Photosynthetic dimensions of global change

Abstract

The CO2 concentration of the atmosphere is rising 0.4% per year. Photosynthesis is the pivotal process in the direct response of the terrestrial biosphere and the global carbon cycle to atmospheric change. Despite initial skepticism, the conserved kinetic properties of Rubisco are now proving invaluable in scaling predictions from leaf photosynthesis to region, and provide the mechanistic base both for predicting the future global carbon cycle and C3 crop production. Elevated CO2 initially stimulates photosynthesis, via increased velocity of carboxylation and inhibition of oxygenation leading to photorespiration. The long-term significance of this initial stimulation has been questioned, due to acclimation in the form of decreased Rubisco content, especially when nitrogen supply is low. Insight from recent long-term, Free-Air Carbon dioxide Enrichment (FACE) experiments suggests that acclimation has only a limited effect on total carbon gain, and may play a key role in increasing nitrogen use efficiency in elevated CO2. Secondary effects of elevated CO2 on photosynthesis can also affect the composition and function of communities. Interspecific differences in acclimation affect relative fitness in natural communities. Furthermore, a variety of stresses interact with elevated CO2 to exacerbate photoinhibition and recovery of photosystem II. Until now, photosynthesis research has focused on how plants will respond to change. The new challenge is understanding how the effects of rising CO2 on photosynthesis will interact with other changes, in particular rising tropospheric ozone, temperature and incidence of drought. How can we apply this knowledge to adapt crops to the changed atmosphere and how can it be used to provide at least some temporary amelioration of the rate of rise in global CO2 concentration?