Browsing by Subject "Photosynthesis"

Now showing 1 - 5 of 5
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    Blinded by the Light: The Functional Ecology of Plant-Light Interactions
    (2020-07) Kothari, Shan
    The capture of sunlight by plants and other primary producers is the greatest driver of the world’s carbon cycle. The photosynthetic machinery that plants use to fix carbon dioxide and light energy into storable carbohydrates must be able to handle intense fluxes of energy, and both lack and excess of light put plants at a disadvantage—either from starvation or from damage. Plant leaves evolve in how they absorb, reflect, or avoid light in ways that can be explained as functional adaptations to their environment. Here, I present four studies on the interactions between plant tissue and the light environment—two of which concern the functional role of light capture or avoidance in ecological strategies, and two of which are methodological studies that explain how we can use plants’ interactions with light to understand their strategies more broadly. Chapter 1 reports on a study in the Big Biodiversity (BioDIV) experiment that seeks to characterize the range of strategies that plants have to cope with excess light under stressful conditions. In a survey of prairie plants, we find that species may either primarily use biochemical or structural strategies to protect themselves from excess light. The position along this continuum is phylogenetically conserved. Communities with more species relying on biochemical mechanisms are more resilient aboveground during water-limited periods. Chapter 2 uses growth surveys and physiological measurements in the Forests and Biodiversity (FAB) experiment to show how broadleaf trees respond to shade from faster-growing conifer neighbors. While most species were harmed by shade, growing slower and assimilating less carbon, two species showed the opposite trend. These two species were the most shade-tolerant in the experiment and were exceptionally susceptible to photoinhibition, such that shade from their neighbors facilitated their growth. All species relied on photoprotection more in sunnier environments. Chapters 3 and 4 use reflectance spectroscopy to estimate traits in different kinds of leaf tissue. Chapter 3 focuses on leaf litter, whose chemical traits are often measured to gain insight into components of nutrient cycle such as nutrient resorption and decomposition. We show that we can estimate a fiber content and elemental composition using pressed-leaf spectra and, with somewhat higher accuracy, ground-leaf spectra. Chapter 4 is about pressed leaves, such as herbarium specimens, whose functional traits ecologists increasingly seek to measure in order to fill in trait databases or understand the impacts of global anthropogenic changes. We show that reflectance spectroscopy can provide non-destructive estimates of several leaf functional traits from pressed leaves, which may extend the possibility of using a wider variety of herbarium specimens in functional ecology.
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    Engineering light-energy conversion into nonphotosynthetic hosts
    (2013-12) Tikh, Ilya
    Over billions of years photosynthetic organisms have refined the molecular machinery required for the capture and conversion of light into chemical energy. To date, much research has been devoted into harnessing this unique trait from photosynthetic organisms and utilizing them for ecologically clean production of valuable resources, such as alternatives to fossil fuels or commodity chemicals. Unfortunately, photosynthetic organisms are not always ideal host for the production of desired chemicals and are frequently difficult to engineer. In order to bypass those hurdles, this work focused on introducing the machinery responsible for the light-energy conversion into a nonphotosynthetic host. The supplementation of a heterologous host with the energy captured via the light-energy conversion could alleviate some of the host's metabolic burden and allow for greater yields of desired compounds. In order to achieve our goals, we set out to engineer functional expression of the bacterial reaction center from R. sphaeroides as well as the enzymes required for the production of bacteriochlorophyll into E. coli. For the first time we were able to demonstrate the expression of the reaction center complex as well as its primarily polar localization with E. coli cells. Furthermore, we characterized two previously poorly understood enzymes involved in the production bacteriochlorophyll, the 8-vinyl reductase (BciA) and the Mg protoporphyrin monomethylester cyclase (BchE). In the case of BciA, we showed that unexpectedly the BciA from R. sphaeroides was not functional when expressed in E. coli, unlike the BciA from C. tepidum. At the beginning of this work, BchE was the only enzyme involved in the biosynthesis of bacteriochlorophyll that has not been heterologously expressed and had no published biochemical or biophysical data. Through our efforts, we were able to demonstrate that BchE contained an oxygen sensitive 4Fe-4S cluster able to interact with SAM, the predicted co-factor. Additionally, for the first time, we showed the interaction of BchE with several intermediates of the bacteriochlorophyll biosynthetic pathways. Complementary to our efforts, we also produced a set of protein expression vectors for use in R. sphaeroides. R. sphaeroides is a photosynthetic organism which has been used extensively for the production of value added compounds and has the potential to be used for the production of membrane proteins. The novel vectors are BioBrickTM compatible and contain DsRed as a reporter protein driven by the photosynthetic puf promoter. We demonstrated that by selecting which section of the promoter was utilized in combination with various culture conditions, final reporter levels could be modulated. Reporter levels ranged from virtually undetectable to higher than what is present in E. coli when expression is driven from a constitutive lac promoter from the same vector backbone.
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    Foliar anthocyanins in coleus and ornamental grasses: accumulation, localization, and function
    (2013-04) Boldt, Jennifer Kay
    Anthocyanins provide red coloration in plants. The research objectives were to (1) investigate the influence of environmental factors on anthocyanin accumulation, (2) compare photosynthetic rates of red and green leaves, (3) determine anthocyanin localization in leaves, and (4) determine anthocyanin function(s) in leaves. Coleus (Solenostemon scutellarioides) and ornamental grasses, commonly cultivated for their foliage coloration, were selected as model plants. Irradiance and temperature influenced anthocyanin content in red coleus. Anthocyanin content increased with increasing irradiance, although photobleaching occurred in some cultivars at the highest irradiance. Exposure to low temperature (12 °C) resulted in maximum anthocyanin content in two cultivars but minimal anthocyanin content in another. In switchgrass and purple fountaingrass, anthocyanin content in individual leaves and the percent red leaves increased with increasing irradiance. Intensified seasonal leaf coloration in red-leaved grasses (Imperata cylindrica, Panicum virgatum, Pennisetum advena, Pennisetum purpureum, and Schizachyrium scoparium) resulted from increased anthocyanins and decreased chlorophyll. Anthocyanins were negatively correlated with average daily temperature and daily light integral (DLI) and positively correlated with total growing degree days and total DLI. Annual and non-native grasses had minimal seasonal fluctuations in pigmentation relative to native grasses (P. virgatum and S. scoparium), and this seasonal increase in anthocyanins might be an adaptive mechanism. At saturating irradiance, neither leaf color had a distinct advantage. Maximum photosynthetic rates (Amax) in red and green coleus were similar per area, higher in red per fresh or dry weight, and higher in green per unit chlorophyll. Amax in switchgrass was higher in green leaves per area, fresh, or dry weight, and similar in red and green leaves per unit chlorophyll. Anthocyanins in coleus and switchgrass localized in epidermal cells. They were ideally situated to provide a photoprotection role as light attenuators. Anthocyanins offered minimal photoprotection in switchgrass and their presence may simply be due to selection for desired ornamental attributes. Photoprotection by anthocyanins was most evident in coleus during low temperature/high irradiance stress. Red coleus exhibited less of a decline in Fv/Fm, photosynthesis, electron transport rate, and effective quantum yield than green coleus, and Fv/Fm and photosynthetic rate recovered to pre-stress levels more quickly.
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    Predicting the effects of climate change on water yield and forest production in the northeastern United States
    (1995) Aber, John D; Ollinger, Scott V; Federer, C. Anthony; Reich, Peter B; Goulden, Michael L; Kicklighter, David W; Melillo, Jerry M; Lathrop, Richard G Jr
    Rapid and simultaneous changes in temperature, precipitation and the atmospheric concentration of CO2 are predicted to occur over the next century. Simple, well-validated models of ecosystem function are required to predict the effects of these changes. This paper describes an improved version of a forest carbon and water balance model (PnET-II) and the application of the model to predict stand- and regional-level effects of changes in temperature, precipitation and atmospheric CO2 concentration. PnET-II is a simple, generalized, monthly time-step model of water and carbon balances (gross and net) driven by nitrogen availability as expressed through foliar N concentration. Improvements from the original model include a complete carbon balance and improvements in the prediction of canopy phenology, as well as in the computation of canopy structure and photosynthesis. The model was parameterized and run for 4 forest/site combinations and validated against available data for water yield, gross and net carbon exchange and biomass production. The validation exercise suggests that the determination of actual water availability to stands and the occurrence or non-occurrence of soil-based water stress are critical to accurate modeling of forest net primary production (NPP) and net ecosystem production (NEP). The model was then run for the entire NewEngland/New York (USA) region using a 1 km resolution geographic information system. Predicted long-term NEP ranged from -85 to +275 g C m-2 yr-1 for the 4 forest/site combinations, and from -150 to 350 g C m-2 yr-1 for the region, with a regional average of 76 g C m-2 yr-1. A combination of increased temperature (+6*C), decreased precipitation (-15%) and increased water use efficiency (2x, due to doubling of CO2) resulted generally in increases in NPP and decreases in water yield over the region.
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    Size-related variation in physiology, carbon gain, and growth of trees in deciduous and evergreen forests
    (2012-12) Sendall, Kerrie M.
    A better understanding of species’ light requirements throughout developmental stages is required to improve models of forest dynamics. Although it has recently been shown that light requirements of many species may change as trees increase in size, the traits that underlie these ontogenetic patterns are not well understood. This dissertation characterizes the relationships of tree size with physiological and growth responses of eight tree species varying in leaf habit, biome, and shade tolerance. I examined morphological traits and physiological mechanisms operating at the leaf and whole-plant scale, thus allowing for identification of mechanisms that underlie observed ontogenetic variations in growth rates and shade tolerance. Size-related variation in leaf nutrients and gas exchange rates of each of the eight species were measured. While the general light conditions under which each of the eight species evolved were similar (i.e. all are trees common in forest gaps and understories and vary in shade tolerance within those environments), four of the eight species were temperate deciduous and four were subtropical evergreens. Therefore, my data are most relevant at the species or local community level and in qualitative comparisons across leaf habit. Generally speaking, shade-tolerant species and species with long-lived leaves expressed low rates of gas exchange and nitrogen content, while light-demanding species and species with shorter leaf lifespans showed higher rates of gas exchange and leaf nitrogen. However, size-related patterns of leaf-level traits were inconsistent in both deciduous and evergreen species, making it difficult to disentangle the factors responsible for these changes. To further investigate the effect of tree size on shade tolerance, we examined a combination of leaf and whole-plant traits of juvenile trees. Increased sapling size caused significant declines in shade tolerance and relative growth rates (RGR). Among the four evergreens, the slope of the relationship between light availability and RGR was steepest in light-demanding species, leading to crossovers in RGR between shade-tolerant and light-demanding species at low light, independent of sapling size. We found that no single factor can explain reductions in growth and shade tolerance with increased tree size, but that variations in self-shading and net daily carbon gain rates per gram of aboveground tissue were strong predictors of the declines. My results indicate that work on saplings and mature trees may detect differences in shade tolerance and associated traits that are not evident in studies utilizing seedlings alone. These differences could have important implications for modeling the dynamics of forest types.