C4 Weeds Competing with C3 Crops: Barnyard Grass vs. Rice
Zeng, Q., Liu, B., Gilna, B., Zhang, Y., Zhu, C., Ma, H., Pang, J., Chen, G. and Zhu, J. 2011. Elevated CO2 effects on nutrient competition between a C3 crop (Oryza sativa L.) and a C4 weed (Echinochloa crusgalli L.). Nutrient Cycling in Agroecosystems 89: 93-104.
In a further study of this nature, Zeng et al. grew rice (Oryza sativa L., a C3 crop) in competition with barnyard grass (Echinochloa crusgalli L., a C4 weed) in a standard paddy-field experiment conducted in ambient air and in air enriched with an extra 200 ppm of CO2 provided via free-air CO2-enrichment or FACE technology that was conducted at Xiaoji Village, Yangzhou City in Eastern China over a period of 120 days.
The eight Chinese researchers and their lone Norwegian colleague report that the elevated CO2 significantly enhanced rice biomass (straw +27.3%, ears +37.6%), tillers (+20%), leaf area index (+11.7%) and net assimilation rate (+50.1%); but they found that it reduced all but the last of these characteristics of barnyard grass: biomass (straw -43.6%, ears -47.9%), tillers (-46.1%), leaf area index (-27.3%), and net assimilation rate (+14.1%, the only positive result, but much less than the +50.1% experienced by rice). In addition, they note that "the absolute uptake of C, N, P, K by rice were increased while those of barnyard grass deceased."
In a significant understatement of the implications of their results, Zeng et al. write that "rising atmospheric CO2 concentration could alter the competition between rice and barnyard grass in paddy fields in favor of rice." We would say it will undoubtedly do so.
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