Effects Of Land Use Change On Soil Microbial Biomass Nitrogen And Phpsphorus In Soil Aggregates

Soil aggregates are the basic units of soil structure,and the niche of micrbbes.Soil microorganism not only plays an important role in soil aggregates formation,but also is of great importance in regulating soil nutrient cycling.Soil aggregates and microorganism are liable to be influenced by land use change.In mid-subtropical mountains area of southern China,land use patterns have greatly changed with the growing population and excessive pursuit of economic interests,which caused the soil quality seriously degradation.In this study,0-10cm and 10-20 layers of soil from six typical land use utilizations in this area were collected,they were Tea Garden,Citrus Aurantium,Chinese Fir Plantation,secondary forest,Cunninghamia lanceolata plantation and Alting gracilipes natural forest.The soil aggregates of＞2mm,2-0.5mm, 0.5-0.25mm and＜0.25mm were respectively obtained by dry-sieving method;the soil total nitrogen(TN),total phosphorus(TP),microbial biomass nitrogen(MBN),microbial phosphorus(MBP) in soil and aggregates were determination.The aim of our study is to explore the impacts of land use change on MBN and MBP in soil and aggregates,and it is of great significance in regulating the availability of soil nitrogen and phosphorus,besides,this can offer some basic data to the evaluation of soil quality and optimization rational utilization of land resources in this area.The following results were obtained in this study.1.Land use change had some effects on contents of TN and TP.The contents of TN were from 0.84 g/kg and 5.81g/kg,the native forest was significantly higher than plantations,secondary forest and garden.When Alting gracilipes natural forest was converted to plantations,secondary forest,and Garden the contents of TN in 0-10cm and 10-20cm layers decreased from 56.63%and 81.29%.The contents of TP were from 0.25 g/kg and 0.46 g/kg,and this was slow for plant growth.The contents of TP under different land utilizations were:Citrus Aurantium＞Chinese Fir plantation＞Alting gracilipes natural forest＞Cunninghamia lanceolata plantation＞secondary forest＞Tea Garden.When native forest was converted to Citrus Aurantium and Chinese Fir Plantation,the TP increased,but when native was converted to secondary forest Cunninghamia lanceolata plantation and Tea Garden,the TP decreased.2.The MBN were from 23.88mg/kg and 103mg/kg,accounting for 1.25%and 4.83%of TN. The MBN under different land utilizations:native forest＞plantations,secondary forest＞garden. When Alting gracilipes natural forest was converted to plantations,secondary forest and garden, the MBN significantly decreased.The MBP were from 10.82mg/kg and 16.54,accounting for 3.33%and 5.10%.The MBP were highest and lowest in the Citrus Aurantium and Tea Garden soils,respectively.3.The contents of TB and TP in aggregates increased with decreasing of aggregates size, MBN and MBP in macro-aggregates increased with decreasing of aggregates size.The contents of TB and TP in micro-aggregates significantly higher than those in macro-aggregates,but the contents of MBB and MBP in micro-aggregates and macro-aggregates had no significant difference,which need further studies.4.The TN,TP,MBN and MBP were mainly stored in＞2mm aggregates.The contributing rates of TN in＞2mm aggregates to TN in soil were from 43.90%and 62.43%,the contributing rates of MBN in＞2mm aggregates to MBN in soil were from 49.99%and 57.78%,the contributing rates of TP in＞2mm aggregates to TP in soil were from 49.99%and 57.78%,and the contributing rates of MBP in＞2mm aggregates to MBN in soil were from 49.99%and 57.78%. The contents of TN,TP,MBN and MBP in soils of Citrus Aurantium and Tea Garden were mainly stored in＜2mm aggregates.5.The contents of＞2mm aggregate had highly significant correlation with TN and TP,so the contents of＞2mm aggregate directly determine the contents of TN and TP.＞2mm aggregate predominate in woodland soils.When woodland was converted to garden,TN substantially decreased,mainly due to the loss of＞2mm aggregate.6.The contents of TN,MBN,TP and MBP declined with the soil depth increasing under different land use pattern.Citrus Aurantium showed reverse trend.7.The contents of MBN and MBP had highly significant correlation with TN and TP, respectively,so they can be used as important index to indicate the soil nitrogen and phosphorus status in this area.