土壤碳及其在地球表层系统碳循环中的意义

SOIL CARBON AND ITS SIGNIFICANCE IN CARBON CYCLING OF EARTH SURFACE SYSTEM

本文回顾了近１０年来国内外对土壤碳研究的主要进展，分析了土壤碳的移动性及其影响因素，着重针对陆地系统碳汇饱和问题介绍了土壤碳对大气ＣＯ２源汇效应的碳转移过程及其在地球表层系统碳循环中的作用，指出应加强对土壤碳转移及其对全球变化的响应、土壤碳固存对大气ＣＯ２调控的机制和动态的研究，以便为缓解陆地系统碳汇饱和提供科学依据。

Terrestrial carbon sink saturation had been increasingly concerned by recent carbon cycle studies in awareness of the current sink being 2Pg / a. As a major and astive carbon pool, soil carbon storage had been extensively investigated, and the main achievements were as follows: (1) Global soil carbon pool estimation. A total C pool of 2 500Pg in global soils had been well accepted with about 1 500Pg as soil organic carbon (SOC) and 1 000Pg as soil inorganic carbon (SIC). Majority of this pool was found in forest ecosystems in tropical and temperate zones, being sensitive to the changing land use and the impacts by global change. (2) The geochemical forms of soil carbon and their lability. The occurrence of soil carbon could be characterized by the association with soil particles in different size classes (soil aggregates), with microorganisms (Cmic) or in much mobile form such as dissolved organic carbon (DOC). The carbon lability was often described with the ratio of Cmic. to SOC, oxidation lability and the turnover time. These parameters could reflect well the variation of carbon availability with type of ecosystems, soil management practices and also with global change. Much attention had been paid to soil mobile carbon forms such as Cmic, carbon in coarse fractions of soil particles and DOC both for their activity in mobilization and translocation in terrestrial system and their sensitivity to global change. (3) Soil carbon transfer and the sink or source effect. Carbon transfer in soil took place in the interface of biomass-SOC-SIC. The degree and direction of this transfer was dependent on the balance of CO2-SOC-SIC in soil systems. UP to now, the accumulation of SOC and the reverse process, SOC mineralization had been considered as the significant soil carbon transfer process and SOC mineralization was believed tO have prompt response to global warming as recognized by incubation studies at laboratory. Most data suggested that soil carbon transfer during the last 50- 100 years tended to lose carbon giving the source effect. Soil carbon sequestration, simply carbon capture by soil geochemical system and SOC storage, was believed to recover 50%-75% of the lost sink in the future 25-50 years. Uncertinties of soil carbon storage and the terrestrial carbon cycles still remain for further studies: (1) The effect of labile forms of carbon both on process and the rate of soil carbon tfansfer, especially when and where the quantitative estimation of their sink or source effects were necessary. For this, systematic field monitoring in representative ecosystems is needed. (2) Soil labile carbon response to soil quality changes, and environmental stresses and the potential feedback to global change. It could be done by dynamical studies using modern tecdriques of incubation and modeling. (3) The coupling of SOC and SIC in soil carbon transfer and its controlling process, the long term (thousand year level) and short term (seasonal and yearly level) dynamics and the relation to atmospheric CO2 oscillations. Solutions could be expected from the future progress of PAGES project.