Precise assessment of soil organic carbon (SOC) storage requires understanding how vegetation and soil physico‐chemical properties differ in SOC fractions. Therefore, we aimed to analyze the dynamics of aggregate‐associated, labile organic carbon (LOC) fractions corresponding to depth to clarify the effect of vegetation and soil properties on water stable aggregate (WSA) mineral adsorption in subtropical, red soil with five vegetation restoration regimes. The results showed that the large macro‐aggregate fraction dominated the degraded red soil, which had the highest content of dissolved organic carbon (DOC). WSA‐associated, easily oxidized organic carbon (EOC) varied from 6.26 to 20.02 g/kg and was not affected by vegetation types. Schima superba pure forest significantly increased DOC (0.38 g/kg on average) and particulate organic carbon (POC, 7.92 g/kg on average), which had the highest biomass. Along with soil depth, WSA‐associated POC declined, while exhibiting a growth trend with decreasing particle size, for example, the highest POC was found in <0.053 mm aggregates. The redundancy analysis ordination indicated that soil porosity and total nitrogen (TN) were the main soil parameters that explained the most variance. Meanwhile, the vegetation biomass, except for litter, were all significantly positively correlated with <0.053 mm aggregates. Leaf biomass played the most important role on DOC in macro‐aggregates with a 53.42% contribution. For aggregate‐related POC, the largest contribution was from the interactions between branch biomass and pH (47.78%) followed by TN (35.1%) of micro‐aggregate‐related POC. Leaf biomass, <0.053 mm aggregates, and TN can be used as indicators to evaluate the impact of vegetation restoration on WSA‐associated SOC fractions. Broad‐leaved forest or in combination with indigenous coniferous species was a better choice for SOC sequestration improvement in the study area for managing C supply, process, and flux in subtropical terrestrial ecosystems.

Phosphorus (P) limitation is common in subtropical and tropical regions. Although phosphate‐solubilizing bacteria (PSB) can transform soil P fractions and enhance soil P availability, the mechanism regarding the linkage between PSB abundance and soil P fractions transformation were still unknown. In this study, Burkholderia sp. ZP‐4, a PSB strain, was inoculated into subtropical bamboo forest soil at the inoculation rates of 0% (bacterial suspension: soil weight = v: w, the control), 2% (2%IR), 6% (6%IR) and 10% (10%IR). The changes in soil P fractions, bacterial community, phosphatase activities, P transforming functional genes and soil properties were also determined after the PSB inoculation. Compared with the control, soil inorganic P extracted by deionized water (H2O‐Pi) and extracted by sodium bicarbonate (NaHCO3‐Pi) in the 6%IR treatments were increased 45.35% and 16.05%, respectively. The lowest content of residual P (residual‐P) was in the 6%IR treatment among the four treatments. The 6%IR treatment contributed to stimulating and inducing soil acid phosphatase activity and P cycling genes (phoD and phoC) abundances, relative to the control. The PSB inoculation significantly decreased soil pH but increased soil available nitrogen P supplies among all treatments. Simultaneously, the PSB inoculation also significantly changed soil bacterial community. The transformation of P fractions in the 6%IR was more efficient than the other treatments, implying that 6% is the proper inoculation rate of functional Burkholderia for accelerating P cycling at subtropical bamboo forest soil. Our findings will provide a scientific guidance for the application of biofertilizer.

Phosphorus (P) is one of the essential macronutrients for plants, but agricultural soil generally lacks available P. This study aims to ascertain the impact of phosphatesolubilizing bacterial inoculation on the development of maize, soil characteristics, P fractions, and the microbial population in the soil. In this experiment, we explored the P solubilizing ability of P-solubilizing bacteria through liquid culture. In a maize pot experiment, soil P fractions and maize growth were examined, and a metagenomic sequence was constructed to analyze the soil microbial community and gene abundances and to link their relationship. In the shaking flask culture experiment, it was found that the Burkholderia (XQP35) and Raoultella (SQP80) have a strong capability for calcium phosphate and calcium phytate. Compared with the blank control, the XQP35 and SQP80 treatments could improve maize biomass and the soil nutrient status. Moreover, SQP80 treatments increased the soil acid phosphatase activity. SQP80 inoculation dramatically decreased the variety of the soil microbial community and the abundance of Acidobacteria. We found that the different treatments had no significant effect on the number of genes but that the SQP80 treatments significantly increased the P-cycling pathway gene family phoA and phoD compared with the CK treatment. Our results demonstrated that inoculation with XQP35 and SQP80 could dissolve varieties of insoluble P and, together with functional pathways of P-cycling, promote the transformation of P fractions and ultimately increase soil

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