Presentations
Most recent presentations include:
3 presentations at the 2011 Annual Botanical Society of America meeting held in St. Louis, MO. July 2011.
*Undergraduate Student at Ithaca College
Melcher, Peter, Zwieniecki, Maciej, Holbrook, N. Michele. Presented, “Functional embolism refilling in red maple (Acer rubrum L.)”.
Abstract
The goal of this study was to assess the ability of mature trees and saplings of Acer rubrum L. to refill artificially embolized vessels in intact branches. Embolism was induced by injecting air (4.5 MPa) into the stem. Following the air-injection treatment, changes in the stems capacity to transport water were determined using grainer-style sap-flow probes inserted into branches located about 1-m distally to the point of air injection. Sap flow was measured continuously over many days following air injection. No measurable effect from air injection on the flow of sap was observed. Air injection also had no effect on stomatal conductance and leaf water potentials. Injecting air at 5.5 MPa pressure into the main stems of potted, three-year-old saplings also had no immediate or prolonged effects on whole plant transpiration. Regression analysis revealed that whole plant transpirational flow rates were either the same, or even greater after air injection than prior to injection treatment. We also measured changes in petiole hydraulic conductivity (Kpet) following air-injection pressures of 0, 3.0 or 5.5 MPa to assess if air-injection treatments resulted in embolisms within petioles. Kpet was found to be reduced to values near zero immediately following air injection into stems (at time zero). However, Kpet completely recovered within 2½ minutes on petioles that had their branches subjected to the 3.0 MPa air injection treatments and it took about 5 to 10 minutes to restore Kpet to 70 % of the initial Kpet values in petioles attached to branches injected with 5.5 MPa of gas pressure. These studies provide further evidence that embolism refilling can occur in tree species when plants are actively transpiring and under negative water potentials. Although we should be aware that the air injection method may cause artificial conditions that do not exist in nature and may result in artifacts that potentially skew our assessment of embolism refilling.
Millan, Pamela*, Melcher, Peter, Sack, Lawren. Poster presentation, “Intracanopy leaf plasticity and the impact of light versus height on carbon and nitrogen isotope discrimination for five temperate deciduous tree species.”
Abstract
The goal of this study was to determine how intracanopy microclimate impacts leaf-level traits. Many leaf traits are known to vary within canopies, such as leaf thickness, leaf area, stomatal conductance and leaf water status, and this suggests potentially strong variation in leaf nutrient composition and carbon isotope discrimination (Δ). We determined the impact of light and height on Δ, nitrogen (N) and carbon (C) concentrations as well as other anatomical and morphological leaf traits. We collected leaves using an aerial lift from three crown positions, top-exposed (TE), basal-exposed (BE), and basal-interior (BI) from five common mature temperate tree species. The Δ related to both height and light with light having a stronger signal in Δ than height for Betula alleghaniensis (birch), Ginkgo biloba (ginkgo) and Quercus rubra (red oak),and height having a stronger signal on Δ for Liriodendron tulipifera (tuliptree) and Sassifras albidum (sassafras). We also found correlations of carbon and nitrogen concentrations measured on a leaf area basis with canopy irradiance and height (r =0.51-0.73, 0.29-0.33 and 0.50-0.73 respectively; P < 0.05). However, when analyzed on a leaf mass basis the N and Cconcentrations and N:C ratios were independent of irradiance and height (r =0.009-0.16; P >0.10). These relationships were supported using an Akaike Information Criterion (AIC) analysis of models indicating that both irradiance and height played an important role in determining Δ; a model based on both factors was selected above models based on either factor alone. By contrast, for Carea,a model based on height alone was selected and for Narea, the model based on irradiance alone was selected. This variation indicates species-differences in the modulation of carbon uptake and water loss across the canopy.
Brouwer, Marieke*, Griffin-Nolan, Robert*, Melcher, Peter. Poster presentation, “Investigating the role of green light in photosynthesis in Coleus spp.”.
ABSTRACT
We measured the ability of green light to power photosynthesis in two varieties of Coleus spp. (Red Head and Henna) grown under high and low-light conditions (900 and 300 mmol m-2 s-1). These plants were able to sequester CO2 using only green light energy (lmax = 550 nm) and shade adapted plants required only 30 umol m-2 s-1 of green-light energy to reach their photosynthetic compensation points. However, even though the high-light adapted plants of both Coleus spp. varieties did sequester CO2 using green-light energy, these plants could not overcome their higher, sun-leaf respiration requirements and only shade-adapted leaves had positive quantum efficiencies when exposed to green light intensities of c.30 umol m-2 s-1and above. To determine how various qualities and quantities of light affected electron flow through the photosystems of isolated chloroplasts, we measured the rate of reduction of an artificial electron acceptor 2,6-Dichlorophenol-Indophenol (DPIP) and found that the t1/2 values of DPIP reduction were the same for chloroplasts exposed to either white, red, blue or green light energy measured at three light intensities of 10, 50 and 500 umol m-2 s-1. We also observed anatomical variations of anthocyanin accumulation within leaves exposed to the two light treatments. With respect to the location of the chlorophyll layer, we observed that the low-light exposed plants had leaves with only a prominent abaxial anthocyanin layer and sun adapted plants had leaves with both an intense adaxial and abaxial anthocyanin layers. From the fact that anthocyanins absorb green light and that the sun-adapted leaves could not use green light energy to effectively power photosynthesis, we hypothesize that the prominent adaxial anthocyanin layer effectively absorbed, and thus blocked green light from reaching the chloroplast layer. The mechanism of using green light to effectively drive photosynthesis in the shade-adapted leaves is still unclear and under investigation. However, we suspect that carotenoids and xanthophylls are playing a major role in this process.
"Turning over a new leaf – hydraulics, light and leaf design". Sabbatical Presentation, Biology Department Seminar Series. September 2010.
Abstract:
Living things rely on the photosynthetic ability of leaves to use solar energy to convert water and carbon dioxide gas to energy rich sugar molecules as the basis for all food. Because light powers this sugar making process, and leaves lose water while absorbing carbon dioxide; leaf photosynthetic performance is directly related to leaf water status and light availability. It is well known that the photosynthetic capacity of leaves is highly dependent on leaf physiology, anatomy and morphology traits. For example, large thin leaves are generally well adapted to understory shaded environments and small thick leaves are well suited for bright light conditions. Because both water availability and light levels are highly varied within individual crowns of trees, it would be expected to find a high degree of intracanopy leaf plasticity. I will discuss results from several of my recent studies on intracanopy leaf plasticity measured on several tree species growing at one location, as well as from trees growing across large latitudinal gradients (e.g., Florida to Nova Scotia). It is believed that these data will provide new insights as to the adaptable potential of trees in response to climate change.
"The impact of xylem wounding on the measure of stem hydraulic resistance". Botany 2010 Conference, Providence, RI. August 2010. Co-authored with Steven Warchocki (Biology '09).
Abstract:
Plant performance is directly related to plant water status and because xylem hydraulic resistance impacts water supply to leaves it has been used to characterize plant adaptations to environment. Xylem tissue in plants contain both living and dead cells. The cells responsible for the mass flow of sap from roots to leaves are composed of numerous dead hollow conduits. The design of these dead conduits e.g., diameter, length and frequency of bordered pit junctions, greatly impact the resistance of sap moving through them. Measurements of xylem hydraulic resistance generally rely on perfusing solution through excised plant tissue. In this study, two non-trivial issues that greatly compromise our ability to fully characterize xylem properties in plants are discussed. The first issue is focused on the role of the living cells in meditating a xylem wound response that was found to increase stem hydraulic resistance by up to 80% in some tree species (in less than a few minutes from excision). Appropriate measurement protocols have been developed that greatly reduce the impact of xylem wounding on the measure of xylem hydraulic resistance. The second issue deals with the difficulty in measurement error that results from opening non-functional flow paths when hydraulic measurements are made on excised tissues that contain multiple years of xylem growth. Results from a new measurement protocol to deal with this issue will be discussed. These two new protocols should allow us to fine tune our estimates of xylem hydraulic resistance in plants. Also, these methods provide a tool to better understand plant response to xylem wounding, a physiological mechanism used by plants to protect and prevent the spread of pathogen invasion into their water conducting systems. Future studies aimed at understanding the role of both the living and dead cells in long-distance sap transport is pertinent in understanding the full influence that plant hydraulic form has on plant drought adaptations.
"Dying for a good cause - xylem pays the ultimate price for transpiration" UCLA's Department of Ecology and Evolutionary Biology: Discovering Nature Series. Spring 2010.
Abstract:
Leaf photosynthetic performance is directly related to leaf water status. The xylem provide the hydraulic connection between water located in the soil and the leaf. Because the hydraulic resistance of this connection impacts the rate of water supply to leaves it has been used to characterize plant adaptations to their environment. In this presentation I will discuss the role of the living and dead cells in translocating fluids from the soil to the leaf. I will also discuss the importance of two non-trivial issues that greatly compromise our ability to fully characterize xylem properties in plants. The first is focused on the role of the living cells in meditating a xylem wound response that causes errors in our estimation of stem hydraulic resistance (by up to 80% in some tree species). The second issue deals with the difficulty in measurement error that results from opening non-functional flow paths when hydraulic measurements are made on excised tissues that contain multiple years of xylem growth. Results from a new measurement protocol to deal with this issue will also be discussed.
