PHOTOSYNTHESIS AND TRANSPIRATION RESPONSE OF REDROOT PIGWEED (AMARANTHUS-RETROFLEXUS)

Redroot pigweed is a major weed worldwide. Increasing emphasis on modeling physiological processes of weeds for use in weed control decision support systems requires a knowledge of the response of weeds to resource levels and environmental conditions. The purpose of this study was to determine functional relationships for carbon exchange rate (CER) and transpiration based on photosynthetic photon flux density (PPFD) and temperature from measurements made on field-grown redroot pigweed. Measurements were made using a portable photosynthesis system on four dates. An equation that had the form of a power function on PPFD and a quadratic polynomial on temperature was fit to the data. The equation fit the measured CER data better than the measured transpiration data. The equations should be useful in modeling the physiological processes of pigweed within crop canopies.