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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2023)

This research venture presents three distinctive studies, employing non-structural carbohydrate (NSC) measurements as an effective tool to evaluate plant responses under varied environmental conditions.

Chapter One focuses on how the rate of drought development impacts energy reserves and the recovery process in Grenache, a cultivar. The research studied fast-developing drought (FDD) and slow-developing drought (SDD). FDD, characterized by rapid stomatal closure and high abscisic acid (ABA) accumulation, showed negligible stem priming for recovery. However, SDD exhibited gradual stomatal closure, lower ABA accumulation, and changes preparing the stem for recovery, including xylem sap acidification and sugar accumulation. Both drought types showed similar trends concerning stomatal conductance recovery, yet displayed different sensitivities to xylem ABA. Total NSC content in plant stems was affected differently by FDD and SDD. FDD didn't significantly alter total carbohydrate content, whereas SDD led to an increase during stress, which normalized post-recovery. FDD resulted in a higher stem starch content during drought and post-rehydration, with no significant change in soluble sugar accumulation. SDD plants accumulated slightly more starch and significantly more soluble sugars, which returned to pre-stress levels swiftly after rehydration. This study indicates plants' unique adaptability to long-term drought and highlights the need for accurately reflecting field conditions when studying plant responses to drought.

Chapter Two investigates the impact of extended smoke exposure on NSC reserves in trees under natural field conditions. The study analyzed a comprehensive regional dataset and detailed spatiotemporal satellite data. Results showed that mid-growth season smoke exposure could transiently deplete plants' NSC reserves, while exposure later in the growth cycle could disrupt the vital carbohydrate reserve buildup, leading to a prolonged reduction in reserves. This introduces an unrecognized risk to plant health and ecosystem stability, threatening both agricultural and natural environments on a regional scale.

Chapter Three explores climate change implications on almond orchard phenology and the subsequent land suitability for almond farming. This study utilized historical climate data, a model incorporating daily minimum/maximum temperatures and NSC dynamics in twigs, and CMIP6 climate predictions. Analysis under two climate change scenarios projected that land suitable for almond farming could remain largely stable over the next three decades. However, under the unchanged emission scenario, the suitable land could see a reduction ranging from 50% to 95% by the century's end, aligning with a shift in bloom time. This signifies the critical role of climate change in shaping almond production's future, emphasizing the need for sustainable agricultural land management, ensuring long-term food security and economic stability amidst evolving climate conditions.

In conclusion, the research presents valuable insights into plants' adaptability and resilience under different environmental stressors. It demonstrates the importance of NSC measurements in understanding these responses, opening avenues for future research and effective adaptation strategies in the face of changing environmental conditions. It also underscores the pressing need to address the risks and challenges posed by climate change and other anthropogenic factors to ensure sustainable agricultural practices and ecosystem stability.

    Cover page: Carbohydrates at the Crossroads: A Multiscale View of the Role of Carbohydrates in the Face of Climate Change
    • Article
    • Peer Reviewed
    UC Davis Previously Published Works (2024)
    Climate change is expected to impact the spring phenology of perennial trees, potentially altering the suitability of land for their cultivation. In this study, we investigate the effects of climate change on the bloom timing of almond orchards, focusing on California, the worlds leading region for almond production. By analyzing historical climatic data, employing a model that considers hourly temperatures and fall non-structural carbohydrates to predict bloom dates, and examining various Coupled Model Intercomparison Project Phase 6 (CMIP6) scenarios, we assess the potential impacts of climate shifts on plant phenology and, consequently, on land suitability for almond farming. Our findings reveal that, within the next 30 years, the land suitable for almond production will not undergo significant changes. However, under unchanged emission scenarios, the available land to support almond orchard farming could decline between 48 to 73% by the end of the century. This reduction corresponds with an early shift in bloom time from the average Day of Year (DOY) 64 observed over the past 40 years to a projected earlier bloom between DOY 28-33 by 2100. These results emphasize the critical role climate shifts have in shaping future land use strategies for almond production in Central Valley, California. Consequently, understanding and addressing these factors is essential for the sustainable management and preservation of agricultural land, ensuring long-term food security and economic stability in the face of a rapidly changing climate.
      Cover page: Losing ground: projections of climate-driven bloom shifts and their implications for the future of Californias almond orchards.
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2022)
      Successful yield in orchards is the culmination of a series of events that start with plants entering dormancy with adequate energy reserves (non-structural carbohydrates; NSC). These NSC are responsible for the maintenance of activities during dormancy and extending onto the period of activeness. Using multi-year yield information and monthly NSC content in twigs, we show that high levels of carbohydrate in Prunus dulcis, Pistachio vera, and Juglans regia during the winter months are indeed associated with high yield, while high levels of the NSC in late summer often correlate with low yield. An evaluation of monthly NSC level importance on yield revealed that for P. dulcis high levels in February were a good predictor of yield and that low levels throughout summer were associated with high yield. In P. vera, high levels of NSC in December were best predictors of yield. J. regia exhibited peculiar patterns; while high pre-budbreak reserves were associated with high yields they only played a minor role in explaining crop, the most important months for predicting yields were June and July. Results suggest that NSC levels can serve as good predictors of orchard yield potential and should be monitored to inform orchard management.
        Cover page: The impact of non-structural carbohydrates (NSC) concentration on yield in Prunus dulcis, Pistacia vera, and Juglans regia
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2022)
        Plants are frequently exposed to prolonged and intense drought events. To survive, species must implement strategies to overcome progressive drought while maintaining sufficient resources to sustain the recovery of functions. Our objective was to understand how stress rate development modulates energy reserves and affects the recovery process. Grenache Vitis vinifera cultivar was exposed to either fast-developing drought (within few days; FDD), typical of pot experiments, or slow-developing drought (few weeks, SDD), more typical for natural conditions. FDD was characterized by fast (2-3 days) stomatal closure in response to increased stress level, high abscisic acid (ABA) accumulation in xylem sap (>400 μg L-1 ) without the substantial changes associated with stem priming for recovery (no accumulation of sugar or drop in xylem sap pH). In contrast, SDD was characterized by gradual stomatal closure, low ABA accumulation (<100 μg L-1 ) and changes that primed the stem for recovery (xylem sap acidification from 6 to 5.5 pH and sugar accumulation from 1 to 3 g L-1 ). Despite FDD and SDD demonstrating similar trends over time in the recovery of stomatal conductance, they differed in their sensitivity to xylem ABA. Grenache showed near-isohydric and near-anisohydric behavior depending on the rate of drought progression, gauging the risk between hydraulic integrity and photosynthetic gain. The isohydry observed during FDD could potentially provide protection from large sudden swings in tension, while transitioning to anisohydry during SDD could prioritize the maintenance of photosynthetic activity over hydraulic security.
          Cover page: Do the ends justify the means? Impact of drought progression rate on stress response and recovery in Vitis vinifera
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2022)

          Premise

          Trees in wet forests often have features that prevent water films from covering stomata and inhibiting gas exchange, while many trees in drier environments use foliar water uptake to reduce water stress. In forests with both wet and dry seasons, evergreen trees would benefit from producing leaves capable of balancing rainy-season photosynthesis with summertime water absorption.

          Methods

          Using samples collected from across the vertical gradient in tall redwood (Sequoia sempervirens) crowns, we estimated tree-level foliar water uptake and employed physics-based causative modeling to identify key functional traits that determine uptake potential by setting hydraulic resistance.

          Results

          We showed that Sequoia has two functionally distinct shoot morphotypes. While most shoots specialize in photosynthesis, the axial shoot type is capable of much greater foliar water uptake, and its within-crown distribution varies with latitude. A suite of leaf surface traits cause hydraulic resistance, leading to variation in uptake capacity among samples.

          Conclusions

          Shoot dimorphism gives tall Sequoia trees the capacity to absorb up to 48 kg H2 O h-1 during the first hour of leaf wetting, ameliorating water stress while presumably maintaining high photosynthetic capacity year round. Geographic variation in shoot dimorphism suggests that plasticity in shoot-type distribution and leaf surface traits helps Sequoia maintain a dominate presence in both wet and dry forests.
            Cover page: Shoot dimorphism enables Sequoia sempervirens to separate requirements for foliar water uptake and photosynthesis
            • Article
            • Peer Reviewed
            UC Santa Cruz Previously Published Works (2021)
            The global lockdown to mitigate COVID-19 pandemic health risks has altered human interactions with nature. Here, we report immediate impacts of changes in human activities on wildlife and environmental threats during the early lockdown months of 2020, based on 877 qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of reports of unusual species observations from around the world suggest that animals quickly responded to the reductions in human presence. However, negative effects of lockdown on conservation also emerged, as confinement resulted in some park officials being unable to perform conservation, restoration and enforcement tasks, resulting in local increases in illegal activities such as hunting. Overall, there is a complex mixture of positive and negative effects of the pandemic lockdown on nature, all of which have the potential to lead to cascading responses which in turn impact wildlife and nature conservation. While the net effect of the lockdown will need to be assessed over years as data becomes available and persistent effects emerge, immediate responses were detected across the world. Thus, initial qualitative and quantitative data arising from this serendipitous global quasi-experimental perturbation highlights the dual role that humans play in threatening and protecting species and ecosystems. Pathways to favorably tilt this delicate balance include reducing impacts and increasing conservation effectiveness.
              Cover page: Global COVID-19 lockdown highlights humans as both threats and custodians of the environment
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