Drying and rewetting of forest floors: dynamics of soluble phosphorus,microbial biomass-phosphorus,and the composition of microbial communities

Drying and rewetting (D/W) of soils often leads to a pulse of total dissolved phosphorus (TDP) by lysis of sensitive microorganisms. The relevance of D/W on the P cycle in ecosystems depends on the duration of the TDP release. In forest soils, the forest floor represents a hotspot of microbial activity and is often prone to D/W. Here, we investigated the dynamics of TDP, the microbial P pool (Pmic), and the composition of microbial communities after D/W. Samples were taken from Oi and Oe layers of a European beech and a Norway spruce site and desiccated up to ??100 MPa (pF 6) at 20 °C, while controls were kept moist. TDP and Pmic were measured 0, 1, 3, 7, and 14 days after rewetting and the composition of microbial communities was analyzed by automated ribosomal intergenic spacer analysis after 14 days. After D/W, the largest TDP net release (D/W-control) was from Oe layers with 40–50 mg P kg^?1 and inorganic P as the dominant fraction. The TDP concentrations decreased strongly in Oi layers within 1 (beech) to 4 (spruce) days, while remaining stable in Oe layers. The TDP dynamics were linked to the decrease and recovery of Pmic after D/W. Pmic dynamics differed between layers and stand types, suggesting the influence of microbial communities with different D/W sensitivities. The composition of microbial communities varied strongly among sites and layers, while D/W only affected the composition of bacterial and fungal communities in the spruce Oe layer. D/W of forest floors increases the plant available P and affects the P cycle in forest ecosystems.