Soil carbon and nitrogen storage in alluvial wet meadows of the Southern Sierra Nevada Mountains,USA

Purpose

Wet meadows formed on alluvial deposits potentially store large amounts of soil carbon (C) but its stability is subject to the impacts of management practices. The objective of this study was to quantify and characterize soil organic carbon (SOC) and nitrogen (N) in mountain wet meadows across ranges of meadow hydrology and livestock utilization.

Materials and methods

Eighteen wetlands in the southern Sierra Nevada Mountains representing a range of wetness and livestock utilization levels were selected for soil sampling. In each wetland meadow, whole-solum soil cores delineated by horizon were analyzed for total and dissolved organic C (DOC) total (TN) and mineral nitrogen and soil water content (SWC). Multiple regression and GIS analysis was used to estimate the role of wet meadows in C storage across the study area landscape.

Results and discussion

Average solum SOC contents by wetland ranged from 130 to 805 Mg ha^?1. All SOC and TN components were highly correlated with SWC. Regression analyses indicated subtle impacts of forage utilization level on SOC and TN concentrations, but not on whole-solum, mass-per-area stocks of SOC and TN. Proportions of DOC and TN under seasonally wet meadows increased with increasing utilization. GIS analysis indicated that the montane landscape contains about 54.3 Mg SOC ha^?1, with wet meadows covering about 1.7% of the area and containing about 12.3% of the SOC.

Conclusions

Results indicate that soil organic C and N content of meadows we sampled are resilient to current light to moderate levels of grazing. In seasonally wet meadows, higher proportions of DOC and N with increasing utilization indicate vulnerability to loss. Partial drying of the wettest and seasonally wet meadows could result in losses of over five % of landscape SOC.     

Land use affects soil organic carbon of paddy soils: empirical evidence from 6280 years BP to present

Purpose

Submerged rice cultivation has been practiced in China for 7000 years. Empirical evidence on changes of soil organic carbon (SOC) contents in paddy soils over this historical time period is scarce. Therefore, a field study was conducted to investigate the effect of submerged rice cultivation on the accumulation and preservation of SOC in paddies.

Materials and methods

Two buried ancient paddy profiles (6280 years BP, named P-01 and P-03) in the Yangtze Delta of eastern China were excavated to illustrate the development of SOC contents in soils during the evolution of paddies under anthropogenic land use and environmental changes from the prehistoric period to the present time. Trends in SOC concentrations, total nitrogen concentrations, and stable carbon isotope ratio were identified for different points in time.

Results and discussion

Accumulation of organic carbon was found in the paddy soil layers of P-01 at 100–174 cm depth. This site was taken under submerged rice cultivation in about 6280 years BP. The average SOC concentration in the prehistoric paddy topsoil in 100–130 cm depth was 1.27 %, which is seven times higher than that in the adjacent uncultivated land at 103–130 cm depth of P-03. This implies that the paddy soil has experienced substantial CO₂ sequestration under submerged management during that time. By about 3320 years BP, organic carbon contents were halved, potentially due to marine inundation by sea level rise. Up to the year 2003, the SOC contents in all horizons in the present time paddy soil have increased, especially in the surface layer, indicative of continuous rice cultivation. However, due to rapid urbanization and industrialization, the cultivation of paddies in eastern China has gradually been discontinued leading to the loss of SOC stocks of approximately 10 % in a 6-year interval (from 2003 to 2009). A significant relationship between SOC and rice phytolith contents was found in the paddy soil horizons of P-01 (r?=?0.71, p?<?0.01) and P-03 (r?=?0.72, p?<?0.01), suggesting that phytolith-occluded organic carbon could be used as a biomarker to ascertain the development of SOC in the evolution of rice paddies over the past 6000 years.

Conclusions

Submerged rice cultivation led to a noticeable accumulation of SOC in paddies. Phytolith-occluded organic carbon could be used as a biomarker to monitor changes of OC contents in paddy soils.

     

碳氮添加对雨养农田土壤全氮、有机碳及其组分的影响

为探明碳氮添加4年后,土壤全氮、有机碳及其组分(可溶性有机碳、微生物量碳、轻组和重组有机碳)的变化特征,依托布设于甘肃省定西市安定区李家堡镇的不同碳源配施氮素田间定位试验,涉及秸秆、生物质炭、氮素3个因素,秸秆设置为不施、施用秸秆2水平;生物质炭为不施和施用生物质炭2个水平;氮素设置为不施氮、施纯氮50 kg/hm^2、施纯氮100 kg/hm^2 3个水平,共9个处理。结果表明:不同处理下土壤全氮、有机碳及其组分的含量均随土层的加深而降低。添加生物质炭对土壤全氮、有机碳及其组分均具有不同程度的提升效应。添加秸秆对土壤全氮、有机碳和可溶性有机碳、微生物量碳、轻组有机碳均具有显著提升效应,仅在0-5 cm土层对重组有机碳有显著提高。添加氮素可显著提升土壤全氮、有机碳和可溶性有机碳、微生物量碳、轻组有机碳含量。较其他处理,添加生物质炭对土壤全氮、有机碳和重组有机碳的提升效应最高,添加秸秆对可溶性有机碳、微生物量碳、轻组有机碳的提升效果最优。从提升土壤质量的角度出发,推荐秸秆配施氮素模式,该模式下土壤碳素有效性高、易于被微生物利用,有利于作物生长。从提高土壤固碳角度考虑,推荐生物质炭配施氮素模式,该模式有利于碳的封存。     

Stability and saturation of soil organic carbon in rice fields: evidence from a long-term fertilization experiment in subtropical China

Purpose

Soil organic carbon (SOC) sequestration in croplands plays a critical role in climate change mitigation and food security, whereas the stability and saturation of the sequestered SOC have not been well understood yet, particularly in rice (Oryza sativa L.) fields. The objective of this study was to determine the long-term effect of inorganic fertilization alone or combined with organic amendments on SOC stability in a double rice cropping system, and to characterize the saturation behavior of the total SOC and its fractions in the paddy soil.

Materials and methods

Soils were collected from a long-term field experiment in subtropical China where different fertilization regimes have been carried out for 31 years. The total SOC pool was separated into four fractions, characteristic of different turnover rates through chemical fractionation. Annual organic carbon (C) inputs were also estimated by determining the C content in crop residues and organic amendments.

Results and discussion

Relative to the initial level, long-term double rice cropping without any fertilizer application significantly increased SOC concentration, suggesting that double rice cropping facilitates the storage and accumulation of SOC. The partial substitution of inorganic fertilizers with organic amendments significantly increased total SOC concentration compared to the unfertilized control. Total SOC increased significantly with greater C inputs and did not show any saturation behavior. Increased SOC was primarily stored in the labile fraction with input from organic amendments. However, other less labile SOC fractions showed no further increase with greater C inputs exhibiting C saturation.

Conclusions

While the paddy soil holds a high potential for SOC sequestration, stable C fractions saturate with increasing C inputs, and thus, additional C inputs mainly accumulate in labile soil C pools.     

Land use and climate change impacts on soil organic carbon stocks in semi-arid Spain

Purpose

The sensitivity of soil organic carbon to global change drivers, according to the depth profile, is receiving increasing attention because of its importance in the global carbon cycle and its potential feedback to climate change. A better knowledge of the vertical distribution of SOC and its controlling factors—the aim of this study—will help scientists predict the consequences of global change.

Materials and methods

The study area was the Murcia Province (S.E. Spain) under semiarid Mediterranean conditions. The database used consists of 312 soil profiles collected in a systematic grid, each 12 km² covering a total area of 11,004 km². Statistical analysis to study the relationships between SOC concentration and control factors in different soil use scenarios was conducted at fixed depths of 0–20, 20–40, 40–60, and 60–100 cm.

Results and discussion

SOC concentration in the top 40 cm ranged between 6.1 and 31.5 g?kg^?1, with significant differences according to land use, soil type and lithology, while below this depth, no differences were observed (SOC concentration 2.1–6.8 g?kg^?1). The ANOVA showed that land use was the most important factor controlling SOC concentration in the 0–40 cm depth. Significant differences were found in the relative importance of environmental and textural factors according to land use and soil depth. In forestland, mean annual precipitation and texture were the main predictors of SOC, while in cropland and shrubland, the main predictors were mean annual temperature and lithology. Total SOC stored in the top 1 m in the region was about 79 Tg with a low mean density of 7.18 kg?Cm^?3. The vertical distribution of SOC was shallower in forestland and deeper in cropland. A reduction in rainfall would lead to SOC decrease in forestland and shrubland, and an increase of mean annual temperature would adversely affect SOC in croplands and shrubland. With increasing depth, the relative importance of climatic factors decreases and texture becomes more important in controlling SOC in all land uses.

Conclusions

Due to climate change, impacts will be much greater in surface SOC, the strategies for C sequestration should be focused on subsoil sequestration, which was hindered in forestland due to bedrock limitations to soil depth. In these conditions, sequestration in cropland through appropriate management practices is recommended.     

长期施用有机肥对稻麦轮作体系土壤有机碳氮组分的影响

【目的】 以湖北武汉地区长期稻麦轮作制度下施肥试验地作为研究对象,研究了长期不同施肥处理对耕层土壤有机碳、全氮及活性碳氮组分的影响,为优化稻麦轮作体系下施肥措施,实现土壤固碳减排,培肥土壤提供理论依据。 【方法】 长期施肥试验开始于1981年,试验处理包括不施肥 (CK)、施化学氮肥 (N)、施化学氮磷肥 (NP)、施化学氮磷钾肥 (NPK)、单施有机肥 (M) 及有机无机肥配施处理 (NPKM)。收集2017年小麦收获后耕层 (0—20 cm) 土壤,测定各小区土壤中的有机碳 (SOC)、全氮 (TN)、微生物量碳氮 (MBC、MBN)、水溶性碳 (DOC)、热水溶性有机碳 (HWSC)、颗粒有机碳氮 (POC和PON)、轻组有机碳氮 (LFOC和LFON) 及氯化钾浸提氮 (KEN,即水溶性无机氮) 的含量并分析各指标间的关系。 【结果】 1) 除KEN外,长期施用有机肥显著增加耕层土壤的各碳氮组分含量,特别是有机无机肥配施处理。2) 各活性有机碳组分占SOC的百分比由高到低排序为POC > LFOC > HWSC > MBC > DOC,各氮组分占TN的百分比由高到低排序为PON > LFON > MBN > KEN,其中POC占SOC的24.04%～37.64%,PON占TN的12.09%～20.24%,且有机肥处理下POC/SOC、PON/TN显著高于其余处理。3) 通过对土壤有机碳及各活性有机碳的对施肥的敏感性分析可得,各活性碳敏感性指数均显著高于SOC,且DOC的敏感性最高。4) 通过各组分间相关性分析可知,除KEN外,各碳、氮组分间显著正相关,其中DOC与SOC、PON与TN关系更为紧密,表明DOC及PON可较好地反应出SOC、TN的变化情况。 【结论】 在湖北稻麦轮作地区,长期有机无机肥配施处理显著增加了土壤碳库及氮库,促进了土壤碳、氮的积累,尤其是颗粒有机碳和有机氮 (POC和PON)。水溶性碳 (DOC) 对施肥反应最为敏感,可作为指示该地区有机物早期变化的指示物。      

小兴安岭森林沼泽湿地土地利用变化对土壤活性碳组分的影响

[目的]以小兴安岭森林沼泽为研究对象,研究湿地经过人类活动开垦为农田,和排水造林,以及弃耕地的土壤活性碳组分,为深入了解土壤活性碳组分动态变化及其可能影响全球变暖的机制研究提供科学依据。[方法]选择小兴安岭森林沼泽湿地4种土地利用方式(天然沼泽、排水湿地、弃耕地、农田)为研究对象,在野外调查和室内分析的基础上,对比分析土壤有机碳(SOC)、溶解性有机碳(DOC)、微生物碳(MBC)、易氧化碳(EOC)、轻组有机碳(LFOC)、颗粒有机碳(POC)的含量变化和比例关系,并用相关分析法分析土壤有机碳各活性组分之间的关系。[结果]不同土地利用方式土壤有机碳含量随土层深度增加而降低,总体上,在土壤剖面上,天然沼泽的SOC含量大于其他土地利用方式,其他3种土地利用方式之间差异不显著(p0.05)。不同土地利用方式下土壤活性碳组分(DOC,MBC,EOC,POC,LFOC)含量在垂直分布上均呈现出随土壤深度的增加而降低的趋势,土壤活性碳组分含量顺序总体上呈:天然沼泽排水湿地弃耕地农田。4种土地利用类型土壤DOC占SOC的比例,在垂直剖面上,无明显规律变化。土壤SOC含量与DOC,MBC,EOC,POC,LFOC之间的相关性均达到显著水平(p0.05)。土壤DOC和MBC之间呈显著性正相关(p0.05),LFOC和POC之间呈极显著性正相关(p0.05),EOC与其他活性碳组分相关性均不显著(p0.05)。[结论]土地利用变化会对小兴安岭森林沼泽土壤活性碳组分产生影响,应该合理开发小兴安岭森林沼泽湿地。     

长期施肥下黑土活性有机碳变化特征

观测分析了黑土长期不同施肥30年后不同形态的活性有机碳含量(易氧化有机碳>轻组有机碳>微生物量碳>水溶性有机碳)的变化特征。结果表明,长期施用氮、氮磷和氮磷钾化肥对土壤活性有机碳无显著影响;长期施用有机肥以及有机肥配施化肥均显著提高了土壤活性有机碳含量,与不施有机肥相比,有机肥区组中土壤轻组有机碳和水溶性有机碳含量增幅较大,分别在122%～258%和237%～351%之间,而土壤易氧化有机碳和微生物量碳含量增幅分别在72%～98%和83%～112%。黑土不同形态活性有机碳对施肥的响应灵敏度为,轻组有机碳>水溶性有机碳>微生物量碳≈易氧化有机碳。因此,轻组有机碳是指示土壤有机碳变化的较好指标。     

Warming and grazing affect soil labile carbon and nitrogen pools differently in an alpine meadow of the Qinghai�CTibet Plateau in China

Purpose

Small but highly bioactive labile carbon (C) and nitrogen (N) pools are of great importance in controlling terrestrial C and N fluxes, whilst long-term C and N storage is determined by less labile but relatively large sizes of C and N pools. Little information is available about the effects of global warming and grazing on different forms of C and N pools in the Qinghai?CTibet Plateau of China. The aim of this study was to investigate the effects of warming and grazing on the sizes of different soil labile C and N pools and N transformation in this region.

Materials and methods

A free-air temperature enhancement system in a controlled warming?Cgrazing experiment had been implemented since May 2006. Infrared heaters were used to manipulate temperature, and a moderate grazing intensity was simulated by Tibetan sheep. After 3 years?? warming, soil samples were taken from the four treatment plots: no warming with no grazing; no warming with grazing; warming with no grazing; and warming with grazing. Concentrations of inorganic N in the 40?Ccm soil profiles were measured by a flow injection analyser. Microbial biomass C (MBC) and microbial biomass N (MBN) were measured by the fumigation?Cextraction method, and soluble organic C (SOC) and soluble organic N (SON) were determined by high-temperature catalytic oxidation. Total N (TN), C isotope composition (??¹³C) and N isotope composition (??¹⁵N) were determined using an isotope ratio mass spectrometer. Net N transformation under low temperature was studied in a laboratory incubation experiment.

Results and discussion

Warming and grazing treatments affected soil C and N pools differently, and these effects varied with soil depth. Warming significantly increased TN, MBC, MBN, and SON and decreased ??¹³C at the 10?C20 and 20?C30 cm soil depths, whilst grazing generally decreased SON at the 10?C20 and 20?C30 cm, and MBC at 20?C30 cm. At the 0?C10 cm depth, neither warming nor grazing alone affects these soil parameters significantly, indicating that there could be considerable perturbation on the soil surface. However, grazing alone increased NO ₃ ^? ?CN, total inorganic N, SOC and ??¹⁵N at the 0?C10 cm depth. Incubated at 4°C, warming (particularly with grazing) led to net immobilization of N, but no-warming treatments led to net N mineralization, whilst nitrification was strong across all these treatments. Correlations between MBC and SOC, and TN and MBN or SON were positive. However, SON was less well correlated with TN and MBN compared with the highly positive correlations between SOC and MBC.

Conclusions

It is clearly demonstrated that warming and grazing affected labile C and N pools significantly, but differently after 3 years?? treatments: Warming tended to enlarge labile C and N pools through increased litter inputs, whilst grazing tended to increase inorganic N pools, decrease SON and accelerate N cycling. Grazing might modify the mode that warming affected soil C and N pools through its strong impacts on microbial processes and N cycling. These results suggested that interactive effects of warming and grazing on C and N pools might have significant implications for the long-term C and N storage and productivity of alpine meadow ecosystem in the Qinghai?CTibet Plateau of China.     

Organic carbon and nitrogen stocks in reed meadow soils converted to alfalfa fields

Soil organic carbon and nitrogen are key elements of sustainable agriculture. Converting forest land and grassland to arable land is known to decrease the content of soil organic carbon (SOC), whereas converting land under annual crops into perennial grasslands has the potential to increase organic C and N sequestration, an assumption tested in this study. Compared to the levels in reed meadows, SOC and total nitrogen (TN) stocks in the top layer of 2489 Mg soil ha⁻¹ (about 0–15 cm depth) significantly increased 3 years after the conversion, despite a slight decrease numerically in the first year following the conversion. And the mass of light fraction organic carbon (LFOC), total extractable carbon (TEC), humic acid carbon (HAC), and fulvic acid carbon (FAC) stocks all decreased significantly in the first year in the top layer but recovered after 3 years. In the deeper layer of 2549 Mg soil ha⁻¹ (about 15–30 cm depth), however, the levels of SOC and heavy fraction organic carbon (HFOC) stocks began increasing from the first year itself. During the period of 1–10 years after the conversion, the degree of humification rate (HR) for the deeper layer were consistent, averaging 30%, whereas the same parameters in the top layer stabilized after 3 years at 33%. After 10 years of conversion, the soil recorded higher levels of SOC and TN stocks, used as indicators in this study, than those that had prevailed in the reed meadows, demonstrating the positive combined effects of the conversion on the retention of atmospheric C-CO₂ in the soil. This study suggests that proper management of alfalfa fields can maintain or even improve chemical and physical quality of converted reed meadows soils.     

Electron transfer capacity of soil dissolved organic matter and its potential impact on soil respiration

Purpose

Soil dissolved organic matter (DOM) as the labile fraction of soil organic carbon (SOC) is able to facilitate biogeochemical redox reactions effecting soil respiration and carbon sequestration. In this study, we took soil samples from 20 sites differing in land use (forest and agriculture) to investigate the electron transfer capacity of soil DOM and its potential relationship with soil respiration.

Materials and methods

DOM was extracted from 20 soil samples representing different land uses: forest (nos. 1–12) and agriculture (nos. 13–20) in Guangdong Province, China. Chronoamperometry was employed to quantify the electron transfer capacity (ETC) of the DOM, including electron acceptor capacity (EAC) and electron donor capacity (EDC), by applying fixed positive or negative potentials to a working electrode in a conventional three-electrode cell. The reversibility of electron accepting from or donating to DOM was measured by applying switchable potentials to the working electrode in the electrochemical system with the multiple-step potential technique. Carbon dioxide produced by soil respiration was measured with a gas chromatograph.

Results and discussion

Forest soil DOM samples showed higher ETC and electron reversible rate (ERR) than agricultural soil DOM samples, which may be indicative of higher humification rate and microbial activity in forest soils. The average soil respiration of forest soil (nos. 1–12) and agricultural soil (nos. 13–10) was 26.34 and 18.58 mg C g^?1 SOC, respectively. Both EDC and EAC of soil DOM had close relationship with soil respiration (p?<?0.01). The results implied that soil respiration might be accelerated by the electroactive moieties contained in soil DOM, which serve as electron shuttles and facilitate electron transfer reactions in soil respiration and SOC mineralization.

Conclusions

DOM of forest soils showed higher ETC and ERR than DOM of agricultural soils. As soil represents one of the largest reservoirs of organic carbon, soil respiration affects C cycle and subsequently CO₂ concentration in the atmosphere. As one of the important characteristics of soil DOM related to soil respiration, ETC has a significant impact on greenhouse gas emission and soil carbon sequestration but has not been paid attention to.     

Carbon flux from decomposing 13C-labeled transgenic and nontransgenic parental rice straw in paddy soil

Purpose

Genetic modification of Bt rice may affect straw decomposition and soil carbon pool under flood conditions. This study aims to assess the effects of cry gene transformation in rice on the residue decomposition and fate of C from residues under flooded conditions.

Materials and methods

A decomposition experiment was set up using ¹³C-enriched rice straws from transgenic and nontransgenic Bt rice to evaluate the soil C dynamics and CH₄ or CO₂ emission rates in the root and non-root zones. The concentrations and stable carbon isotope compositions of the soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), CH₄, and CO₂ of the root and non-root zones were determined from 7 to 110 days after rice straw incorporation.

Results and discussion

Rice straw incorporation into soil significantly increased the SOC, DOC, and MBC concentrations and the CH₄ and CO₂ emission rates. The percentage of ¹³C-SOC remaining in the root zone was significantly lower than that in the non-root zone with rice straw decomposition. The DOC and MBC concentrations significantly increased in both the root and non-root zones between 0 and 80 days after rice straw incorporation. However, no significant differences were found after Bts (Bt rice straw added into soil) and Cks (nontransgenic Bt rice straw added into soil) incorporation in the root and non-root zones. This result may be attributed to the priming effects of sufficient oxygen and nutrients on straw degradation in the root zone.

Conclusions

Bt gene insertion did not affect the SOC, DOC, and MBC concentrations and the CH₄ and CO₂ emission rates in both the root and non-root zones. However, rice straw incorporation and root exudation significantly increased the SOC, DOC, and MBC concentrations and the CH₄ and CO₂ emission rates.     

Land use changes induced soil organic carbon variations in agricultural soils of Fuyang County, China

Purpose

The purpose of this study is to understand spatial and temporal variations of soil organic carbon (SOC) under rapid urbanization and support soil and environmental management.

Materials and methods

SOC data in 1979 and 2006, of 228 and 1,104 soil samples respectively, were collected from surface agricultural lands in Fuyang County, East of China. Land use data were also gathered at the same time.

Results and discussion

The mean SOC was 17.3 (±4.6) g/kg for the 1979 data and 18.5(±5.8) g/kg for 2006. There was a significant difference in SOC between the 2 years according to the t test result. Geostatistical analysis indicated that SOC had a moderate spatial correlation controlled by extrinsic anthropogenic activities. The spatial distribution of SOC, derived from ordinary kriging, matched the distribution of industry and urbanization. Using a six-level SOC classification scheme (<3.5, 3.5–5.8, 5.8–11.6, 11.6–17.4, 17.4–23.2, and >23.2 g/kg) created by Zhejiang Province, approximately 15 % of soil had SOC increase from low to high levels from 1979 to 2006.

Conclusions

The main cause of SOC variation in the study area was land use change from agriculture to industrial or urbanized uses. The increasing SOC trend near most towns may be attributed to use of organic manure, urban wastes, sewage sludge, and chemical fertilizers on agricultural land.     

Soil carbon pool and effects of soil fertility in seeded alfalfa fields on the semi-arid Loess Plateau in China

The dynamics of the soil organic carbon pool and soil fertility were studied in soils with different number of growing years of alfalfa (Medicago sativa L.) in the semiarid Loess Plateau of China. The soil water content and soil water potential decreased and the depth of desiccated layers grew with the number of growing years of alfalfa. The soil organic C (SOC) cannot be enhanced on short timescales in these unfertilized and mowed-alfalfa grasslands in the topsoil, but the light fraction of organic C (LFOC), soil microbial biomass C (MBC) and microbial biomass N (MBN) all increased with the number of growing years. When alfalfa had been growing for more than 13 yr, the soil MBC increased slowly, suggesting that the MBC value is likely to reach a constant level. SOC, soil total P (STP), available P (AvaiP) and the ratio of SOC to soil total N (C/N) all decreased monotonically with the growing years of alfalfa up to 13 yr and then increased. SOC was significantly positively correlated with STP, AvaiP, soil total C (STC) and soil total N (STN) (R=0.627**, 0.691**, 0.497*, 0.546*, respectively). MBC and LFOC were significantly positively correlated with the number of growing years of alfalfa (R=0.873*** and 0.521*, respectively), and LFOC was more sensitive to vegetation components, degree of cover and landform than to the number of years of growth. SOC showed a significant negative correlation with LFOC/SOC and MBC/SOC (R=−0.689**, −0.693**, respectively). A significant positive correlation exists between MBC and soil inorganic C (SIC). LFOC, MBC, LFOC/SOC and MBC/SOC were all significantly positively correlated with each other. Therefore, practices that involve water-harvesting technologies and add residues and phosphate fertilizer to soils should be promoted to improve soil nutrients and hydration and to postpone the degradation of alfalfa grasslands under long-term alfalfa production.     

新疆艾比湖地区不同土地利用类型土壤养分及活性有机碳组分研究

土壤有机碳及其组分是土壤质量的重要指标,在土壤许多物理、化学和生物特性中发挥着重要作用。通过对我国内陆荒漠自然生态系统中新疆艾比湖地区不同土地利用类型土壤进行采样和分析,系统地研究和比较了不同土地利用类型土壤养分及有机碳组分。结果表明:新疆艾比湖不同土地利用类型土壤总孔隙度与土壤容重变化趋势相反。不同土地利用类型对土壤养分具有较大影响,土壤有机碳、全氮、全磷和全钾均呈现出一致性规律,大致表现为林地草地耕地未利用地,而不同土地利用类型土壤全磷差异并不显著(p0.05)。不同土地利用类型土壤易氧化有机碳(EOC)、颗粒有机碳(POC)、轻组有机碳(LFOC)、水溶性有机碳(WSOC)、土壤微生物量碳(MBC)和微生物量氮(MBN)均呈现出一致性规律,大致表现为林地耕地草地未利用地。林地和草地EOC/SOC比例显著低于耕地和未利用地,说明林地和草地转变成耕地降低了土壤有机碳的稳定性;微生物商(MBC/SOC)基本表现为耕地林地草地未利用地,其中耕地和林地土壤MBC/SOC比例差异不显著(p0.05)。相关性分析表明,土壤活性有机碳各组分与SOC,TN,TK均具有极显著相关性关系,并且不同土地利用类型土壤EOC,POC,LFOC,WSOC和MBC含量之间均具有极显著相关性(p0.05),说明土壤活性有机碳很大程度上依赖于有机碳含量,活性有机碳各组分之间相互影响和密切联系,其中SOC,TN和TK是不同土地利用类型土壤活性有机碳变化的重要影响因子。     

黄土高原半干旱区不同土地利用下的土壤有机碳、碳组分和土壤营养

Cropland (CP), native grassland (NG) and two shrub land treatments which were converted from cropland in 1985:seabuckthorn (Hippophae rhamnoides L. ) (ST), and branchytamarisk (Tamarix ramosissima) (BT) were investigated to evaluate effects of land use conversion on soil organic carbon (SOC) and soil nutrients in the semi-arid region of the Loess Plateau of China. Total organic carbon (TOC), light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), total N (TN), nitrate nitrogen (NO₃^--N) and nitrite nitrogen (NO₂^--N), ammonium nitrogen (NH₄⁺-N), total P, and available P (AP) were measured. The results showed that SOC in NG, ST and BT were 12.7%, 27.7% and 34.8% higher than that of the cropland, respectively. LFOC, light fraction (LF) dry matter, ratio of TOC to TN (C/N) and the ratio of TOC to AP (C/P) were higher in the shrub land or native grassland than in the cropland. Cropland had the highest TN, the sum of NO₃^--N and NO₂^--N, TP and AP due to the use of chemical fertilizers. TOC significantly correlated with LFOC, HFOC and C/N. LFOC significantly correlated with dry matter of the LF and C/N. TN, the sum of NO₃^--N and NO₂^--N and AP were significantly negatively correlated with TOC and LFOC. Therefore, land use conversion from cropland to shrub land, or maybe grassland, contributed to SOC sequestration and improved soil nutrients stabilization.     

五台山高山林线典型植被土壤有机碳特征

在全球变暖背景下,土壤有机碳(SOC)已经成为全球碳循环和全球变化生态学研究热点,特别是高山林线生态交错带这一气候变化敏感区。对五台山高山林线附近亚高山草甸(CD)、华北落叶松林(HL)和云杉×华北落叶松混交林(YH)SOC含量与土壤有机碳密度(SOCD)进行探讨,结果表明:3种植被SOC含量随土壤深度增加而减少,SOCD则与之相反,且其SOC和SOCD分布均具有"表聚效应"。五台山亚高山森林(HL、YH)土壤SOC总含量和总SOCD都高于亚高山草甸(CD),与中国亚高山土壤一致,但与亚洲以外的世界各大洲不同;且五台山亚高山土壤总SOC含量和SOCD与中国亚高山土壤均值近似,大于其他各大洲均值。显著影响五台山SOC的因素(P0.05)与世界尺度亚高山土壤不同,且土壤厚度和气候因子(P0.05)对世界尺度亚高山森林SOC的影响比亚高山草甸/草原土壤(P0.05)显著。因此,五台山亚高山森林土壤固碳能力比亚高山草甸强,其亚高山土壤的SOC总含量和总SOCD在全国范围内处于平均水平,而中国亚高山土壤碳库在世界范围内占据领先地位,但仍需进一步探讨来减少多尺度研究的不确定性。     

Soil organic carbon in the rocky desert of northern Negev (Israel)

Purpose

So far, the soil organic carbon (SOC) literature is dominated by studies in the humid environments with huge stocks of vulnerable carbon. Limited attention has been given to dryland ecosystems despite being often considered to be highly sensitive to environmental change. Thus, there is insufficient research about the spatial patterns of SOC stocks and the interaction between soil depth, ecohydrology, geomorphic processes, and SOC stocks. This study aimed at identifying the relationship between surface characteristics, vegetation coverage, SOC, and SOC stocks in the arid northern Negev in Israel.

Materials and methods

The study site Sede Boker is ideally suited because of well-researched but variable ecohydrology. For this purpose, we sampled five slope sections with different ecohydrologic characteristics (e.g., soil and vegetation) and calculate SOC stocks. To identify controlling factors of SOC stocks on rocky desert slopes, we compared soil properties, vegetation coverage, SOC concentration, and stocks between the five ecohydrologic units.

Results and discussion

The results show that in Sede Boker, rocky desert slopes represent a significant SOC pool with a mean SOC stock of 0.58?kg?C?m^?2 averaged over the entire study area. The spatial variability of the soil coverage represents a strong control on SOC stocks, which varies between zero in uncovered areas and 1.54?kg?C?m^?2 on average in the soil-covered areas. Aspect-driven changes of solar radiation and thus of water availability are the dominant control of vegetation coverage and SOC stock in the study area.

Conclusions

The data indicate that dryland soils contain a significant amount of SOC. The SOC varies between the ecohydrologic units, which reflect (1) aspect-driven differences, (2) microscale topography, (3) soil formation, and (4) vegetation coverage, which are of greatest importance for estimating SOC stocks in drylands.     

Distribution and storage of soil organic carbon in a coastal wetland under the pressure of human activities

Purpose

Soil organic carbon (SOC) stock is one of the most important carbon reservoirs on the earth and plays a vital role in the global climate change. However, research on the carbon sequestration and storage of coastal wetland soil is very scarce. Therefore, a study in the coastal wetland was conducted to investigate the SOC distribution, storage, and variation under the influence of human activities.

Materials and methods

Surface soil samples in different seasons and profile soil samples were collected in the Changyi coastal wetland. SOC content, soil physicochemical properties, and sedimentation rate were determined. Organic carbon storage and burial flux were calculated. On the basis of correlation analysis and comparative study, factors affecting the distribution and storage of SOC were investigated.

Results and discussion

The average SOC content of the surface soil in June and November was 4.65 and 6.13 g kg^?1, respectively. The distribution of surface SOC content was consistent with the distribution of vegetation and was affected by the soil particle size. In plant-covered area, the relationship between SOC content and depth could be expressed by the power function y?=?ax ^b . The contribution of plants to SOC was only significant in the shallow layer. As for the deep layer, the SOC content was higher in the mudflat. The organic carbon storage in the upper 1 m soil was estimated at 1.795 kg m^?2 in average and the total organic carbon storage of Changyi wetland was estimated at 6.373?×?10⁷ kg. The sedimentation rate was very low and the average organic carbon burial flux of the whole wetland was 17.5 g m^?2 a^?1.

Conclusions

Low sedimentation rate, weak downward migration, and high decomposition rate of organic matter caused by poor hydrological condition were the reasons why the SOC storage in Changyi wetland was low. Under intensive human activities, the Changyi wetland was drying and the organic carbon storage was reducing. Strategies were proposed to be taken urgently to restore the wetland for the long-term benefit.

     

Stability of soil organic carbon and potential carbon sequestration at eroding and deposition sites

Purpose

This study aims to explore the dynamics of the factors influencing soil organic carbon (SOC) sequestration and stability at erosion and deposition sites.

Materials and methods

Thermal properties and dissolved aromatic carbon concentration along with Al, Fe concentration and soil specific surface area (SSA) were studied to 1 meter depth at two contrasting sites.

Results and discussion

Fe, Al concentrations and SSA size increased with depth and were negatively correlated with SOC concentration at the erosion site (P?<?0.05), while at the deposition site, these values decreased with increasing depth and were positively correlated with SOC concentration (P?<?0.05). TG mass loss showed that SOC components in the two contrasting sites were similar, but the soils in deposition site contained a larger proportion of labile organic carbon and smaller quantities of stable organic carbon compared to the erosion site. SOC stability increased with soil depth at the erosion site. However, it was slightly variable in the depositional zone. Changes in SUVA₂₅₄ spectroscopy values indicated that aromatic moieties of DOC at the erosion site were more concentrated in the superficial soil layer (0–20 cm), but at the deposition site they changed little with depth and the SUVA₂₅₄ values less than those at the erosion site.

Conclusions

Though large amounts of SOC accumulated in the deposition site, SOC may be vulnerable to severe losses if environmental conditions become more favorable for mineralization in the future due to accretion of more labile carbon. Deep soil layers at the erosion site (>30 cm deep) had a large carbon sink potential.