Now showing 1 - 7 of 7
  • 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.
      195Scopus© Citations 5
  • Publication
    Does size matter? Atmospheric CO2 may be a stronger driver of stomatal closing rate than stomatal size in taxa that diversified under low CO2
    (1) One strategy for plants to optimise stomatal function is to open and close their stomata quickly in response to environmental signals.  It is generally assumed that small stomata can alter aperture faster than large stomata. (2) We tested the hypothesis that species with small stomata close faster than species with larger stomata in response to darkness by comparing rate of stomatal closure across an evolutionary range of species including ferns, cycads, conifers and angiosperms under controlled ambient conditions (380ppm CO2; 20.9% O2).  (3) The two species with fastest half-closure time and the two species with slowest half-closure time had large stomata while the remaining three species had small stomata, implying that closing rate was not correlated with stomatal size in these species. Neither was response time correlated with stomatal density, phylogeny, functional group or life strategy. (4) Our results suggest that past atmospheric CO2 concentration during time of taxa diversification may influence stomatal response time.  We show that species which last diversified under low or declining atmospheric CO2 concentration close stomata faster than species that last diversified in a high CO2 world.  Low atmospheric [CO2] during taxa diversification may have placed a selection pressure on plants to accelerate stomatal closing to maintain adequate internal CO2 and optimise water use efficiency.
      900Scopus© Citations 66
  • 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.
      377Scopus© Citations 28
  • Publication
    Teaching and assessment strategies for active student learning in university horticultural education
    (International Society for Horticultural Science, 2016) ;
    Many of the goals of the university teacher today are to enthuse, drive and challenge students academically, intellectually and personally; to advance their capacity for critical thinking, judgement and communication; and to equip them with sufficient scientific and technical knowledge to make them competent horticultural practitioners. Given that most programme modules are delivered by lectures, there is general consensus that student learning is primarily passive. Similarly, module assessment tends to be summative. Thus, student-centred learning to foster an environment for active learning and encourage greater student class participation was introduced into a horticulture module (Nursery Production and Management HORT 40090). Similarly, formative assessment methods were also introduced. To this end, a segment of the above module relating to vegetative plant propagation was selected. The students were asked to work in self selected groups to thoroughly research the different aspects of the topic and to prepare a short PowerPoint slide presentation for delivery to the class. Additionally, they were required to peer assess each presentation and to agree a suitable grade with staff members in attendance. It is considered that the introduction of active learning and formative assessment to the module resulted in more meaningful learning for the students concerned and moved them higher up the student-centred learning curve towards more, responsibility and accountability. The concept is being gradually rolled out to other modules.
      417Scopus© Citations 1
  • 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. 
      457Scopus© Citations 5
  • Publication
    Benefits of Scenario-based Learning in university education
    (International Society for Horticultural Science, 2016) ; ;
    As an applied science, horticulture is particularly suited to interactive teaching and learning methods.  Much of the undergraduate learning in horticulture is passive; therefore, more active learning strategies should be introduced. One such active learning technique is scenario-based learning (SBL).  This form of learning allows students to apply academic knowledge to a simulated 'real-life' situation.  It is particularly suited to promoting group participation and learning.  Its use provides students with the opportunity to recognise and solve problems, to think critically and to develop teamwork skills.  Recently, an SBL project was introduced to the Fruit Production (HORT30190) undergraduate module at University College Dublin.  In order to implement the project, the class was divided into groups and each group was required to establish a hypothetical commercial dessert, culinary or cider apple orchard in Ireland.  The groups were required to consider site characteristics, growing and pruning systems, rootstocks, cultivars, pollinator selection and planting density. They presented their results in class using posters and submitted a personal learning journal associated with the project, both of which were assessed by staff. Student response to the SBL project was evaluated for benefits such as increased understanding of course material, acquisition of transferable skills and enjoyment of the learning method. This project is an example of formative assessment in action.  Scenario-based learning allows students to contextualise learning while acquiring transferable skills.  It is suitable for implementation in a wide range of diverse university modules.
      766Scopus© Citations 1
  • Publication
    Introducing landscape design techniques to horticulture students
    (International Society for Horticultural Science, 2016) ; ; ;
    Students majoring in Horticulture Landscape and Sportsturf Management take an introductory module in Landscape Design. During a seven week period through a series of lectures, studio based graphic and design exercises, and site visits students are introduced to landscape design principles. Following an introduction to garden history each student prepares a precedent study based on the work of an international landscape designer. Furthermore, they must prepare a domestic or commercial landscape design plan. In the last academic year the class was invited to develop landscape design proposals for Beech Hill College in Monaghan. Ordnance survey maps of the site were obtained in preparation for the site visit and meeting with the School Principal who outlined the specific requirements. The students were sub-divided into three working groups and assigned a specific area of the school campus to survey and evaluate existing vegetation. Each student created design proposals, drew cross sections and a planting plan for their areas. At the end of the semester each student presented their work to peers, staff and the School Principal and was given immediate feedback. Student response to the project was highly positive and in comparison to previous years, the design proposals were suitable for implementation. Students participated in individual and group work, developed critical thinking skills, presentation skills, and all transferable skills required of university graduates. Engaging in a 'live' project for a school campus emphasised their contribution to a local community. The students have been invited to return and to further develop the site.