Canopy Light Signals and Crop Yield in Sickness and in Health

Figure 3

Canopy architecture affects multiple aspects of the environment experienced by the shoot, which in turn impact on multiple aspects of plant physiology. Environmental features are shown in blue, and plant processes are shown in green. Arrowheads indicate the direction of the effect. The model represents a simplification of the real world. Canopy architecture affects the sunlight radiation and wind impact received by each plant (1); these features of the environment in turn affect tissue temperature (2). The radiation environment involves three functional categories: the light signals (perceived by sensory receptors), PAR, and damaging UV-B (3). These categories overlap in terms of spectral wavebands (e.g., some wavebands are active both photosynthetically and as a signal). Light signals control plant form (photo-morphogenesis), the status of defences against pathogens and herbivores, and stomatal aperture, which modulates the rates of carbon and water vapour exchange (photosynthesis, respiration) (4). Photosynthesis and transpiration are also affected by photomorphogenesis (e.g., via changes in in stomatal density) (5). The altered photomorphogenesis also modifies canopy architecture (e.g., by changes in stem height, leaf position, etc.) (5). Both PAR (as the source of energy) (6) and UV-B (via its damaging effect) (7) affect photosynthesis, which also depends on temperature (8). Temperature (9), wind impact (10), and photosynthesis (via effects on carbon dioxide concentration and stomatal conductance) (11) affect transpiration rates.