Date of Defense
7-11-2024 11:00 AM
Location
F3-035
Document Type
Dissertation Defense
Degree Name
Doctor of Philosophy in Cellular and Molecular Biology
College
College of Science
Department
Biology
First Advisor
Dr. Sunil Mundra
Keywords
Arid Environment, Date palm (Phoenix dactylifera), Extremozymes, Fungal and bacterial community, Irrigation water source, Soil salinity
Abstract
Soil salinization poses a critical challenge in arid and semi-arid regions, where water scarcity is exacerbated by climate change and unsustainable agricultural practices. This phenomenon not only reduces soil fertility but also significantly impacts groundwater quality, leading to detrimental effects on crop yields and ecosystem health. Date palm (Phoenix dactylifera) cultivation, a key agricultural practice in many arid regions, often relies on saline groundwater for irrigation due to limited freshwater resources and low precipitation rates. The use of saline water can create an intricate balance between providing necessary nutrients and introducing harmful salts into the soil. While the role of plant-associated microbiota is vital for nutrient cycling, plant health, and overall ecosystem functioning, the impact of increasing salinity on these microbial communities remains underexplored. Understanding how different irrigation practices and soil salinity influence microbial diversity and community structure is essential for developing sustainable agricultural strategies in arid environments. This study aims to fill this knowledge gap by investigating the effects of freshwater and saline groundwater irrigation on the fungi associated with date palms using high-throughput sequencing of the Internal Transcribed Spacer 2 (ITS2) gene region. Additionally, we examine bacterial diversity in the salt flats of Abu Dhabi, UAE, focusing on seasonal variations through culturomics-based methods, as well as the salt tolerance and enzymatic capabilities of these bacteria. The findings indicate that root-associated fungal communities differ significantly between irrigation water sources, with water pH and electrical conductivity (EC) as major influencing factors. Under saline groundwater irrigation, we observed a higher abundance of saprotrophic operational taxonomic units (OTUs) such as Acrocalymma vagum, Coprinopsis sp., and Myrothecium sp. Conversely, saline groundwater irrigation reduced the number of unique fungal OTUs in the soil while increasing the abundance of pathotrophs. In the bulk soil, fungal richness negatively correlated with soil pH, with both dispersal limitation and demographic stochastic processes shaping community structure. Interestingly, saline groundwater irrigation did not affect fungal richness or diversity in leaves; however, comparatively a higher percentage of unique OTUs was identified in leaves irrigated with saline water, with richness negatively correlated to soil EC, pH, and soil OM. The diversity index showed a positive correlation with irrigation groundwater pH in leaves. The members of the order Dothideales and Aureobasidium sp. were more abundant under saline groundwater irrigation in leaves. Also, stochastic drift was identified as the major ecological process in leaf fungal assembly. In the salt-flat study, the Bacillota phylum dominated across all seasons, with prevalent species including Bacillus paralicheniformis, B. licheniformis, B. vallismortis, and B. tropicus. Seasonal variations were evident, with greater bacterial richness noted at the end of the growing season. Most isolates showed tolerance to 10% NaCl and exhibited significant enzymatic activities, including cellulases (90%), proteases (85%), hydrolases (100%), and transferases (100%). The findings show that irrigation with saline groundwater profoundly influences fungal diversity and community composition, with pH and EC emerging as critical environmental factors. Increased abundance of saprotrophic fungi under saline conditions suggests their potential role in enhancing nutrient cycling and promoting plant growth, even in challenging environments. Conversely, the reduction of unique OTUs in soil and the prevalence of pathotrophs highlight the potential risks associated with saline irrigation, which may threaten soil health and plant vitality. Moreover, the salt flats study displays the resilience of microbes in extreme conditions, revealing high salt tolerance and significant enzymatic activity among the dominant species which opens avenues for biotechnological applications, particularly in agriculture and industrial enzyme production. The implications extend beyond local agricultural systems, informing global strategies for managing soil health and ensuring food security in an era of climate variability. Future studies should explore the long-term effects of saline groundwater irrigation on microbial communities and their functional capacities, further elucidating the potential for harnessing microbial resilience in sustainable agricultural practices.
Included in
ASSESSING THE IMPACT OF IRRIGATION WATER AND SOIL SALINITY ON DATE PALM AND DESERT SOIL ASSOCIATED MICROBIOTA
F3-035
Soil salinization poses a critical challenge in arid and semi-arid regions, where water scarcity is exacerbated by climate change and unsustainable agricultural practices. This phenomenon not only reduces soil fertility but also significantly impacts groundwater quality, leading to detrimental effects on crop yields and ecosystem health. Date palm (Phoenix dactylifera) cultivation, a key agricultural practice in many arid regions, often relies on saline groundwater for irrigation due to limited freshwater resources and low precipitation rates. The use of saline water can create an intricate balance between providing necessary nutrients and introducing harmful salts into the soil. While the role of plant-associated microbiota is vital for nutrient cycling, plant health, and overall ecosystem functioning, the impact of increasing salinity on these microbial communities remains underexplored. Understanding how different irrigation practices and soil salinity influence microbial diversity and community structure is essential for developing sustainable agricultural strategies in arid environments. This study aims to fill this knowledge gap by investigating the effects of freshwater and saline groundwater irrigation on the fungi associated with date palms using high-throughput sequencing of the Internal Transcribed Spacer 2 (ITS2) gene region. Additionally, we examine bacterial diversity in the salt flats of Abu Dhabi, UAE, focusing on seasonal variations through culturomics-based methods, as well as the salt tolerance and enzymatic capabilities of these bacteria. The findings indicate that root-associated fungal communities differ significantly between irrigation water sources, with water pH and electrical conductivity (EC) as major influencing factors. Under saline groundwater irrigation, we observed a higher abundance of saprotrophic operational taxonomic units (OTUs) such as Acrocalymma vagum, Coprinopsis sp., and Myrothecium sp. Conversely, saline groundwater irrigation reduced the number of unique fungal OTUs in the soil while increasing the abundance of pathotrophs. In the bulk soil, fungal richness negatively correlated with soil pH, with both dispersal limitation and demographic stochastic processes shaping community structure. Interestingly, saline groundwater irrigation did not affect fungal richness or diversity in leaves; however, comparatively a higher percentage of unique OTUs was identified in leaves irrigated with saline water, with richness negatively correlated to soil EC, pH, and soil OM. The diversity index showed a positive correlation with irrigation groundwater pH in leaves. The members of the order Dothideales and Aureobasidium sp. were more abundant under saline groundwater irrigation in leaves. Also, stochastic drift was identified as the major ecological process in leaf fungal assembly. In the salt-flat study, the Bacillota phylum dominated across all seasons, with prevalent species including Bacillus paralicheniformis, B. licheniformis, B. vallismortis, and B. tropicus. Seasonal variations were evident, with greater bacterial richness noted at the end of the growing season. Most isolates showed tolerance to 10% NaCl and exhibited significant enzymatic activities, including cellulases (90%), proteases (85%), hydrolases (100%), and transferases (100%). The findings show that irrigation with saline groundwater profoundly influences fungal diversity and community composition, with pH and EC emerging as critical environmental factors. Increased abundance of saprotrophic fungi under saline conditions suggests their potential role in enhancing nutrient cycling and promoting plant growth, even in challenging environments. Conversely, the reduction of unique OTUs in soil and the prevalence of pathotrophs highlight the potential risks associated with saline irrigation, which may threaten soil health and plant vitality. Moreover, the salt flats study displays the resilience of microbes in extreme conditions, revealing high salt tolerance and significant enzymatic activity among the dominant species which opens avenues for biotechnological applications, particularly in agriculture and industrial enzyme production. The implications extend beyond local agricultural systems, informing global strategies for managing soil health and ensuring food security in an era of climate variability. Future studies should explore the long-term effects of saline groundwater irrigation on microbial communities and their functional capacities, further elucidating the potential for harnessing microbial resilience in sustainable agricultural practices.