Spatial distribution of phosphorus in marsh soils of a typical land/inland water ecotone along a hydrological gradient

Profile samples from 0 to 70 cm depth were collected in five plant zones along a hydrological gradient in a typical land/inland water ecotone, Northeast China. Total phosphorous (TP), organic phosphorous (OP), inorganic phosphorous (IP) and available phosphorous (AP) were measured to study their horizontal and vertical distribution patterns in the land/inland water ecotone, as well as their important influencing factors such as soil organic carbon (SOC) and water level. Our results demonstrated that the levels of TP, OP, IP and AP were generally higher in the flooding zone (zone A), the over-wetted zone (zone B) and the drying and wetting zone (zone C), but the drying zones (zones D and E) contained lower P concentrations. Soil P was mainly concentrated in upper soils (0–30 cm) and the P levels decreased with depth, except for small accumulative peaks in the 50 to 70 cm soil increment for TP and OP in zone C and for IP and AP in zone A. Surface soils in zones D and E had a lower mean SOC:OP ratio than zones A, B and C, reflecting the higher probability of OP mineralization in the drying zones. However, higher mean values of the IP:OP and AP:TP ratios were found in zone A (P < 0.05), indicating that increasing soil moisture may be the most important agent determining IP release rate and biological availability. The significantly positive correlations with soil organic matter (SOM) and clay content would contribute to P retention in zones A, B and C (P < 0.01) where the soils contained relatively high organic matter and clay content. The results obtained in this study suggest that the distributions and dynamics of P forms in soil, especially in the land/inland water ecotone, can be significantly impacted by various biogeochemical and environmental factors (i.e., soil moisture, SOM, and clay content).

► The drying zones contain lower soil P levles compared to the wetting zones.
► Soil P mainly concentrates in the top 30cm soils and decreased with depth.
► Soils of the flooding zone shows higher mean values of the IP:OP and AP:TP ratios.
► SOM and clay content can contribute to P retention in zones A, B and C.
► The relative altitude and distance related to water tables can influence IP levels.