Damage-Induced Spatial Heterogeneity of Photosynthesis: Mechanisms and Analysis

110 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.Damage to leaves caused by biotic agents may indirectly influence photosynthesis in areas not directly injured, and these indirect depressions of photosynthesis may sometimes be greater than those associated with tissue directly damaged. I investigated the indirect effects of herbivore and pathogen damage in soybean and hardwood species using spatially resolved measurements of Photosystem II quantum efficiency (phiPSII). I hypothesized that distinct classes of foliar damage differentially influence the spatial pattern of photosynthesis of the remaining tissue by various mechanisms, including photosynthetic down-regulation, production of defense-related oxidative species, and disruption of water transport leading to stomatal closure. Using a novel approach, which I adapted from geographical imaging, to analyze the spatial patterns of photosynthesis, its component processes, stomatal conductance, and defense deployment, I investigated the mechanisms underlying these effects under field and controlled environmental conditions. Quantitative analysis of images of chlorophyll fluorescence and the production of reactive oxygen species (ROS) following simultaneous exposure of soybean leaves to atmospheric O3 and soybean mosaic virus revealed that areas of the leaf where phi PSII was depressed also experienced an accumulation of ROS. This correlation suggests a causal relationship between oxidative stress and inhibition of photosynthesis. Herbivory by Popillia japonica and Helicoverpa zea (Boddie) caused a 20--90% increase in transpiration from soybean leaflets without affecting carbon assimilation rates or photosynthetic efficiency (phiPSII). The depression of phiPSII caused by fungal infections and galls on hardwood tree saplings extended > 2.5 times further from the visible damage and was ∼40% larger than for chewing damage. Areas of depressed phiPSII around fungal infections on oaks growing in elevated CO2 were more than five times larger than those grown in ambient conditions, suggesting that this element of global change may influence the indirect effects of biotic damage on photosynthesis. Whereas chewing damage did not propagate, the depression of photosynthetic performance surrounding fungal and gall infections may add up to an impact 2--50 times greater than that estimated based on visible injuries alone. This research provides a mechanistic and quantitative understanding of the spatial patterns of photosynthesis that develop on leaves exposed to biotic damage.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD