Phylogenetic Underpinning of Groundwater Use by Trees

Root water uptake (RWU) strategies shape climate-vegetation feedbacks and ecosystem productivity. A fundamental relationship between RWU strategies and evolutionary histories (phylogeny) of trees, however, remains poorly understood. Establishing a phylogenetic basis for tree RWU, particularly groundwater use, could improve their representation in terrestrial biosphere models (TBMs) that are crucial for understanding hydrologic and ecosystem responses to climate perturbations. We explored possible phylogenetic bases for tree RWU using two independent data sets: (a) observed root and local groundwater depths representing 502 tree species, and (b) groundwater, soil, and xylem water isotopic evidence for groundwater uptake representing 412 species. Maximum rooting depths (RDMAX), the ratio between RDMAX and mean water table depth (WT) (RDMAX/WT), and isotopic evidence of groundwater uptake showed significant phylogenetic signals, suggesting that tree RWU strategies are more similar among closely related species. Our findings may be used to parameterize species-level RWU in TBMs, particularly for data-poor regions.