Abstract: In this study, genetic variation and niche differentiation of two closely related speciesAllium forrestii Diels andA. changduense J. M. Xu were investigated based on three chloroplast DNA regions (atpI-atpH,trnL-trnF and ndhC-trnV). Fresh leaves from 232 individuals of 16 natural populations were collected. Field investigation showed that the distributions of the two species were discontinuous, with substantial differences in their habitats. According to the results from analysis of genetic variation, neither shared haplotype nor obvious gene flow was detected between those two species, indicating the independent evolution of the two species. The results of ecological niche modeling showed that the optimum ecological niche of both species were overlapped, except for the temperature seasonality and the mean temperature of coldest season. Our results indicated that the extreme temperature seasonality, lower mean temperature of coldest season, and highly specific habitat may be the major reasons for the differentiation of A. forrestiiandA. changduense.

Key words: nosZ, potential denitrification activity, rhizosphere, denitrification, community composition, narG