10 research outputs found
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Approaches for Characterizing Plant Physiological Responses to Environmental Stress
It is uncertain how predicted changes in climate will impact vegetation responses and plant species’ distributions because the physiological mechanisms underlying thresholds for damage are not well understood, and responses to stress vary by functional type and developmental stage. Thus, it is crucial to investigate physiological responses to heat and drought stress on multiple species, populations, and growth stages with diverse approaches. In this dissertation, I employ a suite of physiological and modeling methods to inform our knowledge of plant physiological responses to environmental stress in Coffea arabica saplings, Pseudotsuga mensizeii (PSME) and Pinus ponderosa (PIPO) seedlings, and old-growth PIPO.
In Chapter 2, I evaluate the effect of leaf age and methodology on the thermotolerance or heat tolerance of C. arabica leaf discs using chlorophyll fluorescence and electrolyte leakage methods. I found that mature leaves were more heat tolerant than expanding leaves, longer time between temperature exposure and measurement yielded more accurate thermotolerance assessments, and photochemistry was more heat-sensitive than cell membranes.
To complement the second chapter investigating heat stress responses on detached leaf discs, Chapter 3 examines the effect of leaf age and heat stress duration (45 min or 90 min) on whole-plant physiological responses and capacity to recover in C. arabica by monitoring chlorophyll fluorescence (F[subscript V]/F[subscript M]), gas exchange, and foliar non-structural carbohydrate (NSC) dynamics in situ in response to a simulated heat wave (49°C) in a growth chamber. I found that the 90 min treatment resulted in greater photosynthetic damage and slower recovery than the 45 min treatment, expanding leaves recovered more slowly than in mature leaves, and both heat treatments inhibited flowering. A leaf energy balance model demonstrated that heat stress would be exacerbated by drought-induced stomatal closure. Heat treatment duration significantly impacted NSC dynamics that were closely related to reproduction and repair.
Because seedling establishment governs species’ distributions, and because seedlings are particularly threatened by high temperatures at the soil surface, in Chapter 4 I examined the thermotolerance and heat stress responses of PIPO and PSME seedling populations from contrasting climates. Unexpectedly, I found that PSME was more heat tolerant the PIPO. I also monitored physiological recovery after exposure to a simulated heat wave (45°C) by measuring photosynthesis, F[subscript V]/F[subscript M], foliar NSC, and carbon stable isotope ratios (proxy for intrinsic water use efficiency, iWUE). Heat stress responses were consistent with phenotypic plasticity and reflected the conditions under which the plants were grown, while iWUE, a measure of potential drought resistance, was consistent with ecotypic differentiation and the climates from which the seedlings originated.
To investigate responses to environmental stress on larger temporal and spatial scales without the challenges of making repeated physiological measurements on old-growth trees, in Chapter 5 I used long-term trajectories of tree-ring growth and carbon and oxygen isotopes of tree-ring cellulose (δ¹³Ccell, and δ¹⁸Ocell) to successfully predict the stand characteristics of two sets (upland, riparian) of old-growth PIPO using the Physiological Principles in Predicting Growth (3-PG) model, the δ¹³Ccell submodel, and a δ¹⁸Ocell submodel added by me. The expanded model helped to explain physiological drivers underlying the different tree-ring growth, δ¹³Ccell, and δ¹⁸Ocell trajectories measured at the upland and riparian sites. The combination of both δ¹⁸O and δ¹³Ccell submodels provided a useful and novel way to constrain 3-PG.
This dissertation demonstrates an innovative strategy of applying diverse approaches to understand the physiological mechanisms behind vegetation responses to environmental stress
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Impacts of dwarf mistletoe on the physiology of host Tsuga heterophylla trees as recorded in tree ring C and O stable isotopes
Dwarf mistletoes, obligate, parasitic plants with diminutive aerial shoots, have long-term effects on host tree water relations, hydraulic architecture, and photosynthetic gas exchange and can eventually lead to tree death. To investigate the long-term impacts of dwarf mistletoe on gas exchange of host western hemlock trees, I compared growth, gas exchange, and tree-ring cellulose stable carbon and oxygen isotope ratios (δ¹³Ccₑcell and δ¹⁸Ocₑcell) of heavily infected and uninfected trees. Relative basal area growth declined more rapidly with increasing tree size in infected than uninfected trees. Both radial growth and δ¹³Ccₑcell was significantly lower in infected than uninfected trees when trees were heavily infected. The combination of radial growth and δ¹³Ccₑcell patterns described the intensification of dwarf mistletoe throughout tree crowns through time. δ¹³Ccₑcell and δ¹⁸Ocₑcell were significantly lower in infected trees than uninfected trees, an unexpected result given that stomatal conductance, relative humidity and other external variables expected to influence the δ¹⁸O values of leaf water were similar for infected and uninfected trees. Leaf mesophyll conductance (gm) and effective pathlength (L) were estimated to explain observed differences in δ¹⁸Ocₑcell between infected and uninfected trees. Infected trees had significantly lower gm and greater L than uninfected trees. These results point to the limitations of the dual isotope approach for identifying sources of variation in δ¹³Ccₑcell and indicate that changes in leaf internal properties such as L that affect δ¹⁸Ocₑcell must be considered. The significantly greater L and significantly lower gm in infected compared to uninfected trees suggest that dwarf mistletoe may influence leaf structural and anatomical characteristics that are related to L and gm
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Expression of functional traits during seedling establishment in two populations of Pinus ponderosa from contrasting climates
First-year tree seedlings represent a particularly vulnerable life stage and successful seedling establishment is crucial for forest regeneration. We investigated the extent to which Pinus ponderosa P. & C. Lawson populations from different climate zones exhibit differential expression of functional traits that may facilitate their establishment. Seeds from two populations from sites with contrasting precipitation and temperature regimes east (PIPOdry) and west (PIPOmesic) of the Oregon Cascade mountains were sown in a common garden experiment and grown under two water availability treatments (control and drought). Aboveground biomass accumulation, vegetative phenology, xylem anatomy, plant hydraulic architecture, foliar stable carbon isotope ratios (δ13C), gas exchange and leaf water relations characteristics were measured. No treatment or population-related differences in leaf water potential were detected. At the end of the first growing season, aboveground biomass was 74 and 44% greater in PIPOmesic in the control and drought treatments, respectively. By early October, 73% of PIPOdry seedlings had formed dormant buds compared with only 15% of PIPOmesic seedlings. Stem theoretical specific conductivity, calculated from tracheid dimensions and packing density, declined from June through September and was nearly twice as high in PIPOmesic during most of the growing season, consistent with measured values of specific conductivity. Intrinsic water-use efficiency based on δ13C values was higher in PIPOdry seedlings for both treatments across all sampling dates. There was a negative relationship between values of δ13C and leaf-specific hydraulic conductivity across populations and treatments, consistent with greater stomatal constraints on gas exchange with declining seedling hydraulic capacity. Integrated growing season assimilation and stomatal conductance estimated from foliar δ13C values and photosynthetic CO2-response curves were 6 and 28% lower, respectively, in PIPOdry seedlings. Leaf water potential at the turgor loss point was 0.33 MPa more negative in PIPOdry, independent of treatment. Overall, PIPOdry seedlings exhibited more conservative behavior, suggesting reduced growth is traded off for increased resistance to drought and extreme temperatures.Keywords: gas exchange, carbon isotope discrimination, phenology, osmotic potential, hydraulic architecture, genetic variatio
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Linking nonstructural carbohydrate dynamics to gas exchange and leaf hydraulic behavior in Pinus edulis and Juniperus monosperma
Leaf hydraulics, gas exchange and carbon storage in Pinus edulis and Juniperus monosperma, two tree species on opposite ends of the isohydry–anisohydry spectrum, were analyzed to examine relationships between hydraulic function and carbohydrate dynamics. Leaf hydraulic vulnerability, leaf water potential (Wl), leaf hydraulic conductance (Kleaf), photosynthesis (A), stomatal conductance (gs) and nonstructural carbohydrate (NSC) content were analyzed throughout the growing season. Leaf hydraulic vulnerability was significantly lower in the relatively anisohydric J. monosperma than in the more isohydric P. edulis. In P. edulis, ψ₁ dropped and stayed below 50% loss of leaf hydraulic conductance (P₅₀) early in the day during May, August and around midday in September, leading to sustained reductions in K[subscript leaf]. In J. monosperma, ψ₁ dropped below P₅₀ only during August, resulting in the maintenance of K[subscript leaf] during much of the growing season. Mean A and g[subscript s] during September were significantly lower in P. edulis than in J. monosperma. Foliar total NSC was two to three times greater in J. monosperma than in P. edulis in June, August and September. Consistently lower levels of total NSC in P. edulis suggest that its isohydric strategy pushes it towards the exhaustion of carbon reserves during much of the growing season.Keywords: Juniperus monosperma, Carbon storage, Leaf hydraulics, Pinus edulis, Carbon starvation, Growth limitation, Nonstructural carbohydrate (NSC), Drough
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Impacts of dwarf mistletoe on the physiology of host Tsuga heterophylla trees as recorded in tree-ring C and O stable isotopes
See article for Abstract. Keywords: mesophyll conductance, effective path lengt
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KerrKellyForEcosystemSocExpressionFunctionalTraitsSuppTable1.pdf
First-year tree seedlings represent a particularly vulnerable life stage and successful seedling establishment is crucial for forest
regeneration. We investigated the extent to which Pinus ponderosa P. & C. Lawson populations from different climate zones
exhibit differential expression of functional traits that may facilitate their establishment. Seeds from two populations from sites
with contrasting precipitation and temperature regimes east (PIPOdry) and west (PIPOmesic) of the Oregon Cascade mountains were
sown in a common garden experiment and grown under two water availability treatments (control and drought). Aboveground
biomass accumulation, vegetative phenology, xylem anatomy, plant hydraulic architecture, foliar stable carbon isotope ratios
(δ13C), gas exchange and leaf water relations characteristics were measured. No treatment or population-related differences in
leaf water potential were detected. At the end of the first growing season, aboveground biomass was 74 and 44% greater in
PIPOmesic in the control and drought treatments, respectively. By early October, 73% of PIPOdry seedlings had formed dormant
buds compared with only 15% of PIPOmesic seedlings. Stem theoretical specific conductivity, calculated from tracheid dimensions
and packing density, declined from June through September and was nearly twice as high in PIPOmesic during most of the growing
season, consistent with measured values of specific conductivity. Intrinsic water-use efficiency based on δ13C values was
higher in PIPOdry seedlings for both treatments across all sampling dates. There was a negative relationship between values of
δ13C and leaf-specific hydraulic conductivity across populations and treatments, consistent with greater stomatal constraints on
gas exchange with declining seedling hydraulic capacity. Integrated growing season assimilation and stomatal conductance
estimated from foliar δ13C values and photosynthetic CO2-response curves were 6 and 28% lower, respectively, in PIPOdry seedlings.
Leaf water potential at the turgor loss point was 0.33 MPa more negative in PIPOdry, independent of treatment. Overall,
PIPOdry seedlings exhibited more conservative behavior, suggesting reduced growth is traded off for increased resistance to
drought and extreme temperatures.Keywords: carbon isotope discrimination, hydraulic architecture, genetic variation, phenology, gas exchange, osmotic potentialKeywords: carbon isotope discrimination, hydraulic architecture, genetic variation, phenology, gas exchange, osmotic potentia
Recommended from our members
KerrKellyForEcosystemSocExpressionFunctionalTraits.pdf
First-year tree seedlings represent a particularly vulnerable life stage and successful seedling establishment is crucial for forest
regeneration. We investigated the extent to which Pinus ponderosa P. & C. Lawson populations from different climate zones
exhibit differential expression of functional traits that may facilitate their establishment. Seeds from two populations from sites
with contrasting precipitation and temperature regimes east (PIPOdry) and west (PIPOmesic) of the Oregon Cascade mountains were
sown in a common garden experiment and grown under two water availability treatments (control and drought). Aboveground
biomass accumulation, vegetative phenology, xylem anatomy, plant hydraulic architecture, foliar stable carbon isotope ratios
(δ13C), gas exchange and leaf water relations characteristics were measured. No treatment or population-related differences in
leaf water potential were detected. At the end of the first growing season, aboveground biomass was 74 and 44% greater in
PIPOmesic in the control and drought treatments, respectively. By early October, 73% of PIPOdry seedlings had formed dormant
buds compared with only 15% of PIPOmesic seedlings. Stem theoretical specific conductivity, calculated from tracheid dimensions
and packing density, declined from June through September and was nearly twice as high in PIPOmesic during most of the growing
season, consistent with measured values of specific conductivity. Intrinsic water-use efficiency based on δ13C values was
higher in PIPOdry seedlings for both treatments across all sampling dates. There was a negative relationship between values of
δ13C and leaf-specific hydraulic conductivity across populations and treatments, consistent with greater stomatal constraints on
gas exchange with declining seedling hydraulic capacity. Integrated growing season assimilation and stomatal conductance
estimated from foliar δ13C values and photosynthetic CO2-response curves were 6 and 28% lower, respectively, in PIPOdry seedlings.
Leaf water potential at the turgor loss point was 0.33 MPa more negative in PIPOdry, independent of treatment. Overall,
PIPOdry seedlings exhibited more conservative behavior, suggesting reduced growth is traded off for increased resistance to
drought and extreme temperatures.Keywords: gas exchange, phenology, hydraulic architecture, genetic variation, osmotic potential, carbon isotope discriminatio
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MariasDanielleForestryImpactsDwarfMistletoe.pdf
See article for Abstract.Keywords: mesophyll conductance, effective path lengthKeywords: mesophyll conductance, effective path lengt
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MariasDanielleForestryImpactsDwarfMistletoe_SupplementaryData.docx
See article for Abstract.Keywords: mesophyll conductance, effective path lengthKeywords: mesophyll conductance, effective path lengthKeywords: mesophyll conductance, effective path lengthKeywords: mesophyll conductance, effective path lengt