Stomatal regulation in Douglas fir following a fungal-mediated chronic reduction in leaf area

Abstract

Pathogens can cause chronic premature needle abscission in coniferous species. To assess the potential impacts on tree productivity, stomatal regulation was investigated in Douglas fir with chronic stomatal occlusion and defoliation from varying levels of the Swiss needle cast (SNC) fungus, Phaeocryptopus gaeumannii. Levels of SNC disease and subsequent defoliation were manipulated by choosing six sites with varying levels of disease and by foliar applications of fungicides on six trees per site. Diurnal measurements of leaf water potential (Y leaf ), stomatal conductance (g s ) and vapor pressure deficit (D) were made on six fungicide treated and six control trees per site. In addition, leaf specific hydraulic conductance was calculated on a single branch (K L_B ) from three trees per treatment per site. Stomatal conductance at D=1 kPa (g sref ) was negatively correlated with fungal colonization (number of fruiting bodies present in needle stomata) and positively correlated with K L_B . Despite reduced needle retention in diseased trees, K L declined due to a reduction in sapwood area and permeability (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 (Y soil Y leaf )/ D], which assumes strict stomatal regulation of Y leaf . 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 .The results indicate that losses in productivity associated with physical blockage of stomata and defoliation are compounded by additional losses in K L and a reduction in g s in remaining functional stomata.

Swiss Needle Cast in Western Oregon Douglas-Fir Plantations: 20‐Year Monitoring Results

“…Only current-year foliage is colonized, and there appears to be no resistance to infection by the tree [19,20]. The fungus may be characterized as an endophyte or biotroph [9] because it does not kill cells of the leaf, and disease is caused when stomates of one-and two-year old leaves are occluded. Carbon uptake is directly related to percent of stomatal occlusion [9].…”

“…The fungus may be characterized as an endophyte or biotroph [9] because it does not kill cells of the leaf, and disease is caused when stomates of one-and two-year old leaves are occluded. Carbon uptake is directly related to percent of stomatal occlusion [9]. Disease emergence is associated with increased colonization of needles, stomatal plugging, inoculum load, loss of needles, needle chlorosis, and reduced growth.…”

Comparison of photosynthetic damage from arthropod herbivory and pathogen infection in understory hardwood saplings

“…Moreover, defenses against diVerent classes of damage such as herbivores and pathogens may not oVer cross-protection, thus exacerbating the costs of defense (Faeth 1992;Saikkonen et al 2001). Indeed, the costs of defense may be great enough that leaf abscission becomes a viable alternative to defense (Hoad et al 1998;Manter and Kavanagh 2003).…”

Physiological responses to folivory and phytopathogens in a riparian tree, Brabejum stellatifolium, native to the fynbos biome of South Africa

“…The diversion of carbon and nitrogen away from primary metabolism may be exacerbated when it is necessary for a plant to produce defence compounds against damage caused by folivorous insects and/or phytopathogens simultaneously (Mith€ ofer & Boland, 2012). This may increase the rate of leaf abscission (Manter & Kavanagh, 2003) instead of offering cross-protection (Aldea et al, 2006). Plant nutritional quality and plant water relations may be impacted negatively through a reduction in photosynthesis as a result of folivory or polypathogen activities (Robert, Bancal, & Lannou, 2002;Santos, Alves-Silva, Cornelissen, & Fernandes, 2013;Snoeijers, P erez-Garcia, Joosten, & Wit, 2000).…”