Date of Award

Fall 12-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Yongjiang Zhang

Second Committee Member

Jay Wason

Third Committee Member

Lily Calderwood

Abstract

As the global temperature rises, a need exists for understanding the potential impacts of warming on the wild blueberry industry in Maine. Warming can change the physiology, growth, and pest pressure of crops, and also accelerates the evapotranspiration rate, resulting in decreased soil moisture. The objectives of this study were: (1) To characterize the response of phenological, morphological, and physiological traits of the wild blueberries to warming; (2) To quantify the impacts of different temperature levels on yield and berry quality; (3) To determine the abiotic and biotic factors that may influence yield, such as winter damages, freezing temperatures, the severity of weeds, insect pests and diseases under warming environment as they all contribute to production. Six genotypes of wild blueberries (Vaccinium angustifolium) were randomly selected from a commercially managed two-year cropping cycle wild blueberry field in Jonesboro, Maine, USA to simulate the global warming trend. A randomized block design was used consistently for this study in 2019 and 2020. For simulation, the open-top-chambers (OTCs) were with three treatment levels, namely active-heating OTCs with the chambers and heating tapes, passive-heating OTCs with the chambers but without heating tapes, and control sites without chambers and heating tapes. The results illustrated that elevated temperatures affected the morphology, phenology, and physiological performance of wild blueberries. Warming resulted in thinner leaves, lower leaf mass per area (LMA), lower stomatal density, and longer stem length in wild blueberries. Additionally, warming lengthened the senescence of the leaves; wild blueberries under warming treatments preserved chlorophyll concentration for a longer period and accumulated higher anthocyanin concentration during the fall. In the following season, vegetative growth, flowering, and fruiting of wild blueberries occurred earlier under the warming treatments. Despite lower leaf water potentials and soil moisture at midday under the warming treatments, wild blueberries showed higher stomatal conductance and transpiration rate. In the 2020 crop year, the wild blueberries produced a larger number of berries under warming than that at ambient temperatures (controls), where stems retained better fruit integrity with a larger berry cluster height per stem and generated larger berries. There was no significant difference in berry soluble solids content, pH, and acidity among different temperature treatments. In summary, wild blueberries responded to a warmer growing environment through alternation in morphology, physiology, and phenology. The responses of wild blueberries to warming include delayed defoliation in the fall, reduced leaf thickness, changes in stomatal density, altered stomatal regulation, earlier spring development, and increased fruit production. Based on the assumption about the consistency of the warmer temperature, our results suggest that although warming reduced the amount of water in the soil, it did not threaten the production of wild blueberries. Instead, reduced risk of frost exposure, a longer growing season, and the synchronization of flowering and emergence of pollinators may benefit berry production. The warming treatment also resulted in a lower incidence of leaf spot diseases at the end of the crop year compared to the control. The mechanisms explaining the higher yield of blueberries despite enhanced water deficits under warming need to be investigated further. For wild blueberries growers, the results of this study can facilitate and improve the management of farms impacted by global warming. Firstly, the extended growing season of wild blueberries means that growers need to modify the schedule of pollinator management, fertilization, and pesticide application to match the plant growth. For example, growers may need to rent beehives earlier for advanced spring-flowering events and plan for an earlier harvesting season. Secondly, wild blueberries altered their structure and physiological performance to cope with the moderate drought caused by increased temperatures. Therefore, building additional irrigation systems that could further improve production under climate change should be investigated.

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