The Effect Of Thinning On Root Exudation Rate Of C And Microbial Activity In The Rhizosphere Of Chinese Fir Plantation

Understanding the carbon cycle process in forest ecosystem is central to realizing the structure and function of planted forest.To study the effect of thinning treatments on root exudation rate and rhizosphere effects of microbial activity,root exudates and soils were sampled to measure the root exudation rate,microbial biomass C,N(MBC,MBN)and soil enzymatic activity at different thinning intensity sites,i.e.,CK(no thinning),LIT(30% trees removed),HIT(70% trees removed)from Chinese fir plantations of LiShui,South-east NanJing,The main results were as follows:(1)In summer,thinning treatments significantly increased the root activity of Chinese fir and the root exudation rate of C(p<0.05).Root activity,root exudation rate of C per fine biomass,length,surface area and tip increased with the increase of thinning intensities.The effect of thinning on root activity is not consistent throughout the year except in summer.Thinning treatments had no effect on root exudation rate of C(p>0.05)except in summer.(2)Significant differences among different thinning intensities were found for soil MBC and MBN(p<0.05)and thinning treatments had a greater impact in the rhizosphere.Compared with the control site,light-intensity thinning practice significantly decreased soil MBC and MBN between rhizosphere and nonrhizosphere whereas high-intensity thinning treatment increased soil MBC and MBN between rhizosphere and nonrhizosphere.Soil MBC and MBN among different thinning intensities had positive rhizosphere effects in varying degrees throughout the year except in winter.Mid-intensity thinning treatment given a more positive rhizosphere effects on soil MBC and MBN than any other treatments throughout the year.(3)Thinning treatments significantly influenced the activities of cellulase,urease,dehydrogenase,invertase and peroxidase(p<0.05)between rhizosphere and nonrhizosphere.Compared with nonrhizosphere,thinning treatments had a greater impact in the rhizosphere.The difference of several soil enzymatic activities depended on season and thinning intensities.Thinning had a great influence on the activities of urease,dehydrogenase,invertase and had less effect on the activities of peroxidase and cellulase.These five kinds of soil enzymatic activities among different thinning intensities had positive rhizosphere effects in varying degrees throughout the year except in winter.Mid-intensity thinning treatment given a more positive rhizosphere effects on soil enzymatic activities than any other treatments throughout the year.The results indicated that moderate thinning intensity in the experimental sample could improve the environment of under-forest and made for the ecological process of Chinese fir plantation underground.To some extent,this motivated positive rhizosphere effects on soil MBC,soil MBN and soil enzymatic activities.