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University of California Davis (2022)

The Microscopic and Macroscopic Response of Biological Soil Crust to Fire

Palmer, Brianne

Titre : The Microscopic and Macroscopic Response of Biological Soil Crust to Fire

Auteur : Palmer, Brianne

Université de soutenance : University of California Davis

Grade : Doctor Philosophy (PhD) in Ecology 2022

Résumé partiel
Fires are becoming increasingly frequent and more severe across the Western United States and there is a need to understand how all ecological systems respond to this disturbance, including the soil microbial community. Biological soil crusts (biocrusts) house a diverse soil microbial community and are common in drylands and are composed of visible macroscopic constituents (lichens, bryophytes, cyanobacteria biofilms) and a diverse microscopic community. These communities have been historically understudied in California grasslands, which frequently experience both prescribed and wildfires. The purpose of this research is to understand how biocrusts recover after grassland fires by measuring changes in the macroscopic community cover, microscopic community composition, key biocrust ecosystem functions, and understand mechanisms of biocrust recovery. The first chapter is a meta-analysis of the current understanding of biocrust response to fire. It revealed that overall, fire reduced biocrust cover, particularly cyanobacteria cover, and demonstrated that over time, lichen, and bryophyte cover gradually recover 200-300 months after the initial burn. The meta-analysis confirmed the gap in our knowledge about the response of biocrusts in California grasslands which is addressed in the subsequent chapter. The second chapter uses a recently burned grassland on San Clemente Island (SCI) to understand how fire changes biocrust cover in a California coastal grassland. This is the first biocrust study on San Clemente Island and we found that the biocrusts are primarily dominated by cyanobacteria with some lichens and bryophytes. One year after a prescribed fire, biocrust cover surpasses the cover of biocrusts in unburned control plots. Two years after the fire, the total biocrust cover declined but still had greater cover than the controls. I collected biocrust samples from the same SCI sites for my third chapter. Chapter three uses laboratory measurement and shotgun metagenomics to understand how the microscopic community and the ecosystem function changes after a fire by comparing communities in paired burned and unburned plots on SCI. My analyses showed that one year after a prescribed fire and six years after a wildfire, the biocrust microbial community is similar between both fire types and the controls. Additionally, photosynthetic biomass, nitrogen fixation, and exopolysaccharide content did not vary between treatments, indicating similar ecosystem function. Although, there were differences in the functional genes present between the wildfire and control samples and difference configurations of the microbial network.

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Page publiée le 28 novembre 2022