Organic management improves soil phosphorus availability and microbial properties in a tea plantation after land conversion from longan ( Dimocarpus longan )

Studies on the transformation of P fractions under different land uses and management practices remain scarce, especially in tropical regions. Hence, we investigated the P fraction, microbial communities and soil chemical properties after the conversion of a longan orchard (LO) into an organic tea plantation (OTP) and a conventional tea plantation (CTP) in Hainan, China. At 010 cm and 1020 cm soil depths, the conversion of the LO into the OTP increased the contents of labile P (Resin-P, NaHCO3-P-i and NaHCO3-P-o), moderately labile P (NaOH-P-i and NaOH-P-o) and occluded P (Sonicate-P-i and Sonicate-P-o) but decreased the contents of Ca-P (HCl-P-i) and residual P (stable P), whereas converting the LO into the CTP increased the Ca-P and residual P but decreased the labile P, moderately labile P and occluded P. In addition, at the 010 cm soil depth, the bacteria, fungi, actinomycetes, arbuscular mycorrhizal fungal (AMF) and total phospholipid fatty acid (PLFA) biomass were decreased in the CTP, but only the total PLFA was increased in the OTP. However, at the 1020 cm soil depth, the total PLFA, fungi, and AMF were increased in the OTP, whereas all the PLFA biomarkers remained unchanged in the CTP compared to those in the LO. Furthermore, the labile P, moderately labile P, occluded P and Ca-P in the 010 cm layer were related to the soil chemical properties and microbially related groups such as the TK, NO3-, NH4+, acid phosphatase activity (APA), fungi, AMF and bacteria. However, at the 1020 cm soil depth, these fractions were only associated with soil chemical properties such as the TK, NO3-, NH4+ and APA. Our results revealed that the land use altered the soil P fractions as well as the microbial biomass and activity related to soil P cycling, and organic management practices enhanced the soil P availability more than conventional management practices.