Now showing 1 - 3 of 3
  • Publication
    Plant responses to decadal scale increments in atmospheric CO2 concentration - comparing two stomatal conductance sampling methods
    There are several lines of evidence suggesting that the vast majority of C3 plants respond to elevated atmospheric CO2 by decreasing their stomatal conductance (gs). However, in the majority of CO2 enrichment studies, the response to elevated CO2 are tested between plants grown under ambient (380–420 ppm) and high (538–680 ppm) CO2 concentrations and measured usually at single time points in a diurnal cycle. We investigated gs responses to simulated decadal increments in CO2 predicted over the next 4 decades and tested how measurements of gs may differ when two alternative sampling methods are employed (infrared gas analyzer [IRGA] vs. leaf porometer). We exposed Populus tremula, Popolus tremuloides and Sambucus racemosa to four different CO2 concentrations over 126 days in experimental growth chambers at 350, 420, 490 and 560 ppm CO2; representing the years 1987, 2025, 2051, and 2070, respectively (RCP4.5 scenario). Our study demonstrated that the species respond non-linearly to increases in CO2 concentration when exposed to decadal changes in CO2. Under natural conditions, maximum operational gs is often reached in the late morning to early afternoon, with a mid-day depression around noon. However, we showed that the daily maximum gs can, in some species, shift later into the day when plants are exposed to only small increases (70 ppm) in CO2. A non-linear decreases in gs and a shifting diurnal stomatal behavior under elevated CO2, could affect the long-term daily water and carbon budget of many plants in the future, and therefore alter soil–plant–atmospheric processes.
    Scopus© Citations 5  330
  • Publication
    How well do you know your growth chambers? Testing for chamber effect using plant traits
    Background: 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  444
  • Publication
    Co-ordination in morphological leaf traits of early diverging angiosperms is maintained following exposure to experimental palaeoatmospheric conditions of sub-ambient O2 and elevated CO2
    In 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 6  510