Abstract Detail

The evolution of functional traits in plants: is the giant still sleeping?

Veromann-Jürgenson, Linda-Liisa [1], Tosens, Tiina [1], Brodribb, Timothy J. [2], Laanisto, Lauri [1], Niinemets, Ülo [3].

Evolution of photosynthetic limitations: mesophyll conductance in gymnosperms.

Mesophyll conductance is thought to be an important photosynthetic limitation in gymnosperms, but they currently constitute the most understudied plant group in the extent to which photosynthesis and intrinsic water use efficiency (WUE_i) are limited by mesophyll conductance. However, in gymnosperms, photosynthetic limitations, particularly how limitation combinations contribute to realized photosynthetic rates, have been studied in very few species precluding any broad conclusions about the share of different controls, hindering reliable global modelling of the gymnosperm forest contributions to global carbon cycle and responses to climate change. A comprehensive analysis of leaf gas-exchange, photosynthetic limitations, and mesophyll conductance (g_m) of 7% of extant gymnosperm species were performed to gain insight into the evolution of physiological controls on photosynthesis at the lower return end of the leaf economics spectrum. The studied species were grown in a common garden but originated from globally contrasting habitats and evolutionary histories. Low mesophyll conductance was the main limiting factor of photosynthesis in the majority of species. Remarkably, g_m varied 21-fold extending almost across the whole range of values observed in vascular plants to-date. Photosynthetic limitation analysis revealed that mesophyll and stomatal limitations were dominant. Both limitations were correlated with foliage structural characteristics, challenging the hypothesis that species phylogenetic background directly determines the partitioning of photosynthetic limitations. Ultra-structural analysis in 11 species revealed that the strongest sources of limitation were extremely thick mesophyll cell walls (T_cwm), high chloroplast thickness and variation in its shape and size, and the exposed surface area of chloroplasts per unit leaf area. In gymnosperms, the negative relationship between net assimilation per mass and leaf mass per area (LMA) reflected an increased T_cwm, whereas the easy-to-measure integrative trait, LMA failed to predict g_m. These adaptations may be relics from the atmospheric concentrations in which these genera evolved, still present due to evolutionary constraints, but may give evergreen gymnosperms an advantage over angiosperms in the rising CO₂ levels of this century.

1 - Estonian University of Life Sciences, Kreutzwaldi 1, Tartu, Tartumaa, 51014, Estonia
2 - University of Tasmania
3 - Estonian Academy of Sciences

Keywords:
gymnosperm
mesophyll conductance
photosynthetic limitation.

Presentation Type: Colloquium Presentations
Session: CO04, The Evolution of Functional Traits in Plant: Is the Giant Still Sleeping?
Location: Tucson J/Starr Pass
Date: Monday, July 29th, 2019
Time: 1:45 PM
Number: CO04002
Abstract ID:539
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize