- Award ID(s):
- 1561755
- NSF-PAR ID:
- 10227541
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 20
- Issue:
- 19
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 11287 to 11304
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract. Dry deposition is a key process for surface ozone(O3) removal. Stomatal uptake is a major component of O3 drydeposition, which is parameterized differently in current land surfacemodels and chemical transport models. We developed and used a standaloneterrestrial biosphere model, driven by a unified set of prescribedmeteorology, to evaluate two widely used dry deposition modeling frameworks,Wesely (1989) and Zhang et al. (2003), with different configurations ofstomatal resistance: (1) the default multiplicative method in the Weselyscheme (W89) and Zhang et al. (2003) scheme (Z03), (2) the traditionalphotosynthesis-based Farquhar–Ball–Berry (FBB) stomatal algorithm, and (3) theMedlyn stomatal algorithm (MED) based on optimization theory. We found thatusing the FBB stomatal approach that captures ecophysiological responses toenvironmental factors, especially to water stress, can generally improve thesimulated dry deposition velocities compared with multiplicative schemes.The MED stomatal approach produces higher stomatal conductance than FBB andis likely to overestimate dry deposition velocities for major vegetationtypes, but its performance is greatly improved when spatially varying slopeparameters based on annual mean precipitation are used. Large discrepancieswere also found in stomatal responses to rising CO2 levels from 390to 550 ppm: the multiplicative stomatal method with an empirical CO2response function produces reduction (−35 %) in global stomatalconductance on average much larger than that with the photosynthesis-basedstomatal method (−14 %–19 %). Our results show the potential biases inO3 sink caused by errors in model structure especially in the Weselydry deposition scheme and the importance of using photosynthesis-basedrepresentation of stomatal resistance in dry deposition schemes under achanging climate and rising CO2 concentration.more » « less
-
Summary Rising temperatures are influencing forests on many scales, with potentially strong variation vertically across forest strata. Using published research and new analyses, we evaluate how microclimate and leaf temperatures, traits, and gas exchange vary vertically in forests, shaping tree, and ecosystem ecology. In closed‐canopy forests, upper canopy leaves are exposed to the highest solar radiation and evaporative demand, which can elevate leaf temperature (
T leaf), particularly when transpirational cooling is curtailed by limited stomatal conductance. However, foliar traits also vary across height or light gradients, partially mitigating and protecting against the elevation of upper canopyT leaf. Leaf metabolism generally increases with height across the vertical gradient, yet differences in thermal sensitivity across the gradient appear modest. Scaling from leaves to trees, canopy trees have higher absolute metabolic capacity and growth, yet are more vulnerable to drought and damagingT leafthan their smaller counterparts, particularly under climate change. By contrast, understory trees experience fewer extreme highT leaf's but have fewer cooling mechanisms and thus may be strongly impacted by warming under some conditions, particularly when exposed to a harsher microenvironment through canopy disturbance. As the climate changes, integrating the patterns and mechanisms reviewed here into models will be critical to forecasting forest–climate feedback. -
Abstract. Ground-level ozone (O3) is a major air pollutant that adversely affects human health and ecosystem productivity. Removal of troposphericO3 by plant stomatal uptake can in turn cause damage to plant tissues with ramifications for ecosystem and crop health. In manyatmospheric and land surface models, the functionality of stomata opening is represented by a bulk stomatal conductance, which is oftensemi-empirically parameterized and highly fitted to historical observations. A lack of mechanistic linkage to ecophysiological processes such asphotosynthesis may render models inadequate to represent plant-mediated responses of atmospheric chemistry to long-term changes in CO2,climate, and short-lived air pollutant concentrations. A new ecophysiology module was thus developed to mechanistically simulate land−atmosphereexchange of important gas species in GEOS-Chem, a chemical transport model widely used in atmospheric chemistry studies. The implementation not onlyallows for dry deposition to be coupled with plant ecophysiology but also enables plant and crop productivity and functions to respond dynamically toatmospheric chemical changes. We conduct simulations to evaluate the effects of the ecophysiology module on simulated dry deposition velocity andconcentration of surface O3 against an observation-derived dataset known as SynFlux. Our estimated stomatal conductance and dry depositionvelocity of O3 are close to SynFlux with root-mean-squared errors (RMSEs) below 0.3 cm s−1 across different plant functionaltypes (PFTs), despite an overall positive bias in surface O3 concentration (by up to 16 ppbv). Representing ecophysiology wasfound to reduce the simulated biases in deposition fluxes from the prior model but worsen the positive biases in simulated O3concentrations. The increase in positive concentration biases is mostly attributable to the ecophysiology-based stomatal conductance being generallysmaller (and closer to SynFlux values) than that estimated by the prior semi-empirical formulation, calling for further improvements in non-stomataldepositional and non-depositional processes relevant for O3 simulations. The estimated global O3 deposition flux is864 Tg O3 yr−1 with GEOS-Chem, and the new module decreases this estimate by 92 Tg O3 yr−1. Estimated global grossprimary production (GPP) without O3 damage is 119 Pg C yr−1. O3-induced reduction in GPP is 4.2 Pg C yr−1(3.5 %). An elevated CO2 scenario (580 ppm) yields higher global GPP (+16.8 %) and lower global O3depositional sink (−3.3 %). Global isoprene emission simulated with a photosynthesis-based scheme is 317.9 Tg C yr−1, which is31.2 Tg C yr−1 (−8.9 %) less than that calculated using the MEGAN(Model of Emissions of Gases and Aerosols from Nature) emission algorithm. This new model development dynamicallyrepresents the two-way interactions between vegetation and air pollutants and thus provides a unique capability in evaluating vegetation-mediatedprocesses and feedbacks that can shape atmospheric chemistry and air quality, as well as pollutant impacts on vegetation health, especially for anytimescales shorter than the multidecadal timescale.more » « less
-
Abstract Tropical forest canopies cycle vast amounts of carbon, yet we still have a limited understanding of how these critical ecosystems will respond to climate warming. We implemented in situ leaf‐level + 3°C experimental warming from the understory to the upper canopy of two Puerto Rican tropical tree species,
Guarea guidonia andOcotea sintenisii . After approximately 1 month of continuous warming, we assessed adjustments in photosynthesis, chlorophyll fluorescence, stomatal conductance, leaf traits and foliar respiration. Warming did not alter net photosynthetic temperature response for either species; however, the optimum temperature ofOcotea understory leaf photosynthetic electron transport shifted upward. There was noOcotea respiratory treatment effect, whileGuarea respiratory temperature sensitivity (Q 10) was down‐regulated in heated leaves. The optimum temperatures for photosynthesis (T opt) decreased 3–5°C from understory to the highest canopy position, perhaps due to upper canopy stomatal conductance limitations.Guarea upper canopyT optwas similar to the mean daytime temperatures, whileOcotea canopy leaves often operated aboveT opt. With minimal acclimation to warmer temperatures in the upper canopy, further warming could put these forests at risk of reduced CO2uptake, which could weaken the overall carbon sink strength of this tropical forest. -
Abstract Within the North American boreal forest, a widespread outbreak of the epidermal leaf miner Phyllocnistis populiella has damaged quaking aspen (Populus tremuloides) for nearly 20 years. In a series of experiments, we tested the effects of feeding damage by P. populiella on leaf water relations and gas exchange. Relative to insecticide-treated trees, the leaves of naturally-mined trees had lower photosynthesis, stomatal conductance to water vapor, transpiration, water use efficiency, predawn water potential, and water content, as well as more enriched foliar δ13C. The magnitude of the difference between naturally-mined and insecticide-treated trees did not change significantly throughout the growing season, suggesting the effect is not caused by accumulation of incidental damage to mined portions of the epidermis over time. The contributions of mining-related stomatal malfunction and cuticular transpiration to these overall effects were investigated by restricting mining damage to stomatous abaxial and astomatous adaxial leaf surfaces. Mining of the abaxial epidermis decreased photosynthesis and enriched leaf δ13C, while increasing leaf water potential and water content relative to unmined leaves; effects consistent with stomatal closure due to disfunction of mined guard cells. Mining of the adaxial epidermis also reduced photosynthesis but had different effects on water relations, reducing midday leaf water potential and water content relative to unmined leaves, and did not affect δ13C. In the laboratory, extent of mining damage to the adaxial surface was positively related to the rate of water loss by leaves treated to prevent water loss through stomata. We conclude that overall, despite water savings due to closure of mined stomata, natural levels of damage by P. populiella negatively impact water relations due to increased cuticular permeability to water vapor across the mined portions of the epidermis. Leaf mining by P. populiella could exacerbate the negative effects of climate warming and water deficit in interior Alaska.more » « less