Effects Of Plant-Soil Collaborative Recovery And Microbial Responses In The Loess Plateau

During the vegetation restoration,studying the collaborative recovery of plant-soil is the basis for understanding the fragile ecosystem's ability that can form a stable self-sustainability.It is a scientific problem that the mutual adaptation strategies,induced effects,and the mutual-feedback mechanisms are proven to achieve the coordinated recovery of plant and soil,aiming to improve and repair the fragile ecological environment.Therefore,the study took the perspectives of the collaborative restoration of“plant-soil-microbes”and combined eco-chemical stoichiometry to systematically study the effects of plant-soil collaborative recovery and microbial responses in the typical ecologically fragile area of Loess Plateau,thus this study can provide a scientific basis for the selection and optimization of plant-soil co-recovery configuration models for the restoration and reconstruction of regional fragile eco-environment.Moreover,based on regional and global scales,we used the field experiments and meta-analysis to study the geographical distribution pattern,spatial-temporal differences and energy metabolism of soil microbes under different vegetation types and recovery periods.Together with macro-ecology theory(Odum theory),this study demonstrated the plant-soil interaction during plant restoration from the view of microbiological point,and reveal the stability of the ecosystem after vegetation restoration.Altogether,the results can provide theoretical basis for further investigation of microbial processes and mechanisms(i.e.,element cycling and gas emissions)in plant-soil continuum after vegetation restoration.The main results are as followed:(1)The plant-soil-microbial biomass C,N,and P contents increased significantly after afforestation and were also affected by vegetation types and recovery periodsThe contents of C,N and P in plant-soil-microbial biomass showed an increasing trend with the increase of recovery time,and ranked as Arboreal forest(Robinia pseudoacacia:RP)>Shrubwood(Caragana Korshinskii Kom:CK)>Abandon lands(AL)>Farmland(FL).The C and N contents of the above-ground plant parts(leaves,herbs,and litters)in RP and AL increased first and then decreased with the increases of the recovery periods,while the C and N contents in CK showed increasing trend.In contrast,the P contents increased but were not significant.Moreover,compared with FL,soil and microbial biomass C,N,P contents significantly increased but differed with vegetation types and recovery periods.Particularly for the C,N,and P contents in microbial biomass.(2)The stoichiometric ratios of C:N,C:P,and N:P differed with vegetation types and recovery periods.Particularly,the N:P ratio indicated the soil elements limitations after afforestation.After afforestation,the plant-soil-microbial biomass C:N,C:P and N:P ratios differed with vegetation types and recovery periods.In detail,plant-soil-microbe C:P and N:P ratios in RP and CK showed increased trends with the increases of the recovery periods,but these two ratios in AL increased first and then decreased.In contrast,with the increases of the recovery periods,the C:N ratio in the above-ground parts of RP(leaves,herbs,and litter)decreased but increased in the below-ground parts.While the C:N ratio was also affected by recovery periods but responded differently.Furthermore,we also found that,before 42 years,N:P ratio in RP was lower than 14,but was higher than 16 after 42 years,suggesting that the P limitation may occur in the later stage of RP;the leaf N:P ratio in CK was all higher than16,while this ratio in AL was all lower than 14,indicating that P limitation may occur in CK and N limitation may occur in AL.(3)Microbial diversity and abundance significantly increased after afforestation;microbial community compositions and energy metabolism differed with vegetation types and recovery periods,and such changes were associated with changes of plant-soil-microbes C:N:P stoichiometry,especially for C:P and N:P ratios.After afforestation,soil microbial diversity and abundance significantly increased but differed with the recovery periods.For the community compositions,bacterial community transitionedfromAcidobacteria-dominant(nutrient-poorbacteria)to Proteobacteria-dominant communities(nutrient-rich bacteria)at the early stage of recovery but showed the opposite trends at the later period of recovery.Fungal dominant phylum Ascomycota and Basidiomycota also differed with vegetation types and recovery periods.Moreover,after afforestation,microbial energy indicators(F:B,MBC:SOC,and MR:MBC)also differed with vegetation types and recovery periods,and these trends supported the ecological succession theory(Odum theory).In detail,F:B and MBC:SOC ratios in CK and AL showed an increasing trend with the increase of recovery periods,and these two ratios in RP also increased before 42 years but decreased after 42 years.However,the MR:MBC ratio showed the opposite trends.These results suggested that the stability of these three vegetation increased with the increases of the restoration periods,except for the RP that showed the decreased trends after 42 years.Moreover,further analysis revealed that soil microbial community and energy metabolism were closely related to the stoichiometric ratios of plant-soil-microbes C:N:P stoichiometry.In contrast,the microbial community was more sensitive to changes of N:P ratio,while microbial energy metabolism was more sensitive to changes of C:P ratio.(4)Soil microbial communities have obvious geographic distribution in typical ecologically fragile areas after afforestation,and such patterns were affected by vegetation types and climatic factors such as rainfall.In the fragile areas,there were significant differences in soil microbial(bacterial and fungal)diversity(alpha and beta diversity).In detail,from the Yulin area to the Fuxian secondary forest area,microbial alpha diversity significantly increased,and microbial beta diversity differed among these three regions,indicating that there was a clear spatial distribution of soil microbes in fragile habitats and such changes were also affected by vegetation types and climatic factors.In addition,Proteobacteria,Actinobacteria,Nitrospirae,and Bacteroidetes belonging to bacterial community compositions,and Ascomycota,Basidiomycota belonging to fungal community compositions were significantly different,revealing the geographical distribution patterns of soil microbial communities at the regional scale.(5)Based on the global scale,soil microbial biomass,bacterial,and fungal abundances increased first and then decreased at the later recovery periods;while the characteristics of microbial energy metabolism also revealed the microbial stability after afforestation.Meta-analysis showed that soil microbial biomass C and N(MBC and MBN)significantly increased after afforestation but differed with recovery periods.In detail,soil microbial biomass C and N increased during the early periods(0-10 years)by 52.84%and61.08%,respectively;during the medium recovery period(10-30 years),MBC and MBN increased by 171.50%and 128.86%,respectively.Although MBC and MBN increased in the later period of recovery(>30 years),the increase ratios decreased.Additionally,soil bacterial and fungi abundances had similar trends to those of soil microbial C and N.Across all studies,soil microbial energy metabolism also changed,in detail,F:B,G~+:G~-,and MBC:MBN ratios significantly increased with recovery periods.Particularly,the amplitude ranges of F:B ratio and MBC:SOC ratio were from-4.32%to 13.00%and 31.16%to 6.29%,respectively.In contrast,MR and MR:MBC showed a decreasing trend with the recovery periods.Together with the succession theory of Odum macro-ecosystem,these findings revealed that the microbial ecosystem tends to be stable after afforestation.