Date of Award

Summer 8-18-2023

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Advisor

Yong-Jiang Zhang

Second Committee Member

Gregory Porter

Third Committee Member

Lily Calderwood

Additional Committee Members

José Meireles

Jianjun Hao

Abstract

Under anthropogenic global climate change associated with greenhouse gas emissions, the mean surface temperature of the earth has increased by approximately 1 oC since the industrial age and is projected to rise by 2.6 to 4.6 oC by 2100. Wild blueberry fields in Maine are experiencing unprecedented warming, which may affect the fruit flavor and nutritional quality, soil health and microbial community, and consequently impact yield, human nutrition, and the economic well-being of wild blueberry producers. It is therefore important to assess the impact of climate warming on fruit crop nutritional quality and soil microbial community, and test potential strategies to mitigate the potential negative effects. Additionally, the genetic diversity of wild blueberries has not been well-studied, which will influence their response to climate change. The objectives of this research were to: 1) quantify the impact of warming on the nutritional qualities of wild blueberries, 2) assess the effect of biochar-compost mix and mulching on mitigating the negative impact of warming on fruit nutritional qualities, 3) investigate the impact of warming on the wild blueberry soil bacterial communities, and 4) evaluate the genetic diversity and structure of wild blueberry populations in managed and unmanaged fields using single nucleotide polymorphic markers. First, I examined the nutritional quality (i.e., berry minerals, total soluble protein, total soluble solids, soluble sugars, anthocyanin) of wild blueberries grown under three temperature conditions: (1) ambient conditions, (2) passive open-top heating that elevated average temperatures by 1.2 oC, (3) active open-top heating that elevated average temperatures by 3.3 oC. Our results suggest that total soluble solids, fructose, total soluble sugars, and total soluble protein concentrations decreased as temperature increased. These changes need to be further studied to determine if they would impact consumer preference or human nutrition, and if so, mitigation techniques should be developed and tested. Second, I assessed the potential of two mitigation strategies, biochar-compost mix (BCM) and mulching, for mitigating the detrimental impacts of warming on the nutritional quality of wild blueberries. The negative effect of warming on total soluble protein and total soluble solids, as well as demonstrating strong negative effects on secondary metabolites, antioxidants, organic acids, and phenolic components, was confirmed. The mitigation strategies did not reduce the negative effect of warming on wild blueberry fruit quality except for potassium and magnesium mineral concentrations. The application rate of the biochar-compost mix and mulching currently used may not be sufficient to mitigate the negative effect of warming on berry nutritional quality. Third, I studied how bacterial communities respond to warming during the growing season, using the passive and active open-top chambers to simulate climate warming scenarios in wild blueberry fields. Overall, soil bacteria diversity and richness (June, July, and August data combined) under the warming (passive and active) treatments and ambient controls did not show significant differences after experimental warming for two years. However, significantly higher bacterial evenness and diversity under warming treatments were found in the early growing season (June). The increased bacteria evenness and diversity under warming treatments in June could be related to advanced plant phenology, suggesting a future shift of seasonal dynamics in bacterial activity under global warming. Last but not the least, I evaluated the genetic variation of two wild blueberry species across four fields in Maine using single nucleotide polymorphic markers. Most of the wild blueberry plants were genetically related, regardless of the region. Overall, no distinct genetic differentiation and no difference in genetic diversity was found between managed and unmanaged fields. This study quantified the genetic variation of wild blueberries within and among fields and provided some insights about the impact of warming on wild blueberry nutritional quality and soil microbial communities. Further studies could be done to determine if changes in nutritional quality would impact consumer preference and human nutrition, and if longer-term warming will change soil microbial communities. Techniques to mitigate the negative effects of warming on wild blueberry nutritional quality should be developed and tested.

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