Root distribution of three dominant desert shrubs and their water uptake dynamics

Aims Root architecture is a crucial determinant in the water use of desert shrubs. However, lack of integrated research on the root functional type and water uptake dynamic hinders our current understanding of the water-use strategies of desert species. Methods A field experiment was conducted to investigate the root functional type of three dominant desert species, Haloxylon ammodendron, Nitraria tangutorum and Calligonum mongolicum, and the dynamics of their root water uptake. The stem sap flow and microclimate were monitored, and the intact root systems of these shrubs were excavated in their native habitats on the oasis-desert ecotone of northwestern China during the summer of 2014. Important Findings Based on root functional type, H. ammodendron is phreatophytic, while N. tangutorum and C. mongolicum are non-phreatophytic species, which means H. ammodendron can utilize multiple potential water sources, N. tangutorum and C. mongolicum mainly utilize shallow and middle soil water. The average root water uptake rates (RWU) of H. ammodendron, N. tangutorum and C. mongolicum were 0.56 (+/- 0.12), 1.18 (+/- 0.19) and 1.31 (+/- 0.30) kg m(-2) h(-1), respectively, during the experimental period; the contributions of night-time RWU to total water uptake amount for the corresponding species were 12.7, 2.9 and 10.6%, respectively. The diurnal and seasonal dynamics of RWU in the three species were significantly different (P < 0.05), and closely related to environmental variables, especially to photosynthetically active radiation and vapor pressure deficit. Our results suggested that the three species have distinct water-use patterns in combination with the patterns of root distribution, which may alleviate water competition during long-term water shortages. H. ammodendron appears to be more drought tolerant than the other species due to its use of multiple water sources and stable water uptake rates during growing season.