The Study On Soil Phosphorus In The Major Communities Of Songnen Meadow

This thesis focuses on Leymus chinensis community, Carex.duriuscula community, Puccinellia chinampoensis community, Chloris virgata community and Suaeda salsa community in Songnen Meadow. The research on the seasonal dynamics of soil phosphorus and vertical distribution was completed during the period from Jun 2002 to Oct 2004. Soil samples were randomly taken from each block at depths of 0-10cm,10-20cm and 20-30cm. It has been revealed that there was no significant difference of soil total phosphorus (total-P) at the same soil layer among Leymus chinensis community, Carex.duriuscula community, Puccinellia chinampoensis community, Chloris virgata community and Suaeda salsa community in Songnen Meadow, indicating that soil total phosphorus had little change while plant community varied. It has also be seen that soil degradation went more slowly than the succession of plant community. There was a similar trend in the seasonal variation of total-P between Leymus chinensis community and Carex.duriuscula community, and between Puccinellia chinampoensis community and Chloris virgata community. This process included a phase during which total-P increased quickly, a phase during which total-P declined after reaching its peak value, and a phase when total-P accumulated slowly again. As to the vertical distribution of total-P in Leymus chinensis community, Carex.duriuscula community, Puccinellia chinampoensis community and Suaeda salsa community, the content descended while soil layer deepened; in Chloris virgata community the content was higher in 10-20cm than that in 0-10cm and 20-30cm. Compared with other communities, the ratio of soil available phosphorus(avail-P) to total-P in Chloris virgata community and Suaeda salsa community was much higher, which demonstrated that the plant growth in severer habitats could not make the best of soil avail-P. The content of soil microbial biomass phosphorus (MBP) was much more than avail-P in all communities. The seasonal variation of MBP could be described as an unimodal curve, and it was in August that the content of MBP reached its peak value in all communities. In Chloris virgata community MBP distributed mainly in 10-20cm soil layer, while in the other communities accumulating more in 0-10cm soil layer. The results of grey relational analysis revealed that the content of soil nutrients, in particular C and N, had a major effect on avail-P. However, soil factors, such as soil temperature, soil water content, pH value and conductance, strongly influenced on the MBP in all communities. Soil organic matters was the main factor influencing on the availability of soil phosphorus in Leymus chinensis community and Chloris virgata community, while soil Potassium(total-K) had a major effect on the availability of soil phosphorus in the other three communities. Analysis on the relationship between soil factors and soil microbial biomass phosphorus inflected that soil organic matters and total nitrogen (total-N) played the main nutrient factors in Leymus chinensis community, Carex.duriuscula community and Puccinellia chinampoensis community, soil slowly available Potassium (slowly avail-K) and available Potassium(avail-K) were the major nutrient factors in Chloris virgata community and Suaeda salsa community. Soil microbial biomass phosphorus was influenced mainly by soil temperature in Leymus chinensis community, Carex.duriuscula community and Puccinellia chinampoensis community, and in Chloris virgata community and Suaeda salsa community soil MBP was mainly affected by soil water content. The analysis of soil fertility proved that, soil fertility in the Leymus chinensis grassland all made up of the main aspects of soil organic matters,content of nitrogen, content of phosphorus, slowly available potassium, soil water content and soil pH value. Among them the status of phosphorus was reflected mainly on total-P and MBP. According to soil fertility, the communities could be classified into four clusters. Each of Leymus chinensis community, Chloris virgata community and Suaeda salsa communi...