Posters & Presentations

The Effect of Nighttime Transpiration on the Magnitude of Hydraulic Redistribution in Four Diverse Species. Ecological Society of America. August 2007. 

Nighttime water losses by C₃ plants can include both transpiration (E_night) from the canopy and hydraulic redistribution (HR) from roots.  HR is thought to provide plants with nutrient and water benefits.  We tested the hypothesis that the magnitude of HR is inversely related to the magnitude of E_night in a greenhouse study using Artemisia tridentata and Quercus laevis.  Plants were grown with their roots split between two compartments.  HR was initiated by briefly withholding all water, followed by watering only one compartment.  HR was defined as the difference between initial and maximal soil water potential overnight as measured by screen cage psychrometers in the compartment from which water was withheld.  Under these conditions both A. tridentata and Q. laevis showed significant E_night (0.027 – 0.41 and 0.24 – 0.62 mmol m^-2 s^-1, respectively).  Bagging plant canopies over night to minimize E_night significantly increased the magnitude of HR by A. tridentata, but had no effect on HR by Q. laevis.  Magnitude of HR was additionally affected by environmental variables including nighttime vapor pressure deficit and photosynthetically active radiation the previous day.  Thus our results suggest that for some species E_night may have further water costs to plants beyond direct losses to the atmosphere and may also negatively impact plant nutrient acquisition.  Similar studies are currently underway with Helianthus anomalus and Populus balsamifera spp. trichocarpa.

 

Using plants and inquiry-based approaches in P-12 classrooms.  Georgia Science Teachers Association. February, 2007. view

This presentation will focus on teaching P-12 science concepts by using plants in laboratory activities.  Participants will become more knowledgeable about plant biology and add to their repertoire of inquiry labs to use in their classrooms.  Inquiry labs based on plant content are effective and easily replicated teaching strategies for engaging students as “scientists” in real world activities.  Participants will experience approximately 10 lab exercises through a combination of experimental demonstration, PowerPoint presentation and discussion of laboratory exercises.  A handout package will describe additional inquiry-based lab exercises using plants.  All exercises will be aligned to GPS (Georgia Performance Standards).  Participants will have the opportunity to discuss how the lab exercises fit into an “inquiry continuum” from structured to open and will discuss how plant-related concepts are addressed at different grade levels. 

 

Nighttime stomatal conductance and transpiration in Helianthus.  American Society of Plant Biologists. October, 2006. view

We investigated regulation of C₃ plant nighttime stomatal conductance (g_night) and transpiration (E_night), when CO₂ uptake is not occurring and traditional paradigms for stomatal regulation do not apply.  While many studies have reported substantial g_night and E_night, few have included experimental manipulations to test individual factors potentially affecting stomatal regulation.  We examined the response of g_night and E_night (instantaneous gas exchange) to soil nutrient and water limitations in nine greenhouse studies.  We primarily used wild Helianthus annuus, but also included a commercial and a land-race domesticate of H. annuus, and three additional wild species (H. petiolaris, H. deserticola, and H. anomalus).  Based on the potential for transpiration to increases mass flow of mobile nutrients to roots, six studies tested whether regulation for increased E_night occurred when soil nutrient availability was limited.  All six studies showed that Helianthus g_night and E_night did not respond to reduced soil N or NPK.  Based on known daytime responses to water limitation, four studies tested whether stomatal regulation to decrease E_night occurred when soil water availability was limited.  All four studies showed that g_night and E_night decreased as hypothesized.  Additionally we established that cuticular conductance varied between species, and that g_night and E_night varied diurnally and across plant developmental stages while remaining relatively constant as leaves aged.  For Helianthus, g_night is regulated in response to water stress and is naturally variable across temporal scales.  These results further our understanding of factors that must be considered for scaling to whole plant and ecosystem water use and for predicting conditions under which nighttime water loss will be biologically significant. 

   

Regulation of nighttime water loss in Populus in response to soil nitrogen and water manipulation.  Ecological Society of America. August, 2006. view

Nighttime water loss from C₃ plants is receiving increasing attention due to potential interactions with plant water and nutrient relations.  We investigated the regulation of C₃ plant stomatal conductance (g) and transpiration (E) at night using instantaneous gas exchange measures in a greenhouse study of Populus angustifolia (narrowleaf cottonwood) and P. balsamifera spp. trichocarpa (black cottonwood).  As a baseline, we established that nighttime g is generally greater than cuticular g and showed that the magnitude of g and E changes for each species over the course of a night.  For soil nutrient availability, we tested the hypothesis that regulation for increased nighttime E would occur to increase uptake of mobile nitrate under nitrogen limiting conditions. We imposed a soil nitrogen limitation that was sufficient to reduce above ground biomass of both species.  In the low nitrogen treatment, black cottonwood nighttime g and E increased while narrowleaf cottonwood nighttime g and E were unaffected.  Black cottonwood also exhibited significant genotype variation in nighttime g and E.  For soil water availability, we tested the hypothesis that, similar to daytime responses, nighttime stomatal regulation would occur to conserve water under conditions of limiting availability.  Withholding water from black cottonwood resulted in decreased nighttime g and E and daytime g, E and photosynthesis.  We support the conclusion that nighttime water loss may be regulated in response to soil conditions.  We also demonstrate the potential for substantial variability in nighttime g and E responses to soil nitrogen, even between closely related woody plant species.

 

Nighttime Conductance and Transpiration in Four C₃ Annuals Under Sufficient and Limiting Nitrate availability.  Ecological Society of America. August, 2005.  view

C₃ plants are predicted to close their stomata at night, yet many plants with the capability to do so exhibit significant nighttime stomatal opening. Little is known about regulation of, and species differences in, nighttime stomatal conductance (g) and transpiration (E). In the greenhouse, we tested two hypotheses using instantaneous measures of nighttime g and E (LiCor 6400) in four closely related desert annuals. First, we hypothesized that under well-watered conditions nighttime g and E would be higher in the species native to nutrient poor habitats, Helianthus anomalus and H. deserticola, compared to the species native to relatively nutrient rich habitats, H. annuus and H. petiolaris. All species showed significant nighttime g and E (averaged across species 0.1 mol m^-2 s^-1 and 1.5 mol m^-2 s^-1 respectively), and there were significant species differences: H. deserticola was highest and H. petiolaris was lowest. However, our hypothesis was only partially supported because differences were modest and only significant between H. deserticola and H. petiolaris. Cuticular g and E also differed between species and may explain the species differences observed for nighttime g and E. Second, we hypothesized nitrogen availability would affect nighttime g and E. For all species, the low nitrogen treatment was sufficient to reduce biomass, stem diameter, height, leaf number, and nitrogen concentration of the gas exchange leaves. However, the nitrogen treatments did not affect nighttime or daytime g and E. For all species, we also noted that nighttime g was negatively correlated with leaf to air vapor pressure deficit (VPD). Overall, we show that regulation of nighttime g and E is affected by VPD but unaffected by nitrogen availability and species differences in nighttime g and E parallel differences in cuticular conductance.