| Stipa bungeana T., also called Changmangcao in China, is a thermophilic and xerophyticbunchgrass, which belongs to Sect.Leiostipa Dum, Stipa L., Gramineae. S. Bungeana has awide ecological amplitude. Especially in Loess Plateau in China with rich wild resources, it isthe constructive species or the dominant species of the grassland ecosystem. With strongdrought-resistance, high ecological plasticity and strong ability in spontaneous recovry andsoil and water conservation, S. Bungeana plays an important role in improving ecologicalenvironment in Loess Plateau. Based on the investigation of the distribution of S. Bungeananatural populations in semi-arid regions in Loess Plateau in China, this paper studied droughtadaptive characteristic, nutrient composition characteristic and genetic diversity of280individuals from14different populations collected in4provinces (or autonomous regions), toenrich the basic study on S. Bungeana’s resources, to uncover the vegetation communitystructure and succession in Loess Plateau, and to provide scientific basis for the protection ofS. Bungeana’s biodiversity and the rational use of the resources. The main results wereobtained as followings:(1) Stipa bungeana Trin. is widely distributed in semiarid regions in Loess Plateau, suchas the forest steppe, typical steppe and desert steppe, which are suited between33°48′N and38°06′N and105°01′E and109°45′E, at the elevation from430to2081m. Communityspecies composition was complicated and S. bungeana had an obvious advantage in goodhabit conditions, while community species composition was simple and the advantage of S.bungeana declined in poor habit conditions. Accompanying plants mostly consisted ofherbaceous plants with a few vines, trees and shrubs. When community structure wasunreasonable, S. bungeana could rely on seed propagation and tillering to renew population.And the numbers of individuals and populations would decline dramatically when the habitwas heavily damaged.(2) The contents of chlorophyll and malondialdehyde (MDA) among different S.Bungeana populations could reflect the drought degree of habitats. The variation of protectiveenzyme activity among populations did not follow a regular pattern. There was acomplementary phenomenon about osmotic adjustment material content within the samepopulation. Pearson correlation analysis found that most indicators showed no significant correlation with each other and they were inconsistent with the changing trend of habitats.The clustering diagram among populations, which was constructed by an unweightedpair-group method of the arithmetic averages (UPGMA), showed no similarity betweengeographic distance and habitats among populations, neither. The general trend of droughtresistance was that drought resistance increased with the water condition decrease.(3) The distributions of leaf C, N and P contents among different S. Bungeana puplationswere relatively centralized. The variation ranges of C, N and P contents were48.07~52.90%,1.14~2.25%and0.17~0.37%, with the mean values of50.14,1.71and0.25mg·g-1,respectively. The ratios of C to N, C to P and N to P had a large variation, and the ranges were21.33~45.20,156.24~284.36and4.32~9.75, with the mean values of30.29,204.59and6.86,respectively. The C content had significantly negative correlations with N and P contents,while N content was significantly positively correlated with P content. Nutrient content ofleaves was affected by annual average temperature with a large variation, and had nocorrelation with latitude.(4) Sequence-Related Amplified Polymorphism (SRAP) and Inter Simple SequenceRepeat (ISSR) molecular marker techniques were used to analyze the genetic differentiationand population genetic structure of different S. Bungeana populations. Fifteen selected SRAPprimer pairs were used in PCR amplification of the280individual genomic DNA, and a totalnumber of505statistical fragments were amplified, of which503bands were polymorphic,with the percentage of polymorphic bands (PPB) being99.60%. While fifteen selected ISSRprimers amplified a total number of387statistical fragments, of which372bands werepolymorphic, and the percentage of polymorphic bands (PPB) was96.12%. Ner’s geneticdiversity (H) detected by the two molecular marker techniques was0.0842and0.0822at thepopulation level,0.2028and0.2070at the species level, respectively. While Shannon’sinformation index (I) was0.1289and0.1255at the population level,0.3292and0.3353at thespecies level, respectively. Genetic differentiation coefficient (Gst) estimated by Ner’s geneticdiversity based on the two molecular marker techniques indicated that a large geneticdifferentiation existed among different S. Bungeana populations (0.5788and0.6301) with avery limited gene flow (0.3639and0.3290). Genetic differentiation coefficient (Gst)estimated by Shannon’s information index was0.6084and0.6257, which was consistent withNer’s genetic diversity coefficient, and both of them showed that genetic differentiation wasmainly distributed among populations, while the variation within the same population wasrelatively small. Based on the two molecular marker techniques, the results of Mantel’s testshowed no significant correlation, and the correlation analysis indicated that altitude, annualaverage temperature and annual precipitation had little influence on genetic diversity indexes of S. Bungeana. Based on the analysis of genetic variation, we proposed the protectivestrategy of genetic diversity for S. Bungeana.The following conclusions were summarized from the above results. The obviousdifferentiation and variation were observed among different S. bungeana populations. Thepopulation differentiation was the results of many factors, and rich genetic variations in DNAlevel provided the genetic basis for biochemical variations, drought-resistance reactions andnutrient distribution. While distribution characteristic of S. bungeana populations was theexternal apperance of long-term adaption to environmental variations and the continuedaccumulation of genetic variations. The decreased S. bungeana populations were mainlyresulted from low germination rate, human utilization and the damaged habits. Hence, there isa need to take effective and reasonable measures, such as insitu protection, ex-situ protectionand artificial breeding, to protect S. bungeana populations. |
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