Predicting photosynthesis and transpiration responses to ozone: decoupling modeled photosynthesis and stomatal conductance

Abstract

Abstract. Plants exchange greenhouse gases carbon dioxide and water with the atmosphere through the processes of photosynthesis and transpiration, making them essential in climate regulation. Carbon dioxide and water exchange are typically coupled through the control of stomatal conductance, and the parameterization in many models often predict conductance based on photosynthesis values. Some environmental conditions, like exposure to high ozone (O 3 ) concentrations, alter photosynthesis independent of stomatal conductance, so models that couple these processes cannot accurately predict both. The goals of this study were to test direct and indirect photosynthesis and stomatal conductance modifications based on O 3 damage to tulip poplar (Liriodendron tulipifera) in a coupled Farquhar/Ball-Berry model. The same modifications were then tested in the Community Land Model (CLM) to determine the impacts on gross primary productivity (GPP) and transpiration at a constant O 3 concentration of 100 parts per billion (ppb). Modifying the V cmax parameter and directly modifying stomatal conductance best predicts photosynthesis and stomatal conductance responses to chronic O 3 over a range of environmental conditions. On a global scale, directly modifying conductance reduces the effect of O 3 on both transpiration and GPP compared to indirectly modifying conductance, particularly in the tropics. The results of this study suggest that independently modifying stomatal conductance can improve the ability of models to predict hydrologic cycling, and therefore improve future climate predictions.

A photosynthesis‐based two‐leaf canopy stomatal conductance model for meteorology and air quality modeling with WRF/CMAQ PX LSM

“…Thus, the system with improved land surface representation and vegetation processes can be used in research and applications in coupling air quality, climate, and vegetation productivity directly with CO 2 concentration which changes temporally and spatially. In addition, the effects of air pollutants such as O 3 on ecosystem productivity can also be easily implemented in this advanced approach [ Sitch et al ., ; Lombardozzi et al ., ] for the U.S. EPA's secondary standard assessments under the Clean Air Act to protect the environment.…”

Large but decreasing effect of ozone on the European carbon sink

“…Because of the relationship between these two fluxes, the direct effect of O 3 damage on photosynthetic rate also leads to a reduction in g s . An alternative approach was taken by Lombardozzi et al (2012) in the CLM model in which photosynthesis and g s are decoupled, so that O 3 exposure affects carbon assimilation and transpiration independently. In JULES, changes in atmospheric CO 2 concentration also affect photosynthetic rate and g s ; consequently the interactive effects of changing concentrations of both CO 2 and O 3 are allowed for.…”

Beneficial effects of zeolites on plant photosynthesis

“…Photosynthesis responds to changes in many environmental parameters, such as light, temperature and CO 2 concentrations [18,19]. These three main factors, also called the limiting factors, play a crucial role on leaf level controlling the stomatal aperture [19][20][21]. Table 1).…”