Original article Water extraction by tree fine roots in the forest floor of a temperate Fagus-Quercus forest

Abstract- Water retention and water turnover were investigated in the forest floor of a temperate mixed Fagus-Quercus forest on poor soil in NW Germany. By field and laboratory measurements the aim was to quantify the water extraction by those tree fine roots that concentrate in the super-ficial organic layers. The 8-10.5-cm-thick organic profiles stored up to 45 mm of water under Quercus trees but significantly smaller amounts under Fagus (and even less under Pinus trees in a nearby stand). The water retention capacity (i.e. the difference between saturating water con-tent after wetting and water content prior to wetting) and the resulting percolation rate out of the forest floor were measured by infiltration experiments in relation to their dependence on the initial water content of the humus material. The water retention characteristics of the humus material differed from the sandy mineral soil material by i) a much higher maximum water con-tent (porosity), ii) a higher storage capacity for water in the plant-available water potential range, and iii) a marked temporal variability of the water retention capacity. A one-dimensional water flux model for the forest floor of this stand has been developed. According to the model results