Submitted to: Integrated Biological Systems Conference
Publication Type: Abstract Only
Publication Acceptance Date: 4/13/2003
Publication Date: 4/13/2003
Citation: Baker, J.T., Allen Jr, L.H., Boothe, K.J. 2003. Impacts of drought, high temperature and carbon dioxide on rice physiological processes[abstract]. Integrated Biological Systems Conference. Interpretive Summary: When farmers refer to "drought conditions" in the field, plant scientists recognize that this is really a combination of at least two individual conditions: a lack of soil water and air and plant temperatures that are too high for maximum crop growth and yield. Separating these two conditions in field experiments is often not possible because lack of soil water and high temperatures usually happen at the same time in the field. To overcome this, plant scientists utilize outdoor, naturally sunlit plant growth chambers to control the plant's environment and study lack of soil water and high temperature stress individually. This paper reports on the results of a series of experiments conducted in outdoor plant growth chambers where the effects of wide ranges of both soil water and air temperatures were studied separately on rice crops. We also looked at the effects of these two stress factors in combination with elevated atmospheric carbon dioxide concentrations that are expected to occur towards the later half of the 21st century. We found that lack of soil water, high temperature stress and high carbon dioxide concentrations all affected a wide range of individual plant processes differently.
Technical Abstract: Field crops under drought often experience two quite different but related and simultaneous stresses: soil water deficit and high temperature stresses. Separating the effects of these two different stresses and then studying their interaction is difficult in field experiments. In this paper we examine the effects of these two stresses separately as well as the interactions of these two stresses with elevated atmospheric carbon dioxide concentrations for rice experiments conducted in naturally sunlit, controlled environment chambers by the University of Florida and USDA-ARS at Gainesville, FL, USA. For rice, we found that soil water deficit, high temperature stresses and elevated atmospheric carbon dioxide concentration affected specific physiological processes quite differently. Both vegetative biomass accumulation and canopy photosynthesis had broad temperature optimums while canopy evapotranspiration increased exponentially with increasing air temperature treatment. Grain yield had a clear temperature optimum near 26ºC and declined by about 10% per 1ºC increase above this optimum. Soil water deficit accelerated leaf senescence, reduced leaf area and aboveground biomass and delayed crop ontogeny. Severe water deficit resulted in the complete photosynthetic collapse of rice canopies. Both soil water deficit and high temperature stress more severely affected reproductive than vegetative growth. Elevated CO2 increased rice growth, grain yield and canopy photosynthesis while reducing evapotranspiration by about 10%. During drought stress cycles, this water savings under elevated CO2 allowed photosynthesis to continue for one to two days longer compared with the ambient CO2 treatment so increased drought avoidance. Elevated atmospheric CO2 concentration ameliorated, to various degrees, the negative impacts of soil water deficit and high temperature stresses on specific crop physiological processes.