOC content in the early successional stage, and soil carbon sequestrations gradually reach saturation in the late successional stage. The findings of this study strengthen our understanding of the changes in litter decomposition and its contribution to SOC sequestration following vegetation succession.

Reduced turnover rate of topsoil organic carbon in old-growth forests: a case study in subtropical China

BackgroundOld-growth forests are irreplaceable with respect to climate change mitigation and have considerable carbon (C) sink potential in soils. However, the relationship between the soil organic carbon (SOC) turnover rate and forest development is poorly understood, which hinders our ability to assess the C sequestration capacity of soil in old-growth forests.MethodsIn this study, we evaluated the SOC turnover rate by calculating the isotopic enrichment factor β (defined as the slope of the regression between 13C natural abundance and log-transformed C concentrations) along 0–30 cm soil profiles in three successional forests in subtropical China. A lower β (steeper slope) is associated with a higher turnover rate. The three forests were a 60-year-old P. massoniana forest (PF), a 100-year-old coniferous and broadleaved mixed forest (MF), and a 400-year-old monsoon evergreen broadleaved forest (BF). We also analyzed the soil physicochemical properties in these forests to examine the dynamics of SOC turnover during forest succession and the main regulators.ResultsThe β value for the upper 30-cm soils in the BF was significantly (p < 0.05) higher than that in the PF, in addition to the SOC stock, although there were nonsignificant differences between the BF and MF. The β value was significantly (p < 0.05) positively correlated with the soil recalcitrance index, total nitrogen, and available nitrogen contents but was significantly (p < 0.01) negatively correlated with soil pH.ConclusionsOur results demonstrate that SOC has lower turnover rates in old-growth forests, accompanied by higher soil chemical recalcitrance, nitrogen status, and lower soil pH. This finding helps to elucidate the mechanism underlying C sequestration in old-growth forest soils, and emphasizes the important value of old-growth forests among global C sinks.

Shrub colonization regulates δ13C enrichment between soil and vegetation in deserts by affecting edaphic variables

δ13C enrichment (Δ δ13C) is an effective indicator to reflect the temporal dynamics of soil organic carbon (SOC) stock which is usually difficult to detect due to the slow turnover rate of SOC; however, because of the rare simultaneous measurements of both plant and soil δ13C, it is usually difficult to explore the geographic variations and controlling factors of Δ δ13C (δ13C of surface soil subtracting that of plant leaf). In this study, plant leaf δ13C, soil δ13C, and Δ δ13C were investigated along steep climatic and edaphic gradients to improve the understanding of SOC dynamics in deserts of northern China. Both soil δ13C and plant leaf δ13C decreased with mean annual precipitation (MAP), and soil δ13C was positively related to plant leaf δ13C and was higher than plant leaf δ13C across all C3 plant-dominated deserts (Alkaline soil desert, Gobi desert, alpine desert, and temperate steppe desert) except C4 woody shrub-dominated sandy desert. Δ δ13C was positively related to the SOC and soil silt contents across the C3-dominated desert transect, suggesting a faster decomposition of SOC at higher Δ δ13C sites. The shrub importance value index in the plant community enhanced Δ δ13C by increasing the soil silt and SOC contents in both steppe and alkaline soil deserts, indicating that shrub encroachment can increase the SOC content and SOC decomposition. Our results indicate that shrub colonization not only increases SOC content but also regulates SOC decomposition via changing vegetation cover and edaphic variables.

The effect of dolomite amendment on soil organic carbon mineralization is determined by the dolomite size

BackgroundThe size of lime material is vital for the efficiency of ameliorating soil acidity, thereby influencing soil biochemical processes. However, the effects of different sized lime material application on soil organic carbon (SOC) mineralization are yet to be elucidated. Therefore, a 35-day incubation experiment was conducted to determine the effects of three particle size fractions (0.5 to 0.25, 0.25 to 0.15, and < 0.15 mm) of dolomite on SOC mineralization of two acidic paddy soils.ResultsCO2 emission was increased by 3–7%, 11–21%, and 32–49% for coarse-, medium-, and fine-sized dolomite treatments, respectively, compared to the control in both soils. They also well conformed to a first-order model in all treatments, and the estimated decomposition rate constant was significantly higher in the fine-sized treatment than that of other treatments (P < 0.05), indicating that SOC turnover rate was dependent on the dolomite size. The finer particle sizes were characterized with higher efficiencies of modifying soil pH, consequently resulting in higher dissolved organic carbon contents and microbial biomass carbon, eventually leading to higher CO2 emissions.ConclusionsThe results demonstrate that the size of dolomite is a key factor in regulating SOC mineralization in acidic paddy soils when dolomite is applied to manipulate soil pH.

Soil carbon storage and mineralization rates are affected by carbon inputs rather than physical disturbance: Evidence from a 47-year tillage experiment

In spite of the large number of studies conducted on the drivers of soil organic carbon (SOC) stocks, there is still no consensus on the impact of tillage on the distribution and turnover rate of SOC in the soil profile. Few studies have characterized precisely the turnover of SOC using 13C natural tracing or simulated the SOC evolution per soil layer. In this study, we combined several approaches (diachronic analysis of SOC stocks, isotopic tracing and modelling) for characterizing the SOC evolution per soil layer in one of the oldest tillage experiments comparing no-till (NT), shallow till (ST) and full inversion tillage (FIT) combined with six crop managements. The new measurements made in 2017 reported in this paper confirm that i) tillage had no effect on SOC stocks integrated over the old ploughed layer (∼0−28 cm) or deeper (∼0−58 cm) and ii) reduced tillage affected the SOC distribution in the soil profile, with SOC storage in the upper layer (∼0−10 cm) offset by a SOC loss in the underlying layer (∼10−28 cm). The change in rotation (from C4 to C3 crops) in two crop management treatments allowed to quantify the decrease in C4 stocks during 19 years and calculate the specific mineralization rates relative to tillage treatments and soil layers. The mineralization rates did not vary significantly between tillage treatments in the whole (old) ploughed layer (∼0−28 cm) but varied according to depth and tillage. The highest rates were found in the layer 0−5 cm of NT or ST and the lowest rates in the layer 10−28 cm of the same tillage treatments. The rates were highly correlated with estimated C inputs and particulate organic matter contents in each layer, but not with tillage intensity. The evolution of total SOC and C4 stocks of each soil layer was simulated with AMG model during 47 years. The standard model (with a single mineralization rate) gave a good prediction of SOC evolution when applied to the whole profile (∼0−28 cm) but not for each individual layer. Including a relationship between C input and mineralization rate in the model allowed to well simulate the SOC evolution in all soil layers. This study shows that the main effect of a change in tillage on SOC storage is the change in the distribution of C input throughout the profile and the corresponding variation of the priming effect rather than the change in physical soil disturbance.

Vegetation and species impacts on soil organic carbon sequestration following ecological restoration over the Loess Plateau, China

Extensive soil organic carbon (SOC) accumulation has been reported following ecological restoration on the Loess Plateau of northwest China. While previous studies have found the restoration age to be a major factor controlling SOC change, potential effects of vegetation type and plant species have been largely neglected. Here, we compiled a database of 331 measurements of SOC changes following cropland restoration across the entire Loess Plateau. Results from stepwise multiple linear regressions indicated dominant contributions by restoration age, vegetation type or plant species, and/or their interactions in post-restoration SOC accumulation, accounting for 67–86% of the variation in SOC sequestration being explained by the model. Of the four restoration types examined, managed grassland was found to have the highest SOC sequestration rate (0.41 Mg C hm−2 yr−1), followed by plantation (0.27 Mg C hm−2 yr−1) and shrubland (0.25 Mg C hm−2 yr−1), with the lowest value found for naturally recovered grassland (0.13 Mg C hm−2 yr−1). The different SOC sequestration capacities for these vegetation types were further confirmed by an independent mechanistic modeling approach based on SOC turnover rate. Our results highlight the critical role of plant type in determining SOC sequestration following revegetation over cropland. Such management-relevant information should be considered in future restoration efforts.

Does Grazing Matter for Soil Organic Carbon Sequestration in the Western North American Great Plains?

Considerable uncertainty remains regarding grazing-induced influences on soil organic carbon (SOC) sequestration in semiarid grassland ecosystems due to three important complications associated with studying such effects: (1) Ecologically meaningful shifts in SOC pools attributable to grazing are difficult to detect relative to inherently large grassland SOC pools, (2) a lack of baseline (pre-treatment) data, and (3) frequent lack of or limited replication of long-term grazing manipulations. SOC sequestration rates were determined in 74-year-old grazing exclosures and paired moderately grazed sites, established across a soil texture gradient, in the western North American shortgrass steppe in northeastern Colorado. We sampled soils (0–20 cm) from 12 exclosures and paired grazed sites to measure SOC concentration and soil radiocarbon ∆14C (‰); the latter allowed us to determine turnover of the SOC pool over a 7-decade period in the presence versus the absence of grazing. Removal of grazing for more than 7 decades substantially altered plant community composition but did not affect total soil C, SOC, soil ∆14C, SOC turnover rate, or total soil N. Grazing effect also did not interact with soil texture to influence any of those soil properties. Soil texture (silt + clay content) did influence total soil C and SOC, and total soil N, but not ∆14C or SOC turnover. Results provide evidence that long-term removal of grazing from semiarid grassland ecosystems in the western North American Great Plains does not enhance long-term SOC sequestration, despite changes in the relative dominance of C3 versus C4 grasses.

Distribution of fresh carbon in different particle-size aggregates of different soil type

In order to study the effects of application of fresh carbon on distribution in soil aggregate fractions of red soil and lime concretion black soil, the stable carbon isotope (δ13C) technique was used, and explore the dynamic variation and distribution of soil organic carbon(SOC) in soil aggregates during 13C-labelled rice straw decomposition by an indoor incubation experiment. This experiment was put under incubation at 28°C for 120 days, which included two treatments: CK (no straw) and Str (added with 1% straw), all samples were separated into four aggregate-size classes (>2000, 2000~250, 250~53, <53 μm) by wet sieving in the different incubation period, while soil aggregates in different size fraction and organic carbon in soil aggregates were determined. The results showed that the δ13C value of organic carbon in different particle-size water-stable aggregates of Str treatment was significantly higher than that of CK treatment, the δ13C value varied greatly both in red soil and lime concretion black soil, but the turnover rate of native SOC was slow and the degradation degree was relatively close. The quantity of new organic carbon supplied by rice straw found in different levels of aggregates followed a same increasing order of 2000~250 μm < (>2000 μm) < (<53 μm) < 250~53 μm in red soil and lime concretion black soil at 120 days, which further indicates that the added fresh carbon was mainly accumulated in small-sized soil aggregates. The result shows that the addition of rice straw could increase soil organic carbon content in all sizes of aggregates, which provide theory basis for soil quality improvement and organic carbon recycle.

Grazing-induced microbiome alterations drive soil organic carbon turnover and productivity in meadow steppe

BackgroundGrazing is a major modulator of biodiversity and productivity in grasslands. However, our understanding of grazing-induced changes in below-ground communities, processes, and soil productivity is limited. Here, using a long-term enclosed grazing meadow steppe, we investigated the impacts of grazing on the soil organic carbon (SOC) turnover, the microbial community composition, resistance and activity under seasonal changes, and the microbial contributions to soil productivity.ResultsThe results demonstrated that grazing had significant impacts on soil microbial communities and ecosystem functions in meadow steppe. The highest microbial α-diversity was observed under light grazing intensity, while the highest β-diversity was observed under moderate grazing intensity. Grazing shifted the microbial composition from fungi dominated to bacteria dominated and from slow growing to fast growing, thereby resulting in a shift from fungi-dominated food webs primarily utilizing recalcitrant SOC to bacteria-dominated food webs mainly utilizing labile SOC. Moreover, the higher fungal recalcitrant-SOC-decomposing activities and bacterial labile-SOC-decomposing activities were observed in fungi- and bacteria-dominated communities, respectively. Notably, the robustness of bacterial community and the stability of bacterial activity were associated with α-diversity, while this was not the case for the robustness of fungal community and its associated activities. Finally, we observed that microbial α-diversity rather than SOC turnover rate can predict soil productivity.ConclusionsOur findings indicate the strong influence of grazing on soil microbial community, SOC turnover, and soil productivity and the important positive role of soil microbial α-diversity in steering the functions of meadow steppe ecosystems.

Temporal response of soil organic carbon after grassland-related land-use change.

The net flux of CO2 exchanged with the atmosphere following grassland-related land-use change (LUC) depends on the subsequent temporal dynamics of soil organic carbon (SOC). Yet, the magnitude and timing of these dynamics are still unclear. We compiled a global data set of 836 paired-sites to quantify temporal SOC changes after grassland-related LUC. In order to discriminate between SOC losses from the initial ecosystem and gains from the secondary one, the post-LUC time series of SOC data was combined with satellite-based net primary production observations as a proxy of carbon input to the soil. Globally, land conversion from either cropland or forest into grassland leads to SOC accumulation; the reverse shows net SOC loss. The SOC response curves vary between different regions. Conversion of cropland to managed grassland results in more SOC accumulation than natural grassland recovery from abandoned cropland. We did not consider the biophysical variables (e.g., climate conditions and soil properties) when fitting the SOC turnover rate into the observation data but analyzed the relationships between the fitted turnover rate and these variables. The SOC turnover rate is significantly correlated with temperature and precipitation (p<0.05), but not with the clay fraction of soils (p>0.05). Comparing our results with predictions from bookkeeping models, we found that bookkeeping models overestimate by 56% of the long-term (100years horizon) cumulative SOC emissions for grassland-related LUC types in tropical and temperate regions since 2000. We also tested the spatial representativeness of our data set and calculated SOC response curves using the representative subset of sites in each region. Our study provides new insight into the impact grassland-related LUC on the global carbon budget and sheds light on the potential of grassland conservation for climate mitigation.

菌渣化肥配施对稻田土壤微生物量碳氮和可溶性碳氮的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 菌渣化肥配施对稻田土壤微生物量碳氮和可溶性碳氮的影响 DOI: 10.5846/stxb201711272117 作者: 作者单位: 浙江农林大学环境与资源学院,浙江农林大学环境与资源学院,浙江农林大学环境与资源学院,浙江农林大学环境与资源学院,浙江农林大学环境与资源学院,浙江农林大学环境与资源学院,浙江农林大学环境与资源学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31601271）；浙江省自然科学基金（LY16D010010） Effects of the combination of fungal residue and chemical fertilizer on soil microbial biomass carbon and nitrogen and dissolved organic carbon and nitrogen in paddy soil Author: Affiliation: School of Environmental and Resource Science，Zhejiang A＆F University,School of Environmental and Resource Science，Zhejiang A＆F University,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:菌渣作为一种养分丰富的有机物料还田，可减少化肥施用，同时保持土壤肥力；而土壤微生物量碳、氮和可溶性碳、氮是土壤活性碳氮库的重要组成部分，其含量和比例变化对土壤肥力均具有重要作用。因此，探讨不同比例菌渣化肥配施对土壤微生物量碳、氮及可溶性碳、氮的影响，评价菌渣在优化土壤肥力方面的生态作用具有重要意义。在水稻田间定位试验条件下，设置3个化肥水平（C）0、50%、100%，菌渣相对用量（F）0、50%、100%，共9个处理，分析了各处理土壤微生物量碳（MBC）、氮（MBN）和可溶性碳（DOC）、氮（DON）的变化特征，及其占土壤有机碳（SOC）和全氮（TN）的比例与相关关系。结果表明：菌渣化肥配施后，微生物量碳和可溶性碳、氮均在C100F50最高，微生物量氮在C50F100最高，与不施肥处理相比，分别显著增加了49.40%、43.65%、83.52%、207.19%；MBC/SOC和DOC/SOC均随着菌渣化肥配施量的增加而减少，MBN/TN和DON/TN均在C100F50最高。相关分析表明，MBC、DOC与SOC，MBN与TN均呈极显著正相关，DON和TN呈显著正相关。总体来讲，菌渣化肥配施能够显著提高土壤微生物量碳、氮和可溶性碳、氮含量，但不是随着用量的增加一直呈增加趋势，高量菌渣或者化肥下会有降低趋势；菌渣化肥配施降低了土壤微生物量和可溶性碳氮比，因此适宜的菌渣化肥配施是提高土壤有机碳周转速度、微生物活性及其氮素供应能力和有效性的最佳选择。 Abstract:As an excellent organic material additive to soil, fungal residue can reduce the application of chemical fertilizer and also plays an important role in maintaining soil fertility. As the most active organic components, soil microbial biomass carbon (MBC) and nitrogen (MBN) and dissolved organic carbon (DOC) and nitrogen (DON) are usually regarded as important and sensitive indices for soil fertility change. Therefore, it is vital to evaluate the ecological and soil fertility significance of fungal residue application under different rates return to the paddy soil. In our study, a randomized complete block field experiment with nine treatments(0,50%, and 100% levels of chemical fertilizers (C) and edible fungal residue (F) were considered, C100F50 stands for 100% of chemical fertilizer and 50% of fungal residue application, etc.) was set up. The changes of MBC, MBN, DOC, and DON, and ratios of these parameters to soil organic carbon (SOC) and total nitrogen (TN) were analyzed. Results showed that the highest contents of MBC, DOC and DON were observed under treatment of C100F50, which were 49.40%, 43.65% and 83.52% higher than that under the treatment of control. Meanwhile highest MBN content was found under treatment of C50F100 which was 207.19% higher than that under the treatment of control. Both ratios of MBC and DOC to SOC were decreased with increased application rate of fungal residue and chemical fertilizer; the highest ratios of MBN and DON to TN were observed in C100F50. There were highly significant positive correlations between MBC, DOC and SOC, respectively, and between MBN and TN as well. The correlation between DON and TN was significantly positive too. In conclusion, application of fungal residue with chemical fertilizer in paddy soil could increase the contents of MBC, MBN, DOC, and DON, but over dosage of fungal residue or chemical fertilizer application could lead to a negative effect. Consequently, the appropriate application rate of chemical fertilizer combined with fungal residue was the optimum choice to improve the SOC turnover rate, microbial activity, and nitrogen supply capacity and efficiency in paddy soil. 参考文献 相似文献 引证文献

Soil organic carbon dynamics study bias deduced from isotopic fractionation in corn plant

Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon (SOC) across a land-use change involving a shift to vegetation with different photosynthetic pathways. Based on the isotopic mass balance equation, relative contributions of new versus old SOC, and SOC turnover rate in corn fields were evaluated world-wide. However, most previous research had not analyzed corn debris left in the field, instead using an average corn plant δ 13C value or a measured value to calculate the proportion of corn-derived SOC, either of which could bias results. This paper carried out a detailed analysis of isotopic fractionation in corn plants and deduced the maximum possible bias of SOC dynamics study. The results show approximately 3‰ isotopic fractionation from top to bottom of the corn leaf. The 13C enrichment sequence in corn plant was tassel > stalk or cob > root > leaves. Individual parts accounting for the total dry mass of corn returned distinct values. Consequently, the average δ 13C value of corn does not represent the actual isotopic composition of corn debris. Furthermore, we deduced that the greater the fractionation in corn plant, the greater the possible bias. To alleviate bias of SOC dynamics study, we suggest two measures: analyze isotopic compositions and proportions of each part of the corn and determine which parts of the corn plant are left in the field and incorporated into SOC.

Physico-chemical protection, rather than biochemical composition, governs the responses of soil organic carbon decomposition to nitrogen addition in a temperate agroecosystem

The heterogeneous responses of soil organic carbon (SOC) decomposition in different soil fractions to nitrogen (N) addition remain elusive. In this study, turnover rates of SOC in different aggregate fractions were quantified based on changes in δ13C following the conversion of C3 to C4 vegetation in a temperate agroecosystem. The turnover of both total organic matter and specific organic compound classes within each aggregate fraction was inhibited by N addition. Moreover, the intensity of inhibition increases with decreasing aggregate size and increasing N addition level, but does not vary among chemical compound classes within each aggregate fraction. Overall, the response of SOC decomposition to N addition is dependent on the physico-chemical protection of SOC by aggregates and minerals, rather than the biochemical composition of organic substrates. The results of this study could help to understand the fate of SOC in the context of increasing N deposition.

Al-/Fe-(hydr)oxides–organic carbon associations in Oxisols — From ecosystems to submicron scales

Al-/Fe(hydr)oxides accumulation upon weathering favors soil organic carbon (SOC) protection into mineral-organic associations (MOAs). Paradoxically, tropical ecosystems on highly weathered soils are characterized by high turnover rates of SOC. Our objective was to propose an explanation for such apparent contradiction by inferring the chemical composition of MOAs in Oxisols. To this end, we compiled a large data set from 43 published articles providing chemical and physical properties of 179 Oxisols/Ferralsols and their SOC content in the A horizon. Thermal analysis (TA) coupled to evolved gas detection (EGD) was used to assess mineral dehydroxylation and SOC oxidation in two soils with contrasting SOC content. Scanning transmission electron microscopy (STEM) was used to probe MOAs within the soil fraction <53μm. At large scales, SOC content was strongly correlated to Al extractable by both ammonium oxalate (AO) (r=0.71) and dithionite-citrate-bicarbonate (DCB) (r=0.41). Weaker, but significant correlations occurred for SOC against Fe-AO and Fe-DCB (r=0.38, and r=014, respectively). At micro-scale, SOC also was found associated to Al-/Fe-(hydr)oxides, as inferred from the STEM imaging. TA-EGD indicated that with increasing SOC content, proportionally more organic matter was oxidized following the dehydroxylation of Al-/Fe-(hydr)oxides at temperatures <400°C. Within the first 20 cm of the topsoil of the Oxisols included in our data set, Al-AO explained 62% of the total variation in SOC. However, while SOC content varied from 0.8 up to 145.8gkg−1 soil, Al-AO varied between 0.2 and 15.3gkg−1 soil. From the perspective of mineral control on SOC retention, reactive species of Al-(hydr)oxides should interact with a disproportionally large amount of organic matter. Because mineral protection is seemingly reduced upon increasing C content in MOAs, SOC in Oxisols may be more vulnerable to environmental changes than currently recognized.

Characteristics and Influencing Factors of Soil Microbial Biomass Carbon and Nitrogen in Drawdown Area in the Three Gorges Reservoir

Taking a typical drawdown area located in Wangjiagou of the Three Gorges Reservoir as the study object, four elevations 180,175,165 and 155 m were selected to explore the effect of water level change on soil microbial biomass carbon (SMBC) and microbial biomass nitrogen (SMBN). Wherein, 175,165 and 155 m elevations located in the fluctuating zone, manifested as short, medium and long-term flooding, respectively; 180 m was used as the control, located on the land and never flooded. Sampling depth in soil samples was 0-20 cm, collected once a week. The results indicated that, soil organic carbon (SOC) and total nitrogen (TN) contents at 180 m had no obvious seasonal changes, while they showed remarkable seasonal trends at 175m, which in spring and summer were significantly higher than in autumn and winter; SMBC and SMBN contents and their allocation ratio at four elevations were similar and had significant seasonal fluctuation, which were highest in autumn and lowest in summer at each elevation, indicating that in drawdown area the microbial activity and turnover rate of soil organic carbon and nitrogen were limited by the high-temperature and low-humidity soil environment in summer. Data analysis showed that, compared with the 180 m elevation, contents of SOC, TN, SMBC and microbial quotient, SMBN and its allocation proportion showed varying degrees of increase, while contents of these indexes were significantly lower than control except SMBN and its allocation proportion, meaning that compared with 180 m short and medium-term flooding was conducive to improve soil carbon, nitrogen and their turnover rate and microbial biomass, however, contents of soil carbon and nitrogen and microbial biomass carbon were significantly restricted at 155 m as soil was subjected to flooding stress, meanwhile the turnover rate of SOC was reduced. Correlation analysis implied that SMBC and SMBN had very significant negative correlation with temperature at 5 cm soil depth and pH, meaning that the two environmental factors had a strong effect on soil microbial biomass.

Modelling soil organic carbon in Danish agricultural soils suggests low potential for future carbon sequestration

Soil organic carbon (SOC) is in active exchange with the atmosphere. The amount of organic carbon (OC) input into the soil and SOC turnover rate are important for predicting the carbon (C) sequestration potential of soils subject to changes in land-use and climate. The C-TOOL model was developed to simulate the dynamics of SOC storage on medium- to long-term trends in the whole soil profile (0–100cm), and was used to compare SOC changes under typical Danish farming conditions for two sites in Denmark having the greatest possible temperature differences for the period 1986 and 2012. For this purpose, various agricultural management scenarios were considered including characteristic crop rotations with and without the presence of cover crops, and the application of organic amendments. We compared these simulated management effects with management effects estimated from Danish SOC monitoring network over the same period of time. The results of the C-TOOL simulations demonstrated that application of organic manure, use of cover crop, and converting the croplands to grassland had the potential to increase SOC in Danish mineral soils. The simulated data also suggested that C-TOOL gave a reasonably good account of SOC changes when compared with measured SOC values from a Danish national monitoring network, and the simulated management effects agree well with results of long-term experimental trials. The estimates show rather small potential for increasing SOC in Danish cropping systems, even when there is conversion to rotations with more grasslands or the use of cover crops is increased.