Soil plant atmosphere continuum concepts used in vadose zone hydrology approach plants as physical entities. This approach has proven very valuable in the past decades. The need to upscale such concepts provokes the question if plant functional biology should be considered, as larger scales also imply variation in (micro)climate and soil composition. Habitat manifestation is an expression of its evolutionary history and although the spatial distribution of habitats is largely driven by current climates, a soil's water holding capacity and hence its formation over time may have played a role. Separate mechanisms involved in the soil plant atmosphere continuum are often understood and incorporated in numerical models for predictive purposes, yet interrelationships pose challenges, especially when such relationships cross traditional scientific disciplinary boundaries. In fact, the exact driver for root water uptake is itself subject of scientific debate, as there is no consensus on whether the driver for root water uptake is soil moisture content (e.g. ) or soil water potential (e.g. ). To evaluate soil water availability in relation to crop yield prognoses and the stability of natural vegetation, integrated concepts are sorely needed, especially in the perspective of climate change  and global water scarcity . We present considerations and possible approaches for linking plant functional biology and vadose zone processes.