Browsing by Author "Ulrich, Danielle E. M."

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Creating a Hydraulic Vulnerability Curve for Two-Year Old Ponderosa Pine Seedlings
(Montana State University, 2023-11) Kincy, Sarah; Hoy-Skubik, Sean; Ulrich, Danielle E. M.
Anthropogenic driven climate change and subsequent drought conditions have negatively affected limber pine and ponderosa pine forests through mass mortality events, jeopardizing the future of these species and the overall health of montane and subalpine ecosystems. Hydraulic failure is pervasive in tree mortality caused by drought, and results in the loss of conductivity of the xylem through embolism. Complete hydraulic failure is likely not necessary for tree mortality; therefore, quantifying the levels of xylem percent loss of conductivity (PLC) associated with tree death is important for understanding and predicting landscape scale patterns of tree mortality. Hydraulic vulnerability curves can be utilized to quantify the percent loss of conductivity in the xylem at a given water potential, which can then be used to predict the lethal threshold for the species. We’ve created three hydraulic vulnerability curves, one found from limber pine leaves, one from limber pine stems, and one from ponderosa pine stems. These were created by measuring the water potential and PLC of 30 two-year old seedlings having undergone different levels of water stress, ranging from no stress to severe water stress. The lethal threshold for hydraulic failure on the curves were determined using logistic regression. These curves can be utilized to predict landscape scale mortality events of limber pine and ponderosa pine colonies due to ongoing water stress, and ultimately help to conserve and protect these species from future drought conditions.
Ectomycorrhizal and Dark Septate Fungal Associations of Pinyon Pine Are Differentially Affected by Experimental Drought and Warming
(Frontiers Media SA, 2020-10) Gehring, Catherine; Sevanto, Sanna; Patterson, Adair; Ulrich, Danielle E. M.; Kuske, Cheryl R.
Changing climates can cause shifts in temperature and precipitation, resulting in warming and drought in some regions. Although each of these factors has been shown to detrimentally affect forest ecosystems worldwide, information on the impacts of the combined effects of warming and drought is lacking. Forest trees rely on mutualistic root-associated fungi that contribute significantly to plant health and protection against climate stresses. We used a six-year, ecosystem-scale temperature and precipitation manipulation experiment targeted to simulate the climate in 2100 in the Southwestern United States to quantify the effects of drought, warming and combined drought and warming on the root colonization (abundance), species composition and diversity of ectomycorrhizal fungi (EMF), and dark septate fungal endophytes in a widespread woodland tree, pinyon pine (Pinus edulis E.). Our results show that pinyon shoot growth after 6 years of these treatments was reduced more by drought than warming. The combined drought and warming treatment reduced the abundance and diversity of EMF more than either treatment alone. Individual ectomycorrhizal fungal taxa, including the drought tolerant Cenococcum geophilum, were present in all treatments but the combined drought and warming treatment. The combined drought and warming treatment also reduced the abundance of dark septate endophytes (DSE), but did not affect their diversity or species composition. The current year shoot growth of the trees correlated positively with ectomycorrhizal fungal diversity, highlighting the importance of diversity in mutualistic relationships to plant growth. Our results suggest that EMF may be more important than DSE to aboveground growth in P. edulis, but also more susceptible to the negative effects of combined climate stressors.
Effects of Soil Microbes on Functional Traits of Loblolly Pine (Pinus taeda) Seedling Families From Contrasting Climates
(Frontiers Media SA, 2020-01) Ulrich, Danielle E. M.; Sevanto, Sanna; Peterson, Samantha; Ryan, Max; Dunbar, John
Examining factors that influence seedling establishment is essential for predicting the impacts of climate change on tree species’ distributions. Seedlings originating from contrasting climates differentially express functional traits related to water and nutrient uptake and drought resistance that reflect their climate of origin and influence their responses to drought. Soil microbes may improve seedling establishment because they can enhance water and nutrient uptake and drought resistance. However, the relative influence of soil microbes on the expression of these functional traits between seedling families or populations from contrasting climates is unknown. To determine if soil microbes may differentially alter functional traits to enhance water and nutrient uptake and drought resistance between dry and wet families, seeds of loblolly pine families from the driest and wettest ends of its geographic range (dry, wet) were planted in sterilized sand (controls) or in sterilized sand inoculated with a soil microbial community (inoculated). Functional traits related to seedling establishment (germination), water and nutrient uptake and C allocation (root:shoot biomass ratio, root exudate concentration, leaf C:N, leaf N isotope composition (δ15N)), and drought resistance (turgor loss point, leaf carbon isotope composition (δ13C)) were measured. Then, plants were exposed to a drought treatment and possible shifts in photosynthetic performance were monitored using chlorophyll fluorescence. Inoculated plants exhibited significantly greater germination than controls regardless of family. The inoculation treatment significantly increased root:shoot biomass ratio in the wet family but not in the dry family, suggesting soil microbes alter functional traits that improve water and nutrient uptake more so in a family originating from a wetter climate than in a family originating from a drier climate. Microbial effects on photosynthetic performance during drought also differed between families, as photosynthetic performance of the dry inoculated group declined fastest. Regardless of treatment, the dry family exhibited a greater root:shoot biomass ratio, root exudate concentration, and leaf δ15N than the wet family. This indicates that the dry family allocated more resources belowground than the wet and the two family may have used different sources of plant available N, which may be related to their contrasting climates of origin and influence their drought resistance. Examination of variation in impacts of soil microbes on seedling physiology improves efforts to enhance seedling establishment and beneficial plant-microbe interactions under climate change.
Faster drought recovery in anisohydric beech compared with isohydric spruce
(Oxford University Press, 2023-01) Ulrich, Danielle E. M.; Grossiord, Charlotte
With drought and heat events increasing in frequency and intensity worldwide, global drought-induced tree decline (Allen et al. 2010, Hammond et al. 2022) has resulted in widespread interest in understanding the physiological mechanisms that underlie tree death. Unprecedented mortality rates threaten forest function and ecosystem services, including carbon (C) sequestration, clean air and water, and recreational and emotional value. Researchers have aimed to understand the mechanisms of tree mortality to better predict which trees will die or survive, inform future forest dynamics and improve forest management practices (McDowell et al. 2008, 2011, Raffa et al. 2008, Sevanto et al. 2014, Gaylord et al. 2015, Adams et al. 2017).
Faster drought recovery in anisohydric beech compared with isohydric spruce
(Oxford University Press, 2023-01) Ulrich, Danielle E. M.; Grossiord, Charlotte
With drought and heat events increasing in frequency and intensity worldwide, global drought-induced tree decline (Allen et al. 2010, Hammond et al. 2022) has resulted in widespread interest in understanding the physiological mechanisms that underlie tree death. Unprecedented mortality rates threaten forest function and ecosystem services, including carbon (C) sequestration, clean air and water, and recreational and emotional value. Researchers have aimed to understand the mechanisms of tree mortality to better predict which trees will die or survive, inform future forest dynamics and improve forest management practices (McDowell et al. 2008, 2011, Raffa et al. 2008, Sevanto et al. 2014, Gaylord et al. 2015, Adams et al. 2017).
Functional traits underlie specialist-generalist strategies in whitebark pine and limber pine
(Elsevier BV, 2023-08) Ulrich, Danielle E. M.; Wasteneys, Chloe; Hoy-Skubik, Sean; Alongi, Franklin
Plant species life history strategies are described by functional variation spanning an acquisitive and conservative resource use continuum. Specialist species can exhibit traits promoting one end of the continuum, while generalist species can display traits promoting both acquisitive and conservative resource use. Whitebark pine (Pinus albicaulis, PIAL) and limber pine (Pinus flexilis, PIFL) are two high-elevation pines that have similar growth and morphology, yet contrasting elevational distributions with PIAL viewed as a specialist inhabiting a narrower elevation range, and PIFL as a generalist inhabiting a broader elevation range. We compared the physiological and morphological traits of greenhouse-grown 5-year-old PIAL and PIFL. Our results suggest that PIFL’s acquisitive and conservative resource use traits contribute to its generalist strategy and ability to inhabit a greater range of elevations than PIAL. PIFL had greater acquisitive resource use traits including: high-light tolerance (greater Qsat, greater fascicle density), increased biomass allocation to photosynthetic tissue (higher needle biomass, aboveground:belowground biomass, needle:branch + stem biomass), and higher C and water uptake (greater stomatal density and size, higher C assimilation rate), as well as greater conservative resource use traits including: greater physical stress resistance (shorter height, higher stem and branch diameters, greater branch and stem diameter:length), drought tolerance (higher SWC, leaf starch proportion), and drought avoidance (earlier budburst phenology, smaller hydroscape area) than PIAL. Our results suggest that PIFL may make more efficient use of high-light loads and maximize C and water uptake when moisture is abundant during spring snowmelt before the onset of dry summer conditions. Other conservative resource use traits describing cold tolerance, heat tolerance, and drought tolerance did not differ between species, suggesting that both species exhibit traits that promote similar conservative resource use enabling their overlapping persistence at higher elevations. Comparing the physiology of PIAL and PIFL within the same environment enables us to identify physiological mechanisms that underlie species establishment and survival, and how juvenile physiology contributes to their contrasting distributions and their generalist-specialist strategies.
Insect and Pathogen Influences on Tree-Ring Stable Isotopes
(Springer Nature, 2022-06) Ulrich, Danielle E. M.; Voelker, Steve; Brooks, J. Renée; Meinzer, Frederick C.
Understanding long-term insect and pathogen effects on host tree physiology can help forest managers respond to insect and pathogen outbreaks, and understand when insect and pathogen effects on tree physiology will be exacerbated by climate change. Leaf-level physiological processes modify the carbon (C) and oxygen (O) stable isotopic composition of elements taken up from the environment, and these modifications are recorded in tree-rings (see Chaps. 9, 10, 16 and 17). Therefore, tree-ring stable isotopes are affected by both the tree’s environment and the tree’s physiological responses to the environment, including insects and pathogens. Tree-ring stable isotopes provide unique insights into the long-term effects of insects and pathogens on host tree physiology. However, insect and pathogen impacts on tree-ring stable isotopes are often overlooked, yet can substantially alter interpretations of tree-ring stable isotopes for reconstructions of climate and physiology. In this chapter, we discuss (1) the effects of insects (defoliators, wood-boring, leaf-feeding), pests (parasitic plants), and pathogens (root and foliar fungi) on host physiology (growth, hormonal regulation, gas exchange, water relations, and carbon and nutrient use) as they relate to signals possibly recorded by C and O stable isotopes in tree-rings, (2) how tree-ring stable isotopes reveal insect and pathogen impacts and the interacting effects of pathogens and climate on host physiology, and (3) the importance of considering insect and pathogen impacts for interpreting tree-ring stable isotopes to reconstruct past climate or physiology.
Investigating old‐growth ponderosa pine physiology using tree‐rings, δ13C, δ18O, and a process‐based model
(Wiley, 2019-06) Ulrich, Danielle E. M.; Still, Christopher; Brooks, J. Renée; Kim, Youngil; Meinzer, Frederick C.
In dealing with predicted changes in environmental conditions outside those experienced today, forest managers and researchers rely on process‐based models to inform physiological processes and predict future forest growth responses. The carbon and oxygen isotope ratios of tree‐ring cellulose (δ13Ccell, δ18Ocell) reveal long‐term, integrated physiological responses to environmental conditions. We incorporated a submodel of δ18Ocell into the widely used Physiological Principles in Predicting Growth (3‐PG) model for the first time, to complement a recently added δ13Ccell submodel. We parameterized the model using previously reported stand characteristics and long‐term trajectories of tree‐ring growth, δ13Ccell, and δ18Ocell collected from the Metolius AmeriFlux site in central Oregon (upland trees). We then applied the parameterized model to a nearby set of riparian trees to investigate the physiological drivers of differences in observed basal area increment (BAI) and δ13Ccell trajectories between upland and riparian trees. The model showed that greater available soil water and maximum canopy conductance likely explain the greater observed BAI and lower δ13Ccell of riparian trees. Unexpectedly, both observed and simulated δ18Ocell trajectories did not differ between the upland and riparian trees, likely due to similar δ18O of source water isotope composition. The δ18Ocell submodel with a Peclet effect improved model estimates of δ18Ocell because its calculation utilizes 3‐PG growth and allocation processes. Because simulated stand‐level transpiration (E) is used in the δ18O submodel, aspects of leaf‐level anatomy such as the effective path length for transport of water from the xylem to the sites of evaporation could be estimated.
Root exudate composition reflects drought severity gradient in blue grama (Bouteloua gracilis)
(Springer Nature, 2022-07) Ulrich, Danielle E. M.; Clendinen, Chaevien S.; Alongi, Franklin; Mueller, Rebecca C.; Chu, Rosalie K.; Toyoda, Jason; Gallegos‑Graves, La Verne; Goemann, Hannah M.; Peyton, Brent; Sevanto, Sanna; Dunbar, John
Plant survival during environmental stress greatly affects ecosystem carbon (C) cycling, and plant–microbe interactions are central to plant stress survival. The release of C-rich root exudates is a key mechanism plants use to manage their microbiome, attracting beneficial microbes and/or suppressing harmful microbes to help plants withstand environmental stress. However, a critical knowledge gap is how plants alter root exudate concentration and composition under varying stress levels. In a greenhouse study, we imposed three drought treatments (control, mild, severe) on blue grama (Bouteloua gracilis Kunth Lag. Ex Griffiths), and measured plant physiology and root exudate concentration and composition using GC–MS, NMR, and FTICR. With increasing drought severity, root exudate total C and organic C increased concurrently with declining predawn leaf water potential and photosynthesis. Root exudate composition mirrored the physiological gradient of drought severity treatments. Specific compounds that are known to alter plant drought responses and the rhizosphere microbiome mirrored the drought severity-induced root exudate compositional gradient. Despite reducing C uptake, these plants actively invested C to root exudates with increasing drought severity. Patterns of plant physiology and root exudate concentration and composition co-varied along a gradient of drought severity.