Distribution Of Soil Organic Carbon And Nitrogen And Their Responses To Climatic Change

The carbon cycle is central to the Earth system, being inextricably coupled with climate, the water cycle, nutrient cycles, and the production of biomass by photosynthesis on land and in the oceans. It is very helpful for understanding the environmental history of our planet and its inhabitants, and for predicting and steering their joint future. The soil is an important component of the terrestrial ecosystems and plays the significant role in the global carbon and nitrogen cycle. The understanding the distribution characteristics of soil carbon and nitrogen storage and their relationships with the environmental factors are the key to estimate terrestrial carbon and nitrogen cycle in regional and global scales. Moreover, the amount of soil nutrients directly affects the structure and function of terrestrial systems, and their carbon and nitrogen cycling through the effects on their primary production (NPP). Thus, it is necessary to know the distinctive distribution of soil carbon, nitrogen and their responses to climatic factors.Terrestrial transect has become an important and effective method for global change study, especially for Global Change and Terrestrial Transect (GCTE), the core project of the International Geosphere — Biosphere Programme(IGBP). Northeast China Transect (NECT) is one of the fifteen global transects recognized by IGBP, which is assigned along the latitude 43°30' N in the mid-latitude of the temperate zone, located between longitude 112°~ 130°30' E, latitude42~46°N. It is about 1600km in length and 300km in width. NECT is mainly driven by precipitation, and has become an effective platform of global change study in China.In this paper, the gradient distribution of soil carbon and nitrogen alongNortheast China Transect (NECT) and their responses to climatic change were analyzed in term of the data from a field survey in 2001 along NECT and a simulated experiment of doubled C02and different soil moistures. Moreover, we discussed the effects of crop residues remained in soil on soil carbon and nitrogen transformations and the importance of crop residues retained in soil for mitigation of C02 emission and increase of soil carbon sequestration and soil productivity, based on the data of a long—term experiment associated with crop residues retained in soil for 10 consecutive years and the relevant literature. The main results and conclusions are as follows:The soil labile carbon was significantly related to soil organic carbon (r=0. 993, P< 0. 001). They had a similar trend of the horizontal distribution along precipitation gradient, whereas the vertical distribution of soil labile carbon was different with soil organic carbon. The variations of soil organic carbon and soil labile carbon in subsoil along NECT were relatively smaller than topsoil's. The range of decease of soil labile carbon in depth was bigger than soil organic carbon' s. Soil organic carbon and labile carbon had close linear relationships with soil PH, soil total nitrogen, soil total phosphorus, soil total sulphur, soil total zink, soil available nitrogen, soil available phosphorus, soil available potassium, soil available manganese, soil available zinc, soil bulk density, water holding capacity, soil total porosity. They were significantly related to precipitation. Their correlation coefficients were 0.677 (P< 0.001) and 0.712 (P< 0. 001) respectively. But, soil organic carbon and labile carbon in subsoil had not linear relationship with precipitation. In the short-term simulated experiment, Soil labile carbon was relatively more sensitive to doubled C02 content and different soil moistures than soil organic carbon. Coefficient of variation of soil organic carbon was. 1. 28%. Coefficient of variation of soil labile carbon was 29. 67%. The variation of soil labile carbon resulting from different soil moistures was reduced with doubled C02content.Soil total nitrogen had a similar trend of the distribution to soil organic carbon along precipitation gradient. Soil available nitrogen was similar in the horizontal distribution...