Differential ecophysiological responses and resilience to heat wave events in four co-occurring temperate tree species

Abstract

Extreme summer heat waves are known to induce foliar and stem mortality in temperate forest ecosystems, yet our mechanistic knowledge of physiological thresholds for damage is lacking. Current spatiotemporal simulations of forest growth responses to climate change fail to explain the variability between co-occurring tree species to climate extremes, indicating a need for new model frameworks that include mechanistic understanding of trait-specific responses. In this context, using manipulative heat wave (hw) experiments we investigated ecophysiological responses and physiological recovery in four co-occurring temperate tree species of the southeastern United States including three deciduous angiosperms: southern red oak (Quercus falcata Michx.), shumard oak (Q. shumardii Buckl.) and, tulip-poplar (Liriodendron tulipifera L.) and one evergreen conifer: eastern white pine (Pinus strobus L.). The objectives were to investigate inter-specific differences in ecophysiological responses to hw events to understand mechanistic differences in resilience that may be useful for future model development. Two-year-old, well-irrigated potted saplings were exposed to progressively increasing extreme hw diurnal cycles followed by a recovery cycle, with peak midday air temperature increasing from 37 • C to a maximum of 51 • C on the third day of the hw. Plants were assessed for various photosynthetic and water use responses, chlorophyll fluorescence and photosystem-II (PSII) activity, leaf temperature and foliar pigments. Intense heat caused progressive down-regulation in net photosynthesis, but the stomata remained operational, which helped cool leaves through loss of latent heat. Even though whole plant transpiration increased for all species, the rate plateaued at higher hw events that allowed leaf temperature to exceed 45 • C, well beyond the optimal range. A significant increase in non-photochemical quenching over the hw cycles was evident in all species though indications of both transient and chronic PSII damage were evident in the most heat sensitive species, pine and tulip poplar. The oaks, especially Q. falcata, showed greater thermotolerance than other species with a higher threshold for photodamage to PSII, rapid overnight recovery of photoinhibition and minimal heat-induced canopy necrosis. We conclude that these co-occurring tree species exhibit large variability in thermotolerance and in their capability to repair both transient and chronic photodamage. Our results indicate that extreme heat induced damage to PSII within the leaf chloroplasts may be a mechanistic trait that can be used to project how different species respond to extreme weather events.

Range size and growth temperature influence Eucalyptus species responses to an experimental heatwave

“…These results suggest impairment of energy transfer and production at high temperatures, particularly in EB since that species was most negatively affected by the heatwave. Guha et al, () identified similar relationships between heatwave tissue damage, reductions in A sat , and inhibition of PSII among four northern temperate tree species. We also found that the decline in PSII efficiency ( F v ʹ/ F m ʹ) was smallest in EC and largest in EB, indicating that EB was dissipating more excited energy to non‐photochemical quenching or possibly photorespiration than EC.…”

“…These results suggest impairment of energy transfer and production at high temperatures, particularly in EB since that species was most negatively affected by the heatwave. Guha et al, (2018) However, short-term heat exposure is more likely to inhibit Rubisco activase and cause temporary deactivation of Rubisco than substantially reduce Calvin cycle enzyme concentrations (Haldimann & Feller, 2004;Hozain et al, 2010;Salvucci & Crafts-Brandner, 2004).…”

“…A few studies have demonstrated that tree species may vary in their physiological and biochemical responses to heatwaves (Ameye et al, 2012;Guha, Han, Cummings, McLennan, & Warren, 2018;Wujeska-Klause, Bossinger, & Tausz, 2015). Even when high temperatures reduce A, some tree species maintain high g s (and transpiration) which helps cool leaves (Drake et al, 2018;Urban, Ingwers, McGuire, & Teskey, 2017).…”

Heat Waves Alter Carbon Allocation and Increase Mortality of Aleppo Pine Under Dry Conditions

“…The apparent small decline of chlorophyll fluorescence parameters in the heat treatment, measured 1 day after the last heat wave had ended, may either reflect a relative mild impairment of the photosynthetic apparatus, or indicate a fast recovery of chlorophyll fluorescence parameters 1 day after the acute stress. Fast recovery responses of photosynthetic parameters after acute heat waves (when water was not limiting) were observed in herbaceous plants, as well as in some tree species and typically relate to temperatures <45 • C (Hüve et al, 2011;Ameye et al, 2012;Guha et al, 2018). However, complete recovery of the few surviving seedlings in the heat-drought treatment seemed to be impaired.…”

Understanding the Critical Impact Path on Vegetation Growth under Climate Extremes and Human Influence

“…Furthermore, an increase in heat also negatively influenced the EVIavg, and HW and SU mainly had a negative impact on vegetation health for different elevations and vegetation types. There is evidence that extreme heat waves in summer can induce foliar and stem mortality in temperate forests [59,60]. However, the degree of response and impact can differ by species and region, and this study demonstrated the negative influence of increasing heat on Jeju's vegetation.…”