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 dynam-ics 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%,respec-tively.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.