Invasion of Praxelis clematidea increases the chemically non-labile rather than labile soil organic carbon in a tropical savanna

Soil organic carbon (SOC) consists of various classes of organic substances that can be pooled as labile and non-labile fractions. Previous studies have suggested that plant invasion increases SOC content, but whether invasion consistently alters SOC fractions remains unclear. Consequently, the present study was conducted to observe the effects of Praxelis clematidea invasion on SOC fractions in a tropical savanna of southern China. Soil samples were collected in two surface soil layers (0-10 and 10-20 cm) from non-, slightly and severely invaded plots to analyse the total SOC, readily oxidizable SOC (ROC), and non-readily oxidizable SOC (NROC) content. The results showed that severe P. clematidea invasion significantly increased the SOC content by 47% in the surface soil (p < 0.001). The increase in SOC content largely originated from the accumulation of NROC (the non-labile fraction), rather than ROC which typically is regarded as the labile OC fraction. This change may be beneficial to long-term soil C stabilization because chemical recalcitrance is an important pathway to prevent SOC from decomposition. Although the mechanisms for NROC accumulation have not been thoroughly elucidated to date, our results suggest that P. clematidea invasion may facilitate soil C sequestration in this tropical savanna.