土壤有机碳动态的影响因素研究

作为陆地生态系统中最大的碳库,影响土壤碳循环因素的微小变化都可能会对全球变暖产生意想不到的结果。土壤有机碳的动态变化对全球碳循环起着重要作用,且土壤有机碳对植物生长和可持续性的土壤物理、生物和化学过程都起着一系列的控制作用。气候和土壤因素主要控制陆地生态系统的固碳潜力,为了能更好的了解土壤碳循环对气候变暖的响应机制以及预测土壤有机碳的周转模型,本文系统探讨了影响土壤有机碳动态变化的影响因素,主要包括气候因素和土壤因素。

基于文献计量分析的土壤侵蚀与土壤有机碳动态研究进展与展望

【目的】土壤侵蚀引起的土壤有机碳动态变化对可持续土地利用与管理以及陆地碳收支具有重要意义,为了解该领域的前沿及发展方向,采用文献计量学方法探究近30年来土壤侵蚀与土壤有机碳动态研究进展及热点。【方法】本文基于Web of Science核心数据库和中国知网(CNKI)中文核心期刊数据库,采用CiteSpace软件和文献计量学方法,分析了国内外近30年土壤侵蚀与土壤有机碳动态研究的发展历程、研究热点和趋势。【结果】研究表明欧美国家在该领域的研究发展较早,尤其是美国无论是国际影响力还是国际合作紧密性均处于领先地位,我国虽起步较晚但处于稳步快速发展态势;国际上该领域的研究在1995~2004年间主要围绕耕作方式和农艺措施对土壤侵蚀与土壤有机碳动态的影响,进而发展为侵蚀条件下土壤微生物及其群落对土壤有机碳的影响;近十年逐渐向基于稳定性同位素技术的土壤侵蚀与土壤有机碳动态定量研究转变,同时土壤侵蚀导致的碳氮流失所造成的面源污染及侵蚀碳在全球碳循环中的作用也是近年来的研究热点。国内于1995~2004年在本领域的研究主要集中土壤侵蚀所造成的有机碳和养分流失的研究,而后逐渐发展为结合“3S”技术和土壤侵蚀模型,研究人类活动、土地利用及气候变化等因素对土壤侵蚀与土壤有机碳动态的影响。近五年结合核素示踪、光谱等技术,在国家政策引导下该领域逐步发展为从生态综合治理向生态文明建设为核心的问题导向研究。【结论】通过分析对比国内外土壤侵蚀与土壤有机碳动态研究的热点和前沿,提出我国在该领域今后研究的展望。

施肥对新垦绿洲风沙土肥力及碳积累的影响

利用2005年安排在临泽边缘绿洲沙地农田的长期施肥定位试验,研究不同用量有机肥、化肥、有机肥和化肥配施对绿洲沙地土壤肥力及有机碳积累的影响。试验包括高量有机肥单施(M3),氮磷化肥单施(NP3),低、中、高量氮磷钾化肥单施(NPK1,NPK2,NPK3),及低、中、高量氮磷钾化肥配施高、中、低量有机肥9个处理(NPK1M3,NPK2M2,NPK3M1),测定分析10年后不同施肥处理耕层(0~20 cm)土壤物理化学性状特征及有机碳动态。结果表明:施有机肥及有机无机配施处理较单施化肥处理容重下降0.13 g·cm^-3,田间持水量提高6.7%,单施有机肥、有机无机配施较单施化肥,土壤有机碳(SOC)和全氮含量分别提高64.8%、36.3%和64.9%、49.5%。高量施用氮磷化肥和氮磷钾化肥处理全磷含量最高,有机肥及有机无机配施较单施化肥有效氮含量显著增加,有机无机配施及高量施用磷肥土壤有效磷积累明显,高量施用有机肥能显著提升有效钾含量。连续施肥处理10年后,SOC含量提高了1.68~2.84倍,土壤全氮、全磷、碱解氮及有效磷均有一定程度的提高,但单施化肥及有机肥与氮磷化肥配施有效钾含量下降。SOC的积累速率单施化肥、有机无机配施、单施有机肥处理分别为0.27、0.59,0.87 g·kg^-1·a^-1。增施有机肥、适量减少化肥投入、氮磷钾化肥的平衡施用是绿洲沙地农田土壤肥力持续提升的施肥管理对策。

Dynamic Relationship Between Biologically Active Soil Organic Carbon and Aggregate Stability in Long-Term Organically Fertilized Soils

Biologically active soil organic carbon （BASOC） is an important fraction of soil organic carbon （SOC）, but our understanding of the correlation between BASOC and soil aggregate stability is limited. At an ecological experimental station （28° 04＇-28° 37＇ N, 116° 41＇-117° 09＇ E） in Yujiang County, Jiangxi Province, China, we analyzed the dynamic relationship between soil aggregate stability and BASOC content over time in the red soil （Udic Ferrosols） fertilized with a nitrogen-phosphorus-potassium chemical fertilizer （NPK） without manure or with NPK plus livestock manure or green manure. The dynamics of BASOC was evaluated using CO2 efflux, and soil aggregates were separated according to size using a wet-sieving technique. The soils fertilized with NPK plus livestock manure had a significantly higher content of BASOC and an improved aggregate stability compared to the soils fertilized with NPK plus green manure or NPK alone. The BASOC contents in all fertilized soils decreased over time. The contents of large aggregates （800-2 000 μm） dramatically decreased over the first 7 d of incubation, but the contents of small aggregates （〈 800 μm） either remained the same or increased, depending on the incubation time and specific aggregate sizes. The aggregate stability did not differ significantly at the beginning and end of incubation, but the lowest stability in all fertilized soils occurred in the middle of the incubation, which implied that the soils had a strong resilience for aggregate stability. The change in BASOC content was only correlated with aggregate stability during the first 27 d of incubation.

Conservation Tillage Influence on Carbon Dynamics Under Mediterranean Conditions

Intensity of tillage practices can enhance organic matter decomposition, increasing CO2 emissions from soil to the atmosphere. Conservation tillage （CT） has been proposed as a means of counteracting potential damages to the environment. In this study the effects of two CT systems, reduced tillage in a long-term experiment （RTL） and no-tillage in a short-term experiment （NTs）, were compared to traditional tillage （TT） in the long （TTL） and short-term experiments （TTs）. CO2 fluxes, total soil organic carbon （SOC） and dehydrogenase activity （DHA） were evaluated at 0-5, 5-10 and 10-15 cm depths throughout the three years studied （Oct. 2006 Jul. 2009）. Traditional tillage increased C02 emissions compared to CT. The CT treatments （RTL and NTs） accumulated more SOC in the surface layer （0 5 cm） than the TT treatments （TTL and TTs）. SOC accumulation was moderate but DHA consistently increased in CT in the surface soil, especially with a legume crop included in the crop rotation. Values of stratification ratio of all parameters studied were higher in the CT treatments （RTL and NTs）. The agricultural and environmental benefits derived from CT make this system recommendable for semi-arid Mediterranean rain-fed agriculture.

Changes in Soil Organic Carbon Dynamics in a Native C4 Plant-Dominated Tidal Marsh Following Spartina alterniflora Invasion

Invasion of an exotic C4 plant Spartina alterniflora has been shown to increase soil organic carbon （SOC） concentrations in native C3 plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflora invasion on SOC concentrations and fractions in tidal marshes dominated by native C4 plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C4 plant Cyperus malaccensis in the Minjiang River estuary, China. Concentrations of SOC and liable SOC fractions, dissolved organic carbon （DOG）, microbial biomass carbon （MBC）, and easily oxidizable carbon （EOC）, were measured in the top 50-cm soils of the C. malaccensis community, as well as those of three S. alterniflova communities with an invasion duration of 0-4 years （SA-4）, 4-8 years （SA-8）, and 8-12 years （SA-12）, respectively. Results showed that both SOC stocks in the 50-cm soils and mean SOC concentrations in the surface soils （0-10 cm） of the C. malaccensis community increased with the duration of S. alterniflora invasion, whereas SOC concentrations in the 10-50-cm soils decreased slightly during the initial period of S. alterniflora invasion, before increasing again. The pattern of changes in labile SOC fractions （DOC, MBC, and EOC） with invasion duration was generally similar to that of SOC, while the ratios of labile SOC fractions to total SOC （DOC：SOC, MBC：SOC, and EOC：SOC） decreased significantly with the duration of S. alterniflora invasion. The findings of this study suggest that invasion of the exotic C4 plant S. alternifora into a marsh dominated by the native C4 plant C. malaecensis would enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alterniflora communities.

Uncertainty and Sensitivity Analyses for Modeling Long-Term Soil Organic Carbon Dynamics of Paddy Soils Under Different Climate-Soil-Management Combinations

Reporting modeling results with uncertainty information can benefit decision making by decreasing the extent that variability exerts a disproportionate influence on the options selected. For making decisions with more confidence, the uncertainty interval should be as narrow as possible. Here, the soil organic carbon （SOC） dynamics of the major paddy soil subgroup from 4 different paddy field regions of China （located in 4 counties under different climate-soil-management combinations） were modeled using the DeNitrification- DeComposition （DNDC） model for the period from 1980 to 2008. Uncertainty intervals associated with the SOC dynamics for these 4 subgroups were estimated by a long-term global sensitivity and uncertainty analysis （i. e., the Sobolt method）, and their sensitivities to 7 influential factors were quantified using the total effect sensitivity index. The results, modeled with high confidence, indicated that in the past 29 years, the studied paddy soils in Xinxing, Yixing, and Zhongjiang counties were carbon （C） sinks, while the paddy soil in Helong County was a C source. The 3 C sinks sequestered 12.2 （5.4, 19.6）, 17.1 （8.9, 25.0）, and 16.9 （-1.2, 33.6） t C ha-1 （values in the parentheses are the 5th and 95th percentiles, respectively）. Conversely, the C source had a loss of -5.4 （-14.2, 0.06） t C ha-1 in the past 29 years. The 7 factors, which changed with the climate-soil-management context, exhibited variable influences on modeled SOC. Measures with potential to conserve or sequestrate more C into paddy soils, such as incorporating more crop residues into soils and reducing chemical fertilizer application rates, were recommended for specific soils based on the sensitivity analysis results.