Spatiotemporal variability of leaf photosynthesis and its linkage with microclimates across an environment-controlled greenhouse

Environmental controls in a greenhouse improve microclimates, thereby enhancing photosynthesis, but they create spatiotemporal non-uniformity of photosynthesis, with implications for unstable crop production. However, there has been no research focussing on the spatiotemporal variability of photosynthesis arising from greenhouse environmental controls. Here we visualise spatiotemporal distributions of leaf photosynthetic rate (A) and assess its linkages with microclimates [air temperature (T_a), water vapour concentration (W_a), CO₂ concentration (C_a), and leaf-boundary-layer conductance (g_a)] across a strawberry greenhouse during daytime under roof ventilation and CO₂ enrichment, using physical, physiological, and biochemical models for A and mobile observations of the microclimates. The distributions of A were variable during the daytime and were non-uniform across the greenhouse under the influence of the microclimate distributions arising from the environmental controls. In particular, with the roof ventilation, spatial variations of T_a and g_a were most associated with non-uniformity in A through the physical process of the energy budget determining the leaf temperature and thus affecting leaf physiological properties (photosynthetic capacities and stomatal conductance). With CO₂ enrichment, in addition to the roof ventilation, spatial variations of C_a further increased non-uniformity in A through large variations of Rubisco-limited and RuBP-limited rates in the biochemical process of leaf photosynthesis. Spatial non-uniformity of A arising from the environmental controls ranged from 15% to 69% during the daytime. These findings indicate the importance of considering the spatiotemporal variability of photosynthesis with respect to its physical, physiological, and biochemical processes, in addition to that due to microclimates, for optimising greenhouse environmental controls.