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.

Shifting from homogeneous to heterogeneous surfaces in estimating terrestrial evapotranspiration: Review and perspectives

Terrestrial evapotranspiration(ET)is a crucial link between Earth’s water cycle and the surface energy budget.Accurate measurement and estimation remain a major challenge in geophysical,biological,and environmental studies.Pioneering work,represented by Dalton and Penman,and the development of theories and experiments on turbulent exchange in the atmospheric boundary layer(ABL),laid the foundation for mainstream methodologies in ET estimation.Since the 1990s,eddy covariance(EC)systems and satellite remote sensing have been widely applied from cold to tropical and from arid to humid regions.They cover water surfaces,wetlands,forests,croplands,grasslands,barelands,and urban areas,offering an exceptional number of reports on diverse ET processes.Surface nocturnal ET,hysteresis between ET and environmental forces,turbulence intermittency,island effects on heterogeneous surfaces,and phase transition between underlying surfaces are examples of reported new phenomena,posing theoretical and practical challenges to mainstream ET methodologies.Additionally,based on non-conventional theories,new methods have emerged,such as maximum entropy production and nonparametric approaches.Furthermore,high-frequency on-site observation and aerospace remote sensing technology in combination form multi-scale observations across plant stomata,leaves,plants,canopies,landscapes,and basins.This promotes an insightful understanding of diverse ET processes and synthesizes the common mechanisms of the processes between and across spatial and temporal scales.All the recent achievements in conception,model,and technology serve as the basis for breaking through the known difficulties in ET estimation.We expect that they will provide a rigorous,reliable scientific basis and experimental support to address theoretical arguments of global significance,such as the water-heat-carbon cycle,and solve practical needs of national importance,including agricultural irrigation and food security,precise management of water resources and eco-environmental protection,and regulation of the urban thermal environment and climate change adaptation.