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As one of the most important and wide distribution community type among terrestrial ecosystems, grassland ecosystem plays a critical role in the global carbon cycles and climate regulation. China has extremely rich grassland resources, which have a huge carbon sequestration potential and are an important part of the global carbon cycle. Drying and rewetting is a common natural phenomenon in soil, which might accelerate soil carbon mineralization process, increase soil respiration and exert profound influence on microbial activity and community structure. Under the background of the global change, the changes in rainfall capacity, strength and frequency would inevitably affect soil drying and wetting cycles, and thus change the microbial activity and community structure as well as soil respiration, and then exert important influence on global carbon budget. In this paper, related references in recent ten years were reviewed. The source of soil released, the trend of soil respiration over time and the relationship between soil respiration and microbial biomass, microbial activity and microbial community structure during the processes of dry-rewetting cycle were analyzed and summarized, in order to better understand the microbial response mechanism for drying and rewetting effecting on soil respiration in grassland ecosystem, and provide a certain theoretical basis for more accurate evaluation and prediction of future global carbon balance of terrestrial ecosystems and climate change. [ABSTRACT FROM AUTHOR]

Based on a field manipulative nitrogen (N) addition experiment, the effects of atmospheric N deposition level change on the contents, inter-annual variation and profile distribution of soil total organic carbon (TOC) and dissolved organic carbon (DOC) were investigated from May, 2008 to October, 2011 in a temperate typical steppe in Inner Mongolia of China, and the relationship between TOC and DOC was also discussed. The treatments in the manipulative experiment included N additions at rates of 0, 5, 10, and 20 g x (m2 x a)(-1), representing the control (CK), low N (LN), medium N (MN), and high N (HN) treatment, respectively. The results indicated that the concentrations of soil TOC and DOC decreased progressively with soil depth in all cases except for the DOC at 10-20 cm depth in individual years. The increase of N input in typical steppe did not change the vertical distribution of soil TOC and DOC, but reduced the vertical variation of TOC and increased the vertical variation of DOC in the surface soil horizon. In addition, the contents of soil TOC and DOC at 0- 10 cm and 10- 20 cm soil layers changed insignificantly after the continuous increase in anthropogenic N input for four years. The soil organic C density of 0-20 cm soil layer for different N treatment levels varied between 3.9 kg x m(-2) and 5.6 kg x m(-2), and the soil organic C densities of fertilized treatments in the first two years were similar to or slightly lower than those of CK, while in the following two years, the increase in N deposition gradually played a positive role in increasing soil organic C density, but the differences in soil TOC and DOC contents between CK and fertilized plots were not significant (P > 0.05). The ratio of soil DOC to TOC (DOC/TOC) varied from 0.32% to 1.09%. The increase in N deposition generally lowered the proportion of DOC in soil TOC, which was conducive to the accumulation of soil organic C. The change of soil DOC was positively correlated with that of TOC (P < 0.01). The temporal variations of soil DOC in different N treatments were all far greater than those of TOC, and the soil DOC was the important sensitive indicator for predicting and evaluating the response of soil C pool to the change in atmospheric N deposition in the temperate grassland ecosystem.