Response Of Soil AMF And Diazotrophs Communities To Gradients Of Precipitation And Temperature And Vegetation Restoration In Karst Areas

Rocky desertification restricts the sustainable development of economic and social in karst area.Vegetation restoration is the most effective measure to control rocky desertification,but striking variation in hydrothermal conditions among karst area leads to difficulty in restoration vegetation.Soil functional microorganisms,such as Arbuscular Mycorrhizal Fungi(AMF)and diazotrophs,play important roles in vegetation restoration.Revealing the characteristics of soil AMF and diazotrophs communities and their responses to gradients of precipitation and temperature and vegetation restoration in karst area,which is the premise for reasonable application of AMF and diazotrophs to restore karst degraded ecosystem.In this study,four vegetation restoration stages(i.e.,Mature forest,shrubbery,plantation forest and cropland)locating in different gradients of precipitation and temperature(i.e.,moderate drought,mild drought,semi humid,humid)of karst area were selected.Composition,structure and diversity of soil AMF and diazotrophs communities were examined by Illumina sequencing technology.The main findings are as follows:(1)The precipitation and temperature condition,vegetation restoration stages and their interaction significantly influenced soil AMF communities.A total of 9 families and10 genera of soil AMF community were detected in present study.Glomus was the dominant genus(relative abundance more than 80%).The relative abundance of Glomus,Claroideoglomus,Diversispora,Scutellospora and Ambispora were significant different under the different gradients of precipitation and temperature(P<0.05);The relative abundance of Glomus,Claroideoglomus,Diversispora and Acaulospora were significant different under the different vegetation restoration(P<0.05);In addition,the genus Pacispora was unique to the wet abandoned area,while the genus Scutellospora(relative abundance less than 0.1%)only exists in the dry sub-humid secondary forest and the wet abandoned area.AMF diversity showed significant differences in both precipitation and temperature and vegetation restoration.In the same vegetation condition,the Shannon diversity index of AMF in humid area was significantly lower than other 3 areas(P<0.05).Shannon diversity of soil AMF community increased with increasing in disturbance.The soil pH,total phosphorus and soil organic carbon had great effect on AMF community.(2)The precipitation and temperature condition,vegetation restoration stages and their interaction significantly influenced soil diazotrophs communities.The dominant genera in the study area were Bradyrhizobium,with a relative abundance ratio of more than25%.The secondary dominant genera were Geobacter,Mesorhizobium and Rhizobium,with a relative abundance of more than 10%.The diversity index of diazotrophs decreased with an increase in drought degree.The diversity index of diazotrophs declined with an increase in disturbance.The soil pH,total phosphorus and soil organic carbon were the main factors,which affected diazotrophs community.(3)Close relationships between AMF and diazotrophs were detected in karst soils.The results showed that Glomus and the Bradyrhizobium are positive correlated.The network analysis based on genus level showed that the structure of soil AMF and diazotrophs network tended to be simple with a decrease in wetting degree.The more relation abundance of genera,such as Glomus,Claroideoglomus,Claroideoglomus and Geobacter,had more cooperative and competitive association with others.Similar trends had also found in rare genera,such as Scutellospora(0.001%)and Methylobacter(1.26%).In conclusion,the gradients precipitation and temperature and the vegetation restoration play key roles in influencing AMF and diazotroph communities.Soil pH,total phosphorus and soil organic carbon were the main factors that affected AMF and diazotrophs community.Therefore,when applying soil AMF and diazotrophs to restoration vegetation of karst areas,interspecific species with synergistic effects(such as Glomus and Bradyrhizobium)and rare species(such as Scutellospora and Methylobacter)should be selected.Also,environmental factors(i.e.,soil pH,total phosphorus and organic carbon)and vegetation restoration stages should be considerable.