Increased leaf area compensated photosynthetic downregulation in response to elevated CO₂ and warming in white birch

Abstract

Predicting photosynthetic acclimation to elevated CO2 and warming is difficult because they have opposite effects. We investigated physiological and morphological responses in white birch (Betula papyrifera Msrsh.) to a combination of CO2 and temperature (ACT: 400 µmol mol−1 CO2, current temperature; ECT: 750 µmol mol−1 CO2, current + 4 ºC temperature). ECT reduced photosynthesis, maximum Rubisco carboxylation (Vcmax), maximum electron transport rate (Jmax), photorespiration, daytime respiration, leaf N, stomatal and mesophyll conductance, but increased biomass, height, total leaf area, electron partitioning to carboxylation and oxygenation ratio and CO2 compensation point. The photosynthetic acclimation is consistent with the optimal carbon gain theory (carbon gain drives the coordination of carboxylation, electron transport and respiration). While the photosynthetic acclimation was similar to acclimation to elevated CO2, ECT reduced Jmax/Vcmax, which is consistent with the response to warming but opposite to the response to elevated CO2, suggesting that thermal acclimation may be the primary mechanism of photosynthetic acclimation to ECT and ECT probably altered N allocation between machinery for carboxylation and that for RuBP regeneration. The increase in total leaf area by ECT more than offset the negative effect of photosynthetic downregulation on carbon sequestration, resulting in faster growth and greater biomass under ECT.

Using leaf economic spectrum and photosynthetic acclimation to evaluate the potential performance of wintersweet under future climate conditions

“…We observed that Wintersweet exhibited a typical photosynthetic acclimation reaction. The effect of photosynthetic downregulation, however, is generally smaller than the stimulation of photosynthesis by the elevation of CO 2 , resulting in a higher actual rate of A n‐g under eCO 2 than under aCO 2 (Wang et al, 2022), as we have observed in this current study.…”

“…An interesting finding of this study is that wintersweet had very low stomatal conductance, less than 50 mmol m −2 s −1 in all treatments, which is much lower than typical values for deciduous broad‐leaved tree species under non‐stress conditions (Wang et al, 2022). In contrast, the mesophyll conductance values, gm, were comparable to those reported for other deciduous tree species (Elferjani et al, 2021).…”

Effects of CO2 Treatments on Functional Carbon Efficiencies and Growth of Forest Tree Seedlings: A Study of Four Early-Successional Deciduous Species

“…Under eCO 2 , these traits either remained the same or were upregulated in alders, whereas birches either downregulated or showed no change. Previous study [20] observed downregulation of V cmax and J max in white birch in response to eCO 2 and increased temperature, while [21] found increased stem dry mass growth in speckled alder and green alder in response to eCO 2 , indicating greater photosynthetic efficiency. Stomatal conductance (G wv600 ) is the only variable for which genus was not a significant factor and for which CO 2 had the largest effect, accounting for 15.4% of total variation, and downregulated for all species.…”

Nitrogen use strategy drives interspecific differences in plant photosynthetic CO2 acclimation

“…In addition, PAC is also accompanied by increased leaf mass per area (LMA) under elevated CO 2 concentration. This morphological change involves increased nonstructural carbohydrates storage, leaf thickness, and mesophyll tissue, partially compensating for the decreased photosynthetic capacity limited by N m (Gardiner et al, 2009; Wang et al, 2022; Yin, 2002).…”