Phosphorus sorption by freeze–thaw treated wetland soils derived from a winter-cold zone (Sanjiang Plain, Northeast China)

Little attention has been given to the influence of freezing on P cycling in wetlands. The purpose of this study was to explore the effects of freeze–thaw treatments on the P sorption properties of wetland soils, and to determine possible further impact on P retention in wetland soils. In laboratory incubations, six surface soils with varying amounts of P added (0–320 mg P L− 1), was continuously frozen at − 15 °C for 13 h, and then thawed at + 5, + 15 and + 25 °C for 10 h, finally refrozen and thawed again for 6 cycles. The freezing effects were quantified by comparisons with control samples. The results demonstrated that freeze–thaw of wetland soils can significantly increase sorption of P at a certain temperature range (5–15 °C), consequently, the wetland soils will have much more buffering capacity after freeze–thaw cycles. The P sorption maximum for the six soils were 1770–2577, 1847–2533, and 2093–2810 mg kg− 1 for + 5 °C to + 15 °C and + 25 °C, respectively. In addition, P sorption maximum of the controls were 1550–2427, 1736–2463, and 1724–2757 mg kg− 1, respectively. The effects of freeze–thaw cycles on P appear to be more pronounced in soils containing a lot of organic matter or clay.