Response of phosphorus distribution to burn frequency and seasonality in the Sanjiang Plain wetlands (Northeast China)

Abstract

Fire is an important disturbance of wetland P reservoirs by changing the distribution of P in soils and plants. However, the effects of various fire regimes on the distribution of P in wetlands are not known. In a three-year burn experiment, we evaluated the effects of three burn factors on the P distribution of plants (stem, leaf, and litter) and soils (upper and lowerlayer soil) in the freshwater wetlands of China's Sanjiang Plain. We discovered that when burn frequency increased, soil P content and total plant biomass P also increased. Soil P content peaked at a high of 2198.0 ± 559.0 mg kg−1 after three burns. Three burns increased C. angustifolia biomass and therefore increased total plant biomass P. However, the increase in time after burning caused stem and leaf P content and litter necromass density P to decrease, suggesting a steady transfer of plant P to the soil. Furthermore, the stem biomass P density in September after the three burns was higher in spring burns than in autumn burns (1231.0 ± 129.0 mg m−2 after spring burns compared to 542.0 ± 176.0 mg m−2 after autumn burns). The transfer of litter P to the soil was hindered by spring burns, which conserved more P in the litter than autumn burns, which was the opposite of what was found for litter necromass P. Compared to spring burns, frequent autumn burns will hasten the transfer of plant P to the soil, preserving more P in the soil. Thus, conducting once-a-year prescribed burning in the autumn will be an important tool for improving P cycling in freshwater wetlands compared to spring.