Date of Award

Summer 8-21-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Advisor

Yongjiang Zhang

Second Committee Member

Uri Hochberg

Third Committee Member

Jay Wason

Additional Committee Members

Seanna Annis

Abstract

Climate change is expected to lead to novel climate conditions with an increase in frequency and severity of drought across many places around the globe including the north-eastern (NE) United States. Therefore, experimental studies that test the impacts of changing environmental conditions over long time scales or experimental studies that mimic these conditions are crucial to understand the potential impact on crops in this region. Wild lowbush blueberries and highbush blueberries are two important crops in NE USA. In this study, the leaf functional, structural, nutrient traits across genotypes of wild blueberries (Vaccinium angustifolium and V. myrtilloides) at Blueberry Hill Farm, Jonesboro, Maine were monitored across two crop growth cycles for four years and were related to changing environmental conditions. Additionally, I investigated how four blueberry population- varieties (two V. angustifolium populations and two V. corymbosum varieties) respond to extreme experimental drought conditions to reveal the physiological mechanisms regulating their drought responses.

The results showed that wild blueberries showed strong variation both within and across genotypes in leaf structure, physiology, and nutrient status. The variation could be explained more by intra-genotype variance than by inter-genotype variance. Comparing their leaf economic spectrum (LES) traits to the Glopnet (a global dataset of plant leaf traits), the blueberries fell within the domain of Glopnet species, but global LES relationships were not always found. Also, I found that these two species showed similar or higher values across most traits compared to Vaccinium species in the Glopnet. Further, a principal component analysis (PCA) with all leaf functional, nutrient, structural traits, soil properties, rainfall and temperature showed overlaps in the soil nutrient requirements but clear separation in leaf nutrient, structural traits, physiological traits, and rainfall. Therefore, there was a clear differentiation in water and nutrient use between these two species and temporal variation in environmental conditions also shifted the traits. These findings can help us to predict how these species will respond to future climate change, and how changes in environmental conditions will shape the trait development and coordination, as well as the community composition.

In the drought experiment, the two lowbush populations (Ang 1 and Ang 2) and two highbush varieties (Bluecrop and Patriot) showed a coordinated response of all the physiological processes including stomatal conductance, photosynthesis rate, transpiration rate, photochemistry, and plant hydraulic systems under declining stem water potential (Ψstem; a measure of water tension within the plant) and soil moisture conditions. Notably, there were quick declines in stomatal conductance, photosynthesis, and water loss before the turgor loss point (TLP) and the progressive decline of photochemistry, leaf browning, and leaf dropping after the TLP as Ψstem and soil moisture declined across all population- varieties of blueberries and reached -4.0MPa to -4.5MPa Ψstem and less than 5% soil moisture at the end of the drought treatment. Importantly, physiological processes, for example, Fv/Fm in Ang 2 and Patriot declined more quickly compared to Ang 1 and Bluecrop during the drought treatment. Ang 1 and Patriot showed 100% loss of hydraulic conductivity (PLC), while the Ang 2 and Bluecrop reached 87% and 83% PLC at the end of the 4-week-long drought. Ang 1 and Ang 2 populations had high regrowth of new stems from underground rhizomes in the following season, indicating the resilience of wild lowbush blueberries. All groups showed high stem mortality when water potentials were as low as -4.0MPa to -4.5 MPa, indicating that these population- varieties are vulnerable to extreme drought. The results of this study not only allowed us to understand the drought responses of these population- varieties but also allowed us to understand the turgor loss point as a threshold beyond which damages in photochemistry, leaf shedding, hydraulic failure, and plant mortality occur. In the blueberry fields, blueberry population- varieties may respond to drought in different ways especially for Angustifolium populations. The wild blueberry populations in the field conditions might show higher resistance compared to potted plants because of their large rhizome systems in the field. Therefore, the findings from this study could be further tested at larger scales in the field.

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