Abstract: Whether  genotypic diversity has  similar ecological function to species diversity is a hot topic in the field of restoration ecology and conservation biology. Many studies about  dominant species have proved that genotypic diversity exhibits similar ecological function to species diversity, but experimental tests about companion species are still lacking. In the present study, we selected Koeleria cristata, a common companion species in the grassland community of northern China, as study object, and examined the effects of genotypic diversity on the performance of above and belowground dry weight, number of tillers at two harvest times. Although all results showed that the combination of 4 genotypes had a better performance than a single genotype, only the belowground dry weight at the first harvest showed a significant difference (P<0.05) between  treatments. The net effect of genotypic diversity was significantly higher than zero for only one variable, the belowground dry weight (P<0.05). Partitioning the net effect of diversity by Loreau & Hector method, the results showed that 9/10 of complementary effect values were positive but not significantly higher than zero (P>0.05), and that 7/10 of selection effect values were negative with the value of aboveground wilted leaf dry weight at the second harvest being significantly lower than zero (P<0.05). As for K. cristata  the selection effect of genotypes did not have any positive effect, and the functional complementarity between genotypes of this species was not as important as that between different species. Therefore, only 1/10 of net effect of diversity was positive, and the proportion  was lower than that obtained from species diversity or genotypic diversity of dominant species. Such information would provide a new perspective for evaluating the ecological function of degraded grassland.

Key words: photosynthesis, comprehensive evaluation, drought stress, Hydrangea macrophylla