Abstract: The analysis on the relationships between community structure,functional group composition,species diversity,and productivity of desert steppe in Ningxia showed that the community productivity was affected not only by species diversity,but also by the characters of species and environmental resources.No significant correlation was found between the coverage per functional group and the primary productivity of the community.There was a trade-off relationship between the species diversity and the numbers of species and individuals in the community.

Key words: Rice allelochemicals, Mechanisms of weed suppression, Quantitative trait, Marker assisted selection, Cloning