Changes in plant carbon inputs alter soil phosphorus dynamics in a coniferous forest ecosystem in subtropical mountain area

Plant carbon input aboveground and underground influences soil biological and physicochemical processes in forest ecosystems. However, compared with the well-known interactions between plant carbon and soil carbon or nitrogen, the impact on soil phosphorus (P) dynamics remains unclear. Here we investigated soil P dynamics in aggregates and bulk soil after one-year of plant carbon removal treatments (RL, removing litter; TG, tree girdling; RLTG, combination of removing litter and tree girdling; CK, control) under subtropical Pinus yunnanensis forest in a soil P-enriched degraded mountain area. Compared to CK, tree girdling significantly decreased the macroaggregate proportion and increased the microaggregate proportion by changing soil total carbon (TC) and Fe concentration. With the decrease of soil TC, the increase of HCl-Pi (inorganic P extracted by HCl) in microaggregate and silt and clay was significantly higher than that in macroaggregate. In addition, easily-available P and non-available P at bulk soils significantly declined and increase under RL and TG treatments, respectively. Redundancy analysis revealed that Fe, TC, and acid phosphatase activity were the main factors affecting P fractions in bulk soils. Higher δ¹⁸O_P (oxygen isotope composition of phosphate) values of HCl-Pi pool and its significantly negative relationship with soil TC across the all carbon removal treatments, suggesting the weakened ability for plant to unlock soil bioavailable inorganic P combined with minerals induced by different plant carbon removal treatments. Overall, our results highlight that the importance of litter and root carbon in regulating soil P fractions and dynamics by altering the proportion of soil aggregates and the physicochemical properties of bulk soil.