Growth Response of a Chrysanthemum Crop to the Environment. III, Effects of Radiation and Temperature on Dry Matter Partitioning and Photosynthesis

Abstract

Vegetative crops of chrysanthemum were grown for 5 or 6 week periods in daylit assimilation chambers. Crop responses to different radiation levels and temperatures were analysed into effects on dry matter partitioning, specific leaf area, leaf photosynthesis and canopy light interception. The percentage of newly formed dry matter partitioned to the leaves was almost constant, although with increasing radiation or decreasing temperature, a greater percentage of dry matter was partitioned to stem tissue at the expense of root tissue. There was a positive correlation between the percentage of dry matter in shoot material and the overall carbon: dry matter ratio. Canopy photosynthesis was analysed assuming identical behaviour for all leaves in the crop. Leaf photochemical efficiency was only slightly affected by crop environment. The rate of gross photosynthesis per unit leaf area at light saturation, P_A (max), increased with increasing radiation integral, but the same parameter expressed per unit leaf dry matter, P_w (max) was almost unaffected by growth radiation. In contrast, P_A (max) was hardly affected by temperature but P_w (max) increased with increasing growth temperature. This was because specific leaf area decreased with decreasing temperature and increased with decreasing radiation. There was a positive correlation between canopy respiration integral and photosynthesis integral, and despite a four-fold change in crop mass during the experiments, the maintenance component of canopy respiration remained small and constant. Canopy extinction coefficient showed no consistent variation with radiation integral but was negatively correlated with temperature. This decrease in the efficiency of the canopy at intercepting radiation exactly cancelled the increase in specific carbon assimilation rate that occurred with increasing growth temperature, giving a growth rate depending solely on the incident light level.