Comparison of active soil organic carbon pool between Chinese fir plantations and evergreen broadleaved forests

Forest soil contains more than 70% organic carbon pool of the earth.So small changes in forest soil organic carbon(SOC) pool can remarkably cause the variance in CO₂ density of atmosphere.At Huitong Experimental Station of Forest Ecology,CAS,Hu'nan Province in May 2005,the authors analyzed the active SOC under Chinese fir plantations and evergreen broadleaved forests in the depth of 0—10 cm and 10—20 cm to assess the effects of forest conversion on active SOC pool.Results showed that the contents of soil microbial biomass carbon(MBC),dissolved organic carbon(DOC),free(FLOC) and occluded(OLOC) light fraction organic carbon under Chinese fir plantations were significantly lower than that of evergreen broadleaved forests.However,the rules of percentages of different active SOC to total SOC under two forest soils were not found. The significant correlations were observed between FLOC and SOC,OLOC and SOC,as well as between heavy fraction organic carbon(HOC) and SOC under the two forests.The close relationships between MBC and SOC along with DOC and SOC were only found under evergreen broadleaved forests.It was also found that the correlation coefficients between active fraction organic carbon and soil nutrients under Chinese fir plantations were lower than that of evergreen broadleaved forests,and their relationships with available phosphor were higher than total phosphor.This indicated that phosphor availability affected soil fertility of Chinese fir plantations.