Soil carbon budget in different-aged Chinese fir plantations in south China

Abstract

Understanding the age effect on soil carbon balance in forest ecosystems is important for other material cycles and forest management. In this research we investigated soil organic carbon density, litter production, litter decomposition rate, soil respiration, and soil microbial properties in a chronosequence of four Chinese fir plantations of 7, 16, 23 and 29 years at Dagangshan mountain range, Jiangxi Province, south China. There was a significant increasing trend in litter production with increasing plantation age. Litter decomposition rate and soil respiration, however, declined from the 7-year to the 16-year plantation, and then increased after 16 years. This was largely dependent on soil microorganisms. Soil carbon output was higher than carbon input before 16 years, and total soil carbon stock declined from 35.98 t·ha−1 in the 7-year plantation to 30.12 t·ha−1 in the 16-year plantation. Greater litter production could not explain the greater soil carbon stock, suggesting that forest growth impacted this microbial process that controlled rates of soil carbon balance together with litter and soil respiration. The results highlight the importance of the development stage in assessing soil carbon budget and its significance to future management of Chinese fir plantations.