Sensitivity of plants to changing atmospheric CO₂ concentration: from the geological past to the next century

Abstract

1077I.1078II.1079III.1080IV.1081V.1084VI.1087VII.10881089References1089 Summary The rate of CO2 assimilation by plants is directly influenced by the concentration of CO2 in the atmosphere, ca. As an environmental variable, ca also has a unique global and historic significance. Although relatively stable and uniform in the short term, global ca has varied substantially on the timescale of thousands to millions of years, and currently is increasing at seemingly an unprecedented rate. This may exert profound impacts on both climate and plant function. Here we utilise extensive datasets and models to develop an integrated, multi‐scale assessment of the impact of changing ca on plant carbon dioxide uptake and water use. We find that, overall, the sensitivity of plants to rising or falling ca is qualitatively similar across all scales considered. It is characterised by an adaptive feedback response that tends to maintain 1 − ci/ca, the relative gradient for CO2 diffusion into the leaf, relatively constant. This is achieved through predictable adjustments to stomatal anatomy and chloroplast biochemistry. Importantly, the long‐term response to changing ca can be described by simple equations rooted in the formulation of more commonly studied short‐term responses.

Evidence of recovery of Juniperus virginiana trees from sulfur pollution after the Clean Air Act

“…The breakpoint was identified as 1982, which corresponds to the approximate time when SO 2 emissions began to decline in the United States. This result was surprising because it is counter to the widely observed stomatal response of plants to increasing CO 2 in the 20th century (11,23). Here, decreasing Δ 13 C before ∼1980 suggest stomatal closure as if the trees were responding to increasing atmospheric CO 2 , yet the reversal and increases in Δ 13 C after 1980 suggest reduced stomatal regulation to CO 2 (Fig.…”

“…2C) due to a 23% increase in A and an 18.5% decrease in g c . Many dendroisotopic studies have concluded that the small but progressive increases in atmospheric CO 2 over the last century have improved iWUE (23,33), and suggest that a fundamental way that increasing atmospheric CO 2 stimulates tree growth and forest productivity is by improving the efficiency that trees are using water. Here, acid deposition over many decades contributed to a large portion of the increase in iWUE of Juniperus, and these data signify that the effects of increasing CO 2 on iWUE can be greatly overestimated if other environmental influences are not considered in these estimates.…”

Leveraging abscisic acid receptors for efficient water use in Arabidopsis

“…Whereas the gas exchange of CO 2 and water vapor at the stomatal pore is a physical process controlled by both the ratio in partial pressure gradients and gas diffusivities (4,5), terrestrial plants are able to capture carbon more efficiently under water deficit. Both short-term leaf gas exchange measurements and 13 C isotope discrimination analyses revealed increases of the instantaneous water use efficiency (insWUE) and intrinsic WUE (iWUE), respectively, by a factor of 1.5-2.5 in wheat and other species (6,7).…”

Stomatal Function across Temporal and Spatial Scales: Deep-Time Trends, Land-Atmosphere Coupling and Global Models

“…This adaptation is usually in the direction that would tend to counteract the physiological effects of the change in c a (e.g. higher D with lower c a increases stomatal conductance to counteract the initial drop in CO 2 assimilation rate; Franks et al, 2012bFranks et al, , 2013. What remains unclear about this simple principle is how to characterize this sensitivity quantitatively for the purpose of simulation or prediction.…”

“…1; see discussion in Franks et al, 2013). Importantly, stomata behave as both negative and positive feedback elements, depending on the process.…”