Abstract
Stomatal CO2 responsiveness and photosynthetic capacity vary greatly among plant species, but the factors controlling these physiological leaf traits are often poorly understood. To explore if these traits are linked to taxonomic group identity and/or to other plant functional traits, we investigated the short-term stomatal CO2 responses and the maximum rates of photosynthetic carboxylation (Vcmax) and electron transport (Jmax) in an evolutionary broad range of tropical woody plant species. The study included 21 species representing four major seed plant taxa: gymnosperms, monocots, rosids and asterids. We found that stomatal closure responses to increased CO2 were stronger in angiosperms than in gymnosperms, and in monocots compared to dicots. Stomatal CO2 responsiveness was not significantly related to any of the other functional traits investigated, while a parameter describing the relationship between photosynthesis and stomatal conductance in combined leaf gas exchange models (g1) was related to leaf area-specific plant hydraulic conductance. For photosynthesis, we found that the interspecific variation in Vcmax and Jmax was related to within leaf nitrogen (N) allocation rather than to area-based total leaf N content. Within-leaf N allocation and water use were strongly co-ordinated (r2 = 0.67), such that species with high fractional N investments into compounds maximizing photosynthetic capacity also had high stomatal conductance. We conclude that while stomatal CO2 responsiveness of tropical woody species seems poorly related to other plant functional traits, photosynthetic capacity is linked to fractional within-leaf N allocation rather than total leaf N content and is closely co-ordinated with leaf water use.
Highlights
Anthropogenic fossil fuel burning and land use change have increased the atmospheric carbon dioxide concentration [CO2] by over 40% (Ciais et al 2013), with today’s concentration of over 400 μmol mol−1 being the highest in approximately 40 millions years (Frank et al 2015)
It is plausible that stomatal CO2 responsiveness is linked to hydraulic traits since plants with high hydraulic conductance often exhibit tight stomatal control over transpiration to avoid severe cavitation (Bond and Kavanagh 1999)
To improve the poor understanding of the phylogenetic and functional controls of the large interspecific variation in stomatal CO2 responsiveness and photosynthetic capacity among tropical woody species, we examined physiological, chemical and structural plant traits in an evolutionary broad cross-section of tropical woody seed plant species in a common garden experiment in Rwanda
Summary
Anthropogenic fossil fuel burning and land use change have increased the atmospheric carbon dioxide concentration [CO2] by over 40% (Ciais et al 2013), with today’s concentration of over 400 μmol mol−1 being the highest in approximately 40 millions years (Frank et al 2015). A better understanding of the factors that control the large natural variation in short-term stomatal CO2 responses would provide indication of which plant species and groups that are likely to experience large increases in water-use efficiency in future higher [CO2] scenarios. Both the short-term stomatal CO2 response and the longterm effect of growth under elevated [CO2] on gs have been found to be weaker in gymnosperms compared to angiosperms (Medlyn et al 2001; Brodribb et al 2009). Measurements were done on five individual plants, measuring leaf gas exchange on one fully developed leaf of each individual (except for Phoenix reclinata, where two and three leaves were measured in each of two different plants)
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