Infestation and Hydraulic Consequences of Induced Carbon Starvation

Abstract

Drought impacts on forests, including widespread die-off, are likely to increase with future climate change, although the physiological responses of trees to lethal drought are poorly understood. In particular, in situ examinations of carbon starvation and its interactions with and effects on infestation and hydraulic vulnerability are largely lacking. In this study, we conducted a controlled, in situ, repeated defoliation experiment to induce carbon stress in isolated trembling aspen (Populus tremuloides) ramets. We monitored leaf morphology, leaves per branch, and multitissue carbohydrate concentrations during canopy defoliation. We examined the subsequent effects of defoliation and defoliation-induced carbon stress on vulnerability to insect/fungus infestation and hydraulic vulnerability the following year. Defoliated ramets flushed multiple canopies, which coincided with moderate drawdown of nonstructural carbohydrate reserves. Infestation frequency greatly increased and hydraulic conductivity decreased 1 year after defoliation. Despite incomplete carbohydrate drawdown from defoliation and relatively rapid carbohydrate recovery, suggesting considerable carbohydrate reserves in aspen, defoliation-induced carbon stress held significant consequences for vulnerability to mortality agents and hydraulic performance. Our results indicate that multiyear consequences of drought via feedbacks are likely important for understanding forests' responses to drought and climate change over the coming decades.

Climate Change: Resetting Plant-Insect Interactions

“…Much of what is known about impacts of recurrent defoliation events derives from studies of plant species that are harvested for economic purposes (Endress et al, 2004). The existing literature suggests that repeated defoliation induces carbon (C) stress and increases vulnerability to pest and pathogen infestation as well as drought (Anderegg and Callaway, 2012). In trembling aspen (Populus tremuloides), multiple defoliations can cause multiple leaf flushes, incurring drawdown of nonstructural carbohydrate reserves.…”

Allometric Trajectories and “Stress”: A Quantitative Approach

“…In a similar way, shoots with substantial amounts of stem tissue removed would lose significant amounts of water conducting and nutrient storage volume. Although defoliation experiments show a variety of short term responses to tissue removal (Ferraro and Oesterheld, 2002), both loss of stem as well as loss of leaves are expected on average and in the long run to result in lower net photosynthesis and lowered fitness components (Anderegg and Callaway, 2012) such as seed production (i.e., fecundity). Irreversible damage presumably marks the amount of damage to one or both variables that leads to death.…”

“…If an allometric relationship, e.g., leaf mass vs. stem volume, is maintained within a species by selection, then a drastic displacement from the relationship is expected to result in lower performance. For example, sustained defoliation markedly reduces fitness (Anderegg and Callaway, 2012). Drastic removal of sapwood tissue can have a similar effect.…”

Causes, consequences, and the future of forest mortality due to climate change

“…The processes of hydraulic failure and carbon starvation are nearly always observed to co-occur in both observational studies and during experimental drought-manipulations that induce mortality (Galiano et al 2011, Galvez et al 2011, Levanič et al 2011, Anderegg et al 2012b, Plaut et al 2012, Quirk et al 2013, Sevanto et al 2013, Hartmann et al 2013. However, the relative dominance of hydraulic failure versus carbon starvation in driving mortality appears to depend on the rate of stress onset in plants, with faster drought causing more hydraulic failure and vice versa (Mitchell et al 2013; consistent with the predictions of McDowell et al 2008).…”