Soil Microbes And Respiration Characteristics In Different Vegetation Types In The Loess Hilly Region

The ecological environment has been greatly improved since the large-scale soil and water conservation project in the Loess Plateau.Vegetation restoration can not only maintain soil and water,reduce soil erosion,but also improve soil nutrient status.Characteristics of soil ecosystem after returning farmland to forest,is the basis for further understanding of the function of ecological system,which has important theoretical and practical significance to predict response of soil function to environment.To assess the effects of vegetation types on soil development,the basic physicochemical properties,microbial biomass carbon(MBC)and nitrogen(MBN),and the number of bacteria and fungi of soils were measured.We assessed whether land-use types or soil chemical properties are the primary drivers of soil microbial community composition,and how changes in one part of the ecosystem affect another.We applied Ion Torrent sequencing to the bacterial and fungal communities of five different vegetation types in the Loess Plateau of China,including a secondary natural oak forest,a non-typical natural forest of oriental arborvitae,a natural shrub land,a planted forest of black locust,and a plot of unforested bare land.We found that(1)soil properties improved with the presence of vegetation,compared with the abandoned bare land,and that there were differences in the physicochemical properties of soil from the different land-use types.Soils from the bare land and black locust forest yielded higher pH values than the natural forests,and the overall trend of soil quality was: natural forest > plantation > bare land.This indicated that vegetation coverage,especially natural types,has a beneficial effect on soil nutrient conditions and soil pH.(2)Similar to the trend of the other soil parameters,both MBC and MBN were highest in the oak forest and shrub land and lowest in the bare land and black locust forest.These two indices(MBC and MBN)were also strongly correlated with specific soil properties(soil organic carbon,r~2 = 0.725,total nitrogen,r~2 = 0.736,and phosphorus,r~2 = 0.775;P < 0.001),suggesting that vegetation types and soil properties influence microbial biomass.Thus,microbial biomass can be used to assess soil trophic status and which were lower in oligotrophic soils on the Loess Plateau of China.In our study area,the soil was alkaline(pH 8.18–8.48),and the MBC/MBN ratio was ~6,indicating that actinomycetes were dominant,possibly facilitated by the alkaline soil conditions.(3)Bare land harbored the lowest abundance of bacteria,and the abundance of fungi in the black locust was lower than that in the oak forest.The abundance of bacteria exhibited a strong relationship with specific soil properties and was positively correlated with C/N ratio(r~2 = 0.754,P < 0.001),soil organic carbon(r~2= 0.636,P < 0.05),total nitrogen(r~2 = 0.611,P < 0.05),and phosphorus(r~2 = 0.775,P < 0.05),and negatively correlated with pH(r~2 = 0.761,P < 0.001).In contrast,the abundance of fungi was only correlated with soil pH,thus confirming previous reports that bacteria and fungi respond to different environmental factors.(4)Dominant bacterial phyla consisted of Proteobacteria(42.35%),Actinobacteria(15.61%),Acidobacteria(13.32%),Bacteroidetes(8.43%),and Gemmatimonadetes(6.0%).The dominant fungi phyla were Ascomycota(40.39%),Basidiomycota(38.01%),and Zygomycota(16.86%).The results of Canonical Correspondence Analysis(CCA)and Redundancy Analysis(RDA)based on land-use types displayed groups according to the land-use types.Furthermore,the bacterial communities were mainly organized by soil organic carbon(SOC).The fungal communities were mainly related to available phosphorus.(5)Soil respiration of two typical stands(natural oak forest and black locust)was the maximum at 25oC and Q10 of natural oak forest(1.630)is slightly higher than black locust(1.572),soil respiration was increased with the soil moisture decreased,were the maximum at 60% soil water content.The results suggested that the changes of vegetation type generated changes in soil chemical properties,controlling the composition of microbial community in the semiarid Loess Plateau region.The microbial community could be an indicator for soil quality with respect to ecological restoration.