Abstract: Soil organic carbon content and chemical structure affect carbon sequestration of terrestrial ecosystems and global carbon balance. We collected soil samples from typical tea plantations at different altitudes in Fuding City, Fujian Province. Fourier transform infrared spectroscopy and soil parameter analysis were used to analyze the content of soil carbon fractions, chemical structure and soil carbon pool management index (CPMI). The results showed that soil microbial biomass carbon (MBC) was significantly higher at high altitude than that at middle and low altitude (P<0.05). The content of soil dissolved organic carbon (DOC) was the highest at middle altitude (P<0.05). The content of soil easily oxidized organic carbon (EOC) and soil organic carbon (SOC) in the upper soil layers were the lowest at low altitude. The relative strength of soil alkoxy carbon was the highest. The relative strength of upper soil alkoxy carbon decreased significantly with increasing altitudes (P<0.05), while the relative strength of soil alkyl carbon and aromatic carbon showed no significant differences among altitudes (P>0.05). The relative strength of soil fat carbon was generally low, and it increased first and then decreased with increasing altitudes (P<0.05). With the increases of altitudes, the ratio of aromatic carbon/alkoxy carbon (ARC/ALC) in upper soil increased. The CPMI of upper soil was higher at middle and high altitudes than that at low altitudes. Soil SOC and its fractions were positively correlated with soil TN content and water content, and negatively correlated with bulk density. Soil alkoxy carbon was negatively correlated with soil TN content and carbon pool stability. Soil water content and TN were the key factors affecting the composition and chemical structure of soil organic carbon in tea plantations at different altitudes. The stability of upper soil organic carbon increased with increasing altitudes. In the future management practice of tea plantations, carbon sink function of upper soil at low altitude should be further strengthened.

Key words: altitude, organic carbon fraction, carbon structure, soil carbon pool management index, tea garden