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Dynamics of available and enzymatically hydrolysable soil phosphorus fractions during repeated freeze-thaw cycles

Sun, Dasheng, Yang, Xinbing, Wang, Chunling, Hao, Xianjun, Hong, Jianping, Lin, Xianyong
Geoderma 2019 v.345 pp. 1-4
freeze-thaw cycles, inorganic phosphorus, organic matter, soil types
Freeze-thaw cycles strongly affect the transformation of soil phosphorus (P) and shape the composition of P pools. This study aimed to investigate the effects of successive freeze-thaw cycles on the transformation of soil labile P and enzymatically hydrolysable organic P (Po) fractions. Accordingly, five physico-chemically distinct soils were subjected to two, five, and ten freeze-thaw cycles, with each cycle including incubation at −10 °C (freeze) for 12 h and 5 °C (thaw) for 12 h. Control soils were maintained at 5 °C, and the bicarbonate-extractable P and hydrolysable Po fractions were analysed at the end of the incubation period (10 d). Freeze-thaw cycles increased the levels of bicarbonate-extractable inorganic P, bicarbonate-extractable Po, labile monoester P, and phytate-like P, but had no effect on the diester P and unknown Po contents. The interaction between soil type and freeze-thaw cycles significantly affected the NaHCO3-extractable Pi, and phytate-like P fractions, but did not affect the bicarbonate-extractable Po, and labile monoester P fractions. The extent of increase in NaHCO3-extractable Pi largely depended on the amount of organic matter in the soil. In most cases, bicarbonate-extractable P and hydrolysable Po fractions reached their maximum levels after two freeze-thaw cycles and declined or remained constant thereafter. Our results suggest that freeze-thaw cycles exacerbated the transformation of soil labile P fractions, including enzymatically hydrolysable Po species, especially in the earlier stages.