Plant species interact with at least one, likely many, microbial mutualist throughout their life cycles. These microbial mutualists can have strong effects on plant communities and ecosystem processes. Fungal endophytes within the genus Epichloë associate with ~20%–30% of grass species and have been shown to have strong effects on plant communities. Here I described the effect of Epichloë amarillans associated with the dominant grass species, Ammophila breviligulata, on nutrient cycling, below-ground microbial community, and compare the strength of its effects on plant communities to plant-plant competition.
In chapters one and two, I examine the effects of Epichloë on litter decomposition and below-ground microbial communities in the Great Lake dunes within the context of altered precipitation and soil moisture. In chapter 1, using litterbags, I found that the endophyte presence in litter increased initial rates of decomposition, though the effect disappeared after one growing season. Later litter decomposition was slowed by endophyte presence in A. breviligulata conditioning the soil microenvironment. In chapter 2, using microscopy and 454 pyrosequencing, I found that the endophyte reduced the abundance of soil fungi and the diversity of an important fungal group, arbuscular mycorrhizal fungi, though this effect on diversity disappeared with altered precipitation. The presence of the endophyte also shifted the positive relationship between root associated bacteria and soil moisture to a negative relationship where diversity decreased with increasing soil moisture.
In chapter three, I tested the relative effects of Epichloë and competition on plant community dynamics by jointly manipulating plant-plant interactions and the presence of the endophyte within the context of altered timing of precipitation events. I found that plant-plant interactions were the strongest driver of plant community composition and diversity. However, the endophyte altered the effects of plant-plant interactions on the plant community by increasing the negative effects of competition on A. breviligulata growth while increasing facilitative effects of its host on the dune plant community. Increased precipitation did not alter the effects of the endophyte but did reduced the strength of plant-plant interactions. Microbial mutualisms are drivers of ecosystem and community processes playing as important a role as antagonistic interactions.
Ammophila breviligulata, Epichloë amarillans, plant-fungal interactions, community ecology, soil microbial ecology, ecosystem services
Level of Degree
UNM Biology Department
First Committee Member (Chair)
Second Committee Member
Scott L. Collins
Third Committee Member
Robert L. Sinsabaugh
Fourth Committee Member
Bell-Dereske, Lukas P.. "Shifts in the relative importance of competition and mutualism for communities and ecosystems." (2016). https://digitalrepository.unm.edu/biol_etds/153