Labile Organic Carbon Pools Research Articles

若尔盖沙化草地不同生态恢复模式土壤活性有机碳及碳库管理指数变化

若尔盖沙化草地不同生态恢复模式土壤活性有机碳及碳库管理指数变化

Total and labile forms of soil organic carbon as affected by land use change in southwestern Iran

The labile pools of soil organic matter enable assessment of the variation in land use changes and other management practices. This study aims to: (1) examine the effect of forest (F) and pasture (P) conversion on total and labile forms of soil organic C (SOC), (2) quantify the relationship among different labile SOC, and (3) determine whether labile SOC fractions are more sensitive indicators of soil quality than total organic C (TOC) after F and P conversion to agricultural use (forests converted (F to A) and pasture converted (P to A) soils) in southwestern Iran. Accordingly, composite soil samples with eight replicates were collected from 0–15cm of each land use in December 2014. The samples were then analyzed for TOC, microbial biomass C, permanganate oxidizable C, and cold- and hot-water extractable organic C. The results illustrated that the TOC and all labile pools of soil organic carbon followed the trend: F>P>F to A>P to A. However, from the four land uses studied, P soils showed a better and different quality of organic C than other land use systems, which was indicated by the highest proportion of microbial biomass C (3.3%), permanganate oxidizable C (4.8%), and cold- (0.55%) and hot-water extractable organic C (3.7%), but the lowest proportion of non-labile C (95.2%) to the TOC contents of the soils. The highest amounts of SOC stocks were spotted in the F soils (42.1Mgha−1) followed by P (29.7Mgha−1), F to A (26.7Mgha−1) and P to A (19.5Mgha−1) land use systems. Accordingly, organic carbon storage of the soils decreased by land use conversion from F (36.6%) and P (34.3%) to agriculture. The carbon management index, whose variation was mainly caused by carbon pool index, was higher in P to A soils than F to A soils suggesting that organic C compounds are less degraded and contain higher amounts of labile C than F to A soils. The results also showed that labile organic carbon pools are more sensitive to changes in management practices than TOC contents of the soils. However, a single carbon pool cannot be used as the most sensitive indicator of soil quality to reflect land use differences. The permanganate oxidizable C, hot water extractable organic C and microbial biomass C demonstrated the highest sensitivity to the land use induced changes in forest soils and cold water extractable organic C and microbial biomass C were realized as the most sensitive parameters in pasture conversion to arable lands. In conclusion, it seems that the quality of both F and P soils was decreased with adoption of agriculture and therefore sustainable management practices should be employed in order to achieve soil stability and biological productivity in the area.

Impact of conservation practices on soil aggregation and the carbon management index after seven years of maize–wheat cropping system in the Indian Himalayas

The carbon management index (CMI) and labile organic carbon (LOC) pools are postulated as very sensitive indicators of changes in soil organic carbon (SOC) due to land degradation within a short time in response to management practices. To test this hypothesis, we investigated LOC and CMI under a field experiment (2007–2013) in relation to runoff, soil loss, maize and wheat yields on a 2% (1.15°) land slope of the Indian Himalayas. In this study, the impacts of several resource conservation practices, including different combinations of vegetative barriers (VB), minimum tillage (MT), different organic amendments (OA) and weed mulch, were evaluated. Results revealed that the plots under MT+OA with three applications of weed mulch had more SOC, macroaggregate-associated C concentrations and macroaggregates than conventional tillage (CT)+NPK with chemical weed control. Carbon management index varied from 47 to 59 and 42 to 55% with different conservation practices at depths of 0–5 and 5–15cm depths, respectively. Incorporation of weed mulch along with application of OM, MT and VB (by Palmarosa) under MT improved CMI by 19.7 and 24.2% compared to CT plots with VB (by Panicum) and inorganic NPK at depths of 0–5 and 5–15cm, respectively. Significant positive correlations were observed between CMI and maize yield (r=0.948; n=24; P<0.01), CMI and wheat yield (r=0.872; n=24; P<0.01) and CMI and wheat equivalent yield (r=0.906; n=24; P<0.01). However, significant negative correlations were obtained for CMI and runoff (r=−0.701; n=20; P<0.01) and CMI and soil loss (r=−0.768; n=20; P<0.01). Results established that Palmarosa as VB along with OA plus weed-mulch under MT was the best management practice for decreasing runoff and soil loss and increasing system productivity on a 2% slope in the region. The single value CMI was strongly positively correlated with crop productivity and negatively correlated with soil loss. Hence, this single value CMI could potentially be used for assessment of soil degradation elsewhere.

Soil organic carbon associated in size-fractions as affected by different land uses in karst region of Guizhou, Southwest China

Land use change has a significant effect on soil organic carbon (SOC), especially on labile organic carbon (LOC) due to its rapid response to soil changes and carbon supply. The objective of the study was to assess the effects of different land uses on soil fraction size distribution, SOC and LOC concentrations and their stocks in karst region of Guizhou Province, Southwest China. Studies were based on soil sampling in paddy, dryland, abandoned cultivated land for 3-years (AC-3), and abandoned cultivated land for 15-years (AC-15) in the 0–10, 10–20, and 20–30 cm depths in karst mountain area of Guizhou Province. Three fraction-size classes [macro (250–2000 μm), micro (53–250 μm), silt + clay (<53 μm)] were fractioned, and SOC and LOC concentrations in whole soil (non-fractionated) and different fraction sizes were also determined. The results showed that paddy contained the highest SOC and LOC concentrations in whole soil and different size-fractions as compared with other land uses down to 30 cm depth. However, the proportions of LOC to SOC were higher in AC-3 than the other land uses, especially pronounced in whole soil, which ranged from 17.5 to 26.3 % in different soil depths. Paddy also contained 23.7 % (100.9 Mg ha−1) more SOC and 17.6 % (19.7 Mg ha−1) more LOC stocks than dryland, whereas the SOC and LOC stocks in AC-15 and dryland were very close to each other in each soil depth. In paddy field, we found that macro-sized fractions contributed the greatest quantities of SOC to whole soil. In addition, paddy had significantly higher SOC stock values in macro-sized fractions than the other land uses in the both 0–10 and 10–20 cm depths. In the present study, there were no obvious increases of SOC and LOC pools among whole soil and different soil size-fractions after 15 years of land abandonment. These results suggest that natural recovery of SOC may take a long time after land abandonment, and paddy could serve as an important land use type for long-term carbon sequestration in karst region of Southwest China.

Understory management and fertilization affected soil greenhouse gas emissions and labile organic carbon pools in a Chinese chestnut plantation

Management practices markedly impact carbon (C) cycling in forest plantations. However, the interactive effects of understory management and fertilization on soil greenhouse gas (GHG) fluxes and labile organic C pools remain unclear in forest plantations. To investigate the effects of understory replacement, fertilization, and their interaction on soil GHG fluxes and labile organic C pools in a Chinese chestnut plantation, we conducted a 2×2 factorial experiment over a 12-month field study with four treatments: Control (understory removed without understory replacement or fertilization), understory replacement (understory removed and seeded with Medicago sativa L., MS), fertilization (F), and MS+F. The GHG fluxes were determined using a static chamber/GC technique. The seasonal pattern of GHG fluxes did not change in any of the treatments in this one-year study; however, soil GHG fluxes, total global warming potential (GWP) of GHG fluxes, and soil organic C (SOC), water soluble organic C (WSOC), microbial biomass C (MBC), and NO3−–N concentrations were significantly affected by MS, F, and their interaction. In addition, GHG fluxes, GWP, and SOC, WSOC, MBC and NO3−–N concentrations were markedly increased by fertilization, regardless of the understory replacement treatment (P<0.05), but they were increased by understory replacement only in the fertilized plots. The GHG fluxes were correlated with soil temperature and WSOC in all plots (P<0.05), but not with soil moisture and MBC. These findings suggest that understory replacement likely is the optimum management technique for reducing/minimizing GHG fluxes, while F can enhance the effects of MS on increasing soil organic C and nutrient availability. We conclude that a combination of a moderate rate of fertilization and understory replacement with legume species should be adopted to increase soil C sequestration, maintain soil fertility and sustainably develop chestnut plantations.

Temperature Sensitivity and Soil Organic Carbon Pools Decomposition under Different Moisture Regimes: Effect on Total Microbial and Enzymatic Activity

The soils of the world store significantly more carbon than present in the atmosphere. However, there is still no consensus regarding the effects of climate change, i.e. increase in temperature on global soil carbon stocks. An incubation experiment was conducted under a temperature range (5–45°C) and moisture conditions, i.e. U1–U5 (20–100% water‐holding capacity) with the objective to investigate temperature sensitivity of labile and recalcitrant organic carbon pools, total microbial activity, and soil extracellular enzymes, i.e. phenol oxidase and catalase activity in an Ultisol soil. The maximum increase in the labile organic carbon pool, i.e. water soluble organic carbon (3.52‐fold), microbial biomass carbon (2.31‐fold), readily mineralizable carbon (6.16‐fold), permanganate oxidized organic carbon (2.81‐fold), and reducing sugar carbon (3.97‐fold) was observed at 35°C, whereas the effect at other temperatures was in the order 25 &gt; 45 &gt; 15 &gt; 5°C. The total organic carbon (TOC) tended to decrease with the increased temperature (from 5–35°C), therefore, maximum TOC (14.7 g kg−1) was observed at 5°C, and minimum (1.76 g kg−1) at 45°C. Conversely, the highest increase (6.48‐fold) in the recalcitrant organic carbon pool was noticed at 45°C, and the impact of other temperatures was in the order 35 &gt; 25 &gt; 15 &gt; 5°C. The maximum increase in the total microbial activity (13.68‐fold) and soil enzymes, phenol oxidase and catalase (3.94 and 3.98‐fold, respectively) activity was observed at 35°C, while the influence of other temperature ranges was in the order 25 &gt; 45 &gt; 15 &gt; 5°C. The effect of moisture regimes on the temperature sensitivity of organic carbon pools, total microbial and enzymatic activity was in the order U3 &gt; U4 &gt; U2 &gt; U1 &gt; U5.

Effect of temperature on the decomposition rate of labile and stable organic matter in an agrochernozem

An hypothesis about the different temperature dependences of the decomposition of the labile and stable organic carbon pools has been tested using an agrochernozem sampled from an experimental plot of 42-year-old continuous corn in Voronezh oblast. The partitioning of the CO2 loss during the decomposition of the labile and stable soil organic matter (SOM) at 2, 12, and 22°C in a long-term incubation experiment was performed using the method of 13C natural abundance by C3–C4 transition. On the basis of the determined decomposition constants, the SOM pools have been arranged in an order according to their increasing stability: plant residues < new (C4) SOM < old (C3) SOM. The tested hypothesis has been found valid only for a limited temperature interval. The temperature coefficient Q 10 increases in the stability order from 1.2 to 4.3 in the interval of 12–22°C. At low temperatures (2–12°C), the values of Q 10 insignificantly vary among the SOM pools and lie in the range of 2.2–2.8. Along with the decomposition constants of the SOM, the new-to-old carbon ratio in the CO2 efflux from the soil and the magnitude of the negative priming effect for the old SOM caused by the input of new organic matter depend on the temperature. In the soil under continuous corn fertilized with NPK, the increased decomposition of C3 SOM is observed compared to the unfertilized control; the temperature dependences of the SOM decomposition are similar in both agrochernozem treatments.

土壤碳库构成研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 土壤碳库构成研究进展 DOI: 10.5846/stxb201301050036 作者: 作者单位: 中国矿业大学环境与测绘学院,安徽师范大学国土资源与旅游学院,中国矿业大学环境与测绘学院,安徽师范大学国土资源与旅游学院,南京林业大学森林资源与环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41101529，41101502，31270664）；自然地理学省级重点学科和安徽师范大学国土资源与旅游学院科研团队资助项目（Asdgl102）；安徽师范大学科研培育基金项目（2010xmpy015） A review of the composition of soil carbon pool Author: Affiliation: College of Environment and Spatial Informatics,China University of Ming and Technology,Xuzhou Jiangsu,College of Territorial Resources and Tourism,Anhui Normal University,Wuhu,College of Environment and Spatial Informatics,China University of Ming and Technology,Xuzhou Jiangsu,College of Territorial Resources and Tourism,Anhui Normal University,Wuhu, 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:土壤碳库是陆地生态系统中最大的碳库。土壤碳库的构成影响其累积和分解，并直接影响全球陆地生态系统碳平衡，同时也影响土壤质量变化。弄清土壤碳库的组分及构成，是进一步研究土壤碳库变化机制的关键。综述了土壤碳库的组分和构成，对有机碳库进行不稳定性有机碳库和稳定有机碳库归类，描述各类碳库的性质，并对各类碳库的分析测定方法进行了评述。提出在土壤碳构成中增加黑碳和煤炭（碳）以完善土壤有机碳构成框架。在未来研究中，应加强土壤无机碳及湿地土壤和新开发新复垦的重构土壤碳库构成及变化，各类碳库化学构成，交叉重叠的定量关系，碳库之间的转化及在土壤中的迁移，黑碳对土壤碳库稳定性及土壤质量的影响，煤开采扰动区煤炭（碳）对土壤质量的影响及环境效应等科学问题的研究。 Abstract:The soil carbon pool is the biggest one in the terrestrial ecosystem. The composition of soil carbon pool influences carbon accumulation and decomposition, and directly controls global terrestrial carbon balance, and influences soil quality. Making clear the constitutes of soil carbon pool is the key process in revealing the mechanism of soil carbon pools change. This paper overviewed the structure and composition of the soil carbon pools. Soil carbon pools include soil inorganic carbon pool and soil organic carbon pool. Soil inorganic carbon pool includes HCO3- in soil solution,CO2 in soil air, and CaCO3 in soil. And CaCO3 is the main component in soil inorganic carbon pool. Soil inorganic carbon pool can influence soil organic carbon pool by affecting composition of soil aggregates, microbial activity, soil pH, and soil organic matter decomposition rate. Soil organic carbon is a very complex continuous mixture, which includes a variety of organic carbon fractions and forms with different nature. And the content of all kind of soil organic carbon affects the transformation of soil carbon pool and thereby influences soil quality and carbon cycle in terrestrial ecosystem. Soil organic carbon pools are categorized into soil labile organic carbon pool and soil stable organic carbon pool. Among them, soil labile organic carbon can turnover within a certain time, and can be utilized by plant and microorganism, and have a major impact on the carbon balance. Soil labile organic carbon is also named soil activated organic carbon or effective carbon by some authors, and includes terms as available carbon (AC), dissolved organic carbon (DOC), water soil organic carbon (WSOC), readily oxidation carbon (ROC), microbial biomass carbon (MBC), biodegradable carbon, light fraction organic carbon (LFOC), particulate organic carbon (POC) and so on. Black carbon (BC) and coal carbon are suggested to be categorized into soil organic carbon pool to perfect the frame of soil organic carbon pool composition. Black carbon is a C-rich organic material derived from incomplete combustion of fossil fuels and vegetation and from weathering of graphitic C in rocks, and very stabile. Black carbon captures and sequesters carbon from the bio-atmospheric cycle, which, in the long term, reduces greenhouse gas emissions and thus mitigates the greenhouse effect. Meanwhile, resistant black carbon amendation increase soil organic matter, thus regulating soil structure and enhancing soil fertility. Because of its high adsorption capacity, black carbon adsorbs organic pollutants, heavy metals, nutrients to decrease ecosystem risk. The coal (carbon) in the surface layer soil mainly come from outside source; include garbage, filling, atmospheric sedimentation and so on. The coal mine area is usually the district absorbing the most coal (carbon). In future studies, we should strengthen the researches on the scientific issues including the chemical composition, overlapping quantitative relationship of the soil organic carbon pools, transformation and migration of soil organic carbon in the soil, the impact of black carbon on the stability of the soil carbon pool and soil quality, the impact of coal (carbon) on soil quality and environmental effects in the coal mining disturbed zone, and organic carbon change and mechanism in newly developed soil, reclamation soil and reconstruction soil. 参考文献 相似文献 引证文献

Changes of CO2 emission and labile organic carbon as influenced by rice straw and different water regimes

Crop residues under different water regimes can cause significant alterations in soil organic carbon fractions, and in turn, soil-atmospheric carbon dioxide (CO2) emissions. To evaluate the effect of rice straw application on CO2 emissions and labile organic carbon fractions under different water regimes, an incubation experiment was conducted for 90 days. Ten treatments were developed from the interaction between five water levels (100, 85, 70, 55, and 40 % of water-holding capacity (WHC)) with and without incorporation of rice straw. Peaks of CO2 fluxes were observed after 13 days of rice straw incorporation, which decreased gradually till the end of the incubation period. The incorporation of rice straw caused significant increases in CO2 fluxes by 2.77-2.83 times from the paddy soil. In the presence of rice straw, the highest CO2 fluxes were generally observed at W3 (70 % of WHC), whereas the lowest fluxes were occurred at W1 (100 % of WHC). Addition of rice straw under a range of water regimes markedly improved the transformation of soil organic carbon and labile organic carbon pools such as dissolved organic carbon, microbial biomass carbon, light fraction organic carbon, particulate organic carbon, and permanganate oxidizable carbon. The significant correla- tions between all labile soil organic carbon fractions and CO2 concentrations confirmed their important roles in the emission of CO2 from the paddy soil. In summary, the results suggest that light fraction organic carbon, particu- late organic carbon, and permanganate oxidizable carbon were more sensitive indicators for CO2 emissions and organic matter alterations as compared to other carbon fractions.

Understory vegetation management affected greenhouse gas emissions and labile organic carbon pools in an intensively managed Chinese chestnut plantation

Background and aims The impact of understory vegetation control or replacement with selected plant species, which are common forest plantation management practices, on soil C pool and greenhouse gas (GHG, including CO2, CH4 and N2O) emissions are poorly understood. The objective of this paper was to investigate the effects of understory vegetation management on the dynamics of soil GHG emissions and labile C pools in an intensively managed Chinese chestnut (Castanea mollissima Blume) plantation in subtropical China.

Consequences of short-term C4 plant Spartina alterniflora invasions for soil organic carbon dynamics in a coastal wetland of Eastern China

The impacts of plant invasions are of great concern in the terrestrial carbon (C) cycling. However, the consequences of plant invasions for soil organic carbon (SOC) dynamics are not well understood. In this study, we conducted a field experiment to examine the effects of an exotic C4 perennial grass, Spartina alterniflora, on SOC pool and its fractions by comparing with native C3 plant Suaeda salsa and Phragmites australis soils and bare flat in a coastal wetland of Eastern China for one year. Soil samples from S. alterniflora invaded soil, bare flat, S. salsa and P. australis soils were measured for the soil water-soluble organic carbon (WSOC), microbial biomass carbon (MBC), cumulative CO2-C mineralization (MINC), soil organic carbon (SOC), total nitrogen (TN) and the C:N ratio. Short-term S. alterniflora invasions significantly increased WSOC, MBC, MINC, SOC and TN levels in the upper 0–30cm soil layer compared to bare flat and native C3 plant communities, but significantly decreased WSOC/SOC, MBC/SOC and MINC/SOC ratios relative to bare flat. S. alterniflora invasions also considerably increased aboveground and root biomass. The C:N ratio in S. alterniflora soil was significantly higher than that in S. salsa and P. australis soils, but with no difference from bare flat. Our results suggest that S. alterniflora invasions could enhance SOC sequestration possibly due to large amounts of litter biomass input but lower proportion of soil labile organic carbon pool fractions and mineralizable carbon in per unit SOC. Plant invasions could change the quantity and quality of the SOC pool and thus, have potential impacts on ecosystem functioning and global C cycling.

Profile distribution and seasonal dynamics of water-extractable carbohydrate in soils under mixed broad-leaved Korean pine forest on Changbai Mountain

Carbohydrate represents an important part of the soil labile organic carbon pool. Water soluble carbohydrate drives the C cycle in forest soil by affecting microbial activity and hot water extractable carbohydrate is thought related to soil carbon sequestration due to the association with soil aggregation. In a temperate forest region of northeast China, Changbai Mountain, we investigated the abundance, spacial distribution, and seasonal dynamics of cool and hot-water extractable carbohydrate in soils under mixed broad-leaved Korean pine forest. The concentrations of cool-water extractable carbohydrate (CWECH) in three soil layers (0–5, 5–10, 10–20 cm) ranged from 4.1 to 193.3 g·kg−1 dry soil, decreasing rapidly with soil depth. On an annual average, the CWECH concentrations in soils at depths of 5–10 and 10–20 cm were 54.2% and 24.0%, respectively, of that in the 0–5 cm soil layer. CWECH showed distinct seasonal dynamics with the highest concentrations in early spring, lowest in summer, and increasing concentrations in autumn. Hot-water extractable carbohydrate (HWECH) concentrations in three soil layers ranged from 121.4 to 2026.2 g·kg−1 dry soil, which were about one order of magnitude higher than CWECH. The abundance of HWECH was even more profile-dependent than CWECH, and decreased more rapidly with soil depth. On an annual average, the HWECH concentration in soils 10–20 cm deep was about one order of magnitude lower than that in the top 0–5 cm soil. The seasonality of HWECH roughly tracked that of CWECH but with seasonal fluctuations of smaller amplitude. The carbohydrate concentrations in cool/hot water extracts of soil were positively correlated with UV254 and UV280 of the same solution, which has implications for predicting the leaching loss of water soluble organic carbon.

Long-term intensive management effects on soil organic carbon pools and chemical composition in Moso bamboo (Phyllostachys pubescens) forests in subtropical China

Intensive forest management practices, such as fertilization, tillage, and understory removal, could markedly change the soil organic carbon (SOC) stock and labile organic carbon (C) pools. However, the combined effects of such intensive management practices on the quantity and quality of soil SOC in bamboo forests are poorly understood. The objectives of this study were to investigate the impact of long-term intensive management practices, including inorganic fertilizer application, tillage, and understory removal, on total and labile SOC pools and chemical composition of SOC in Moso bamboo (Phyllostachys pubescens) forests and to explore relationships between different soil organic C forms. We used a chronosequence approach (consisting of Moso bamboo forests with 0, 5, 10, 20, 30years of intensive management) to examine the effects of long-term intensive management on SOC storage, water soluble organic C (WSOC), hot-water soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), and SOC chemistry. Our results showed that SOC stock and concentrations of WSOC, HWSOC, MBC, and ROC decreased with increasing duration under intensive management. For the chemical composition of SOC, the contents of alkyl C and carbonyl C and the alkyl C to O-alkyl C (A/O-A) ratio increased, while the contents of O-alkyl C and aromatic C and aromaticity decreased as duration under intensive management increased, suggesting that long-term intensive management changed the SOC chemical composition. Soil MBC was negatively correlated with both alkyl C content and the A/O-A ratio (P<0.01 for both), and was positively correlated with O-alkyl content (P<0.01), indicating that soil microbial population size may be partly dependent on the chemical composition of SOC. In addition, O-alkyl C content was correlated with concentrations of WSOC (P<0.05), HWSOC (P<0.01), and ROC (P<0.01), which implied that O-alkyl C might be the main C component of WSOC, HWSOC, and ROC. We conclude that long-term intensive management reduced the total and labile SOC stocks in bamboo forests and alternative management regimes should be developed to increase C sequestration of soils in intensively managed Moso bamboo forests in subtropical China.

Converting paddy fields to Lei bamboo (Phyllostachys praecox) stands affected soil nutrient concentrations, labile organic carbon pools, and organic carbon chemical compositions

Land-use change often markedly alters soil carbon (C) and nitrogen (N) pool sizes with implications for climate change and soil sustainability. The objective of this research was to study the effect of converting paddy fields to Lei bamboo (Phyllostachys praecox) stands on soil C and N and other nutrient pools as well as the chemical structure of soil organic C (SOC) in the soil profile. Soils (Anthrosols) from four adjacent paddy field–bamboo forest pairs with a known land-use history were sampled from Lin’an County, Zhejiang Province. Soil water soluble organic C (WSOC), hot water soluble organic C (HWSOC), microbial biomass C (MBC), readily oxidizable C (ROC), water soluble organic N (WSON), and other soil chemical and physical properties were determined. Soil organic C functional group compositions were determined by 13C-nuclear magnetic resonance (NMR). Concentrations of soil available P, available K, and different N forms increased (P < 0.05) by the land-use conversion. Higher concentrations of SOC and total N (TN) were observed in the subsoil (20–40 and 40–60 cm soil layers) but not in the topsoil (0–20 cm layer) in the bamboo stands than in the paddy fields. The storage of SOC and TN in the entire soil profile (0–60 cm) increased by 56.7 and 70.7 %, respectively, after the land-use change. The increases in the SOC stock of the three soil layers were 11.0, 14.3, and 9.5 Mg C ha−1, respectively. The conversion decreased WSOC concentrations in the subsoil but increased the ROC concentration in the topsoil. Solid-state NMR spectroscopy of soil samples showed that the conversion increased (P < 0.05) the O-alkyl C content while decreased the aromatic C content, alkyl C to O-alkyl C ratio (A/O-A), and aromaticity of SOC. Conversion of paddy fields to bamboo stands increased soil nutrient availability, and SOC and TN stocks. Effects of land-use change on C pools and C chemistry of SOC varied among different soil layers in the profile. The impact of the land-use conversion on soil organic C pools was not restricted to the topsoil, but changes in the subsoil were equally large and should be accounted for.

Seasonal Changes in Various Soil Organic Carbon Pools with Different Soil Amendments

In a sustainable agriculture farming systems experiment, the dynamics of soil organic carbon (OC), carbon/nitrogen (C/N) ratio and labile organic carbon pool in soil amended with maize stalk (MS), rice straw (RS) and alfalfa (AF) were studied from August 2005 to August 2006. The results showed that organic material with low N content decomposed slowly, while that with absolutely high N content depressed decomposition rate. After one year’s decomposition, the humification process of organic materials was basically complete. Soil labile carbon content was dramatically improved compared with the control after the addition of organic materials to the soil. The leached DOC was highly correlated with micro-organisms activity and MBC was highly dependent on N incorporation.

Soil labile carbon and nitrogen pools and microbial metabolic diversity under winter crops in an arid environment

The conservation farming systems coupled with stubble retention are now widely adopted in southern Australia to improve soil fertility. However, little information is available about the effects of winter crops on soil labile organic carbon (C) and nitrogen (N) pools, especially in an arid agricultural ecosystem. In this study, eight winter cover crop treatments were used to investigate their effects on soil labile organic C and N pools and microbial metabolic profiles and diversity in temperate Australia. These treatments included two legume crops (capello woolly pod vetch and field pea), four non-legume crops (rye, wheat, Saia oat and Indian mustard), and a mixture of rye and capello woolly pod vetch as well as a nil-crop control. At the crop flowering stage, soil and crop samples were collected from the field and we examined aboveground crop biomass, soil NH4+-N, NO3−-N, extractable organic C (EOC) and N (EON) concentrations using methods of 2M KCl and hot water, microbial biomass, biologically active organic C (CBio), and substrate-induced respiration (SIR) using the MicroResp method. Results showed that the crop treatments had lower soil moisture content, NO3−-N and the ratios of EOC to EON, but higher pH, NH4+-N, EOC, EON, CBio, microbial metabolic diversity index (H) and evenness index compared with the control. There were no significant differences in microbial biomass C and N among the treatments. Although no pronounced differences in EOC and EON concentrations were found between the legumes and non-legumes, the legume treatments had lower SIR and higher H than the non-legume treatments. Principal component analysis showed that soil microbial metabolic profiles under the crops were different from those of the control, and the crop treatments had a clear separation along principal component 2. In addition, redundancy analysis showed that soil pH and moisture content were the most important influencing factors, along with EON and crop biomass, determining the patterns of microbial metabolic profiles under the crops.

Labile Organic Carbon Pool of Forest Soil in the Badaling Mountainous Area of Beijing

Labile Organic Carbon Pool of Forest Soil in the Badaling Mountainous Area of Beijing

Impact of Long-Term Organic Fertilizer Application on Lignin in Mollisol

Fertilization is one of the essential managements to maintain and increase soil organic carbon (SOC) level in agroecosystems. It has been realized that fertilizer applications influenced the turnover of labile and refractory organic carbon pools in arable soil markedly. However, the dynamic of relatively refractory lignin in response to fertilization is still kept unclear. Therefore, the impact of long-term organic fertilization on the content and degradation degree of lignin in Mollisol was investigated. Lignin monomers were released by alkaline CuO oxidation method and quantified by gas chromatography (GC). At the time scale of decades, lignin was clearly accumulated in soil and the relative accumulation of lignin in SOC was evident after long-term organic fertilizer application. Compared with the unfertilized soil, lower acid to aldehyde ratios of vanillyl and syringyl units induced by organic fertilization suggested a lower degradation degree of lignin incorporated into soil to some extent. It could be concluded that long-term organic fertilization was an effective fertilizer practice for lignin accumulation in soil and SOC sequestration in Mollisol in northeast of China.

Carbon Mineralization and Labile Organic Carbon Pools in the Sandy Soils of a North Florida Watershed

The large pool of actively cycling carbon (C) held in soils is susceptible to release due to changes in landuse, management, or climate. Yet, the amount and distribution of potentially mineralizable C present in soils of various types and the method by which this soil C fraction can best be quantified, are not well established. The distribution of total organic C (TOC), extractable C pools (hot-water-extractable and acid-hydrolyzable), and in vitro mineralizable C in 138 surface soils across a north Florida watershed was found to be quite heterogeneous. Thus, these C quality parameters could not statistically distinguish the eight landuses or four major soil orders represented. Only wetland and upland forest soils, with the largest and smallest C pool size, respectively, were consistently different from the soils of other landuse types. Variations in potential C mineralization were best explained by TOC (62%) and hot-water-extractable C (59%), whereas acid-hydrolyzable C (32%) and clay content (35%) were generally not adequate indicators of C bioavailability. Within certain landuse and soil orders (Alfisol, Wetland and Rangeland, all with >3% clay content), however, C mineralization and clay content were directly linearly correlated, indicating a possible stimulatory effect of clay on microbial processing of C. Generally, the sandy nature of these surface soils imparted a lack of protection against C mineralization and likely resulted in the lack of landuse/soil order differences in the soil C pools. If a single parameter is to be chosen to quantify the potential for soil C mineralization in southeastern U.S. coastal plain soils, we recommend TOC as the most efficient soil variable to measure.

Content and seasonal change in soil labile organic carbon under different forest covers

Based on the concentrations of soil labile organic carbon (SLOC) pools under native evergreen broad-leaved forest (NBF), and three plantations of pure Cunninghamia lanceolata , pure Michelia macclurei and their mixed forest in different seasons, the effect of forest types on the content and seasonal changes of SLOC was analyzed for Huitong County of Hunan Province. The results show that SLOC content decreases after native evergreen broad-leaved forest are substituted by planted forest. Compared with C. lanceolata plantation, C. lanceolata and M. macclurei mixed forest (MCM) increases SLOC content. However, the difference is statistically insignificant except for water-soluble organic carbon (WSOC). Substantial seasonal fluctuations in SLOC under forests are observed. Throughout the year, WSOC decreases in the following order of NBF MCM pure M. macclurei plantation (PM) pure C. lanceolata plantation (PCF). For soil microbial biomass carbon (MBC), hot-water extractable C (HWC) and hot-water ex-tractable carbohydrate-C (HWcC) is in the following order of NBF PM MCM PCF. Compared with PCF, MCM increases soil quality. However, seasonal trends of SLOC under different forest covers are not completely consistent, suggesting that seasonal fluctuations in SLOC are influenced not only by climatic factors like temperature and precipitation, but also by vegetation type.