CROP AND WEED RESPONSES TO INCREASING ATMOSPHERIC CARBON DIOXIDE
Title: Competitive interactions between cultivated and red rice as a function of recent and projected increases in atmospheric carbon dioxide
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 5, 2009
Publication Date: January 1, 2010
Citation: Ziska, L.H., Tomecek, M.B., Gealy, D.R. 2010. Competitive interactions between cultivated and red rice as a function of recent and projected increases in atmospheric carbon dioxide. Agronomy Journal. 102:118-123.
Interpretive Summary: Carbon dioxide (CO2) provides the carbon needed for the growth of all plants, including weeds and crops. However, it is unclear if weeds or crops will show the same relative increase to rising carbon dioxide in the atmosphere. Knowing whether weeds or crops will be the "winner" as CO2 levels increase is important for determining crop losses due to weeds and weed management. Using cultivated rice and a weedy red rice relative, we compared their growth and seed production to CO2 levels that corresponded to the 1940s, current levels, and that projected for the middle for the current century. Overall, we found that as CO2 increased, the weed did better (grew faster and produced more seed) than the crop. Because the weedy rice responded so much more to the increase in atmospheric carbon dioxide, competition increased with greater losses observed for the cultivated rice with respect to biomass and seed yield. Overall, these are the first data to indicate that for rice, weedy red lines may be favored as a function of rising carbon dioxide, with greater relative impact on the seed yield and biomass of cultivated rice lines. These data will be of interest to land managers, weed biologists and scientists.
Although carbon dioxide represents a fundamental resource for plant function, increases in atmospheric concentration may differentially stimulate cultivated and weedy types of the same species. Because wild types often represent a weedy constraint to cultivated crops in the field, any differential response to CO2 will have fundamental consequences for weed/crop competition and seed yield. To determine the relative response of weedy or cultivated biotypes of the same species we evaluated the growth and reproduction of cultivated rice (Clearfield, "CL 161") and weedy red rice (Stuttgart, "Stg S") in monoculture, and at two competitive densities (8 and 16 plants m-2) using atmospheric CO2 concentrations ([CO2]) that corresponded to the 1940s, current levels, and that projected for the middle for the current century (300, 400 and 500 µmol mol-1, respectively). For monocultures, no significant effect of increasing [CO2] was observed for seed yield in the cultivated line, but a significant increase of 23% was observed for above ground biomass from 300 to 500 µmol mol-1; conversely, for the weedy biotype, the increase in seed yield and above-ground biomass was 122 and 76% respectively. Competition was determined using plant relative yield (PRY) for biomass and seed yield as a function of [CO2]. At maturity, PRY significantly increased for wild rice, but decreased for the cultivated line as a function of competitive density. Increases in [CO2] resulted in significant decreases in the PRY of seed yield at both competitive densities for CL161; while significant increases in seed yield and above ground biomass were noted for Stg S, but only at the higher competitive density. The increase in PRY for the red weedy rice line was consistent with an increase in a number of vegetative and reproductive parameters, with significant line by [CO2] and line by competition interactions observed. In addition, the relative increase in seed yield for CL 161: Stg S, determined at the same competitive density increased as a function of [CO2] suggesting a greater amount of seed rain from the weedy rice. Overall, these are the first data to indicate that for rice, weedy red lines may be favored as a function of rising carbon dioxide, with greater relative impact on the seed yield and biomass of cultivated rice lines.