Community Diversity Of Arbuscular Mycorrhizal(AM) Fungi In Rhizosphere Of Major Afforestation Species From The Loess Plateau And Mechanisms Of Am Fungi In Drought Resistance Of Host Plants

Hippophae rhamnoides and Sophora davidii are both common afforestation species inthe Loess Plateau, China. Fine roots and rhizosphere soil of H. rhamnoides were collectedfrom five ecological areas, three geomorphologic regions and in different seasons in the LoessPlateau. Arbuscular mycorrhizal (AM) spore density, colonization rate and communitydiversity in the rhizosphere of H. rhamnoides were analysed by using microscopy andpolymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) respectively.The relationships between climatic, edaphic factors and colonization status, communitydiversities of AM fungi were analysed by using Correlation Analysis (CA) and CanonicalCorrespondence Analysis (CCA). Based on phylogenetic tree formed by AM18S rRNA genesequences of DGGE bands, the differences of AM community structure from threegeomorphologic regions (plain-gully, hilly-gully and desert-grassland) were also analysed andcompared. The effects of AM fungi on the growth and physiological performance of S. davidiiseedlings and on the soil status of S. davidii rhizosphere under well-watered and water-stressedconditions were also investigated.The results are as follows:1. AM community diversity in the rhizosphere of H. rhamnoides from five ecologicalareas and their related affecting factorsThe overall trends of average annual rainfall and mean annual air temperature wereincreasing from north to south in five different latitudes areas (from south to north in order as:Yongshou, Fuxian, Zhidan, Hengshan, Yulin), however changes of elevation, soil pH, Olsen-P,available N and organic carbon. had no significant regularities. The overall trends of totalmycorrhizal colonization and spore density in five latitudes areas were increasingsuccessively from north to south. Spore density had an obviously negative relationship withOlsen-P, and total colonization presented obviously negative correlation with soil pH. Thedifference of diversity indices in five different latitudes areas were obviously different.Species richness, Simpsom's and Shannon-Weiner indices were highest in Fuxian and lowestin Yongshou, evenness index was highest in Zhidan and lowest in Yulin. AM fungalcommunities in five latitudes areas were clustered into four groups in the canonical correspondence analysis (CCA) biplot, and different groups had their various responses toenvironmental factors. Olsen-P (P=0.025,F=2.62) and spore density (P=0.006,F=1.76)showed significant correlations with AM fungal communities on the basis of Monte Carlo testof CCA.2. Seasonal dynamic of AM community diversity in the rhizosphere of H.rhamnoides and their related affecting factorsThe seasonal dynamic of soil enzyme, glomalin, microbial biomass C and N in therhizosphere of H. rhamnoides had certain regularities. The difference of AM colonizationstatus along easonal changes in the rhizosphere of H. rhamnoides was obvious, totalcolonization and spore density were highest in autumn (October) and lowest in spring (April).AM total colonization presented obviously positive correlation with alkaline phosphatase,total and easily extractable glomalin, microbial biomass C and N, and negative correlationwith catalase. Spore density had obviously negative relationships with total and easilyextractable glomalin, microbial biomass C and N, and negative relationships with catalase.Except evenness index, species richness, Simpsom's and Shannon-Weiner indices wereobviously different along seasonal changes, and thses three indices were increasing graduallyfrom spring to autumn. AM community diversity in different seasons were obvious differentby using the method of principal component analysis (PCA), the typical variable value of AMcommunity in autumn was lowest, and it indicated that AM community in autumn was moststable in the three seasons. AM fungal communities in the three seasons were clustered intothree groups in CCA biplot, and different groups had various responses to environmentalfactors. Microbial biomass C (P=0.002,F=2.676) showed a significant correlation with AMcommunities on the basis of Monte Carlo test of CCA.3. Structural analysis of AM community in the rhizosphere of H. rhamnoides fromthree geomorphologic regionsThe trends of total colonization and spore density in different geomorphologic regions wereas follows: plain-gully> hilly-gully> desert-grassland.34band-types and total180bandswere found in the DGGE pattern of AM community in the rhizosphere of H. rhamnoides fromthree geomorphologic regions. Desert-grassland area had lowest band number (51),plain-gully and hilly-gully areas had almost same band number (63and64respectively). AMcommunity structure in plain-gully area had obvious diference with those in hilly-gully anddesert-grassland areas, AM community structure between hilly-gully and desert-grasslandareas was no obvious different. A total25gene sequences were found in the AM fungalDGGE gel from three geomorphologic regions. Based on the phylogenesis analysis, thesesequences were classified in12different sequence groups of Glomus genus. Glo-C, Glo-D and Glo-G havd a high degree of similarity with G. indicum, G. constrictum and G.iranicumrespectively. Glo-A, C, D, E, G and K were common species, Glo-B, F, H, J and L wereaccidental species, and Glo-I was rare species.4.The effects of AM fungi on growth and physiological performance of S. davidiiunder water-stressed conditionsUnder water-stressed conditions, G. constrictum-inoculated seedlings had higher dryweight of shoot and root, root length, plant height and stem diameter than non-mycorrhizalseedlings, G. mosseae-inoculated seedlings had higher dry weight of shoot and root, plantheight and stem diameter than non-mycorrhizal seedlings; The total trends of net photosyntheticrate and maximum quantum yield were as follows: G. constrictum> G. mosseae>non-inoculation, and there were significantly different in above parameters among the threetreatments; mycorrhizal seedlings had greater relative water content, water use efficiency,actual quantum yield and photochemical quenching coefficient, and lower intercellular CO2concentration and water saturation deficit than no-mycorrhizal seedlings, there were nosignificantly different in above parameters between G. mosseae and G. constrictum-inoculatedseedlings; there were no significantly different in relative chlorophyll content andtranspiration rate among three treatments.5. The effects of AM fungi on nutrition and morphology of S. davidii andrhizosphere soil status under water-stressed conditionsUnder water-stressed conditions, the total trends of total N in leaves and roots and of total P inroots were as follows: G. constrictum> G. mosseae> non-inoculation, and there weresignificantly different in above parameters among the three treatments; mycorrhizal seedlingshad greater total P than no-mycorrhizal seedlings, there were no significantly different in bothparameters between G. mosseae and G. constrictum-inoculated seedlings; the total trends of leafarea, root total length, root area, alkaline phosphatase activity and easily extractable glomalin content wereas follows: G. constrictum> G. mosseae> non-inoculation, and there were significantlydifferent in above parameters among the three treatments; mycorrhizal seedlings had greatertotal glomalin content, invertase and urease enzyme activities than no-mycorrhizal seedlings,there were no significantly different in above parameters between G. mosseae and G.constrictum-inoculated seedlings; there were no significantly different in hydrogen peroxideactivity among three treatments. Inoculation with G. constrictum and G. mosseae obviouslyimproved the proportion of water stable aggregates at>2mm,0.5-1mm,0.25-0.5mm and>0.25mm.6. The effects of AM fungi on osmotic adjustment substances and antioxidantcapacities of S. davidii under water-stressed conditions Under water-stressed conditions, the total content trends of starch in roots, free aminoacids in leaves, flavonoids, alkaloids, polyphenol in leaves and roots were as follows: G.constrictum> G. mosseae> non-inoculation, the total content trends of free amino acids were asfollows: G. mosseae> G. constrictum> non-inoculation, and there were significantly differentin above parameters among the three treatments. mycorrhizal seedlings had greater contentsof reducing sugar, soluble sugar and proline, activities of SOD,CAT and POD in root andleaves and content of starch in leaves than no-mycorrhizal seedlings, there were nosignificantly different in above parameters between G. mosseae and G. constrictum-inoculatedseedlings; the total content trends of the content of MDA,H2O2and O2-in were G. constrictum <G. mosseae <non-inoculation, there were significantly different among the three treatments;mycorrhizal seedling leaves had lower content of MDA,H2O2and O2-than no-mycorrhizalseedlings, there were no significantly different in three parameters between G. mosseae and G.constrictum-inoculated seedling roots.