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Responses of Plant Groups, Diversity and Meadow Quality to High-rate N Fertilization on Alpine Kobresia humilis Community

SHEN Zhen xi 1,CHEN Zuo zhong 2,ZHOU Xing min 1,ZHOU Hua kun 1 (1.Northwest Plateau Institute of Biology, Chinese Academy of Sciences, Xining 810001, China; 2.Institute of Botany, Chinese Academy of Sciences, Beijing 100093 China)  
The experiment with three levels of N fertlizer (0?150 and 300kg N/hm 2) was conducted for three years at alpin Kobresia humilis meadow to study responses of different plant groups and some species. The response of grasses was more significance than Non leguminous forbs to nitrogen addition. The synthetic dominated ratio (SDR) of grasses increased, and that of non leguminous forbs decreased with the increase of nitrogen, whereas the SDR of sedges and leguminous forbs were not significantly affected by N fertilizer. Plant diversity decreased and forage quality increased with the increase of nitrogen. Index of meadow quality (IMQ) was the highest at 150kg N/hm 2 plot, and showed no significant difference between 150 and 300kg N/hm 2 plot. Excessive nitrogen application did not improve the IMQ. Response of above ground biomass of plant groups was lagged when compared with plant diversity and IMQ. Total above ground biomass was significant increased with the nitrogen application. There were different responses of above ground biomass among plant groups to the nitrogen application. The results showed that the above ground biomass of grasses was significantly increased with N fertilizer application, and that of forbs was decreased. The responses of plant grounps to nitrogen application were more affected by precipitation and its distribution in July, therefore, the status of soil water after nitrogen application was a key factor to the responses of plant groups.
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