Author : Alexandria N. Igwe
Publisher :
Page : 0 pages
File Size : 17,9 MB
Release : 2020
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ISBN :
Book Description
Root-associated (rhizosphere and rhizoplane) microbial communities influence plant phenotype, growth, and local abundance, yet the factors that structure these microbial communities are still poorly understood. California landscapes contain serpentine soils, which are nutrient-poor and high in heavy metals, and distinct from neighboring soils. Many plants are unable to grow in serpentine soils and some endemic species cannot compete on non-serpentine soils. Serpentine-indifferent plants, however, can do both. I utilize this class of plants and a serpentine ecosystem to disentangle the relative influences of plant species and soil type on rhizosphere microbial community composition. In Chapter 1, I characterized the microbial communities associated with the rhizoplane of serpentine-indifferent plants growing on serpentine at McLaughlin Natural Reserve. I supplemented that survey with a manipulative greenhouse experiment where I amended sterile serpentine soil with serpentine-adapted microorganisms, non-serpentine-adapted microorganisms, or a sterile control solution. I then measured seedling survival and plant growth. The results of this experiment showed that plant identity was more important than soil type for structuring rhizosphere microbial communities. Also, soil microbial community sources influenced seedling survival, but plant growth phenotypes were largely invariant to microbial communities with a few exceptions. The results from this experiment are published in Plant and Soil (Igwe, A.N. & Vannette, R.L. Plant Soil (2019) 441:423). In Chapter 2, I used 16S rRNA sequencing to determine how drought impacted the rhizosphere microbial community of several species of Streptanthus . Several species of Streptanthus were exposed to high, medium, and low watering treatments. Bacterial abundances were not significantly impacted by watering treatment. The bacterial communities of the lowest and highest watering treatment were significantly dissimilar. Results showed that alpha diversity decreased as watering levels decreased. Plant species and soil affinity did not impact alpha diversity. Several genera within Proteobacteria, Firmicutes, Bacteroidetes, Planctomycetes, and Acidobacteria were differentially abundant between watering treatments. Microbial community dissimilarity was impacted by watering treatment and species, but not soil affinity. Watering treatment shifted the microbial communities such that less water created microbial communities that are more similar. Overall, this research serves to provide insight into the microbial communities shifts we could expect as a result of drought. In Chapter 3, I conducted a manipulative greenhouse experiment using Plantago erecta. I extracted DNA from rhizosphere microbial communities of P. erecta plants at distinct developmental stages: seedling, vegetative growth, early flowering, and late flowering. The plants were grown in serpentine or non-serpentine soil types with adapted or non-adapted microbes. Plant height and leaf number was measured weekly until harvesting and the plant developmental stage was noted. Afterwards, dry mass of above ground parts was collected, and roots were imaged using the WinRhizo system.16S rRNA amplicon sequencing and data analysis showed that alpha diversity was significantly lower in serpentine soil treatments and plant developmental stages. The variation observed in the rhizosphere microbial community was influenced by soil type, plant developmental stage, and the interaction between them both. Plants associated with serpentine microorganisms flowered sooner than those associated with non-serpentine microorganisms. In general, plants growing on serpentine soils were shorter, but leaf number was not impacted. Root length, root surface area, and root volume were all larger in nonserpentine soil treatments, but root diameter was not significantly different across soil types. These results are important for understanding how microbial communities shift to support plant survival on stressful soils.