Plant functional trait differentiation and microbial life-history strategy shifts drive soil respiration under long-term forest restoration

Soil respiration (Rs) represents a major carbon (C) flux linking plant productivity with microbial decomposition; however, the mechanisms by which contrasting forest restoration pathways regulate Rs and its components remain insufficiently understood. We conducted a six-year field observation (2017-2022) across abandoned farmland (AF), Quercus liaotungensis forest (QF), and Robinia pseudoacacia plantation (RP) on the Loess Plateau, China, integrating measurements of Rs, autotrophic (Ra), heterotrophic (Rh), plant functional traits, soil physicochemical properties, and microbial C metabolic potential. Afforestation significantly increased Rs, with a stronger enhancement observed in QF than in RP. Although Ra did not differ significantly between the two forest types, Rh accounted for approximately 70% of Rs and primarily explained the significant differences in Rs between restoration pathways. Elevated Rh in QF was strongly associated with greater abundances of microbial functional genes involved in the degradation of C substrates. Integrated analyses further revealed that differentiation in plant functional traits between QF (conservative strategy) and RP (acquisitive strategy) indirectly amplified Rh contributions to Rs by reshaping soil substrate availability and coordinating shifts in microbial life-history strategies. Collectively, our findings identify plant functional trait differentiation as a key driver of long-term Rs dynamics, mediated by shifts in microbial life-history strategies.