科研之友
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摘要
Drying-rewetting and freezing-thawing can drastically alter P availability in soil. We studied how these weather events affect microbial immobilisation/mobilisation of P on the four soil types from a climatic gradient with increasing annual mean temperatures and a progressive decrease in precipitation: Podzol, Phaeozem, Chernozem and Kastanozem. Soils were exposed to (1) optimal moisture and temperature, (2) drying-rewetting and (3) freezing-thawing. Soils were treated with a P-33 spike immediately after rewetting or thawing to simulate P pulse. Thereafter, P immobilisation by soil microorganisms was estimated by direct fumigation and anion exchange membrane techniques. To ensure correct estimation of microbial P (P-mic), the conversion factors k(P) were determined individually for each soil by P-33 labelling with the correction for P-33 sorption and P-31-P-33 isotopic exchange. The membrane extraction minimised both sorption and isotopic exchange of P released with both sorption and isotopic exchange coefficients close to 0.9 irrespectively of the soil. Specific k(P) varied from 0.19 to 0.38. P-mic values followed the pattern freezing-thawing < drying-rewetting < optimal conditions, varying from 2.0 to 36.6 mg P kg(-1). Intensive microbial immobilisation of P-33 after rewetting (up to 41 %) demonstrated a conversion of dissolved P to P-mic potentially available for plant nutrition. Remarkably, no detectable microbial immobilisation of P-33 was found in the freezing-thawing treatment. In contrast to drying, freezing decreased total P-mic by up to 7.5 times. Values of membrane-extractable P-33 increased in the order drying-rewetting < control < freezing-thawing, and up to 77 % of added P-33 was recovered in dissolved P forms after thawing, indicating the potential risk of P leaching after freezing-thawing events.
- 出版日期2016-7
