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Air-drying changes the distribution of Hedley phosphorus pools in forest soils

WANG, Jipeng, WU, Yanhong, ZHOU, Jun, BING, Haijian, SUN, Hongyang, LUO, Ji, PU, Shengyan
Pedosphere 2017
air drying, annuals, forest types, fractionation, microbial biomass, organic horizons, phosphorus, soil organic matter, solubility, China
Hedley-labile phosphorus (P) pools of soils tend to be several times larger than annual forest requirements, even in highly weathered soils featured by P limitation. We assume that the discrepancy between plant and soil P status is partly attributable to the frequently adopted air-drying pretreatment that tends to increase soil P solubility. In this study, the effects of air-drying on the distribution of Hedley P fractions were examined using soils collected under 4 forest types at Gongga Mountain, southwestern China. The results showed that the microbial biomass P (Pmic) in the organic horizon decreased markedly after air-drying. The concentrations of Hedley-labile P in the air-dried samples increased by 31-73% compared with those in the field-moist samples. Consequently, the air-drying induced increments of Hedley-labile P pools in the surface soil horizons were 0.8-3.8 times the annual plant P requirements. Probably due to the stronger release of the Pmic and disruption of soil organic matter, the organic horizon was more susceptible to the air-drying induced increases in Hedley-labile P than the mineral horizon. The quality of P, indexed by the ratio of Hedley-labile P to slowly cycling P, shifted in favor of the Hedley-labile fractions after air-drying, further revealing that air-drying changed the distribution of Hedley P pools in forest soils. The data from this study indicated that the air-drying effects could not be ignored to interpret the discrepancy between the P status of plants and the Hedley-labile P pools in forest soils. To better evaluate the P status in forest soils by the Hedley fractionation procedure, the use of field-moist soils is recommended.