Phosphorus (P) is an essential nutrient element that is critical for plant growth and ecosystem functionality. The soil P cycle plays multiple roles, such as sustaining plant growth and productivity, regulating nutrient balance within ecosystems, and enhancing ecosystem adaptability and resilience. This cycle is influenced by factors such as the restorationapproachand microbial community dynamics. However, the extent to which the restorationapproach alters the P cycle in karst ecosystems and the underlying microbial mechanisms remain poorly understood. The P-cycle multifunctionality index (P-cycle MFI) serves as a comprehensive indicator for evaluating soil P cycle function, and it provides insights into changes in the P cycle betweendifferentrestorationapproaches. To investigate the shifts in soil P-cycle MFI and microbial mechanisms betweendifferentrestorationapproaches, we analyzed soil available P (AP), total P (TP), microbial biomass P (MBP), and the activities of acid phosphatase (ACP) and alkaline phosphatase (ALP). These data were used to calculate the P-cycle MFI by averaging the Z-scores between tworestoration approaches(artificial restorationof forest(AF)and natural restoration offorest (NF))and a control(cropland, CP) at six subtropical karst ecosystem sites in China. We also determinedthe soil organic carbon (SOC), exchangeable calcium (Ca) and magnesium (Mg), pH, bulk density(BD), microbial biomass C(MBC), and microbial biomass nitrogen (MBN), as well as thecommunity structure,relative abundance, diversity indices, and co-occurrence networks of phoD-harboring bacteria. The results showed that the community structureofphoD-harboring bacteria variedsignificantly among AF, NF, and CPand across differenttemperature gradients. Thesebacteria exhibited increasingcomplexityandtightness in co-occurrence networks from CPto AFand then to NF, along with the ACP and ALP activities,but notthe TP and AP contents. The P-cycle MFI values were significantly higher in NF compared to AF and CP, and the variation was significantly explained byrestoration approach, temperature, MBC, MBN, SOC, exchangeable Ca, BD, community structure ofphoD-harboring bacteria, and exchangeable Mg. Furthermore, natural restoration had a more substantial impact on the P-cycle MFI than temperature by enhancing SOC, microbial biomass, the complexity and co-occurrence network tightness of the phoD-harboring bacterial community structure, and ACP and ALP activities, but it reduced soil BD. The rare genera of phoD-harboring bacteria significantly influenced the variation of soil P-cycle MFI compared to the dominant genera. This study highlights the importance of rare genera of phoD-harboring bacteriain driving soilP-cycle multifunctionality in karst ecosystems, with natural restoration being more effective than artificial methods forenhancing soil organic matter and microbial community complexity.

SOC accumulation efficiency  /  granulated straw  /  upland and paddy  /  plant residues  /  microbial necromass  /  microbial community