DOSE-DEPENDENT SUPPRESSION OF LEAF-LEVEL GAS EXCHANGE BY WILDFIRE SMOKE IN CORN

Abstract

Wildfire events are increasing in frequency and intensity across many regions, raising concern about the effects of smoke on agricultural productivity and ecosystem function. Wildfire smoke contains a complex mixture of particulate matter and gases that can interact with plant leaves and potentially alter photosynthesis and plant gas exchange. However, the mechanisms by which smoke exposure influences plant physiological processes remain poorly understood. We investigated the effects of wildfire smoke particulate matter (PM2.5) on leaf-level gas exchange in corn (Zea mays L.) using controlled chamber fumigation experiments. Plants were exposed to clean air or smoke for four hours at three PM2.5 concentration ranges (400-600, 600-1000, and 1200 2000 µg m-3). Net CO2 assimilation and stomatal conductance were measured before and after exposures and treatment responses were evaluated using net smoke effects and relative percent changes in gas exchange compared between PM2.5 groups. Relative percent change showed a significant (p=0.005) decline in net CO2 assimilation in medium (-36%) and high (-30%) PM2.5 concentrations when compared to control (-12%). Stomatal conductance showed no significant decrease. Interestingly, averaged values for net smoke effect showed a decreasing trend for net CO2 assimilation with increasing PM2.5 concentrations and the opposite trend with stomatal conductance. This observed divergence suggests reduced mesophyll conductance and biochemical impairment by two primary non-stomatal pathways, VOC-driven biochemical and diffusion constraints, and PM2.5-driven internal and chemical effects.