Do Canker Pathogens Limit the Supply of CO2 for Photosynthesis? Estimation of Stomatal and Internal Limitations in Maple Leaves in Response to Phytophthora cactorum Inoculations

Thursday, July 25, 2013: 12:30 PM
Desert Salon 9-10 (Desert Springs J.W Marriott Resort )
Hyungmin Rho , University of Washington, Seattle, WA
Drew Zwart, PhD , Center for Urban Horticulture, School of Forest Resources, University of Washington, Seattle, WA
Soo-Hyung Kim , Center for Urban Horticulture, University of Washington, Seattle, WA
Phytophthora diseases are a major limiting factor to crop, forest, and amenity plant growth worldwide. Canker pathogens can affect net CO2 assimilation (An) though phloem and xylem infections. While prior studies have shown that Phytophthora canker infections limit An, reports regarding the underlying mechanisms are variable. One possible pathway is through lowering CO2 supply by reduced stomatal (gs) and mesophyll conductance (gm). Our objective of this study was to quantify CO2 supply limitations in response to P. cactorum inoculations in red maple (Acer rubrum). We hypothesized that the inoculated plants will reduce both gs and gm, compared with the non-inoculated controls. We tested this hypothesis using the two methods to determine gs and gm: 1) a method combining leaf gas exchange, chlorophyll fluorescence, and the biochemical model of photosynthesis; and 2) a method utilizing the photosynthesis model with leaf gas-exchange measurements made at the two O2 concentrations (2% and 21%). Our results show that gs and gm in the maple leaves decreased due to P. cactorum inoculations, leading to the limitation of CO2 supply to the site of carboxylation. The two different gm estimation methods produced comparable gm values and similar response patterns.