Min, 2017

Dissertation/Thesis

Temperature responses of microbial soil organic matter decomposition and associated respiration at various scales, ranging from exo-enzymes to populations and communities

Min, Kyungjin (2017)
PhD Dissertation, University of Kansas  

Abstract

Knowledge about how temperature will influence microbial decomposition of soil organic matter and resultant CO2 efflux from soils is of importance to understand the global C balance and more accurately project future climate. Yet, it is difficult to quantify microbial activities in their natural habitats due to inherent heterogeneity in soils. Here I investigate microbial activities in controlled experiments ranging in complexity, such that I can parse the temperature responses of multiple processes operating simultaneously in soils. Soil microbes exude exo-enzymes into the soil matrix, where they break down organic molecules into smaller substrates. Microbes assimilate these smaller substrates to grow, while respiring CO2. In chapter 1, I demonstrate that pH can differentially influence temperature responses of distinct exo-enzyme activities relevant to C and N acquisition from soil organic matter. Expanding this, in chapter 2 I find that temperature and substrate availability can interactively influence biomass-specific respiration rates, C use efficiency (CUE), and stable isotope C discrimination from an isolated population of microbes. Enhancing the complexity again, in chapter 3 I show that temperature responses of exo-enzyme activities and respiration of natural microbial communities in soils are conserved at biomass-specific rates across diverse timescales and in spite of distinct community structures, while those at soil mass-specific rates are not. This body of work has ecological implications about microbial adaptation in a warmer world. Different temperature responses of exo-enzymes and CUE with varying environmental conditions can lead to microbial communities with distinct strategies of resource allocation to production of exo-enzymes and biomass for survival and reproduction. These inferences about microbial adaptation obtained from simplified systems can help understand driving mechanisms of apparent temperature responses and guide parameterizations in microbially-explicit Earth-system models to better project microbial feedbacks to climate.

Citation

Min, Kyungjin (2017): Temperature responses of microbial soil organic matter decomposition and associated respiration at various scales, ranging from exo-enzymes to populations and communities. PhD Dissertation, University of Kansas.