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New Mexico State University (2021)

Biogeochemical Function and Microbial Diversity in Chihuahuan Desert Biocrusts

Hoellrich, Mikaela

Titre : Biogeochemical Function and Microbial Diversity in Chihuahuan Desert Biocrusts

Auteur : Hoellrich, Mikaela

Université de soutenance : New Mexico State University

Grade : Master of Science (MS) 2021

Résumé
Biological soil crusts (biocrusts) are living soil aggregates hosting diverse communities of lichens, bryophytes, cyanobacteria, eukaryotic algae, and other microorganisms in the uppermost millimeters of dryland soils. Biocrusts array along a gradient of structural complexity distinguished by the dominant photoautotrophic community member. Consequently, each biocrust type can host a unique microbial community with different associated biogeochemical processes. Yet, most existing studies have assessed the diversity patterns of biocrust microbial communities and functional contributions separately. Additionally, site specific conditions like soil parent material, pH, and nutrient availability influence the microorganisms present in a given location. This project aims to 1) assess the carbon fixation capacity of biocrust types under varying incubation times ; 2) understand microbial community composition as well as biomass differences within these biocrust types ; and 3) identify how geographic location and soil properties can explain differences seen in carbon fixation and microbial diversity. Five biocrust types were collected from four locations in the Chihuahuan Desert. Carbon fixation rates were quantified using a LI-6400XT portable photosynthesis system. Measurements were taken after biocrust wetting and light incubation at five different time periods (30min, 2hr, 6hr, 12hr, 24hr). Microbial biomass was assessed with a single composite sample for each biocrust type at each site using phospholipid fatty acid assays. Microbial community composition was examined using 16S rRNA gene Illumina sequencing for bacteria. We detected a trend of increasing carbon fixation and decreasing respiration over time for all crust types following wetting, although variation between time points was not statistically significant. Generally, greater carbon fixation and respiration rates were found in more structurally complex biocrust. However, due to high respiration, moss crusts recorded the lowest net carbon fixation rates. There was also a slight correlation between thicker crusts and greater carbon fixation and respiration rates. This relationship was explained more by crust type than crust thickness. Different sites followed the same general trends across all biocrust types. However, site was a better predictor of biogeochemical capacity than type. Microbial alpha diversity did not change significantly with increasing biocrust structural complexity. Instead, biocrust communities were unique in accordance with different parent material. Distinct dissimilarity was found between the bacterial communities of sites with different parent materials. This study provides new insights into how microbial diversity and biogeochemical cycling can vary across multiple sites within the same desert biome. It also provides answers to the questions of how biocrust carbon fixation capacity is affected by time, thickness, community composition, geography, and soil conditions.

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Page publiée le 6 décembre 2021