Fine-root Biomass And Root Respiration Of Subtropical Evergreen Broad-leaved Forests In Xiaokeng

In order to understand the role of fine-root in forest ecosystems,fine-root biomass and related nutrients in a subtropical forest were studied in Xiaokeng forested watershed of Southern Anhui.The combining complementary methods,soil drilling law and inner growth law,were used to study fine root biomass distribution and fine-root biomass growth in the subtropical evergreen broad-leaved forest.The major research contents included(a) the seasonal patterns of fine-root biomass and related nutrient contents(N,P,K,Ca,Na, Mg,Fe);(b) fine-root biomass growth;(3) root and soil respiration rate using Li-6400 CO₂ analyzer in the different development stages of the subtropical evergreen broad-leaved forest.The results from the study are shown as follows.(1) The fine-root biomass was greater in the surface soil layer than in the low ones for all sampling stands in subtropical evergreen broad-leaved forest.The fine-root biomass was 3.825 t hm^-2 in the mid-aged stand(40-yr),which was similar to that(3.768 t hm^-2) in the young stand(18-yr).The changes of fine-root biomass apeared largerly seasonal fluctuation,and the highest value for both mid-aged and young stands were in June.(2) The annual production of fine-root in the mid-aged stand was 1.394 t hm^-2 a^-1,which was very close to that of the young stand.The turnover rates of fine-root were,respectively, 0.36 and 0.37 for the evergreen broad-leaved species in mid-aged and young stands.The production of fine-roots varied seasonally,with the range(monthly average) of 0.031～0.228 t hm^-2 a^-1.The largest growth appeared in 3～6 months.(3) The contents of N,P,K,Ca,Mg,Na and Fe and their storages in fine-root were gradually decreased from surface to lower soil layer.There existed significant difference in fine-root biomass between different aged stands.The nutrient content of fine-root in the mid-aged stand were ranked by Fe＞Ca＞N＞K＞Na＞Mg＞P,while were Ca＞F＞K＞N＞Mg＞Na＞P for the young stand.The contents of N,P,K,Na in fine-root were hardly changed annually.However,the content of Ca in fine-root of evergreen broad-leaved trees in both mid-aged and young stand showed significant fluctuation,with the peak values in June and Novenber.Mg and Fe contents showed an abvious seasonal change with the maximum in September and the minimum in January.(4) The nutrient storages of N,P,K,Ca,Na,Mg,Fe of fine-root biomass were gradually decreased from surface to low soil layer,with significant difference between the mid-aged the mid-aged and young stands.The amounts of N,P,K,Na,Fe in fine-roots biomass were higher in the young stand than in the mid-aged stand.The seasonal pattern of nutrient storage in fine-root biomass in mid-aged stand was similar to that in the young stand.(5) The root respiration rate of mid-aged was in the range of 0.259～1.414μmol m^-2 s^-1 and that of young stand was 0.412～1.970μmol m^-2 s^-1,respectively.Te annual average rate of root respiration of young stand(1.198μmol m^-2 S^-1) was 1.13 times as great as that of mid-aged stand(0.937μmol m^-2 s^-1).The root respiration of mid-aged stand and young stand showed similar seasonal change.The percentage of root respiration to soil total respiration also showed the same patterns in both young and mid-aged stands.The basic model of seasonal change was a single peak curve,with the peak value in June.The root respiration rate of young stand was significantly higher than that of mid-aged stand.The proportion of root respiration to soil total respiration in young stand was in range of 31.79%～59.00%,while 23.50%～50.26%in mid-aged stand.(6) The root respiration in both mid-aged and young stands were significantly correlated to soil temperature at 5 cm.The root respiration of mid-aged stand was greater sensitive to the soil temperature than young stand.However,the root respiration was poorly related to the soil moisture.The interaction between soil moisture and temperature was likely to play a significantly effect to promoting root respiration,which needed further study.(7) The root respiration of mid-aged stand was significant with fine root biomass(p＜0.05),which could explain 72.52%on the effect of fine root biomass,and none was the young stand.