水分对土壤呼吸的影响及机理

土壤呼吸是陆地碳循环的重要环节，在全球变化的背景下，研究水分对土壤呼吸的影响，能为探索陆地生态系统在碳循环方面的源—汇功能和揭示碳的失汇之迷提供有力的证据。综述了水分对土壤呼吸的影响及其机理。土壤呼吸是一个复杂的生态学过程，大气降水对土壤呼吸的影响结果是因时、因地而异，在湿润的生态系统或者干湿交替的生态系统中比较湿润的季节．降水事件对土壤呼吸可能会产生比较明显的抑制现象；而在干旱的生态系统或有干湿交替季节的生态系统中比较干旱的季节里，降水事件可能会强烈地激发土壤呼吸。其对土壤呼吸的影响机理包括水分对土壤孔隙中CO2替代、对CO2扩散的阻滞、对微生物活动的刺激和对微生物生物量的影响等。由于实验方法和标准的不一致以及影响土壤呼吸的因素的多样性。水分量的变化对土壤呼吸的影响很难以一个统一的方程来描述，总的来说，最优的水分状况通常是接近最大田间持水力，当土壤处于过于或过湿状态时，土壤呼吸会受到抑制。水分量的变化对土壤呼吸的影响机制在于可溶性有机质、土壤的通透性、微生物与植物根系生命活动等都随土壤水分状况不同而发生相应的改变。关于水分与土壤呼吸的关系研究今后应该主要集中在：(1)水分对根系呼吸和土壤微生物呼吸分别产生的影响；(2)全球变化后水分格局的变化对全球陆地生态系统土壤呼吸格局的潜在影响；(3)人类活动通过直接或间接改变水分状况而对土壤释放CO2的贡献率。

Effects of water content on soil respiration and the mechanisms

Soil respiration in terrestrial ecosystem is a significant component of the global carbon cycle, and its contribution to the global carbon budget has been the focus of wide concern. Because water is one of the most important environmental factors, study on the relationship between water and soil respiration could facilitate the research on the role of terrestrial ecosystem in carbon cycle, and could provide evidence on the riddle of missing carbon sink. Soil respiration is a complicated ecological process. Effects of water on soil respiration and the mechanisms were summarized in this paper. The influence of precipitation on soil respiration may vary with time and place. Soil respiration could be restrained by precipitation in humid ecosystems or humid seasons in ecosystems where dry and humid seasons are alternant, while it might be stimulated by precipitation if the conditions were different. The mechanisms are as follows: seeping water displaces CO 2 in soil, restrains diffusion of CO 2 in soil pores, stimulates activity of microorganism and increases microorganism biomass after rainfall. Because different methods were used to measure the water content, and because different factors could influence soil respiration, it is very difficult to describe the effects of water content on soil respiration with the same function. On all accounts, optimum content of water is usually near to field capability. If the soil was extremely dry or wet, soil respiration would be restricted. Mechanisms of water content on soil respiration are that dissolved organic matter, aeration in soil and the energy allocation of microbe and plant are variant with soil moisture. Further studies on relationship between soil respiration and water should focus on (1) separating effects of water on microbes' respiration from those on roots', (2) discerning potential effects of water distribution change on the pattern of soil respiration in terrestrial ecosystem along with global change, and (3) counting contribution of human activity to the CO 2 efflux from soil by changing water content directly or indirectly.