| As an important ecological barrier in the northwest arid and semi-arid region,the vegetation of the Helan Mountain ecosystem provides an important guarantee for ecological security and regional ecosystem services in China.The arbuscular mycorrhizal fungi(AMF)composed of mycorrhizal network is an important pathway and critical factor in nutrient partitioning among drought-tolerant shrubs and herbaceous plants and affect efficient nutrient uptake by plants.We selected a typical Prunus mongolica(Maxim.)Ricker-Stipa breviflora Griseb.communities(G×S-S,G×-G)in the low altitude of Helan Mountain,and we set up two control treatments,which S.breviflora(G)with shrubs removed and P.mongolica(S)with herbs removed,and benomyl inhibited AMF(M)and non-sterilized(F)treatments,as well as bare ground as a blank control(CK),we determined the rhizosphere soil,plant nutrient characteristics and AMF colonization rate and so on.We also investigated differences in the structure and diversity of rhizosphere soil AMF communities and interrelationships with soil and plant nutrients in the P.mongolica-S.breviflora communities and single vegetation by high-throughput sequencing methods.We used the stable-isotope δ15N labeling technique to analyze the distribution patterns between P.mongolica and S.breviflora as well as between different organs of the same species.The main research results are as follows:1.The rhizosphere soil nutrients of G×S-G and G×S-S were significant higher than those of G,S and CK(P<0.05),it is consistent with the shrubs "fertile island" effect;The rhizosphere soil nutrients of G and G×S-G were significant higher than those of S and G×S-S(P<0.05);The rhizosphere soil nutrients under M were all decreased to different degrees compared with F;The difference were small in the rhizosphere soil stoichiometric characteristics of P.mongolica shrublands.2.The plant nutrients of G×S-G and G×S-S were significant higher than those of G and S(P<0.05);The plant nutrients of G and G×S-G were significant higher than those of S and G×S-S(P<0.05);Plant C and N under M were significant lower than those under F(P<0.05);Plant nutrient stoichiometric characteristics showed S had higher C:N and lower N:P(P<0.05).Correlation analysis and redundancy analysis(RDA)showed that plant nutrients were significantly positive correlation with rhizosphere soil water content,organic matter and so on(P<0.05);Plant nutrient stoichiometric characteristics were significantly positive correlation with rhizosphere soil C:N and negative correlation with N:P(P<0.05).The stable-isotope labeling technique showed that rhizosphere soil organic matter and water content had significant effects on plant nutrients and stoichiometric characteristics.The stable-isotope labeling technique showed that roots δ15N contents of G×S-G were significant higher than those of other vegetation types,the stems δ15N contents of G were significant higher than those of G×S-G and S,the leaves δ15N contents of G were significant higher than those of other vegetation types(P<0.05);δ15N contents of G×SG was significant clustered in the roots and δ15N contents of G×S-S was significant clustered in the stems and leaves(P<0.05).3.Glomalin-related soil protein(GRSP),colonization rate,rhizosphere soil spore density and rhizosphere soil AMF community a diversity showed the same variation characteristics as rhizosphere soil and plant nutrients(P<0.05).Rhizosphere soil AMF community could be classified into 1 phylum,4 class,6 orders,10 families,10 genera and 77 species,dominant genus of AMF was Glomus,accounting for 99.20%(F),98.07%(M)on average.The Ambispora,Claroideoglomus and Paraglomus were significant difference between different vegetation types under F and M(P<0.05).Claroideoglomus was significant difference between G×S-SF and G×S-SM(P<0.05).Non-metric multidimensional scaling analysis(NMDS)indicated that rhizosphere soil AMF community structure showed difference at the species level.4.Correlation analysis showed that GRSP,colonization rate and spore density were significantly positive correlation with rhizosphere soil organic matter,water content and plant nutrients and so on(P<0.05);Plant δ15N contents were significantly positive correlation with colonization rate and spore density(P<0.05);The rhizosphere soil AMF community a diversity and relative abundance of genus level were mainly significant effected with rhizosphere soil pH,water content,organic matter,alkalihydrolyzable N,P,and available K(P<0.05).Mantel test showed that the rhizosphere soil AMF community relative abundance of genus level was significantly positive correlation with rhizosphere soil factors under F(P<0.05).RDA showed that the rhizosphere soil AMF community a diversity and relative abundance of genus level was significantly positive correlation with rhizosphere soil organic matter,water content and total N(P<0.05).Structure equation model(SEM)analysis showed that the main driving factor affecting plant growth and development were dominated by rhizosphere soil nutrients and AMF communities.In summary,this study confirmed that AMF formed a mutualism with plant roots at low altitude in Helan Mountain,effectively enhancing rhizosphere soil nutrients and plant nutrients contents.Through higher colonization rate,it allows P.mongolica-S.breviflora communities to more efficiently absorb and utilize nutrients for coexistence in the resource-poor arid and semi-arid region.AMF communities are important for the stability of ecosystem function,growth and development of vegetation and healthy development in the arid and semi-arid area of Helan Mountain. |
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