| Rhizosphere is a micro-area of soil-root-microorganism interaction,which is affected by the activities of plant roots and is different from the soil itself in physical,chemical and biological properties.The nutrient status of rhizosphere soil affects the growth and development of plants.Understanding the mechanism of soil-rootmicroorganism interaction is of great significance for exploring the strategies of plant nutrient absorption and utilization.In this study,18 common tree species in subtropical zone were selected,and rhizosphere and bulk soil samples were taken at the initial growth stage(April)and the vigorous growth stage(July).Soil pH,nutrient contents,microbial biomass,enzyme activities and nitrogen transformation rates were measured.The differences of rhizosphere effects of soil nutrients,microbial biomass and enzyme activities of different symbiotic tree species in subtropical forest were compared,and the rhizosphere effects of different types(mycorrhizal type and life form)of tree species were discussed.The stoichiometric characteristics of C,N and P of rhizosphere soil,microbial biomass and enzyme of 18 tree species were analyzed,and the principal component analysis of rhizosphere effects of 15 soil indexes was carried out,and the comprehensive scores of rhizosphere effects of 18 tree species were obtained.This study provides a theoretical basis for rhizosphere nutrient cycling,forest cultivation and species selection of subtropical forests.The main results are as follows:(1)The average values of most nutrient contents,microbial biomass and enzyme activities in rhizosphere soil of 18 tree species were higher than in bulk soil,while TK,Fe and Mg contents in rhizosphere soil were lower than in bulk soil.At the initial growth stage,the rates of Nnit and Nmin in rhizosphere soil were significantly higher than in bulk soil.In different growing seasons,most nutrient contents,microbial biomass and enzyme activities of rhizosphere and bulk soils of 18 tree species in vigorous growth stage were higher than in initial growth stage.Mycorrhiza types had a significant impact on most soil properties,among which the SOC,TN,NH4+-N,microbial biomass and enzyme activities of rhizosphere and bulk soils of AM tree species were lower than ECM tree species,while TP,NO3--N,Nnit and Nmin show opposite trends.In addition,life forms also had a significant impact on most soil properties.There was a strong correlation between soil properties,but there were differences between rhizosphere and bulk soils.(2)There were differences in the stoichiometric ratios of soil,microbial biomass and enzyme C,N and P in rhizosphere and bulk soils among different tree species,which indicates differences in nutrient limitation and rhizosphere activation effects among different tree species.Furthermore,the soil in this study area was limited by P as a whole.Compared with bulk soil,the absorption and utilization of P in rhizosphere soil by plant roots may lead to stronger P limitation in rhizosphere soil.Compared with the initial growth stage,plants had higher demand for P in soil during vigorous growth stage,which may lead to more serious P limitation in soil.(3)There were differences in rhizosphere effects of soil properties among different tree species,and the rhizosphere effects of most soil properties were generally as follows:ECM tree species>AM tree species;deciduous species>evergreen species.There was a strong correlation between rhizosphere effects of soil properties,but there was a stronger correlation between rhizosphere effects of soil properties in AM tree species compared with ECM tree species.(4)In this study,the rhizosphere effects of pH,soil water content(SWC),SOC content,TN content,TP content,available nutrient contents,microbial biomass and enzyme activities were selected for principal component analysis.and the rhizosphere effects of enzyme activities,microbial biomass and AP content were the most influential,and then the comprehensive scores of rhizosphere effects of 18 tree species were obtained.Among the 18 tree species,Cunninghamia lanceolata,Cyclobalanopsis glauca,Elaeocarpus japonicus and Ilex formosana had higher comprehensive scores of rhizosphere effect,while Sassafras tzumu and Cinnamomum camphora had middle scores,while Pinus massoniana,Choerospondias axillaris,Liriodendron chinense and Schima superba had lower scores.In this study,most soil nutrient contents,microbial biomass and enzyme activities were higher in the vigorous growth stage(July)than in the initial growth stage(April),and most soil properties showed positive rhizosphere effects.The soil in the study area was limited by P as a whole.Compared with the bulk soil,the rhizosphere soil showed stronger P limitation,and compared with the initial growth stage,the P limitation in soil in the vigorous growth stage was more serious.The rhizosphere effects of most soil properties were generally as follows:ECM tree species>AM tree species,deciduous species>evergreen species.In addition,among the 18 symbiotic tree species,Cunninghamia lanceolata,Cyclobalanopsis glauca,Elaeocarpus japonicus and Ilex formosana had strong rhizosphere effects,while Pinus massoniana,Choerospondias axillaris,Liriodendron chinense and Schima superba had relatively weak rhizosphere effects. |
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