Published online by Cambridge University Press: 12 June 2017
At early stages of canopy development net carbon exchange (NCE) values for redroot pigweed (Amaranthus retroflexus L.), prickly sida (Sida spinosa L.), and birdsfoot trefoil (Lotus corniculatus L.) were determined in an air-sealed leaf chamber. Regardless of light intensity, temperature, CO2 concentration, or competition level, redroot pigweed had a NCE at least 10 mg CO2/dm2 per hr higher than that of birdsfoot trefoil or prickly sida. On a total leaf area basis, CO2 utilization changed as the heteroculture canopies developed and as the microenvironmental parameters changed. Redroot pigweed's rapid attainment of leaf area and leaf display coupled with a high photosynthetic (P) rate greatly enhance its utilization of available CO2. Direct competition for CO2 does not occur between plants with low and high (P) rates under field conditions because CO2 concentrations are always greater than the CO2 compensation point (r) of plants with low (P) rates. More efficient utilization of available CO2 by weeds such as redroot pigweed with greater (P) capacity contributes to more rapid growth and development of these weeds to the ultimate detriment of a plant such as birdsfoot trefoil with lower (P) capacity.
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