Fine Root Longevities Of Two Subtropical Evergreen Broad-leaved Forests

Fine root longevity which determines the quantities of nutrient and carbon allocated to soil each year is the intrinsic mechanism for fine root turnover, Therefore, it affects accurate estimation of potential carbon sequestration in forest ecosystem. Chinese subtropical zone is "the oasis at the Tropic", a typical ecological transitional zone, and a sensitive zone of global change. So we choose the fine roots in castanopsis carlesii(CAC) and altingia gralilipes(ALG) communities as research objects by Minirhzotrons, which are the zonal forest types in Wanmulin Nture Reserve of Jian Ou on the mid-subtropical region in China. It would be a favorable factor for exploring carbon sink and carbon sequestration of subtropical forest. The results are as follows. There was no significant differences between the Survival curves of fine root in two communities(P=0.805), whose median root lifespan(MRL) were 212±8.2d(CAC)and 164±10.2(ALG). Fine root diameters were both mainly less than 0.3mm (CAC:67.5%, ALG:62.5%) with the distribution of "left skewed", and median root lifespan increased with diameter. The number of first-order fine roots was more than that of definite higher-order roots. They were in the ratio 11.8:1 (CAC) and 14.4:1(ALG), and the diameter and median root lifespan of first-order fine roots were much less than that of higher-order roots. Most of new fine roots appeared in 0-40 cm soil depth, and fine root which in the upper soil layer had less median root lifespan than that in deep soil. The number of CAC fine root born in summer was least, and that of ALG appeared in winter with most in summer, but the quantity gap of fine root in different seasons was not obvious. The median root lifespan of fine root born in summer was the shortest time (CAC:64±10.1d; ALG:109±7.0d), but that has no clear different between spring and autumn.