Root water uptake by plants is a vital process that influences terrestrial energy, water, and carbon exchanges. At the soil, vegetation, and atmosphere interfaces, root water uptake and solar radiation predominantly regulate the dynamics and health of vegetation growth, which can be remotely monitored by satellites, using the soil–plant relationship proxy – solar-induced chlorophyll fluorescence. However, most current canopy photosynthesis and fluorescence models do not account for root water uptake, which compromises their applications under water-stressed conditions. To address this limitation, this study integrated photosynthesis, fluorescence emission, and transfer of energy, mass, and momentum in the soil–plant–atmosphere continuum system, via a simplified 1D root growth model and a resistance scheme linking soil, roots, leaves, and the atmosphere. The coupled model was evaluated with field measurements of maize and grass canopies. The results indicated that the simulation of land surface fluxes was significantly improved by the coupled model, especially when the canopy experienced moderate water stress. This finding highlights the importance of enhanced soil heat and moisture transfer, as well as dynamic root growth, on simulating ecosystem functioning.

This study investigates the capability of spectral indices for estimating winter wheat leaf and canopy water content using radiative transfer modeling and field measurements. An irrigation treatment experiment was conducted to investigate response of crop growth to water supply in 2014 and 2015. Plant sampling and canopy spectral reflectance were measured in the two growing seasons. The main goal was to evaluate the potential of selected spectral indices formulated with the Sentinel-2 bands for winter wheat water status assessment. A global sensitivity analysis using reflectance simulated by the PROSPECT-5 and SAILH models showed that leaf water contributed the most to the variation of spectral water indices derived from leaf reflectance but had reduced contribution when the indices were derived from canopy reflectance. Correlation between canopy water content (C _{w, C} ) and canopy spectral water indices was significant, although it was impacted by canopy structural descriptors such as the leaf inclination angle and the leaf area index. Satisfactory estimation of w, C could be achieved using the normalized difference water index (NDWI) (R ² = 0.68, RMSE _cv = 0.148 kg·m ^-2 , and n = 463). The estimated C _{w, C} at the jointing stage was significantly correlated with grain yield. A map of C _{w, C} was generated from Sentinel-2 image acquired on March 30, 2016, showing spatial variation of winter wheat canopy water status comparable with the drought indicators reported by the Meteorological Bureau at the regional scale. It also showed variations at the field scale. Hence, there is a great potential to use the NDWI derived from Sentinel-2 data for detecting crop response to water stress and provide support to irrigation decision.