摘要 :
Labile carbon (C) is a major source of C loss because of its high vulnerability to environmental change. Yet its potential role in regulating soil organic carbon (SOC) dynamics remains unclear. In this study, we tested the effect ...
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Labile carbon (C) is a major source of C loss because of its high vulnerability to environmental change. Yet its potential role in regulating soil organic carbon (SOC) dynamics remains unclear. In this study, we tested the effect of physical disturbance on SOC decomposition using soils from two abandoned farmlands free of management practice for more than 28 years. The soil respiration rate was measured in undisturbed and disturbed soil columns and was inversely modeled using the two-compartment model. We found that the C loss was 16.8 similar to 74.1% higher in disturbed than in undisturbed soil columns. Physical disturbance increased the total amount of labile C (C-1) loss by 136 similar to 241%, while had no effect on the kinetic decomposition rate constants of both labile (k(1)) and stable (k(2)) SOC decomposition. Physical disturbance fragmented the large macroaggregates into small macroaggregates, microaggregates, and free silt and clay-sized fractions. This indicates that C loss was derived from the initially protected labile C, and there was no change of SOC fraction being decomposed. Our results give insights into the understanding of the extent of labile C loss to physical disruption and demonstrate the potential effect of physical disturbance on SOC dynamics.
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Two acidic soils (initial pH, 4.6) with contrasting soil organic C (SOC) contents (11.5 and 40 g C kg(-1)) were incubated with C-13-labelled lime ((CaCO3)-C-13) at four different rates (nil, target pH 5, 5.8 and 6.5) and three app...
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Two acidic soils (initial pH, 4.6) with contrasting soil organic C (SOC) contents (11.5 and 40 g C kg(-1)) were incubated with C-13-labelled lime ((CaCO3)-C-13) at four different rates (nil, target pH 5, 5.8 and 6.5) and three application depths (0-10, 20-30 and 0-30 cm). We hypothesised that liming would stimulate SOC mineralisation by removing pH constraints on soil microbes and that the increase in mineralisation in limed soil would be greatest in the high-C soil and lowest when the lime was applied in the subsoil. While greater SOC mineralisation was observed during the first 3 days, likely due to lime-induced increases in SOC solubility, this effect was transient. In contrast, SOC mineralisation was lower in limed than in non-limed soils over the 87-day study, although only significant in the Tenosol (70 mu g C g(-1) soil, 9.15%). We propose that the decrease in SOC mineralisation following liming in the low-C soil was due to increased microbial C-use efficiency, as soil microbial communities used less energy maintaining intracellular pH or community composition changed. A greater reduction in SOC mineralisation in the Tenosol for low rates of lime (0.3 and 0.5 g column(-1)) or when the high lime rate (0.8 g column(-1)) was mixed through the entire soil column without changes in microbial biomass C (MBC) could indicate a more pronounced stabilising effect of Ca2+ in the Tenosol than the Chromosol with higher clay content and pH buffer capacity. Our study suggests that liming to ameliorate soil acidity constraints on crop productivity may also help to reduce soil C mineralisation in some soils.
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We examined relationships between soil moisture and the temperature sensitivity of decomposition of labile soil organic carbon at a central North American grassland. For soils collected from shallow, xeric uplands, temperature sen...
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We examined relationships between soil moisture and the temperature sensitivity of decomposition of labile soil organic carbon at a central North American grassland. For soils collected from shallow, xeric uplands, temperature sensitivity was greatest at intermediate soil moisture. For soils collected from the deeper, mesic lowlands, temperature sensitivity increased with increasing soil moisture. For example, lowland soils incubated at 75% WHC exhibited an apparent activation energy (E sub(a)) that was 15 kJ mol super(-1) greater than soils incubated at 30% WHC, the equivalent of a Q sub(10) of 2.8 vs. 2.3. Although further research is still needed to understand why moisture-temperature sensitivity relationships would differ between topographic positions, the magnitude of the soil moisture effect is large enough to alter soil C budgets and should be considered explicitly when predicting ecosystem responses to global change scenarios.
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Significant increase in soil organic carbon (SOC) has been found in Chinese croplands. Current literature largely attributes this to the increased organic C inputs from manure, crop straw and root. However, using a meta-analysis o...
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Significant increase in soil organic carbon (SOC) has been found in Chinese croplands. Current literature largely attributes this to the increased organic C inputs from manure, crop straw and root. However, using a meta-analysis of 185 long-term trials and 6669 spatial data pairs across China, we show here that soil acidification is an additional significant cause for the SOC accumulation. Results from long-term experiments showed that soil acidification due to excessive N fertilization coincided with, and significantly (p < 0.01) contributed to, the observed SOC accrual. Spatially, the amount of SOC increase caused by soil acidification decreased with increasing initial content. In addition, the soil's basal respiration rate (SBRR), microbial metabolic quotient (MMQ) and the percentage of dissolved organic carbon (DOC) relative to total SOC decreased significantly (p < 0.01) with soil pH decline. This indicates that soil acidification depresses the decomposition of organic matter, both by decreasing microbial activity and by increasing protection of SOC by mineral phases. Thus, N-induced soil acidification promotes the SOC accumulation in Chinese croplands, by increasing its stability. In contrast to the current view emphasizing the importance of organic C inputs, our meta-analysis reveals an alternative mechanism connecting N-fertilization and the resulting SOC accumulation in agricultural ecosystems. More research is needed to further clarify its operating processes, relative importance, and agro-environmental consequences.
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The dynamics of soil organic carbon (SOC) pools determine potential carbon sequestration and soil nutrient improvement. This study investigated the characteristics of SOC pools in five types of cultivated topsoils (0-15cm) in subt...
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The dynamics of soil organic carbon (SOC) pools determine potential carbon sequestration and soil nutrient improvement. This study investigated the characteristics of SOC pools in five types of cultivated topsoils (0-15cm) in subtropical China using laboratory incubation experiments under aerobic conditions. The sizes and turnover rates of the active, slow and resistant C pools were simulated using a first-order kinetic model. The relative influence of soil environmental properties on the dynamics of different SOC pools was evaluated by applying principal component analysis (PCA) and aggregated boosted trees (ABTs) analysis. The results show that there were significantly greater sizes of different SOC pools and lower turnover rates of slow C pool in two types of paddy soils than in upland soils. Land use exerted the most significant influence on the sizes of all SOC pools, followed by clay content and soil pH. The soil C/N ratio and pH were the major determinants for turnover rates of the active and slow C pools, followed by clay content which had more impact on the turnover rates of the active C pool than the slow C pool. It is concluded that soil type exerts a significant impact on the dynamics of SOC.
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A continuous soil organic carbon (SOC) model (K-model) was developed based on the conceptualization that SOC decomposition consists of three basic steps: the initial decomposition of plant litter, death of microorganisms, and deco...
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A continuous soil organic carbon (SOC) model (K-model) was developed based on the conceptualization that SOC decomposition consists of three basic steps: the initial decomposition of plant litter, death of microorganisms, and decomposition and recycling of dead microbial residues. Eleven parameters describe C decomposition and cycling through three dynamic SOC pools: plant residue, soil microbial biomass, and dead microbial residue. Specific experimental measurements that allow for complete determination of all model parameters were identified and analyzed using examples in the literature. Behavior and ability of K-model are illustrated using examples including laboratory incubations and long-term field studies. The model correctly predicted the surprising observation in a long-term field study that showed higher stabilization of glucose C compared with wheat straw and identified that the higher microbial carbon use efficiency Of glucose accounts for this difference. Microbial carbon use efficiency and microbial metabolic fraction were identified as two of the most sensitive parameters determining C stabilization in soils, with le need for more reliable measurement techniques.
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Abstract Confidence in model estimates of soil CO2 flux depends on assumptions regarding fundamental mechanisms that control the decomposition of litter and soil organic carbon (SOC). Multiple hypotheses have been proposed to expl...
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Abstract Confidence in model estimates of soil CO2 flux depends on assumptions regarding fundamental mechanisms that control the decomposition of litter and soil organic carbon (SOC). Multiple hypotheses have been proposed to explain the role of lignin, an abundant and complex biopolymer that may limit decomposition. We tested competing mechanisms using data‐model fusion with modified versions of the CN‐SIM model and a 571‐day laboratory incubation dataset where decomposition of litter, lignin, and SOC was measured across 80 soil samples from the National Ecological Observatory Network. We found that lignin decomposition consistently decreased over time in 65 samples, whereas in the other 15 samples, lignin decomposition subsequently increased. These “lagged‐peak” samples can be predicted by low soil pH, high extractable Mn, and fungal community composition as measured by ITS PC2 (the second principal component of an ordination of fungal ITS amplicon sequences). The highest‐performing model incorporated soil biogeochemical factors and daily dynamics of substrate availability (labile bulk litter:lignin) that jointly represented two hypotheses (C substrate limitation and co‐metabolism) previously thought to influence lignin decomposition. In contrast, models representing either hypothesis alone were biased and underestimated cumulative decomposition. Our findings reconcile competing hypotheses of lignin decomposition and suggest the need to precisely represent the role of lignin and consider soil metal and fungal characteristics to accurately estimate decomposition in Earth‐system models.
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Kinetic relationship between addition of organic carbon (through unharvested crop biomass and externally applied farmyard manure) and storage in a Vertisol (Typic Haplustert) was studied in a seven-year soybean-wheat rotation expe...
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Kinetic relationship between addition of organic carbon (through unharvested crop biomass and externally applied farmyard manure) and storage in a Vertisol (Typic Haplustert) was studied in a seven-year soybean-wheat rotation experiment. We investigated 16 treatments comprised of combinations of four annual rates of farmyard manure (0, 4, 8 and 16 t ha(-1) on dry weight basis) and four annual rates of fertilizer N (0, 72.5, 145, and 230 kg N ha(-1)). Average annual contribution of C input from soybean was 21.65% and from wheat was 32.32% of the harvestable above ground biomass. Net increases in the contents of soil organic C (C-org) at 0-15 and 15-30 cm depth were observed in all treatments. The annual rate of C-org enrichments ranged from 85 to 739 kg C ha(-1) at 0-15 cm and 54 to 149 kg C ha(-1) at 15-30 cm soil depth. The observed annual rate of change in C-org (delta Cs/Omegat, kg C ha(-1) yr(-1)) at 0-30 cm was positively correlated with the gross annual C input (A, kg C ha(-1) yr(-1)) to the 0-30 cm soil horizon. as described by a linear equation (delta Cs/deltat = 0.1806 X A - 160.34; r = 0.978, P < 0.01). This indicates that 18.06% of the annual gross C input was incorporated in soil organic matter.
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The amount of soil organic carbon (SOC) in stable, slow-turnover pools is likely to change in response to climate warming because processes mediating soil C balance (net primary production and decomposition) vary with environmenta...
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The amount of soil organic carbon (SOC) in stable, slow-turnover pools is likely to change in response to climate warming because processes mediating soil C balance (net primary production and decomposition) vary with environmental conditions. This is important to consider in boreal forests, which constitute one of the world's largest stocks of SOC. We investigated changes in soil C stabilization along four replicate gradients of black spruce (Picea mariana) productivity and soil temperature in interior Alaska, USA to develop empirical relationships between SOC and stand and physiographic features. Total SOC harbored in mineral soil horizons decreased by 4.4 g C m-2 for every degree-day increase in heat sum within the organic soil across all sites. Furthermore, the proportion of relatively labile light-fraction (density <1.6 g cm-3) soil organic matter decreased significantly with increased stand productivity and soil temperature. Mean residence times of SOC (as determined by Delta 14C) in dense-fraction (>1.6 g cm-3) mineral soil ranged from 282 to 672 years. The oldest SOC occurred in the coolest sites, which also harbored the most C and had the lowest rates of stand production. These results suggest that temperature sensitivities of organic matter within discrete soil pools, and not just total soil C stocks, need to be examined to project the effects of changing climate and primary production on soil C balance..
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