A model for photosynthetically active radiation penetration in cotton canopies.

摘要

This study was undertaken to develop a model for photosynthetically active radiation (PAR) distribution within row-planted cotton canopies. Five cultivars, varying in leaf shape, are included in the study: G. hirsutum, cv. DP-50 and Sub-Okra; G. barbadense, cv. PLAN, PS-6 and Okra.; The model is based on the existing formulation of photon transport models within plant canopies and uses information generated by a geometrical model of the cotton canopy architecture. The geometrical model uses tensor product interpolants to generate leaf surfaces from photogrammetrically measured points. Leaf normals at each of the generated points are also calculated. Then, the model distributes those leaves in a canopy, according to statistical distributions of leaves positions (also extracted using photogrammetry). Once that the geometry of the canopy is defined, a radiative transfer model is used to estimate the distribution of photon flux density (PFD) within the foliage. Those estimations are compared to measured PFD data. Finally, the model is coupled with an existing photosynthesis model to theoretically explore optimal plant architectures in terms of canopy photosynthesis.; Model-estimated photosynthetic rates showed that DP50 is the most efficient cotton cultivar. The model also suggests that this efficiency seems to result from the high number of small-to-medium-sized leaves that this plant produces during all the growing season, at mid and low-canopy heights.; The optimization process suggests that a cotton plant that distributes its leaves similarly to the DP50 plant, being those leaves shaped like small-to-medium PS6 leaves, may increase its crop photosynthetic rates by 10%.