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Faculty for Biology, Chemistry and Earth Sciences

Department Soil Ecology - Prof. Dr. Eva Lehndorff

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Dinh, MV; Guhr, A; Weig, A R; Matzner, E: Drying and rewetting of forest floors: Dynamics of soluble phosphorus, microbial biomass-phosphorus and microbial communities, Biology and Fertility of soils, 54(761-768) (2018), doi:10.1007/s00374-018-1300-y
Previous work has shown that drying and rewetting (D/W) of soils leads to a pulse of water soluble P which is partly based on the lysis of sensitive soil microorganisms. The effect of D/W on the P availability for root uptake depends on the duration of the P release. Hence, our goal was to investigate the dynamics of water soluble P, the microbial P pool (Pmic) and the microbial community after rewetting of desiccated forest floor layers. Samples were taken from Oi and Oe layers of a European beech and a Norway spruce site. After a pre-incubation, soils were desiccated up to -100 MPa (pF 6) at 20°C in the laboratory, while the controls were kept permanently at 50% of the water holding capacity (WHC). The D/W samples were then rewetted and maintained at 50% WHC throughout. Water-soluble P and Pmic were measured at different times after rewetting up to 14 days and the microbial community composition was analyzed by an automated ribosomal intergenic spacer analysis (ARISA) 14 days after rewetting.

After rewetting, the largest net release (D/W-control) of total dissolved P (TDP) was from beech and spruce Oe layers, amounting to 40-50 mg P kg -135 . The lowest net release of TDP was from beech Oi layers (12 mg P kg-136 ). Dissolved inorganic P was the dominant fraction of TDP. The TDP concentrations decreased strongly in the Oi layers within one (beech) to four (spruce) days, while the TDP concentrations remained rather stable in both Oe layers for 14 days. The release of TDP and its dynamic was linked to the decrease of Pmic after desiccation and its recovery after rewetting. The decline of Pmic after D/W and its recovery differed between Oi and Oe layers and tree species, suggesting the influence of different soil microbial communities. Correspondingly, microbial communities varied strongly among sites and forest floor layers, while D/W only affected the community in the spruce Oe layer. Our results suggest that D/W of forest floors increases the plant available P and affects the P cycle in forest ecosystems.

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