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- PublicationCo-ordination in morphological leaf traits of early diverging angiosperms is maintained following exposure to experimental palaeoatmospheric conditions of sub-ambient O2 and elevated CO2In order to be successful in a given environment a plant should invest in a vein and stomatal network 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 seven 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 co-ordination between vein and stomatal traits 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 such as assimilation rate, and as a result, lends confidence to future application of palaeo-CO2 proxy models that require robust estimates of palaeo-assimilation rate as key initialisation parameters.
Scopus© Citations 5 502
- PublicationDifferences in the photosynthetic plasticity of ferns and Ginkgo grown in experimentally controlled low [O2]: [CO2] atmospheres may explain their contrasting ecological fate across the Triassic-Jurassic mass extinction boundaryBackground and Aims: Fluctuations in [CO2] have been widely studied as a potential driver of plant evolution; however, the role of a fluctuating [O2]:[CO2] ratio is often overlooked. The present study aimed to investigate the inherent physiological plasticity of early diverging, extant species following acclimation to an atmosphere similar to that across the Triassic–Jurassic mass extinction interval (TJB, approx. 200 Mya), a time of major ecological change. Methods: Mature plants from two angiosperm (Drimys winteri and Chloranthus oldhamii), two monilophyte (Osmunda claytoniana and Cyathea australis) and one gymnosperm (Ginkgo biloba) species were grown for 2 months in replicated walk-in Conviron BDW40 chambers running at TJB treatment conditions of 16 % [O2]– 1900 ppm [CO2] and ambient conditions of 21 % [O2]–400 ppm [CO2], and their physiological plasticity was assessed using gas exchange and chlorophyll fluorescence methods. Key Results: TJB acclimation caused significant reductions in the maximum rate of carboxylation (VCmax) and the maximum electron flow supporting ribulose-1,5-bisphosphate regeneration (Jmax) in all species, yet this downregulation had little effect on their light-saturated photosynthetic rate (Asat). Ginkgo was found to photorespire heavily under ambient conditions, while growth in low [O2]:[CO2] resulted in increased heat dissipation per reaction centre (DIo/RC), severe photodamage, as revealed by the species' decreased maximum efficiency of primary photochemistry (Fv/Fm) and decreased in situ photosynthetic electron flow (Jsitu). Conclusions: It is argued that the observed photodamage reflects the inability of Ginkgo to divert excess photosynthetic electron flow to sinks other than the downregulated C3 and the diminished C2 cycles under low [O2]:[CO2]. This finding, coupled with the remarkable physiological plasticity of the ferns, provides insights into the underlying mechanism of Ginkgoales' near extinction and ferns' proliferation as atmospheric [CO2] increased to maximum levels across the TJB.
Scopus© Citations 11 354
- PublicationHow well do you know your growth chambers? Testing for chamber effect using plant traitsBackground: Plant growth chambers provide a controlled environment to analyse the effects of environmental parameters (light, temperature, atmospheric gas composition etc.) on plant function. However, it has been shown that a ‘chamber effect’ may exist whereby results observed are not due to an experimental treatment but to inconspicuous differences in supposedly identical chambers. In this study, Vicia faba L. 'Aquadulce Claudia' (broad bean) plants were grown in eight walk-in chambers to establish if a chamber effect existed, and if so, what plant traits are best for detecting such an effect. A range of techniques were used to measure differences between chamber plants, including chlorophyll fluorescence measurements, gas exchange analysis, biomass, reproductive yield, anatomical traits and leaf stable carbon isotopes. Results and discussion: Four of the eight chambers exhibited a chamber effect. In particular, we identified two types of chamber effect which we term 'resolvable' or 'unresolved'; a resolvable chamber effect is caused by malfunctioning components of a chamber and an unresolved chamber effect is caused by unknown factors that can only be mitigated by appropriate experimental design and sufficient replication. Not all measured plant traits were able to detect a chamber effect and no single trait was capable of detecting all chamber effects. Fresh weight and flower count detected a chamber effect in three chambers, stable carbon isotopes (δ13C) and net rate CO2 assimilation (An) identified a chamber effect in two chambers, stomatal conductance (gs) and total performance index detected an effect only in one chamber. Conclusion: (1) Chamber effects can be adequately detected by fresh weight measurements and flower counts on Vicia faba plants. These methods were the most effective in terms of detection and most efficient in terms of time. (2) δ13C, gs and An measurements help distinguish between resolvable and unresolved chamber effects. (3) Unresolved chamber effects require experimental unit replication while resolvable chamber effects require investigation, repair and retesting in advance of initiating further experiments.
Scopus© Citations 33 438