PARENT SESSION
Poster Session #40: Water Relations I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Stomatal sensitivity in Douglas-fir following a fungal-mediated reduction in leaf area, maximum stomatal conductance, and hydraulic conductance.

Manter, Daniel^*,1, Kavanagh, Kathleen², ¹ USDA Forest Service, Corvallis, OR² University of Idaho, Moscow, ID

ABSTRACT- Stomatal sensitivity to vapor pressure deficit (D) was investigated in Douglas-fir with chronic defoliation from varying levels of the Swiss needle cast (SNC) fungus, Phaeocryptopus gaeumannii. Regardless of infection level, stomatal conductance (g_s) declined exponentially with increasing D. g_sref (g_s @ D = 1kPa) was positively correlated with leaf-specific hydraulic conductance (K_L) and negatively correlated with fungal colonization (number of fruiting bodies present in needle stomata). Despite reduced needle retention in diseased trees, K_L declined due to a reduction in sapwood quantity and quality (i.e., increasing presence of latewood in functional sapwood). In general, stomatal sensitivity to D for all foliage was consistent with stomatal regulation based on a simple hydraulic model (g_s = K_L(_soil-_leaf)/ D), which assumes strict stomatal regulation of leaf water potential. However, when fungal presence reduced maximum g_s below the potential maximum supported by hydraulic architecture stomatal sensitivity was lower than expected based on the theoretical relationship: dg_s/dlnD = 0.6*g_sref.

KEY WORDS: stomata, conductance, defoliation, water-relations