Leaf photosynthetic, economics and hydraulic traits are decoupled among genotypes of a widespread species of eucalypt grown under ambient and elevatedCO₂

Abstract

Summary Leaf economics and hydraulic traits strongly influence photosynthesis. While the level of coordination among these traits can differ between sets of species, leaf functional trait coordination within species remains poorly understood. Furthermore, elevated concentrations of atmospheric CO2 commonly influence the expression of leaf photosynthetic, economics and hydraulic traits in contrasting ways, yet the effect of variable concentrations of atmospheric CO2 on patterns of trait coordination within species remains largely untested. We examined the relationships among key leaf photosynthetic (e.g. net photosynthesis and photosynthetic biochemistry), economics and water‐use (e.g. leaf mass per unit area and stomatal conductance) and hydraulic traits (e.g. vein density) in 14 genotypes of Eucalyptus camaldulensis grown in ambient (aCO2) and elevated (eCO2) [CO2]. We examined the level of coordination among leaf traits in aCO2 and then assessed whether growth in eCO2 altered that coordination. We found that leaf traits related to photosynthetic capacity, economics and water‐use, and hydraulics were decoupled among genotypes grown in aCO2, yet strong relationships were generally observed among suites of traits within each ‘functional group’. Significant responses to growth in eCO2 were observed for most leaf photosynthetic and economics and water‐use traits, with the magnitude and direction of the response varying among traits. In contrast, leaf hydraulics traits were unaffected by variable growth CO2. Despite this, growth in eCO2 did not substantially alter patterns of leaf trait coordination observed in aCO2. These results suggest suites of leaf traits associated with photosynthetic capacity, economics and water‐use and hydraulics, respectively, can form independent axes of variation among genotypes of a single species, regardless of growth CO2. Although growth in eCO2 did not substantially alter patterns of trait coordination, decoupling of leaf functional traits among genotypes may allow genetically distinct populations to produce novel combinations of traits that may be adaptive in response to changes in their local environment.

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

“…1, Table 2). These results are consistent with Hypothesis 1 and previous findings for this and many other species (Tissue et al 1997;Reddy et al 2010;Blackman et al 2016), and probably reflect higher [CO 2 ] at the carboxylation sites of Rubisco under eCO 2 growth conditions, as well as reduced photorespiration. Because photorespiration is generally higher in aCO 2 than in eCO 2 (Krall and Edwards 1992), the ETR : A ratio should be higher in aCO 2 .…”

“…Previous research has observed genotypic variation in physiological response to eCO 2 within E, camaldulensis var. camaldulensis (Dillon et al 2015;Blackman et al 2016) but this may not be universal across all tree species (Resco de Dios et al 2016b). Here, we did not detect significant effects of genotype in our overall statistical model.…”

“…A shift in correlations was also found for leaf economics, hydraulics and photosynthetic traits in E. camaldulensis var. camaldulensis plants grown in aCO 2 compared with eCO 2 (Blackman et al 2016). These results suggest that some functional components of photosynthesis are differently sensitive to eCO 2 , which results in complex responses to an episodic stress.…”

“…However, for unknown reasons, this was not the case before the heatwave, but was possibly caused by our relatively small sample sizes. On the other hand, Blackman et al (2016) found that specific leaf area and N content on an area basis were different for E. camaldulensis var. camaldulensis in aCO 2 vs. eCO 2 , which may have affected light absorption by the leaves, or perhaps other optical properties that could affect the computation of ETR.…”

“…Photosynthesis can also be constrained by structure, such as vein density, which affects sugar export (Adams et al 2007;Adams et al 2013); however, in a prior study vein density was not affected by eCO 2 for E. camaldulensis var. camaldulensis (Blackman et al 2016).…”