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Title: Differential response of cultivated and weedy (red) rice to recent and projected increases in atmospheric carbon dioxide

Author
item Ziska, Lewis
item McClung, Anna

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2008
Publication Date: 8/1/2008
Citation: Ziska, L.H., Mcclung, A.M. 2008. Differential response of cultivated and weedy (red) rice to recent and projected increases in atmospheric carbon dioxide. Agronomy Journal. 100(5):1259-1263.

Interpretive Summary: Carbon dioxide (CO2), along with sunlight, water and nutrients constitutes one of the four resources needed for plants to grow. As such, the sudden increase in its concentration in the atmosphere (up 22% since 1960) could be exploited in order to boost crop yields. However, the rise in CO2 is indiscriminate with respect to plant species and could stimulate not only the crop, but weed species as well. To determine if recent and projected increases in atmospheric carbon dioxide differentially affected crops and weeds we examined the response of six different varieties of cultivated and wild (weedy) rice to three different CO2 concentrations. These CO2 concentrations correspond roughly to the 1950s, the current concentration, and the concentration anticipated by 2050. Overall, we found that as CO2 increases, the wild or weedy rice was stimulated more than the cultivated rice. This may increase the competitiveness of weeds in rice, with negative consequences for rice yield. However, since both wild and cultivated rice are closely related, it may be possible to transfer desirable, CO2 sensitive characteristics from the wild to cultivated rice plant. This data and its inference for food security will be of interest for policy makers, scientists, agronomists, and plant breeders.

Technical Abstract: Carbon dioxide (CO2) is a principle resource for plant growth; as such, the ongoing increase in its concentration may differentially affect the growth of cultivated and wild types of the same species. Red rice in the U.S. is a weedy relative of cultivated rice that represents a major production constraint in the southern United States. To determine whether recent or projected increases in CO2 favor cultivated rice or its weedy relative, we examined the initial growth and vegetative characteristics of these two groups using six red rice biotypes (RR) and six commercial varieties (VR) in response to increases in carbon dioxide concentration [CO2] that correspond roughly to the 1940s, the current [CO2], and the [CO2] projected for the middle of this century, (300, 400 and 500 umol mol-1, respectively). Increasing [CO2] resulted in significant increases in initial leaf area and root weight, but these increases were greater for RR, with significant differences observed as early as 27 days after sowing (DAS) at 500 umol mol-1. By 55 DAS, significant CO2 by RR/VR interactions were observed for almost all measured vegetative parameters. Overall, these results indicate a greater degree of CO2 responsiveness among RR as compared to VR. This suggests a greater physiological plasticity and genetic diversity among RR biotypes relative to commercial cultivars that may impact weed/crop competition as atmospheric carbon dioxide increases. However, this greater variation may also provide a unique genetic resource that could be incorporated into new rice varieties in order to increase their adaptability to climatic change.