Examining Chronic Nutrient Enrichment Effects on Wetland Plant-Microbe Interactions Using a Trait-Based Approach

ECU Author/Contributor (non-ECU co-authors, if there are any, appear on document)

Aied Garcia (Creator)

Institution

East Carolina University (ECU )

Web Site: http://www.ecu.edu/lib/

Abstract: Mutualistic plant-microbe relationships that have evolved under nutrient starved environmental conditions are important for generating and maintaining plant and microbial biodiversity. However, human activities associated with land use change have altered nutrient cycles in ways that disrupt these long-standing mutualisms. Mutualistic plant-microbe relationships are especially necessary in low-nutrient ecosystems, and previous studies have shown that root-associated microbes enhance plant growth by inhibiting pathogenic fungi, improving nutrient uptake, and increasing plant species richness. Therefore, a deeper understanding of how nutrient enrichment alters the soil microbiome in the context of plant-microbe associations is needed. The goal of this study is to examine how long-term fertilization of a historically low nutrient coastal plain wetland influences plant-microbe associations. An experimental approach was used to test the hypothesis that long-term fertilization alters bacterial traits (e.g., growth rates) that disrupt beneficial plant-microbe associations. Four bacterial isolates from bulk soil were isolated from a long-term fertilization experiment (established in 2003) conducted in a coastal plain wetland located at East Carolina University’s West Research Campus (Greenville, North Carolina, USA). For this study, we compared functional traits (e.g.,\n2\ngrowth rates) of phylogenetically identical soil bacterial isolates (>99% similar in the 16S rRNA gene) that were previously taxonomically classified into fast-growing copiotrophs and slow-growing oligotrophs. These simplified bacterial communities cultured from different soil sources (fertilized, unfertilized) were added to Chasmanthium laxum seedlings that were exposed to a nutrient gradient over five months. Results showed that bacterial isolates cultured from different nutrient enrichment histories displayed different growth rates depending on their life history strategy (i.e., slow growing oligotroph vs. fast growing copiotroph). After five months of growth, Chasmanthium laxum aboveground plant biomass was highest at low fertilization treatments (0x, 0.5x) when exposed to bacterial inocula sourced from unfertilized compared to fertilized soils. Addition of the simplified bacterial community also increased belowground root biomass compared to no bacterial additions. This study revealed that long-term nutrient enrichment does alter soil bacterial traits of cultured isolates and modifies plant-microbe relationships from mutualistic to competitive.

Additional Information

Publication

Thesis

Language: English

Date: 2023

Subjects

plnat-microbe, wetland, trait-based, nutrient enrichment, long-term fertilization, 16S rRNA

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