Understanding the Impact of Drought on NOx Foliar Uptake in native California Species

The NOx cycle in forested regions, and the resistances NOx particles face to deposit onto leaves. The deposition velocity is the inverse of the total resistance, and is proportional to the uptake in the chamber.

There is significant foliar uptake of NOx (NO + NO2) in canopies affecting the amount of NOx, ozone, and other important atmospheric species in the troposphere. NOx uptake occurs through the diffusion into the stomata of leaves, which play an active role to processes like photosynthesis and transpiration. Drought stress in plants affects the opening of the stomata; plants typically adjust the opening of their stomata to minimize water loss while maximizing the rate of photosynthesis. For this study, we performed laboratory drought-stress experiments on Pinus ponderosa and Calocedrus decurrens, two common California native species, to study the relationship between stomatal NOx foliar uptake and drought stress. We found that while drought stress increased mesophyllic resistance, the effects on canopy-scale NOx foliar uptake was negligible. The effects of drought stress on NOx foliar uptake, at both leaf-level and canopy-level, are largely due to drought stress effects on stomatal conductance. At the canopy-level, effects of drought stress on leaf area, and thus total NOx foliar uptake, are likely to be important and need to be considered.

Box and whisker plots of water potentials for the control and drought groups of (a) *P. ponderosa* and (b) *C. decurrens.*

Plot of deposition velocity (Vd) versus total conductance to water vapor (gt) for (left) *P. ponderosa* and (right) *C. decurrens*. Blue markers and lines are data from drought-stressed trees and fits to the resistance model, respectively. Green markers and lines are data from control group trees and fits to the resistance model, respectively.

Publications contributed to by this work:

Delaria, E. R., B. K. Place, A. X. Liu, and R. C. Cohen, “Laboratory measurements of stomatal NO2 deposition to native California trees and the role of forests in the NOx cycle,” Atmos. Chem. Phys., 20, 14023–14041, https://doi.org/10.5194/acp-20-14023-2020, 2020.
Place, B. K., E. R. Delaria, A. X. Liu, and R. C. Cohen, “Leaf stomatal control over acyl peroxynitrate dry deposition to trees,” ACS Earth Space Chem., 4, 11, 2162–2170, https://doi.org/10.1021/acsearthspacechem.0c00152, 2020.

Presentations and Posters given for this work:

AGU Fall Meeting | Poster | San Francisco, CA | Dec 2019