The soil labile pools, small size with a rapid turnover, and recalcitrant pools, large size with slow turnover are largely controlled by plant inputs and climatic conditions and thus influence the short-term and long-term carbon (C) and nitrogen (N) storage in terrestrial soils. However, the interrelation of labile and recalcitrant pools with changes in plant functional groups (i.e., C₃ and C₄) along precipitation gradients have not been carefully examined at a regional scale.  

Supervised under Prof. CHENG Xiaoli, Adugna Feyissa, a PhD student of Key Laboratory of Aquatic Botany and Watershed Ecology at Wuhan Botanical Garden investigated changes in soil organic, labile and recalcitrant C and N fractions in relation to C₃ and C₄ plant inputs from 20 sites across a 600-km precipitation gradient in secondary grasslands of south China. 

The soil organic C content decreased first slightly and then increased along precipitation gradients, largely due to the increase in C₄ plant C inputs in the lower precipitation regions. In contrast, the soil organic N content increased with increasing N inputs from C₃ plant at higher precipitation regions. The labile C and N were also increased with increased precipitation, as well as tightly correlated with plant C and N inputs.  

However, the recalcitrant C and N contents were not significantly affected by precipitation. Increases in labile C and N contents were tightly related to enhanced plant C and N inputs influenced by precipitation, suggesting stronger sensitivity of labile pools to both plant functional groups inputs and precipitation compared to the recalcitrant pool.  

Moreover, the δ¹³C values in recalcitrant C declined with precipitation, while the δ¹⁵N values of both labile and recalcitrant N increased with increasing precipitation, which were attributed to the shift in the C₃ and C₄ plant functional groups along precipitation gradients. 

Results provide new insights into soil C and N dynamics in relation to plant functional groups inputs along climatic gradients, particularly the mean annual precipitation.  

This research was financially supported by the “Strategic Priority Research Program B of the Chinese Academy of Sciences” and the National Natural Science Foundation of China. Results have been published in Environmental Science and Pollution Research entitled “Soil labile and recalcitrant carbon and nitrogen dynamics in relation to functional vegetation groups along precipitation gradients in secondary grasslands of South China”.