Abstract
Background and AimsDiurnal changes in solar position and intensity combined with the structural complexity of plant architecture result in highly variable and dynamic light patterns within the plant canopy. This affects productivity through the complex ways that photosynthesis responds to changes in light intensity. Current methods to characterize light dynamics, such as ray-tracing, are able to produce data with excellent spatio-temporal resolution but are computationally intensive and the resulting data are complex and high-dimensional. This necessitates development of more economical models for summarizing the data and for simulating realistic light patterns over the course of a day.MethodsHigh-resolution reconstructions of field-grown plants are assembled in various configurations to form canopies, and a forward ray-tracing algorithm is applied to the canopies to compute light dynamics at high (1 min) temporal resolution. From the ray-tracer output, the sunlit or shaded state for each patch on the plants is determined, and these data are used to develop a novel stochastic model for the sunlit–shaded patterns. The model is designed to be straightforward to fit to data using maximum likelihood estimation, and fast to simulate from.Key ResultsFor a wide range of contrasting 3-D canopies, the stochastic model is able to summarize, and replicate in simulations, key features of the light dynamics. When light patterns simulated from the stochastic model are used as input to a model of photoinhibition, the predicted reduction in carbon gain is similar to that from calculations based on the (extremely costly) ray-tracer data.ConclusionsThe model provides a way to summarize highly complex data in a small number of parameters, and a cost-effective way to simulate realistic light patterns. Simulations from the model will be particularly useful for feeding into larger-scale photosynthesis models for calculating how light dynamics affects the photosynthetic productivity of canopies.
Highlights
Plant canopies are complex three-dimensional (3-D) structures in which the light distribution is complicated and dynamic, for example due to solar movement
Simulations from the model will be useful for feeding into larger-scale photosynthesis models for calculating how light dynamics affects the photosynthetic productivity of canopies
We have used ray-tracing to compute the light dynamics in complex canopies and developed a novel model to characterize the dynamics
Summary
Plant canopies are complex three-dimensional (3-D) structures in which the light distribution is complicated and dynamic, for example due to solar movement. We construct several different realistic digital canopies and use a ray-tracer to identify the times of switching between sunlit and shaded states at positions throughout the canopies. We present (1) the model definition; (2) how the model can be fitted to experimental data; and (3) how the fitted model can be simulated to generate realistic light patterns In this initial model, we limit attention to a single patch and consider how its rate of switching from sunlit to shaded, or vice versa, changes with time, t, in a time interval of interest, (0,T). The main contribution of this paper is to extend Model 1 in two ways: (1) to incorporate distinct rate functions, λon(t) and λoff(t), for switching ‘on’ (from shaded to sunlit) and ‘off’ (from sunlit to shaded), respectively; and (2) to describe multiple patches, with the rate functions for different patches depending on the normalized height, h, within the canopy (in addition to time, t, as in Model 1). Photoinhibition is a light-dependent decline in the maximal quantum yield of photosynthesis and can lead to a lowering of photosynthesis and potential growth
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