Elevated CO(2) and Water Stress in Combination in Plants: Brothers in Arms or Partners in Crime?

SIMPLE SUMMARY: The changing climate scenario envisages elevated CO(2) (eCO(2)) and drought in many parts of the world. Elevated CO(2) is known to increase yields in C(3) crops like rice and wheat, on the other hand, it does not cause a similar increase in C(4) crops like maize and sorghum. Drought is known to reduce crop growth and yield. In this mini-review we discuss the combined effects of both eCO(2) and drought which is typical of a climate change scenario. We try and explain how C(3) and C(4) crops are differentially affected by these two manifestations of climate change. We specifically show how eCO(2) in addition to its known beneficial effects can also be effective in ameliorating the effects of drought in crops. We have critically analysed the current literature and have come up with some mechanistic explanations in terms of water relations, hormonal regulation, photosynthesis and growth, nutrient uptake, and enzyme dynamics. We present here how these processes operate across a range, from ecosystem to organismal level and from molecular to the whole plant level. The information presented will help researchers to devise strategies for adaptation in crops in agricultural systems. ABSTRACT: The changing dynamics in the climate are the primary and important determinants of agriculture productivity. The effects of this changing climate on overall productivity in agriculture can be understood when we study the effects of individual components contributing to the changing climate on plants and crops. Elevated CO(2) (eCO(2)) and drought due to high variability in rainfall is one of the important manifestations of the changing climate. There is a considerable amount of literature that addresses climate effects on plant systems from molecules to ecosystems. Of particular interest is the effect of increased CO(2) on plants in relation to drought and water stress. As it is known that one of the consistent effects of increased CO(2) in the atmosphere is increased photosynthesis, especially in C(3) plants, it will be interesting to know the effect of drought in relation to elevated CO(2). The potential of elevated CO(2) ameliorating the effects of water deficit stress is evident from literature, which suggests that these two agents are brothers in arms protecting the plant from stress rather than partners in crime, specifically for water deficit when in isolation. The possible mechanisms by which this occurs will be discussed in this minireview. Interpreting the effects of short-term and long-term exposure of plants to elevated CO(2) in the context of ameliorating the negative impacts of drought will show us the possible ways by which there can be effective adaption to crops in the changing climate scenario.