Thermal acclimation of photosynthesis and respiration of southern and northern white spruce seed sources tested along a regional climatic gradient indicates limited potential to cope with temperature warming

Abstract

Background and AimsKnowledge of thermal acclimation of physiological processes of boreal tree species is necessary to determine their ability to adapt to predicted global warming and reduce the uncertainty around the anticipated feedbacks of forest ecosystems and global carbon cycle to climate change. The objective of this work was to examine the extent of thermal acclimation of net photosynthesis (An) and dark respiration (Rd) of two distant white spruce (Picea glauca) seed sources (from south and north of the commerial forest zone in Québec) in response to latitudinal and seasonal variations in growing conditions.MethodsThe temperature responses of An, its biochemical and biophysical limitations, and Rd were measured in 1-year-old needles of seedlings from the seed sources growing in eight forest plantations along a regional thermal gradient of 5.5 °C in Québec, Canada.Key ResultsThe average optimum temperature (Topt) for An was 19 ± 1.2 °C and was similar among seed sources and plantation sites along the thermal gradient. Net photosynthesis at Topt (Aopt) varied significantly among plantation sites and was quadratically related to the mean July temperature (MJT) of plantation sites. Topt for mesophyll conductance, maximum electron transport rate and maximum rate of carboxylation were 28, 22 and 30 °C, respectively. Basal respiration rate (Rd at 10 °C) was linearly and negatively associated with MJT. Q10 of Rd (the rate of change in Rd with a 10 °C increase in temperature) did not show any significant relationship with MJT and averaged 1.5 ± 0.1. The two seed sources were similar in their thermal responses to latitudinal and seasonal variations in growing conditions.ConclusionsThe results showed moderate thermal acclimation of respiration and no evidence for thermal acclimation of photosynthesis or local genetic adaptation for traits related to thermal acclimation. Therefore, growth of local white spruces may decline in future climates.

Taxonomy, together with ontogeny and growing conditions, drives needleleaf species' sensitivity to climate in boreal North America

“…Excess heat during late summer and autumn may lead to declines in carbohydrate reserve accumulation at the end of the growing season, thereby negatively affecting spring growth, as was previously observed in both boreal North America and Northern Europe Ols et al, 2018). The steepest declines in observed growth for individuals that were the most greatly affected by above-average temperature during the summer of the year prior to ring formation suggest that hot extremes are one of the primary determinants of growth trajectories for boreal black spruce forests, as has been observed for white spruce seedlings in plantations by Benomar et al (2018). The steepest declines in observed growth for individuals that were the most greatly affected by above-average temperature during the summer of the year prior to ring formation suggest that hot extremes are one of the primary determinants of growth trajectories for boreal black spruce forests, as has been observed for white spruce seedlings in plantations by Benomar et al (2018).…”

Thermal acclimation of photosynthetic activity and Rubisco content in two hybrid poplar clones

“…The effect of growth temperature on temperature response curve of apparent V cmax and J in terms of their values at reference temperature of 25°C, their T opt and their activation energy is species-dependant as reported by recent studies (Benomar et al, 2018; Hikosaka et al, 2006; Hikosaka et al, 1999; Kattge and Knorr, 2007; Slot and Winter 2017; Way and Yamori 2014). In our study, the apparent V cmax 25 stimulated by warm growth temperature for clone M×B, might explain the noticeable increase of A opt (up to 50 %) by warmer growth conditions under high N level.…”

“…In contrast, no acclimation of R d was observed for clone M×B which may be related to the unchanged density of mitochondria (Atkin and Tjoelker, 2003). Moreover, nitrogen had no effect on thermal acclimation of Q 10 for both clones as observed in other tree species (Benomar et al, 2018; Tjoelker et al, 1999).…”

“…On the other hand, Yamori et al, (2011) found that photosynthesis temperature response of several C 3 plants was generally RuBP carboxylation-limited above the T opt at low leaf nitrogen content while, under high N level, it shifted to a limitation by RuBP regeneration. However, the effect of temperature on the limiting steps of A n ( V cmax vs. J max ) may depend on the reponse of CO 2 conductance ( g s and g m ) as well (Benomar et al, 2018; Qiu et al, 2017; von Caemmerer and Evans, 2015; Warren, 2008). Moreover, RuBisCO-related effect on A n at above-optimal temperature may depend on the plasticity of J max 25 to V cmax 25 ratio.…”

“…Moreover, RuBisCO-related effect on A n at above-optimal temperature may depend on the plasticity of J max 25 to V cmax 25 ratio. From this perspective, this may be applicable only for cold-adapted plant species, which are characterized by a higher J max 25 to V cmax 25 ratio and low or lack of its adjustment in response to both N level and growth temperature (Benomar et al, 2018; Kattge and Knorr, 2007). Weston et al (2007) did not observe any change in RuBisCO concentration for two genotypes of Acer rubrum grown under hot and optimal temperatures.…”