Megan Lewis | ALES Graduate Seminar

Date(s) - 07/04/2022
8:30 am - 9:30 am

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Megan Lewis. This seminar is open to the general public to attend.
Meeting ID: 993 5840 7384 | Passcode: 489089

Thesis Topic: Biological soil crusts in Alberta’s grasslands: increasing our knowledge of their taxonomy, diversity, and sensitivity to drought and defoliation

MSc with Drs. Cameron Carlyle and Diane Haughland.

Seminar Abstract:

Biological soil crusts (BSCs) play a central role in the biodiversity, health, resilience, and function of drylands like Alberta’s grasslands. In Alberta, much of the biocrust cover consists of lichens, and many crusts are dominated by species of Cladonia. Despite the drought-resistant nature of biocrusts, they have been found to be sensitive to changes in precipitation and disturbance in other regions. This finding leads to questions of if, and how, land-management strategies should change to retain rangeland function as drought becomes more frequent.  To answer these questions we need monitoring and experiments investigating biocrust response to change. However, for a group of lichens in Alberta’s grassland biocrusts, the Cladonia cariosa group, taxonomic boundaries are imprecise, potentially obscuring changes in biocrust communities. To clarify boundaries in the Cladonia cariosa group, I implemented an integrative taxonomic study using morphology, secondary chemistry, a multi-locus molecular dataset, and a genotype-by-sequencing (GBS) dataset. While the multi-locus study using the internal transcribed spacer region of nuclear rDNA (ITS) and DNA-dependent RNA polymerase 2 (rpb2) provided low resolution, the GBS dataset generated a highly-supported phylogeny. Three lineages corresponded to previously described species in the group, Cladonia cariosa, Cladonia symphycarpa, and Cladonia acuminata, and two lineages correspond to undescribed species. While Cladonia cariosa, Cladonia symphycarpa, and Cladonia acuminata could clearly be differentiated by morphology and chemistry, the two undescribed species had few distinguishing traits from Cladonia symphycarpa, and are thought to be semi-cryptic. This work results in the addition of two putative species to the Cladonia cariosa group. One of the new putative species, for now referred to as Clade E, occurs in Alberta along with Cladonia cariosa, Cladonia symphycarpa, Cladonia acuminata, and Cladonia decorticata; while the second new putative species, Clade F, appears to have a distribution limited to Europe. Following clarification of species boundaries, I assessed the effects of simulated drought and grazing on grassland BSC using a manipulative experiment conducted over four years at seven North American temperate grasslands sites. A 45% reduction in precipitation and four defoliation treatments simulating common grazing management systems were applied to study responses of biological soil crust cover and community composition, as well as environmental variables. Effects differed by site, with BSC lichen and moss experiencing an increase in cover with defoliation at some sites, but seemed largely resistant to drought treatments. Selaginella densa was sensitive to combined effects of drought and defoliation at some sites, experiencing the largest cover decrease in drought and spring+fall defoliated plots. Both moss and lichen cover were found to have a negative relationship with litter. Lichen had a positive relationship with light at a site with high annual net primary production (ANPP) and a negative relationship with light at a site with low ANPP. Beta-diversity in BSC communities was found to be significantly higher in undefoliated treatments, and lower in spring+fall defoliated treatments. The varying effects of drought and defoliation on BSC by site highlights the importance of using ecological knowledge to make landscape management decisions, and that one-size-fits-all management approaches for grasslands in the Great Plains region are likely inappropriate.

This research has greatly expanded our understanding of the phylogenetics of the Cladonia cariosa group, which is ubiquitous in our area of the Great Plains, as well as the influence of drought and defoliation on BSC composition and cover.