Although root water uptake is an important component in the plant-soil-water relation for single plants and on ecosystem scale, studies investigating the effect of co-existing plant species on community water use have been conducted without estimating root water uptake profiles. However, knowledge of root water uptake is essential for understanding of intra- and interspecific interactions of plants. For those reasons, minimal-invasive and easy to use methods for estimating root water uptake are inevitable. Within this dissertation, an attempt has been made to identify a simple but sufficient accurate method for estimating evapotranspiration and root water uptake profiles from soil water content measurements without a priori information on root distribution parameters. Subsequently, this method was applied to investigate the effect of co-existing plant species on community root water uptake. First, four different complex water balance methods were evaluated regarding their applicability on the ecohydrological issue. Therefore, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. In the second part, an additional accuracy assessment considering magnitudes of evapotranspiration, soil texture variability, and sensor uncertainty was carried out on 12 weighable lysimeters. Third, we investigated the effect of co-existing plant species on the community root water uptake. Analysis of estimated root water uptake profiles were combined with measurements of leaf water potentials and stomatal conductance, which constitutes the novelty of this thesis. The results indicate that the investigated communities with higher species richness are able to adjust their root water uptake strategy in a way that the water use of the entire community is optimized.