Browsing by Subject "ecophysiology"

Now showing 1 - 7 of 7
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    Ecophysiological investigations of understory eastern redcedar in central Missouri
    (1983) Lassoie, James P; Dougherty, Phillip M; Reich, Peter B; Hinckley, Thomas M; Metcalf, Clifford M; Dina, Stephen J
    Eastern redcedar (Juniperus virginiana) is a sun-adapted, drought-resistant pioneer species common to pastures, abandoned fields, fence rows, and calcareous rock outcrops throughout the eastern United States. However, it is also a frequent component of the understory in mature oakhickory forests in central Missouri, where light levels are typically < 10% of full sunlight during much of the growing season. This is below eastern redcedar's reported optimum for photosynthesis. The competitive survival of understory eastern redcedar under such environmental conditions was apparently due to it being an evergreen conifer in a deciduous forest. Hence, its foliage was able to maintain a positive carbon dioxide balance throughout much of the year, with maximum net photosynthetic rates occurring during periods when the overstory was leafless. The greatest daily average net photosynthetic rates (Ph,) occurred during overstory leaf emergence when temperatures were moderate and light levels to the understory trees were annually the highest. Furthermore, since leaf temperatures and tree water deficits were relatively low at this time, daily gas exchange rates were not greatly limited by midday stomatal closure. After the overstory foliage had fully developed, understory light levels averaged -S50-800o below levels observed in early spring. Thus, photosynthesis was severely light limited during the day, resulting in Ph, that were 15-45% of the springtime maxima. The greatest daily average transpiration rates (TR) occurred during the summer due to the high evaporative demand. Increasing leaf temperatures and tree water deficits became more important by late summer, causing stomatal closure during some afternoons, which reduced Ph,, and TR to :730 and 40%, respectively, of the early summer levels. During the autumn, winter, and early spring, understory light levels were normally above the saturation point for photosynthesis. The light saturation point for an understory study tree (expressed as flux of photosynthetically active photons) was ;800 Armol m--2 s1, less than half of that reported for open-grown eastern redcedar. This relatively lower light saturation point suggested an adjustment to shade conditions. During the autumn overstory defoliation period, light levels to understory trees progressively increased, and Ph, eventually reached 80W of the springtime maximum. In contrast, TR only reached ;25% of the summer maximum, owing to relatively low evaporative demands. During the late autumn and winter, low leaf and soil temperatures combined to limit gas exchange severely. The major controlling factors seemed to be cold air temperatures directly inhibiting Ph, and cold soil temperatures indirectly producing tree water deficits due to reduced water uptake at the soil-root interface. Such conditions promoted persistent stomatal closure, resulting in Ph, near zero. However, a temporary warming trend during the winter caused an increase in Ph,, to a level -301O of the springtime maximum. Higher net photosynthetic rates probably were not possible due to the effects of low soil and air temperatures on the stomatal mechanism and on the photosynthetic apparatus.
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    Fire Affects Ecophysiology and Community Dynamics of Central Wisconsin Oak Forest Regeneration
    (1990) Reich, Peter B; Abrams, Marc D; Ellsworth, David S; Kruger, Eric L; Tabone, Tom J
    In order to understand better the ecophysiological differences among competing species that might influence competitive interactions after, or in the absence of, fire, we examined the response to fire of four sympatric woody species found in intermediatesized gaps in a 30-yr-old mixed-oak forest in central Wisconsin. Selected blocks in the forest were burned in April 1987 by a low-intensity controlled surface fire. The fire had significant effects during the following growing season on community structure, foliar nutrient concentrations, and photosynthesis. Acer rubrum seedling density declined by 70% following the fire, while percent cover increased several-fold in Rubus allegheniensis. In general, leaf concentrations of N, P, and K were increased by the fire in all species, although the relative enhancement decreased as the growing season progressed. Daily maximum photosynthetic rates were 30-50% higher in burned than unburned sites for Prunus serotina, Quercus ellipsoidalis, and R. allegheniensis, but did not differ between treatments for A. rubrum. Mean sunlit photosynthetic rates and leaf conductances were stimulated by the burn for all species, with the greatest enhancement in photosynthesis measured in Q. ellipsoidalis. Leaf gas exchange in R. allegheniensis was most sensitive to declining leaf water potential and elevated vapor pressure gradient, with Q. ellipsoidalis the least sensitive. Fire had no discernable effect on water status of these plants during a year of relatively high rainfall. In comparison with other species, A. rubrum seedlings responded negatively after fire-both in terms of survival/reproduction (decline in the number of individuals) and relative leaf physiological performance. Fire enhanced the abundance of R. allegheniensis and the potential photosynthetic performance of R. allegheniensis, P. serotina, and particularly Q. ellipsoidalis. We conclude that post-fire stimulation of net photosynthesis and conductance was largely the result of enhanced leaf N concentrations in these species.
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    The global spectrum of plant form and function
    (2016) Díaz, Sandra; Kattge, Jens; Cornelissen, Johannes H C; Wright, Ian J; Lavorel, Sandra; Dray, Stéphane; Reu, Björn; Kleyer, Michael; Wirth, Christian; Prentice, I. Colin; Garnier, Eric; Bönisch, Gerhard; Westoby, Mark; Poorter, Hendrik; Reich, Peter B; Moles, Angela T; Dickie, John; Gillison, Andrew N; Zanne, Amy E; Chave, Jérôme; Wright, S. Joseph; Sheremet’ev, Serge N; Jactel, Hervé; Baraloto, Christopher; Cerabolini, Bruno; Pierce, Simon; Shipley, Bill; Kirkup, Donald; Casanoves, Fernando; Joswig, Julia S; Günther, Angela; Falczuk, Valeria; Rüger, Nadja; Mahecha, Miguel D; Gorné, Lucas D
    Earth is home to a remarkable diversity of plant forms and life histories, yet comparatively few essential trait combinations have proved evolutionarily viable in today’s terrestrial biosphere. By analysing worldwide variation in six major traits critical to growth, survival and reproduction within the largest sample of vascular plant species ever compiled, we found that occupancy of six-dimensional trait space is strongly concentrated, indicating coordination and trade-offs. Three-quarters of trait variation is captured in a two-dimensional global spectrum of plant form and function. One major dimension within this plane reflects the size of whole plants and their parts; the other represents the leaf economics spectrum, which balances leaf construction costs against growth potential. The global plant trait spectrum provides a backdrop for elucidating constraints on evolution, for functionally qualifying species and ecosystems, and for improving models that predict future vegetation based on continuous variation in plant form and function.
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    Investigation of vascular limitations on floral water loss in temperate woody species
    (2018-12) McMann, Natalie
    In temperate biomes, limitations imposed by vascular physiology may influence floral water use in woody species. Freeze-thaw induced embolism in the xylem can reduce vascular transport capacity in the early spring, potentially limiting growth. To investigate whether xylem transport capacity impacts floral physiology, I quantified inflorescence water loss rates and stem hydraulic conductivity of five woody species that flower before producing leaves. I found inflorescence size and ambient temperature at flowering positively correlated with water loss. However, I detected no correlation between branch level floral water loss and stem hydraulic conductivity within species. Furthermore, a comparison of branch level water loss rates from inflorescences and leaves showed that leaf water loss is 2–4 orders of magnitude greater than that of flowers. To evaluate whether flowers were primarily phloem or xylem hydrated, I modeled the amount of water brought in during floral development and full bloom. Despite their relatively low rates of water loss, the model indicates that flowers in this study obtain the majority of their water from the xylem. Overall, the data suggest that within species floral water loss may not be limited by the xylem during flowering, but large differences in floral water loss and stem conductivity among species could explain hydraulic trait variation between large and small flowered plants.
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    Leaf-level trade-offs between drought avoidance and desiccation recovery drive elevation stratification in arid oaks: site environmental data, individual tree stem and leaf physiological data, and analyses
    (2018-02-14) Fallon, Beth; Cavender-Bares, Jeannine; eafallon@umn.edu; Fallon, Beth
    This dataset and RStudio project includes all processed data, most raw data, and R scripts needed for analysis and figure construction included in the manuscript Fallon and J. Cavender-Bares 2018 (Fallon B. and J. Cavender-Bares. 2018. Leaf-level trade-offs between drought avoidance and desiccation recovery drive elevation stratification in arid oaks. Ecosphere. in press). We investigated whether oak species in the Chiricahua Mountains were 1) elevationally stratified, 2) whether that stratification was correlated with temperature minima, maxima, and water availability, 3) if physiological tolerances to freezing or drought stress correlated with elevation ranges, and 4) if traits important to local (elevation) distributions were correlated with climatic values of the wider species ranges. Data were collected at field sites from wild, adult trees in the Chiricahua Mountains, Arizona, USA from 2014-2015.This research was done with funding to B. Fallon from the Southwestern Research Station (SWRS, American Museum of Natural History), the University of Minnesota Charles J. Brand, Carolyn Crosby, and Dayton Bell Fellowships, and the Department of Plant and Microbial Biology. Additional funding was provided by NSF Award 1146380 (J. Cavender-Bares PI). We performed all data collection under permit with the Coronado National Forest, Douglas Ranger District, managed by the United States Forest Service (USDA).
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    New handbook for standardised measurement of plant functional traits worldwide
    (CSIRO, 2013) Pérez-Harguindeguy, N; Díaz, S; Garnier, E; Lavorel, S; Poorter, H; Jaureguiberry, P; Bret-Harte, M S; Cornwell, W K; Craine, J M; Gurvich, D E; Urcelay, C; Veneklaas, E J; Reich, Peter B; Poorter, L; Wright, I J; Ray, P; Enrico, L; Pausas, J G; de Vos, A C; Buchmann, N; Funes, G; Quétier, F; Hodgson, J G; Thompson, K; Morgan, H D; ter Steege, H; van der Heijden, M G A; Sack, L; Blonder, B; Poschlod, P; Vaieretti, M V; Conti, G; Staver, A C; Aquino, S; Cornelissen, J H C
    Plant functional traits are the features (morphological, physiological, phenological) that represent ecological strategies and determine how plants respond to environmental factors, affect other trophic levels and influence ecosystem properties. Variation in plant functional traits, and trait syndromes, has proven useful for tackling many important ecological questions at a range of scales, giving rise to a demand for standardised ways to measure ecologically meaningful plant traits. This line of research has been among the most fruitful avenues for understanding ecological and evolutionary patterns and processes. It also has the potential both to build a predictive set of local, regional and global relationships between plants and environment and to quantify a wide range of natural and human-driven processes, including changes in biodiversity, the impacts of species invasions, alterations in biogeochemical processes and vegetation–atmosphere interactions. The importance of these topics dictates the urgent need for more and better data, and increases the value of standardised protocols for quantifying trait variation of different species, in particular for traits with power to predict plant- and ecosystemlevel processes, and for traits that can be measured relatively easily. Updated and expanded from the widely used previous version, this handbook retains the focus on clearly presented, widely applicable, step-by-step recipes, with a minimum of text on theory, and not only includes updated methods for the traits previously covered, but also introduces many new protocols for further traits. This new handbook has a better balance between whole-plant traits, leaf traits, root and stem traits and regenerative traits, and puts particular emphasis on traits important for predicting species’ effects on key ecosystem properties.We hope this new handbook becomes a standard companion in local and global efforts to learn about the responses and impacts of different plant species with respect to environmental changes in the present, past and future.
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    Physiological evidence for climate limitations of oak distributions at local and regional scales
    (2017-11) Fallon, Beth
    Understanding the extent to which physiological tolerances of climate may limit plant distributions is critical to predicting the effects of a changing climate. This dissertation research focuses on how responses to drought and cooling influence species ranges among oaks (Quercus L.), a globally-distributed woody genus that is highly diverse within the Americas. I used functional and physiological traits to investigate correlations between cold and drought resistances and climate at two scales: 1) local species elevation limits in a semi-arid montane system and 2) regional range limits among North and Central American oaks. In Chapter 1, I found that a trade-off between the leaf-level drought resistance traits of avoidance (leaf abscission) and desiccation recovery (leaf capacitance), and not stem freezing tolerance, influenced species sorting by elevation in a semi-arid mountain system in the southwestern US. In Chapter 2, I found that stem drought tolerance (xylem vulnerability) is correlated with aridity of climate of origin among oaks from across the Americas, but that the seasonality of precipitation best predicted leaf level drought avoidance (leaf habit and stomatal closure). Finally, in Chapter 3, I found that oak species in the Americas have different leaf level cooling responses (chlorophyll fluorescence measurements of photosynthetic stress and yield) that were correlated with minimum temperatures in their climate of origin, but that ability to acclimate to cold temperatures was best predicted by leaf phenology, not climate of origin. I also found that we could predict chlorophyll fluorescence measurements with models created from hyperspectral reflectance data measured on the same leaves. These models included regions of important biological significance, including wavelengths corresponding with reflectance of photosynthetic and protective pigments. Overall, there I found significant evidence that species distributions are strongly influenced by climate. Oak species have suites of traits as mechanisms of drought resistance, and these strategies are correlated with not only overall aridity in their current habitats, but with the seasonality of precipitation. Oak species may also be able to acclimate to cooler temperatures outside of those commonly experienced in their current range. Oak species within the Americas and the mountainous, arid southwest US, may be vulnerable to range shifts as global temperatures continue to rise and precipitation regimes change.