Stomatal sensitivity to CO₂ diverges between angiosperm and gymnosperm tree species

Abstract

The response of tree leaf gas exchange to elevated CO2 concentrations has been investigated in numerous experiments along the past 30 years. Stomatal regulation is a major plant control over leaf gas exchange, and the response to the increasing CO2 will shape the biological activity of forests in the future. Here, we collected 144 records from 57 species on stomatal conductance in CO2 manipulation experiments on trees (340–980 ppm CO2). CO2‐induced stomatal downregulation was calculated as the slope of the linear regression between stomatal conductance and [CO2]. Among tree species, the slope (a) of change in stomatal conductance per 100 ppm CO2 increase ranged between 0 and −151, indicating stomatal downregulation, and only four species showed upregulation. There was a significant divergence between evergreen gymnosperms (a = −3.6 ± 1.0), deciduous angiosperms (a = −16.3 ± 3.1) and evergreen angiosperms (a = −32.8 ± 7.1). Gymnosperms were less sensitive to CO2 changes than deciduous angiosperms even when considering only field experiments. The significant role of tree functional group in predicting CO2‐induced stomatal downregulation was detected in multiple mixed‐effect models, with p values ranging between 0.0002 and 0.0295. The significantly higher stomatal sensitivity to CO2 of angiosperms versus gymnosperms might be related to the overall higher stomatal conductance of angiosperms; their thinner leaves, in turn losing water faster; and the decreasing atmospheric [CO2] at the time of their taxa diversification. We conclude that species differences must be taken into account in forecasting future forest fluxes. A plain language summary is available for this article.

Photosynthetic plasticity of a tropical tree species, Tabebuia rosea, in response to elevated temperature and [CO2]

“…Indeed, in the tropical tree species A. glandulosa neither warming nor elevated CO 2 significantly reduced V CMax , but the combination of the two did (Fauset et al, 2019). In contrast to common observations in studies in which only CO 2 is increased (e.g., Ainsworth & Rogers, 2007; Klein & Ramon, 2019), stomatal conductance and stomatal density were not reduced in our combined warming and CO 2 enrichment experiment, suggesting that the CO 2 effect may be temperature dependent.…”

Increased Nitrogen Availability in the Soil Under Mature Picea abies Trees Exposed to Elevated CO2 Concentrations

“…In the present study, however, stomatal conductance of the spruce trees was not affected by elevated CO 2 and photosynthetic capacity showed little downward adjustment (Leuzinger and Bader, 2012;Klein et al, 2016a). This finding is in line with a general divergence between broadleaved trees and conifers, with the latter tending to maintain stomatal conductance under elevated CO 2 (Klein and Ramon, 2019). It may also be related to the aforementioned tendency of the conifers needles to maintain or even increase their N concentration under elevated CO 2 .…”

SurEau: a mechanistic model of plant water relations under extreme drought

“…Among the different facets of climate change, there are large uncertainties in the literature regarding the potential effects of increasing atmospheric CO 2 (Cheaib et al 2012). However, it is known that an increase in atmospheric CO 2 can trigger the plasticity of certain traits, but there is little data available so far (Domec et al 2017;Klein and Ramon 2019). In our last simulation exercise, we tried to evaluate the potential effects of trait plasticity on the risk of oak hydraulic failure at the end of the century for the RCP8.5 scenario (900 ppm).…”