UC Irvine

Studying soil carbon (C) losses and carbon dioxide (CO2) feedbacks to the atmosphere under global climate change allows us to quantify and understand how our ecosystems are responding to warming. To accurately project the fate of the terrestrial C, we need to incorporate processes that are pivotal in shaping microbial communities that are responsible of processing the C in the soil. One of these processes is the evolutionary adaptation to warming which has been difficult to study because it may only be noticeable on the long term. The goal of my dissertation was to examine soil microbes, their response and adaptation to warming, and consequences to the C cycle. In Chapter 1, I synthesized data from 25 field warming experiments to assess the effect of microbial responses ─relevant to the C cycle─ to warming over time. I found that the effect of soil respiration decreases as warming progresses and explored the potential microbial-related causes of this decrease. In my second chapter, I experimentally adapted the model fungus Neurospora discreta to warming and analyzed physiological traits important for the C cycle before and after adaptation. I discovered that when N. discreta adapts to warming it allocates more resources to increase its fitness by producing more spores at the expense of biomass. I found that adaptation to warming is accompanied by increases in CO2 respiration potentially due to higher production of energetically expensive spores. In this chapter, I discussed the potential consequences for the terrestrial C if the soil microbial community adapts in a similar manner as N. discreta. Finally, in my third chapter, I quantified decomposition of specific C fractions in litter in a long-term field warming experiment. I found that the proportional losses of recalcitrant vs non-recalcitrant C was higher in warmed plots compared to control plots. Similarly, the ratio of microbial extracellular enzyme activities responsible for breaking down recalcitrant C was higher under warming compared to enzymes that break down non-recalcitrant C. Collectively, in my dissertation research I integrated the process of evolutionary adaptation of microbes to warming, thus providing an overview of the potential long-term effects of warming to decomposition and the C cycle.