Plant litter can influence soil organic carbon dynamics via the priming effect, which is defined as changes in soil organic carbon decomposition rates due to increases in microbial growth and activities responding to plant carbon input. While our current understanding of priming effect induced by plant litter is overwhelmingly from studies with leaf litter addition, we still know little about how root litter decomposes and subsequently the priming effect occurs until now.

Researchers from the Institute of Applied Ecology, Chinese Academy of Sciences investigated the priming effect during decomposition of woody root litter, and underlying mechanisms. Mature trees of Chinese fir were selected, fine roots of which were classified based on the order framework. An incubation study was conducted where roots of each order were added to soils, and root litter chemistry and decomposition, soil organic carbon decomposition, microbial community composition and enzyme activities were measured.

Differences in decomposition rates of woody fine root litter were mainly associated with root tissue chemistry such as non-structural carbon and tannin. The priming effect shifted from negative to positive at the reduced decomposition stage, and was higher for higher order roots than lower order roots. This could be attributed to higher fungi to bacteria ratios and enzyme activities for high order roots compared to lower order roots.

“This is the first study showing that the priming effect varied with root order,” said prof. Wang, the leader of the Belowground Ecological Processes, “future efforts should account for root order-specific effects on soil organic carbon decomposition.”

Relevant results have been published in Soil Biology and Biochemistry entitled "Priming effect varies with root order: A case of Cunninghamia lanceolata."

This study was supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China.