An official website of the United States government
Abstract Uncertainty about long‐term leaf‐level responses to atmospheric CO2rise is a major knowledge gap that exists because of limited empirical data. Thus, it remains unclear how responses of leaf gas exchange to elevated CO2(eCO2) vary among plant species and functional groups, or across different levels of nutrient supply, and whether they persist over time for long‐lived perennials. Here, we report the effects of eCO2on rates of net photosynthesis and stomatal conductance in 14 perennial grassland species from four functional groups over two decades in a Minnesota Free‐Air CO2Enrichment experiment, BioCON. Monocultures of species belonging to C3grasses, C4grasses, forbs, and legumes were exposed to two levels of CO2and nitrogen supply in factorial combinations over 21 years. eCO2increased photosynthesis by 12.9% on average in C3species, substantially less than model predictions of instantaneous responses based on physiological theory and results of other studies, even those spanning multiple years. Acclimation of photosynthesis to eCO2was observed beginning in the first year and did not strengthen through time. Yet, contrary to expectations, the response of photosynthesis to eCO2was not enhanced by increased nitrogen supply. Differences in responses among herbaceous plant functional groups were modest, with legumes responding the most and C4grasses the least as expected, but did not further diverge over time. Leaf‐level water‐use efficiency increased by 50% under eCO2primarily because of reduced stomatal conductance. Our results imply that enhanced nitrogen supply will not necessarily diminish photosynthetic acclimation to eCO2in nitrogen‐limited systems, and that significant and consistent declines in stomatal conductance and increases in water‐use efficiency under eCO2may allow plants to better withstand drought.
more »
« less
Responses of stomatal features and photosynthesis to porewater N enrichment and elevated atmospheric CO 2 in Phragmites australis , the common reed
PREMISEBiological invasions increasingly threaten native biodiversity and ecosystem services. One notable example is the common reed,Phragmites australis, which aggressively invades North American salt marshes. Elevated atmospheric CO2and nitrogen pollution enhance its growth and facilitate invasion becauseP. australisresponds more strongly to these enrichments than do native species. We investigated how modifications to stomatal features contribute to strong photosynthetic responses to CO2and nitrogen enrichment inP. australisby evaluating stomatal shifts under experimental conditions and relating them to maximal stomatal conductance (gwmax) and photosynthetic rates. METHODSPlants were grownin situin open‐top chambers under ambient and elevated atmospheric CO2(eCO2) and porewater nitrogen (Nenr) in a Chesapeake Bay tidal marsh. We measured light‐saturated carbon assimilation rates (Asat) and stomatal characteristics, from which we calculatedgwmaxand determined whether CO2and Nenraltered the relationship betweengwmaxandAsat. RESULTSeCO2and Nenrenhanced bothgwmaxandAsat, but to differing degrees;gwmaxwas more strongly influenced by Nenrthrough increases in stomatal density whileAsatwas more strongly stimulated by eCO2. There was a positive relationship betweengwmaxandAsatthat was not modified by eCO2or Nenr, individually or in combination. CONCLUSIONSChanges in stomatal features co‐occur with previously described responses ofP. australisto eCO2and Nenr. Complementary responses of stomatal length and density to these global change factors may facilitate greater stomatal conductance and carbon gain, contributing to the invasiveness of the introduced lineage.
more »
« less
- Award ID(s):
- 2051343
- PAR ID:
- 10453358
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- American Journal of Botany
- Volume:
- 108
- Issue:
- 4
- ISSN:
- 0002-9122
- Format(s):
- Medium: X Size: p. 718-725
- Size(s):
- p. 718-725
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
<bold>SUMMARY</bold> While the adverse effects of elevated salinity levels on leaf gas exchange in many crops are not in dispute, representing such effects on leaf photosynthetic rates (A) continues to draw research attention. Here, an optimization model for stomatal conductance (gc) that maximizesAwhile accounting for mesophyll conductance (gm) was used to interpret new leaf gas exchange measurements collected for five irrigation water salinity levels. A function between chloroplastic CO2concentration (cc) and intercellular CO2concentration (ci) modified by salinity stress to estimategmwas proposed. Results showed that with increased salinity, the estimatedgmand maximum photosynthetic capacity were both reduced, whereas the marginal water use efficiencyλincreased linearly. Adjustments ofgm,λand photosynthetic capacity were shown to be consistent with a large corpus of drought‐stress experiments. The inferred model parameters were then used to evaluate the combined effects of elevated salinity and atmospheric CO2concentration (ca) on leaf gas exchange. For a given salinity level, increasingcaincreasedAlinearly, but these increases were accompanied by mild reductions ingcand transpiration. Thecalevel needed to ameliorateAreductions due to increased salinity is also discussed using the aforementioned model calculations.more » « less
-
Abstract A mechanistic understanding of plant photosynthetic response is needed to reliably predict changes in terrestrial carbon (C) gain under conditions of chronically elevated atmospheric nitrogen (N) deposition. Here, using 2,683 observations from 240 journal articles, we conducted a global meta‐analysis to reveal effects of N addition on 14 photosynthesis‐related traits and affecting moderators. We found that across 320 terrestrial plant species, leaf N was enhanced comparably on mass basis (Nmass, +18.4%) and area basis (Narea, +14.3%), with no changes in specific leaf area or leaf mass per area. Total leaf area (TLA) was increased significantly, as indicated by the increases in total leaf biomass (+46.5%), leaf area per plant (+29.7%), and leaf area index (LAI, +24.4%). To a lesser extent than for TLA, N addition significantly enhanced leaf photosynthetic rate per area (Aarea, +12.6%), stomatal conductance (gs, +7.5%), and transpiration rate (E, +10.5%). The responses ofAareawere positively related with that ofgs, with no changes in instantaneous water‐use efficiency and only slight increases in long‐term water‐use efficiency (+2.5%) inferred from13C composition. The responses of traits depended on biological, experimental, and environmental moderators. As experimental duration and N load increased, the responses of LAI andAareadiminished while that ofEincreased significantly. The observed patterns of increases in both TLA andEindicate that N deposition will increase the amount of water used by plants. Taken together, N deposition will enhance gross photosynthetic C gain of the terrestrial plants while increasing their water loss to the atmosphere, but the effects on C gain might diminish over time and that on plant water use would be amplified if N deposition persists.more » « less
-
Summary Little is known about long‐distance mesophyll‐driven signals that regulate stomatal conductance. Soluble and/or vapor‐phase molecules have been proposed. In this study, the involvement of the gaseous signal ethylene in the modulation of stomatal conductance inArabidopsis thalianaby CO2/abscisic acid (ABA) was examined.We present a diffusion model which indicates that gaseous signaling molecule/s with a shorter/direct diffusion pathway to guard cells are more probable for rapid mesophyll‐dependent stomatal conductance changes. We, therefore, analyzed different Arabidopsis ethylene‐signaling and biosynthesis mutants for their ethylene production and kinetics of stomatal responses to ABA/[CO2]‐shifts.According to our research, higher [CO2] causes Arabidopsis rosettes to produce more ethylene. An ACC‐synthase octuple mutant with reduced ethylene biosynthesis exhibits dysfunctional CO2‐induced stomatal movements. Ethylene‐insensitive receptor (gain‐of‐function),etr1‐1andetr2‐1, and signaling,ein2‐5andein2‐1, mutants showed intact stomatal responses to [CO2]‐shifts, whereas loss‐of‐function ethylene receptor mutants, includingetr2‐3;ein4‐4;ers2‐3,etr1‐6;etr2‐3andetr1‐6, showed markedly accelerated stomatal responses to [CO2]‐shifts. Further investigation revealed a significantly impaired stomatal closure to ABA in the ACC‐synthase octuple mutant and accelerated stomatal responses in theetr1‐6;etr2‐3, andetr1‐6, but not in theetr2‐3;ein4‐4;ers2‐3mutants.These findings suggest essential functions of ethylene biosynthesis and signaling components in tuning/accelerating stomatal conductance responses to CO2and ABA.more » « less
-
ABSTRACT Stomata control plant water loss and photosynthetic carbon gain. Developing more generalized and accurate stomatal models is essential for earth system models and predicting responses under novel environmental conditions associated with global change. Plant optimality theories offer one promising approach, but most such theories assume that stomatal conductance maximizes photosynthetic net carbon assimilation subject to some cost orconstraintof water. We move beyond this approach by developing a new, generalized optimality theory of stomatal conductance, optimizing any non‐foliar proxy that requires water and carbon reserves, like growth, survival, and reproduction. We overcome two prior limitations. First, we reconcile the computational efficiency ofinstantaneousoptimization with a more biologically meaningfuldynamic feedbackoptimization over plant lifespans. Second, we incorporatenon‐steady‐statephysics in the optimization to account for the temporal changes in the water, carbon, and energy storage within a plant and its environment that occur over the timescales that stomata act, contrary to previous theories. Our optimal stomatal conductance compares well to observations from seedlings, saplings, and mature trees from field and greenhouse experiments. Our model predicts predispositions to mortality during the 2018 European drought and captures realistic responses to environmental cues, including the partial alleviation of heat stress by evaporative cooling and the negative effect of accumulating foliar soluble carbohydrates, promoting closure under elevated CO2. We advance stomatal optimality theory by incorporating generalized evolutionary fitness proxies and enhance its utility without compromising its realism, offering promise for future models to more realistically and accurately predict global carbon and water fluxes.more » « less
