Abstract
In order to be successful in a given environment a plant should invest in a vein network and stomatal distribution that ensures balance between both water supply and demand. Vein density (Dv) and stomatal density (SD) have been shown to be strongly positively correlated in response to a range of environmental variables in more recently evolved plant species, but the extent of this relationship has not been confirmed in earlier diverging plant lineages. In order to examine the effect of a changing atmosphere on the relationship between Dv and SD, five early-diverging plant species representing two different reproductive plant grades were grown for 7 months in a palaeo-treatment comprising an O2:CO2 ratio that has occurred multiple times throughout plant evolutionary history. Results show a range of species-specific Dv and SD responses to the palaeo-treatment, however, we show that the strong relationship between Dv and SD under modern ambient atmospheric composition is maintained following exposure to the palaeo-treatment. This suggests strong inter-specific co-ordination between vein and stomatal traits for our study species even under relatively extreme environmental change. This co-ordination supports existing plant function proxies that use the distance between vein endings and stomata (Dm) to infer plant palaeo-physiology.
Highlights
Global diversity in plant and leaf architecture reflects a plasticity in morphology that allows plants to survive in a range of environments (Díaz et al, 2016)
A significant decrease in stomatal density (SD) is seen in two species (Chimonanthus praecox shows a 24% and Zantedeschia aethiopica a 34% decrease), Magnolia delavayi and Cyathea australis show a non-significant yet noticeable decrease (8 and 15%, respectively), and another angiosperm (Cornus capitata) shows a small (9%), but nonsignificant increase (Figures 2A and 3)
Dv shows a similar mix of responses, three of the species show a significant decrease (Chimonanthus praecox, Zantedeschia aethiopica, and Cyathea australis decrease by 15, 12, and 17%, respectively), Magnolia delavayi shows a very slight (2%) yet non-significant increase, and Cornus capitata shows a significant (14%) increase (Figures 2B and 3)
Summary
Global diversity in plant and leaf architecture reflects a plasticity in morphology that allows plants to survive in a range of environments (Díaz et al, 2016) In this current era of rapid climate change, understanding the relationships between plant morphological traits and how they might be influenced by the surrounding environment is of the utmost importance, enabling predictions of plant responses over the coming decades as atmospheric carbon dioxide (CO2) rises. Minor vein density has been shown to be an important functional plant trait, exerting a strong influence over xylem conductivity (Kx) and outside xylem conductivity (Kox), parameters that determine leaf hydraulic conductance (Kleaf) (Sack and Frole, 2006; McKown et al, 2010). It could be said that in the same way that SD and size influence the water demands of a plant, the vein architecture influences its water supply
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