Date of Award

Fall 12-16-2019

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Biology

College

Honors College

First Advisor

Vladislav Gulis

Abstract/Description

The decomposition of leaf litter in aquatic ecosystems is carried out mostly by microorganisms, including bacteria and fungi. Fungi, known as aquatic hyphomycetes, dominate microbial communities in the decomposition of leaf litter. These fungi produce extracellular enzymes that aid in the sequestration of carbon and nutrients and lead to the breakdown of complex plant polymers. We evaluated the effects of temperature on extracellular enzyme activity within the framework of the Metabolic Theory of Ecology (MTE). The activity of β-1,4-glucosidase and β-1,4-xylosidase was estimated fluorometrically using artificial substrate analogs. Phenol oxidase activity was estimated spectrophotometrically from oxidation of L-DOPA (L-3,4-dihydroxyphenylalanine). We found greater temperature sensitivity of oxidative enzymes (phenol oxidase) involved in degradation of recalcitrant substrates compared to hydrolytic enzymes (β-glucosidase and β-xylosidase). In addition, we found that the activity of microbial enzymes involved in carbon sequestration does not follow simple monotonous response across experimental temperatures (4-20°C) predicted by the MTE. Instead, we observed greater temperature sensitivity (higher apparent activation energy) of hydrolytic enzymes at colder temperatures. These findings may have important implications for stream ecosystems under climate change scenarios since both peak leaf litter availability and microbial activity occur during the coldest seasons in autumn-winter.

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