Submitted to: Plant Biosystems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/12/2010
Publication Date: 2/1/2011
Citation: Ephrath, J., Timlin, D.J., Reddy, V., Baker, J.T. 2011. Irrigation and elevated carbon dioxide effects on whole canopy photosynthesis and water use efficiency in cotton (Gossypium hirsutum L.). Plant Biosystems. 145:202-215. Interpretive Summary: Previous studies have shown that, in the presence of elevated carbon dioxide concentrations, plants use less water than at current (ambient) levels. There is still limited information on the soil profile distribution of water uptake by cotton under elevated carbon dioxide levels when water inputs are limited. Such information is important for developing computer simulation models of plant growth and yield to be used for irrigation management. Our goal was to study the distribution of water uptake rates from shallow and deep soil depths and the relationship with canopy photosynthesis and plant growth in cotton under elevated levels of carbon dioxide. We used outdoor, sunlit growth chambers with soilbins to control irrigation, temperature and carbon dioxide contents. We found that when irrigation is withheld so that plants depend on stored soil water, plants grown under ambient carbon dioxide levels used more soil water and obtained a larger proportion of water from depths below 0.5 meters than did plants grown under elevated carbon dioxide content. Water stress reduced photosynthesis and plant growth earlier where carbon dioxide was maintained at ambient levels compared to plants grown at elevated levels of carbon dioxide. These results have important implications for irrigated crops such as cotton. Elevated carbon dioxide under conditions limited rainfall or irrigation could have the same effect on plant growth as increasing the available water holding capacity of soil.
Technical Abstract: The objective of this study was to compare the effects of water stress under ambient (350 umol mol-1) and elevated (700 umol mol-1) carbon dioxide concentrations on photosynthesis, plant growth, and soil water use of cotton plants. This research was carried out in six sun-lit SPAR (Soil Plant Atmosphere Research) units with soil bins located at Beltsville, Maryland. Whole canopy net photosynthetic rates were measured at five minute intervals, and soil water content was measured hourly using Time-Domain Reflectometery. Pre-dawn and midday leaf water potentials were measured during the water stress and the recovery periods. The soil water use rates for cotton plants grown under elevated carbon dioxide were significantly lower than those for plants grown under ambient carbon dioxide levels for both water stressed and well watered plants. Plants grown under elevated carbon dioxide levels obtained proportionately more of their transpiration water from soil depths above 0.5 m than did the plants grown under ambient conditions. The minimum soil water content for the elevated carbon dioxide plants was significantly higher than for the high carbon dioxide plants. The highest leaf water potentials were associated with the water stressed elevated carbon dioxide plants as compared to the water stressed ambient plants. Water uptake and plant height were more strongly affected by water stress than was canopy photosynthesis and the effects were more pronounced in the non-irrigated ambient CO2 treatment than in the elevated treatment. Computer simulation models of plants subjected to water stress need to account for root water extraction patterns as well as reduced water uptake rates under elevated CO2 scenarios.