Field evidence reveals conservative water use of poplar saplings under high aerosol conditions

Abstract

Anthropogenic aerosols could alter multiple meteorological processes such as radiation regime and air temperature, thereby modifying plant transpiration. However, the lack of field observations at leaf and plant level hinders our ability to understand how aerosols could affect plant water use. Aerosol concentrations in northern China fluctuate periodically over a wide range. Taking advantage of this unique natural experiment opportunity, we conducted a series of physiological and environmental measurements at different times of the day to explore diurnal aerosols' effect on leaf transpiration and sap flow of planted poplar saplings (Populus × canadensis Moench). We found that high aerosol concentrations suppressed sun leaf transpiration by reducing leaf‐to‐air vapour pressure deficit (VPDleaf), while had no effect on shade leaf transpiration mainly because the negative effect of reduced VPDleaf on transpiration offset the positive effects of the increased stomatal conductance (gs). As aerosol concentration increased, the gs of both sun and shade leaves decreased more rapidly with an increase in VPDleaf, which caused their transpiration rates to become less sensitive to VPDleaf. Similarly, aerosols reduced sap flow density and its sensitivity to VPD. Synthesis. Our study provided observational evidence on aerosols' effects on plant transpiration at the leaf and canopy scales. The reduced transpiration and stronger stomatal control indicated that plant water use becomes more conservative under elevated aerosol concentrations.

Distinguishing the impacts of natural and anthropogenic aerosols on global gross primary productivity through diffuse fertilization effect

“…Surface temperature and relative humidity is altered in response to radiative changes caused by aerosols (Jing et al, 2010;Cirino et al, 2014). The increase of relative humidity can increase plant photosynthesis owing to the enhancement of water use efficiency (Lu et al, 2017;Wang et al, 2021), but the impacts of cooling on photosynthesis are dependent on whether local background temperature is over the optimal temperature (Farquhar et al, 1980). Moreover, the changes in cloud from aerosol indirect effects were not considered in this study.…”

Enhanced Ecosystem Water‐Use Efficiency Under the More Diffuse Radiation Conditions

“…Observations have shown different impacts of diffuse and direct radiation on plant biophysics following the unequal light sensitivities of sunlit and shaded leaves because the sunlit leaves are usually light saturated, while the shaded leaves are light limited, leading to their different light demand for plant physiological processes, such as photosynthesis and transpiration (Knohl & Baldocchi, 2008; Pedruzo‐Bagazgoitia et al., 2017; Steiner & Chameides, 2005). As a result, both the magnitude of incident solar radiation and its diffuse fraction can alter ecosystem gross primary production (GPP) and evapotranspiration (ET) (B. Wang et al., 2021; Yang et al., 2013; Zhou et al., 2021a). However, although previous works have extensively explored the diffuse radiation effect on GPP, only few have paid attention to its effect on ET and ecosystem water‐use efficiency (WUE) (Table S1).…”

Large Divergence of Satellite Monitoring of Diffuse Radiation Effect on Ecosystem Water‐Use Efficiency

“…Previous studies also demonstrated that the performance of BESS is better than that of MODIS in simulating WUE (Yang et al., 2020). This might be induced by that BESSv2 and PMLv2 products are simulated simultaneously from a carbon‐water‐coupled model, while MODIS and GLASS used two independent algorithms to estimate GPP and ET ((B. Wang et al., 2021; X. Wang et al., 2021). PMLv2 performed better than BESSv2 in simulating the diffuse radiation effects on WUE.…”