Relationships between climate of origin and photosynthetic responses to an episodic heatwave depend on growth CO2 concentration for Eucalyptus camaldulensis var. camaldulensis

Abstract

Stressful episodic weather is likely to affect the C balance of trees as the climate changes, potentially altering survival. However, the role of elevated CO2 concentration ([CO2]) in tolerating off-season episodic extremes is not clear. We tested for interactive effects of elevated CO2 and springtime heat stress on photosynthesis for seven genotypes of Eucalyptus camaldulensis Dehnh. var. camaldulensis, representing its widespread distribution across south-eastern Australia. We grew clonal material under glasshouse conditions of ambient (aCO2; 400 parts per million (ppm)) or elevated (eCO2; 640 ppm) [CO2], and air temperatures of 25 : 17°C (day : night), and measured the electron transport rate in PSII (ETR), stomatal conductance to water vapour (gs) and net CO2 assimilation (A). Measurements were made before, during and after a four-day temperature excursion of 35 : 27°C. ETR and A were ~17% higher for plants grown in eCO2 than in aCO2. Photosynthesis remained stable for plants in eCO2 during the heatwave. Based on the effect size ratio (eCO2 : aCO2), gs and ETR were temporarily affected more by the heatwave than A. A reduction in ETR in eCO2 was the only lasting effect of the heatwave. There were no significant differences among genotypes. Correlations between photosynthesis and climate of origin differed for plants grown in aCO2 compared with eCO2, suggesting potential complex and multiple control points on photosynthesis.

Repeated extreme heatwaves result in higher leaf thermal tolerances and greater safety margins

“…The extreme temperatures during heatwaves contribute to dry atmospheric conditions with high vapour pressure deficits (Teskey et al ., 2015), and are well known to directly affect plant physiology. Short‐term heatwaves have been shown to change the expression profile of heat shock proteins (Aspinwall et al ., 2019), reduce photosynthetic rates (Duarte et al ., 2016; Loik et al ., 2017), impact photosystem II (PSII; Guha et al ., 2018; Pšidová et al ., 2018), and change carbon allocation (Werner et al ., 2020). This can culminate in major ecosystem effects such as forest dieback events, loss of primary production, and alteration of important ecosystem functions (Ciais et al ., 2005; Reichstein et al ., 2013; Allen et al ., 2015; Teskey et al ., 2015; van Gorsel et al ., 2016).…”

Effects of a Heat Wave on Nocturnal Stomatal Conductance in Eucalyptus camaldulensis

“…Genetic variability in the response to heat waves could be related to the climate of origin [20]. We did not perform detailed analyses based on climate of origin because we only had one genotype from each location.…”

“…In other words, daytime measurements were collected with half of the plants experiencing a heat wave (and the other half not experiencing a heat wave), but nighttime measurements were performed immediately after the heat wave under ambient pre-heat-wave conditions and, consequently, all plants experienced the same environment. Further details on glasshouse design and set-up are given by [17,20].…”

Elevated CO2 Did Not Stimulate Stem Growth in 11 Provenances of a Globally Important Hardwood Plantation Species

“…If CUE is improved under eCO 2 , carbon allocation patterns may change such that increased rates of C assimilation stimulate growth of roots rather than stems (Finzi et al, 2007;De Kauwe et al, 2014;Zaehle et al, 2014), which would be undesirable for the timber growing industry, yet potentially improve resilience during dry conditions (Grote et al, 2016). However, identifying provenances that show net-positive stem growth under eCO 2 is critical to meeting a rising global demand for wood and wood products (Wang et al, 2010;Booth et al, 2015;Loik et al, 2017).…”