Leaching of Colloidal Phosphorus from Organic Layers and Mineral Topsoils of German Beech Forests in Response to Drought and Nutrient Inputs

Abstract

Purpose The purpose of the study was to clarify the relevance of colloidal phosphorus (P coll ) to total P (TP) leaching and its link to dissolved organic P (DOP) leaching in forest topsoils under field conditions. Effects of heavy rainfall after a drought and the influence of P and N inputs to forest soils on P coll leaching from the topsoil were assessed to better understand the causes of P coll leaching. Methods We carried out an irrigation experiment with zero-tension lysimeters collecting leachate from the organic forest floor layers and mineral topsoils of a sandy, low-P and a loamy, high-P soil. Results The contribution of P coll to TP concentrations was on average around 10±14% irrespective of sampling date, season and soil. The highest P coll concentrations were recorded upon irrigation after a summer dry period with the increase in concentrations being most pronounced for the 20–70 nm size fraction with low median C:P ratios (29 to 31) typical for microbial residues. Significant relationships between P coll and DOP concentrations suggested that 27% (low P soil) and 17% (high P soil) of DOP were of colloidal nature. Independent of the soil P stock, the addition of P and P + N affected neither P coll concentrations nor their share of TP significantly. Conclusion While P coll hardly affected the overall estimates of beech forest P budgets, it provides important further insights into processes governing the mobilization, transport, and cycling of P in forest ecosystems.

Bibliographic Information