| Stipa krylovii is a major component of typical steppe vegetation. It is a perennial, thicket, xerophytic bunch grass, with a high drought resistance. It distributes in a large area. Based on the morphological characteristics and genetic diversity, population variation and ecological differentiation of S. krylovii under different geographical conditions and deterioration stages in Inner Mongolia steppe were studied. The results were as follows:Seven morphological traits of S. krylovii (reproductive tiller length, vegetative tiller length, seed shape, etc.) showed abundant variations. Range and sources of variations were different. Variation degrees of the morphological traits were different in corresponding to environmental conditions. Reproductive tiller length, vegetative tiller length, thousand kernel weight, caryopsis length and awn length were shorter and smaller, with decreasing rainfall, while caryopsis diameter was bigger. 35.10% of variation came from inter-population, while the other (64.90%) was within population.Random amplified polymorphic DNA (RAPD) analysis demonstrated that 16 random primers produced 129 loci, obtaining 128 polymorphic loci in 7 populations from different geographical locations. The total percentage of polymorphism was 99.22%, which showed S. krylovii had abundant genetic diversity. Genetic diversity level of population in desert steppe (0.3640) was higher than that in typical steppe (0.3306). Using Un-weighted Pair-group method, the population living in similar ecological conditions and with close geographical distance clustered first. By Shannon index evaluation, 29.25% of genetic variation was between populations and the differentiation among populations was at a high level, in comparison with other species, such as S. grandis.Considering the deterioration series of populations, deterioration degrees led to morphological variations. With the increasing of grassland deterioration, vegetative tiller length and reproductive tiller length became shorter. Medium sized bunch, small sized bunch, reproductive tiller percentage, reproductive tiller number were reduced. Plant minimization was apparent in heavy deteriorated populations.Deterioration series of populations were analyzed by the means of allozyme and RAPD. The results showed that as the deterioration of grassland became heavier, genetic diversity would drop, but there was no distinct linear correlation between genetic diversity and deterioration degree. If grazing stress reached a threshold, genetic diversity of populationemerged a transition point, with genetic diversity increased. Although productivity of deteriorated population diminished obviously, genetic diversity did not totally lost. In contrast, a relatively steady genetic structure was formed to adapt environmental (grazing) stress.Analyses on allozyme and RAPD showed changes of genetic diversity had different models. The pattern for allozyme was that: rnedian>heavy>normal>light, while the pattern for RAPD indicated that: normal>light>heavy>median. The difference of two cluster diagraphs also explained the similar trend. Affected by the grazing stress, patterns of variation in coding allozyme gene-locus and genome were different.S. krylovii has abundant genetic diversity and strong evolutionary tendency, it has been undergoing a long-term evolution and the plant has been retained under natural selection. The most fundamental reason for population differentiation is that, different environmental conditions and grazing stress exert influences upon gene pool and gene rate, which can decide distribution of molecular variation in space and time. The study of different deteriorated grasslands showed, although occurring genetic differentiation and reduced genetic diversity, biodiversity in deteriorated population can still maintain a high level. Additionally, it had gene exchanges with normal populations. The deteriorated grassland can restore its vegetation as normal if rational management was adopted.
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