Studies On Communities And Rhizoibum Of Ammopiptanthus Mongolicus (Maxim.) Cheng F

Ammopiptanthus mongolieus(Maxim.) Cheng f.is an endangered species of evergreen broad-leaf plant in northwest desert zone of China.In this work,community ecology,population ecology,and germination biology of A.mongolicus were studied,providing good background and basic knowledge for the research in this plant in the future.As a legume specieses,A.mongolicus can construct a symbiotic relationship with rhizobium,which is helpful to its development and population recovering.With above novel information,the distribution of nodules in A.mongolicus was analyzed.Subsequently,we studied the resistance of rhizobium isolated from A.mongolicus. The main experimental results are as following:(1) According to soil,water and other ecological factors,Dengkou was defined as research regions,where 3 research plots were selected according different habitats.Plot1 was on the bank of Yellow River,Plot2 was the old route of Yellow River,and Plot3 was on the east of Wulanbuhe Desert.Floristic composition,community structure and species diversity of A.mongolicus communities were studied in the research plots.There were 7 families,13 genera and 14 species shrubs,3 families,4 genera and 4 species perennial herbs,3 families,5 genera and 5 species annual herbs.The biggest families were Compositae(5 species) and Zygophyllaceae(5 species).The second families was Leguminosae(3 species),and the third families were Gramineae(2 species) and Polygonaceae(2 species).The floristic composition of A:mongolicus communities was different under different environmental conditions.According to the floristic composition and their function in the communities,the types of the 3 A.mongolicus communities were defined.The community of Plot1(A.mongolicus—Convolvulus tragacanthoides—Allium mongolicum) was belonged to warm-temperate steppe desert.The communities of Plot2(A. mongolicus—Artemisia ordosica) and of Plot3(A.mongolicus—Artemisia xerophytica) were belonged to typical desert.The community structure of the 3 A.mongolicus communities was also of dissimilitude under different environmental conditions.3 layers of Plot1 community developed well,but Plot2 and Plot3 communities hadn't herb layer,and floristic composition of their only 2 layers was very exiguous.The coverage(C),maximal height(Hmax),maximal width(Wmax), mean height(MH),and mean width(MW) of A.mongolicus were negatively correlated to richness index(S),while the destiny(D) positively correlated to S,and the coefficient of correlation was 0.508.Plant community diversity of A.mongolicus was estimated by species diversity index(H′, D),richness index(S,R) and evenness index(J_sw,J_st,E),which represented accordant trend.The order of diversity was Plot1＞Plot2＞Plot3,while the result of evenness was opposite.(2) The population structure of A.mongolicus in Dengkou,Inner Mongolia was studied. According to the date which was obtained by contiguous grid quadrate method,the height and width of A.mongolicus were classified and analyzed by ANOVA method.The relation of population structure of A.mongolicus and species diversity of A.mongolicus community was analyzed with correlation matrix.The result indicated that the population structure of A. mongolicus was different under different environmental conditions.The mean individual height of different population were significantly different(P＜0.01),while the mean width were markedly different(P＜0.05).The age structure of the 3 A.mongolicus populations presented senescent type. The mean height(MH) and mean width(MW) of A.mongolicus population were negatively correlated to richness index(S) of A.mongolicus community and their coefficient of correlation were -0.994 and -1 in turn.The competition among species influenced the unitary population height and width,while the competition among individuals of A.mongolicus population influenced the height and width of individuals in the same population.(3) According to the data,the height and width of A.mongolicus were classified.The results indicated that the population structures of A.mongolicus were different in diferent environmental conditions.The age structures of three A.mongolicus populations showed the decline trend.The spatial distribution patterns and pattern dynamics of A.mongolicus populations were studied by applying seven aggregate indices(C,K,m^*,I,1/K,m^*/m and I_δ)in different environmental conditions.And the spatial distribution pattern with diferent quadrat scale was examined.The results indicated that the spatial distribution pattern and aggregation intensity were different in diferent environmental conditions,while the tendency of pattern aggregation was generally paralle1.The figure of pattern scale and pattern intensity showed that plot 2 clumped in 25 and 100 m²,and plot 3 clumped in 150 m²,while plot 1 performed the pattern of random distribution in all quadrat scale.With the population age increased,the distribution pattern had a trend from random to clustering and finally to random.The young and old individuals performed the pattern of random distribution,while the individuals of middle age stage clumped.The environmental factors principally influenced the formation and development of the spatial distribution pattern of A.mongolicuus populations.(4) In order to ascertain optimal temperature for germination,seeds were germinated under 15℃,28℃,37℃.It was found that seeds growed slowly under 15℃,while the temperature of 37℃had a detrimental effect on seedling growth,some seeds were less likely to survive in the germination test.Seeds could bourgeond quickly with strong radicel at 28℃.Subsequently the change of saccharide and hormone were tested duing seed germination.Saccharide and hormone changed intensively under 28℃.The level of disaccharide,tetrasaccharide and glucose in seeds increased intensively at 20h,while the peak value of IAA and cytokinin appeared at 4h.28℃is the best temperature for seed germination of A.mongolicus.(5) According to soil,water and other ecological factors,we defined Shapotou,Alashan, Dengkou and Wulatehouqi as our research regions where we studied characters of A.mongolicus plant communities and nodules.The plant community was rich.The components and structure were different in different research regions because of the diversity of ecological factors.Water is the decisive ecological factor which influenced the components and structure of A.mongolicus. plant communities.Nodules morphology of A.mongolicus was various.The best time to collect nodules should be before fruit stage of its host.Nodules were in different root parts in different research regions.Water was the primary ecological factor which influenced the infection of rhizobia and the generation of nodules.Nodules isolated from other legumes had similar morphology with nodules of A.mongolicus.(6) Seventeen rhizobia strains were isolated from A.mongolicus.It was found that nodules were various in their attachment mode,size,shape and color,which were related to the differences of their eco-environment.And water may be the principal influencing factor.Several biochemical characteristics were detected,including resistance to salt,acid-alkali,temperature variation and intrinsic antibiotics.The results indicated that 64.7%strains could tolerate NaCl stress at 3% concentration,94.1%strains could grow during pH 5-11,and all strains could grow after disposed at 60℃C for 10 min.Differences in resistance to different intrinsic antibiotics existed among strains, ZW₄ and Wh₄¹ had high resistance to different intrinsic antibiotics.Rhizobia strains from Dengkou had higher resistance to acid-alkali and temperature,which was the adaptation of rhizobia to its environmentIdentify the potential signaling proteins in downstram of symbiotic receptors from legume model system Medicago truncatula(Appendix).