Multi-scale evapotranspiration of summer maize and the controlling meteorological factors in north China

Evapotranspiration (ET) scale effect influences the understanding of water and energy balance processes at different scales. However, there are fewer studies about the relationships between multi-scale ET and the controlling meteorological factors. In this study, the variations in leaf and plant transpiration and farmland ET of summer maize were systematically analyzed using three-successive-year data from an irrigation experiment station in north China, and the meteorological factors affecting ET at different scales were analyzed based on multivariate regression. The main findings include (1) the transpiration rate (Tr) and stomatal conductance (gs) of sun and shade leaves reduced with the reduction of photosynthetically active radiation (PAR), and the Tr and gs in shade leaves were about half of sun leaves. When the differences in PAR were smaller, leaf Tr and gs at lower part of canopy were slightly lower than those at middle and upper parts of canopy. (2) The sap flow rate (plant transpiration) of summer maize was related to the net radiation but lagged 1 h. (3) Diurnal variation in latent heat flux (λET) of summer maize was similar to that in net radiation but lagged slightly. λET, sensible heat flux and ground heat flux accounted for 66.9-70.7, 23.4-26.1 and 4.0-9.2% of net radiation over the whole growing period, respectively. The Bowen ratio ranged from 0.33 to 0.37 over the whole growing period, and peaked at around 10:00 a.m. (4) Leaf transpiration and farmland ET can be characterized by net radiation, air temperature, vapor pressure deficit and wind speed, but plant transpiration cannot be well characterized by them, possibly due to the change of stored water in the stalk.