Spatial and temporal distribution of leaf photosynthesis in a sweet pepper-stand (Capsicum annuum L.)

Modelling of biomass production and yield requires the quantification of canopy photosynthesis that results from the photosynthesis of single leaves. To investigate the distribution of leaf photosynthesis in a greenhouse sweet pepper canopy (Capsicum annuum L. cv. Mazurka), measurements were carried out on single leaves at different heights during the growing period from the end of April to the end of September. The gas exchange of eight unshaded and eight shaded plants was measured using the LCA-4 gas exchange measuring system (ADC, UK). At approximately one week intervals, measurements were taken 20 to 25 cm above ground, at a height of half the plants' height, and on the top of the plants. The reduction in irradiance by shading was 36%. Gas exchange data were evaluated by analysis of covariance to compare the results under the same conditions (irradiance, temperature, vapour pressure deficit and day of measurement). There were no differences in CO2 gas exchange between unshaded and shaded plants, although a significant height influence was observed. The CO2 gas exchange of the upper leaves (for mean conditions) was highest at about 10 mg CO2 dm(-2) h(-1). In the middle and lowest leaf positions, the CO2 gas exchange was nearly 2 mg CO2 dm(-2) h(-1) lower than the upper leaves. The time course for CO2 gas exchange in the measuring period was not significant. The CO2 gas exchange of the canopy dependence on irradiance, derived from single measurements, agrees largely with calculations on the basis of CO2 gas exchange models, previously reported for single plants and plant canopies within greenhouses.