Effects of CO2 on Plants at Different Timescales

Abstract

How do plants respond to changes in atmospheric CO 2 concentration? The answer depends strongly on the timescale of interest to the questioner. Changes in atmospheric CO 2 concentration ([CO 2 ]) have direct and immediate effects on plant physiology, but as time progresses, a series of plant and ecosystem feed-backs act to modify this direct response. Different feedbacks have different time constants and hence become important on different timescales (Fig. 20.1). For example, changes in growth patterns can occur over months to years, changes in nutrient availability due to soil feedbacks may occur over decades, while adaptation may alter plant responses over centuries or more. Evidence for the effects of changes in atmospheric [CO 2 ] on plants is available on many different timescales, from short-term experiments to longer-term models to paleobotanical studies. Evidence from one timescale can have bearing on responses at another timescale, but to interpret this evidence correctly, it is important to understand how plant responses to atmospheric [CO 2 ] change over time. The aim of this paper is to review our current knowledge of CO 2 effects on plants on different timescales and to examine how responses at different times relate to each other. We consider four general timescales. The first, minutes to hours, is the timescale of direct physiological responses. The second, months to years, is the experimental timescale, or, the duration of most experiments. The third, decades, we denote the human timescale, since it represents the timescale