A trait‐based ecosystem model suggests that long‐term responsiveness to rising atmospheric CO₂ concentration is greater in slow‐growing than fast‐growing plants

Abstract

Summary1. Atmospheric carbon dioxide concentration (C a ) has a direct and measurable effect on plant growth. However, it does not affect all plant species equally, which could lead to shifts in competitive dominance of species in ecosystems. 2. We used a dynamic plant carbon-nitrogen model to systematically examine how species traits affect the long-term C a responsiveness of C 3 plants when growing as established monocultures in the field. The model was tested against responses of 7 C 3 herbaceous species growing in a free-air C a enrichment (FACE) experiment (BioCON) in Minnesota, USA. 3. Model simulations showed that several species traits affected the C a response strongly, giving rise to a number of testable hypotheses about interspecific differences in responsiveness to C a . The largest responses to rising C a were obtained for species with low carbon-use efficiency (net primary production: gross primary production ratio), low foliar carbon allocation, low stomatal conductance, low instantaneous photosynthetic nitrogen use efficiency and low specific leaf area. 4. In general, our model predicted that, for established plants growing in resource-limited field conditions, species with slow growth rates would be most responsive to elevated C a . This prediction was supported by data from the BioCON experiment. 5. Our model also predicts that, for young plants growing in non-resource-limited conditions, species with high growth rates will be most responsive to elevated C a . This difference in species ranking under different resource availabilities is largely explained by the indirect effects of C a on leaf area. Leaf-area feedbacks favour fast-growing species the most during leaf-area expansion, but following stand maturation they favour slow-growing species the most. 6. These results imply that species that respond strongly to elevated C a in short-term (nonresource-limited) glasshouse experiments are unlikely to also be the most responsive in resource-limited field conditions, and therefore that we cannot directly extrapolate from glasshouse experiments to predict which species will be most responsive to elevated C a in the long term.

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2concentration

“…The lack of a growth response of Tabebuia and Chrysophyllum to c a is consistent with previous experiments in which seedlings of tropical tree species were grown in unfertilized soil (Lovelock et al, 1998;Winter et al, 2000;Cernusak et al, 2011). The causes of differential responses of plants to elevated c a in greenhouse experiments have recently been revisited by Ali et al (2013). They contrasted evidence from short-term pot experiments, where species with high RGR are found to be most responsive to elevated c a (Poorter and Navas, 2003;Körner, 2006), with model predictions that species with low C allocation to leaf production (LMR), and low stomatal conductance (g s ), instantaneous PNUE and SLA will be most responsive.…”

“…In agreement with the predictions of Ali et al (2013), the conifers had markedly lower g s , PNUE and SLA, but had the highest LMR. Low LMR in Tabebuia, although this species had the highest SLA, may therefore in part explain its low responsiveness species to c a .…”

“…Results from this study are consistent with the expected growth enhancement for evergreen species with low mesophyll conductance (Niinemets et al, 2011), and more generally for slow-growing species with low carbon-use efficiency (Ali et al 2013). Alternatively, the growth response of the conifers may reflect an advantage in nutrient (N) acquisition.…”

“…They contrasted evidence from short-term pot experiments, where species with high RGR are found to be most responsive to elevated c a (Poorter and Navas, 2003;Körner, 2006), with model predictions that species with low C allocation to leaf production (LMR), and low stomatal conductance (g s ), instantaneous PNUE and SLA will be most responsive. Differences between longer-term, model-predicted responses to c a and those observed in greenhouses were suggested to result from a short-term advantage to fast-growing species able to rapidly increase in leaf area during the quasi-exponential phase of seedling growth (Ali et al, 2013).…”

From plant functional types to plant functional traits

“…For example, a dynamic plant carbon-nitrogen model has been used to simulate the long-term response of plants to increasing atmospheric CO 2 . In this model, a plant species was represented by a vector of trait values, and physiological processes were also presented as traits (Ali et al, 2013). Scheiter et al (2013) proposed a conceptual DGVM based in community ecology and coexistence theory.…”