Soil microbial properties under different grain-for-green patterns in depressions between karst hills

Soil microbial life in vivo is a major component of soils throughout the whole process of soil development.The living environment for soil microorganisms is a very sensitive early-warning indicator of change in soil ecosystems.Using slope cropland as a contrast,we investigated the main soil microbial populations,microbial biomass carbon(MBC),nitrogen(MBN),and phosphorus(MBP) and their fractal characteristic model,as well as soil enzyme activities under seven grain-for-green patterns(cultivation of Zenia insignis,Toona sinensis,Castanea mollissima,Citrus reticulate,Zenia insignis + Guimu No.1 forage,Guimu No.1 forage,and abandoned cropland) in depressions between karst hills.The main soil microbial populations differed under different grain-for-green patterns.Actinomycetes were 71.28% to 96.44% of the microbial population in the slope cropland,Zenia insignis + Guimu No.1,Guimu No.1,and abandoned cropland.Differences in their populations covered up to three orders of magnitude.Bacteria dominated in the other four soils,being 55.24% to 71.79% of the microbial population,but fungi were less than 1%.Bacteria were highest under Guimu No.1 and abandoned cropland,and were lowest in the slope cropland.Fungi populations were in the order: abandoned cropland Zenia insignis Guimu No.1 Citrus reticulate Castanea mollissima slope cropland Toona sinensis Zenia insignis + Guimu No.1,with significant differences between them.All the grain-for-green patterns except Zenia insignis increased total soil microbial populations.The differences between Guimu No.1,abandoned cropland,and Zenia insignis + Guimu No.1 were significant(P0.05),and were significantly higher than the others.Microbial biomass carbon(MBC) in the all grain-for-green patterns except Zenia insignis was significantly higher than in the slope cropland,and was highest in the abandoned cropland.Microbial biomass nitrogen(MBN) varied within a small range,showing a downward trend.Differences in MBN between cultivation of Zenia insignis + Guimu,Citrus reticulata,Zenia insignis and slope cropland were significant(P0.05).Microbial biomass phosphorus(MBP) varied widely in Toona sinensis,Castanea mollissima,abandoned cropland and Guimu No.1 but was significantly higher than in slope cropland.MBC was well correlated with bacteria(D=-4.07,R=0.81,P0.01),followed by the correlation between MBC and actinomycetes(D=3.82,R=0.44,P0.05) and that between MBN and fungi(D=0.58,R=0.61,P0.01).However,there was no fractal relationship between the other microbial biomass and microbial populations.Compared with the slope cropland,all the grain-for-green patterns except Guimu No.1 forage significantly increased the activities of soil sucrase,urease and phosphatase,suggesting an increase in carbon and nitrogen cycling.Under different grain-for-green patterns,the activity of soil sucrase was highest under Toona sinensis,reaching(29.10±7.73) mg g-1 d-1,while the activity of soil urease was highest in the abandoned cropland,reaching(540.7±34.77) μg g-1 d-1,and the activity of soil phosphatase was highest under Castanea mollissima,reaching(991.1±76.28) μg g-1 d-1.All the grain-for-green patterns improved soil microbial properties,suggesting important benefits arising from fragile ecosystem restoration and reconstruction in depressions between karst hills.