The diversity of mechanisms responsible for interactions between the (vegetated) land and the atmosphere range from the size of the stomata (10 – 100μm) to the size of the atmospheric boundary layer (~1 km). This includes temporal dynamics on time scales of minutes (passing clouds and plant responses), days (diurnal solar cycle) and seasons (seasonal solar cycle and vegetation dynamics) (TABLE).
Clouds as well as atmospheric-boundary layer dynamics disturb radiation and turbulence conditions in and above the vegetation canopy and, subsequently, the energy and moisture fluxes that affect clouds. Although these effects occur at short spatiotemporal scales, they have profound impacts on the regional and global CO2 budget. CloudRoots aims to advance current understanding of land-atmosphere dynamics. Therefore, it is essential to investigate, using first-principles, the cross-scale interactions between the relevant processes in an integrated observation – simulation system.
At the leaf level, CloudRoots will observe and attempt to mechanistically represent the exchange of carbon dioxide and water vapor through the stomatal aperture. One crucial aspect of this exchange is to understand to what degree plant stomatal control depends on the partitioning of direct and diffuse radiation perturbed by clouds (cloud flecks). We also need to understand to what extent the penetration of radiation into the canopy as well as temperature and vapor pressure deficit control photosynthesis. Photosynthesis and stomatal aperture are described by the leaf mechanistic model A-gs (A for photosynthesis and gs for the conductivity at leaf level, see figure below). This representation also includes the exchange of the light and heavy stable isotopologues of CO2 and H2O (CHEMISTRY). A-gs is used in the atmospheric models DALES and CLASS (see MODELLING). Soil evaporation and carbon dioxide respiration fluxes are represented by models that link soil properties to the in-canopy atmosphere. All these representations are supported by eco-physiological measurements (see ECOPHYS).
The CloudRoots representation of leaf, soil and cloud droplet CO2 and H2O exchanges