Response Of Nitrogen Mineralization In Soils And Aggregates To Soil Moisture And Temperature

Soil nitrogen mineralization,as one of the key process of nitrogen cycle in terrestrial ecosystems,which directly determines the availability of soil nitrogen and provides source of nitrogen for plant growth and development.Soil aggregates have important physical protection effects on organic matter in soil.Understanding the nitrogen mineralization process of aggregates and their contribution to soil nitrogen mineralization can reveal the dynamic characteristics of soil nitrogen availability and its changing mechanism.In addition,soil N mineralization is mainly affected by hydrothermal conditions.It will provide a basis for prediction of soil C and N processes that analyzing the response characteristics of aggregates-associated N mineralization to changes of soil moisture and temperature.In this study,we analyzed aggregates-associated C and N characteristics and the response of N mineralization to temperature and moisture changes in order to confirm the contribution of aggregate to total soil N mineralization and determine the responses of aggregates-associated N mineralization to land-use types and soil textur.The main results are as follows:(1)The distribution of 1-2 mm soil aggregates was lowest under different land use types,and the aggregates of grassland and forestland were mainly concentrated at 2-7 mm and<0.25 mm size.With the course to fine of soil texture,the proportion of 2-7 and 1-2 mm size in farmland increased significantly,and the proportion of <0.25 mm decreased significantly.The mean values of carbon and nitrogen contents of bulk soil and aggregates were higher in forest lands than grassland or farmland,and similar in grassland and farmland.Moreover,aggregates-associated carbon and nitrogen contents increased gradually with the refinement of soil texture.(2)The contributin of 1-2 mm size aggregates to soil C and N was the lowest in farmland,grassland and forest.The contribution of <0.25 mm size aggregates was the highest in farmland soils,while the contributions of 2-7mm,0.25-1mm,and <0.25 mm size aggregates in grassland and forestland are close and higher than 1-2 mm size aggregates.With coarse to fine of soil texture,the contribution of 2-7 mm and 1-2 mm size aggregated-carbonand nitrogen in farmland soils gradually increased,while the contribution of <0.25 mm gradually decreased.(3)In the range of 20%~100% field capacity,the nitrification rate and net nitrogen mineralization rate of aggregates and bulk soil increased significantly with the increase of soil water content,and the ammoniation rate was highest at 60% field capacity.The effect of water change on the mineralization rate in aggregates and bulk soil was larger in the forestland and smaller in the grassland,and this effect was related to the studying sites.With coarse to fine of soil texture,the effect of moisture changes on the aggregates N mineralization was enhanced.(4)The nitrification rate and net nitrogen mineralization rate of soil and aggregates increased first and then decreased with the increasing of temperature.The mineralization rate increased with the increasing of temperature.The effect of temperature changes on aggregate nitrification rate and N net mineralization rate was larger in forestland,smaller in grassland,and not affected by aggregates size classes.With coarse to fine of soil texture,the effect of temperature changes on the aggregates nitrogen mineralization was enhanced.(5)The contribution of different size aggregates to soil N mineralization was related to land use types.The 2-7 mm and 1-2 mm size aggregates in forest soils had a lower contribution to soil N mineralization,and the contribution of 0.25-1 and <0.25 mm size aggregates was higher.The contribution was opposite in farmland and grassland.With coarse to fine of soil texture,the contribution rate of 2-7 mm size aggregate to soil N mineralization in farmland soils increased significantly,and the contribution rate of <0.25 mm size aggregate decreased significantly.the contribution rate of aggregates to soil N mineralization was not affected by changes in moisture and temperature among soil moisture at 20% to 100% and cultivated temperature of 10? to 30?.