Abstract

Endophytic fungi have been found in every terrestrial plant investigated thus far. They can receive nutritional benefits from their host tissues. Two major modes of nutrition for endophytic fungi include biotrophy and saprotrophy. In chapter 1, I set out to determine whether endophytic fungi isolated from Quercus gambelii in Utah, USA were capable of saprotrophy and, if some were, how much variation in saprotrophic ability exists among them. Because saprotrophy requires moisture and, in Utah, moisture is largely unavailable outside winter and early spring, in chapter 2 I set out to determine if any of our isolated endophytic fungi were capable of saprotrophy under cold conditions (psychrotolerance). If any were, we would then determine how much variation exists in psychrotolerance among them. Additionally, I tested the hypothesis that a tradeoff exists between saprotrophic ability under winter and non-winter temperatures. During these studies, I observed differences in growth patterns among our isolates. Some grew radially quite rapidly but produced little biomass while others produced a great deal of biomass but grew radially slowly. Thus, in chapter 3 I investigated the possibility of a tradeoff between saprotrophic ability in terms of radial growth rate and saprotrophic ability in terms of biomass accumulation among our isolates at winter and non-winter temperatures. In chapter 1 I found that a majority of our isolates were saprotrophic at non-winter temperatures, and that there was a great deal of variability among them in saprotrophic ability. Surprisingly, I found more variability in saprotrophic ability among isolates within a species than among species, which is contrary to the assumption of phylogenetic conservation of important traits. Nevertheless, our results suggest that saprotrophic endophytic fungi have priority over non-endophytic fungi in litter consumption and, therefore, a significant impact on the decomposer community. In chapter 2 I also found that a majority of our isolates were psychrotolerant and that there was a great deal of variability among them in psychrotolerance, more of which was found among isolates within a species than among species. Additionally, I found that there was no tradeoff between saprotrophic ability at winter and non-winter temperatures, but that instead there was a positive correlation. Our results suggest that many of these endophytic fungi are capable of saprotrophy during the cold months of winter and early spring and thus, although the large degree of variation suggests that there may be a lack of phylogenetic conservation of physchrotolerance within species, play significant roles in overwinter decomposition and nutrient cycling. Lastly, in chapter 3, I found that there was no tradeoff between saprotrophic ability in terms of radial growth rate and saprotrophic ability in terms of biomass accumulation at either winter or nonwinter temperatures. In fact, I found no correlation of any kind between the two saprotrophic strategies. These results suggest that, at least theoretically, an isolate could simultaneously possess both rapid radial growth and rapid biomass accumulation and thus be highly competitive, or both slow radial growth and slow biomass accumulation and thus be poorly competitive, although our results did not include a significant number of isolates at either end of this spectrum.

Degree

College and Department

Life Sciences; Biology

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