Shifts in the relative importance of competition and mutualism for communities and ecosystems

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

The ability of three-square bulrush (Schoenoplectus pungens) to expand at the same rate as the climate change driven decline in Great Lakes levels

The declining lake levels in the Great Lakes fit with current climate change models. Costal marshes are especially susceptible to drying events with small changes in lake levels. The three‐square bulrushes (Schoenoplectus pungens) hold important roles of habitat, erosion control, and anthropogenic pollution control within coastal wetlands. The measurement of gradient change perpendicular to the shoreline estimated the ability of bulrush to respond to declining levels. Through sampling of two coastal marshes dominated by S. pungens, we determined the growth pattern in three inundation zones: 1. Dry‐ dry year round and has been dry for many years, 2. Shore‐ fluctuating level of water year round and has been dry in the previous years, and 3. Deep‐ continuously inundated year round and has been for many years. Through sampling, the relative importance of inundation levels and zone characteristics was determined to affect the relative growth with higher inundation perceived to lead to higher growth. The Deep zone had the greatest growth potential with the Shore and Dry zones showing a significant difference only at the terminal node. Zones showed differences in growth patterns between horizontal main rhizome growth and vertical short shoot growth. The rate of growth seems inadequate to respond to declining lake levels.http://deepblue.lib.umich.edu/bitstream/2027.42/62025/1/Bell-Dereske_Lukas_2008_REU.pd

Appendix B. Location and design of experiment in a dune blow-out at Leelanau State Park, Michigan, USA.

Location and design of experiment in a dune blow-out at Leelanau State Park, Michigan, USA

Appendix A. Projected changes in precipitation from General Circulation Models (2071–2100) from the IPCC Fourth Assessment compared to baseline projections from 1971–2000.

Projected changes in precipitation from General Circulation Models (2071–2100) from the IPCC Fourth Assessment compared to baseline projections from 1971–2000

Data from: Fungal symbiont effects on dune plant diversity depend on precipitation

1. Historically, mutualisms have been considered to be less important than antagonisms in affecting the composition of ecological communities. In plant communities, beneficial microbes may feature as keystone mutualists in structuring community composition. Understanding the direction and magnitude of mutualist effects at the community scale may be critical for making accurate predictions on plant responses to climate change, particularly for mutualists that ameliorate climate-induced stressors. Such mitigation could shift outcomes between mutualist-enhanced species diversity and mutualist-reduced diversity, depending on whether a mutualist accelerates habitat modification or competitive exclusion by its partner species. 2. Here, we tested the relative importance and interactive effects of altered precipitation and symbiosis between an epichloid fungal endophyte and a dominant grass species for dune plant communities along the Great Lakes, USA. In 2010, we imposed field manipulations of endophyte presence in the foundation dune grass Ammophila breviligulata in combination with rain-out shelters and rainfall additions. We monitored natural rates of colonization by new plant individuals over three years. 3. Under the current precipitation regime, endophyte symbiosis in A. breviligulata reduced colonizing plant diversity, species richness, and evenness. This effect depended on the amount of precipitation, with the symbiosis having weaker effects on plant diversity under both augmented and reduced rainfall treatments. 4. Despite the overall negative effect of endophyte symbiosis on plant diversity, plant responses to the endophyte were species-specific. A federally threatened forb, Cirsium pitcheri, increased in abundance when the symbiosis was present, regardless of precipitation regime. Endophyte symbiosis in A. breviligulata caused minor reductions in the abundance of other grass species; however, augmented precipitation benefited other grasses. 5. Synthesis. We show that microbial mutualisms can have strong effects on community structure in a native ecosystem and that the amount of precipitation has the potential to alter how these keystone species interactions affect community composition. Predictions on future plant community structure, for both restored and native dunes, can be improved by accounting for the presence of fungal symbionts in the foundation plant species

Plant Community Diversity and Abundance data

Plant Community Diversity and Abundance dat

perMANOVA2013 - Plant species data matrix for 2013

perMANOVA2013 - Plant species data matrix for 201

VWC

Data were collected in the field experiment using a hand-held soil moisture meter (Aquaterr M 300, Costa Mesa, CA) with measurements of volumetric water content taken at 20 cm and 40 cm soil depths. Plot=unique plot number, row=position of plot in the experimental matrix, col=column position of plot in the experimental matrix, EF=endophyte presence(1) or absence(0),Water=reduced(L), ambient(M), or augmented(H), Date=date of observation, VWC20=mean volumetric water content per plot at 20 cm soil depth, VWC40=mean volumetric water content per plot at 40 cm soil depth

perMANOVA2012 - plant species data matrix for 2012

perMANOVA2012 - plant species data matrix for 201

Bell-Dereske et al Oikos data

Data from field collected litter, decomposition bags, and stock plants