Submitted to: European Journal of Agronomy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/1/2013
Publication Date: 10/1/2013
Citation: Valerio, M., Tomecek, M.B., Lovelli, S., Ziska, L.H. 2013. Photosynthetic pathway as a predictor of competitive outcomes and potential yield loss for tomato in competition with a C3 and C4 weed at enhanced atmospheric C02 and two growth temperatures. European Journal of Agronomy. 50:60-65. Interpretive Summary: Carbon dioxide (CO2), in addition to being a global warming gas, is also a source of carbon for photosynthesis and, consequently, is expected to stimulate plant growth. Which plants will be stimulated however, is still unclear. In this study we examined whether different photosynthetic pathways between weeds and crops (tomato) could be used to predict which plant species would show the greatest stimulation during early competition. We found that, no matter the type of photosynthetic pathway, weeds were stimulated to a greater extent than the crop. We used a mathematical model to then estimate potential crop losses from weeds. This model indicated that crop losses increased from 29 to 46% and from 31 to 51% for the 21/12 and 26/18oC day/night temperatures, respectively, as CO2 concentration was increased. Overall, these results suggest that photosynthetic pathway per se, may not be a good indicator of predicting crop-weed competitive outcomes in a future, higher CO2 environment.
Technical Abstract: How different photosynthetic pathways respond to rising levels of atmospheric carbon dioxide (CO2) is particularly relevant to crop/weed interactions in agricultural systems; in part because many of the most troublesome weedy species are C4 plants, while a number of major crops are C3 plants. To determine if different photosynthetic pathways could be used to predict crop: weed competitive outcomes to increasing CO2, tomato (Lycopersicon esculentum), a C3 crop species, was grown at ambient (~400 µmol mol-1) and enhanced carbon dioxide (~800 µmol mol-1) with and without two common weeds, lambsquarters (Chenopodium album), a C3 weed, and redroot pigweed (Amaranthus retroflexus), a C4 weed, from seedling emergence until mutual shading of crop-weed leaves. Because growth temperature is also likely to change in concert with rising CO2, the experiment was repeated at day/night temperatures of 21/12 and 26/18oC. For both day/night temperatures, significant reductions in height, leaf area, leaf and stem weight were observed for tomato with weedy competition as CO2 increased. A model based on weed relative leaf area following emergence was used to determine potential crop losses from weeds. This model indicated that crop losses increased from 29 to 46% and from 31 to 51% for the 21/12 and 26/18oC day/night temperatures, respectively, for ambient and elevated CO2. The extent of crop loss with increasing CO2 did not differ as a function of C3 vs. C4 weed species either singly or in combination. Overall, these results suggest that photosynthetic pathway per se, may not be a good indicator of predicting crop-weed competitive outcomes in a future, higher CO2 environment.