Angelo Coast Range Reserve

22 Nov, 03 AM - 22 Nov, 09 AM

The study of organisms? niches has been touted as central to our understanding of ecology and evolution, driving major advances in our knowledge of species coexistence, speciation, and community assembly and composition. The fundamental niche has been commonly defined as the space an organism can occupy in the absence of interactors (i.e. the abiotic tolerances and requirements of a species) whereas the realized niche has often been defined as the space in which an organism can persist in the presence of interactors (i.e. where a species is actually found). Since the inception of the niche concept, researchers have focused almost exclusively on abiotic limitations of organisms and the negative impact of competition, which reduce the fundamental niche to the realized niche. While this work has provided invaluable insights, a potentially equally important component of niche theory has been virtually ignored: niche expansion. In contrast to competition, positive interactions, such as mutualism (i.e. both species gain a benefit from the association) and facilitation (i.e. one species gains a benefit while the other species is unaffected by the association), can expand the realized niche of a species. Positive interactions may not only reduce the effect of niche-limiting factors (i.e. competition, predation, and parasitism) but can also cause a species? realized niche to be larger than its fundamental niche by ameliorating abiotic stresses. To date, very little work has explicitly considered, much less empirically tested, niche expansion generated by positive interactions. Microbial symbionts of plants, such as mycorrhizae and rhizobia, are known to improve tolerance to abiotic stresses, increase resistance to herbivory and diseases, and enhance plant fitness. Another less well known, but common, plant symbiont ? endophytic fungi ? resides in the above ground tissue of most plants examined to date. In grasses, fungal endophytes of the genus Neotyphodium are systemic and can provide benefits such as drought tolerance, resistance to enemies, and enhanced nutrient uptake. I propose to investigate the role of a newly discovered fungal endophyte (Afkhami unpublished data) in niche expansion of the native California C3 bunchgrass, Bromus laevipes. PART 1: Collecting Seeds As a first step, I would like examine endophyte status of B. laevipes at Angelo. I will collect a few inflorescences with seeds from 20-30 plants from several populations to determine endophyte status and frequency. Endophyte detection will be done in the lab by staining plant tissue and then viewing under a microscope or through culturing methods. This step would be done as soon as possible (ideally Sunday, Nov 22) as seeds will be dropping with increased rainfall. PART 2: Field Experiment I would then like to conduct a small field experiment (setup beginning in January) to test questions related to the role of endophytes in niche expansion of the grass. To determine whether endophyte presence allows this native host grass to expand its niche, I must show that in some locations endophytes not only confer a benefit to their hosts but that they are necessary for a positive population growth rate. To do this, I will plant experimental gardens at several locations in California in which I record demographic data that will allow me to use matrix models to estimate population growth rate. I will include three types of plants: symbiotic B. laevipes, non-symbiotic B. laevipes, and experimentally-disinfected B. laevipes. These grasses will be planted at a size of 1-2 stems into the garden at the reserve and will come from 6 symbiotic and 6 non-symbiotic populations. For the experimentally non-symbiotic plants, endophyte will be removed via fungicide in the lab prior to planting in the field (plants will be several clonal generations removed from fungicide; no fungicide will be used/transferred in the field). I will manipulate the competitive environment by either weeding or not weeding within 15-20cm around plants. Thatch removed from the weeding will be replaced around the base of the experimental plants to maintain natural soil processes, moisture, and other properties. The experiment will remain in the field for two growing seasons as this is the minimum amount of time possible to estimate fitness for B. laevipes (it is a long-lived perennial grass). During the first year, I will record grass mortality and count stems, flowering inflorescences, and seeds to estimate plant fitness. I will also estimate endophyte fitness by examining the percentage of host seeds the endophyte grows into (this endophyte is strictly vertically transmitted through the seeds). A subset of the seeds produced would also be attached to toothpicks and planted in the next season to gain insight into germination vs dormancy rates for symbiotic and non-symbiotic plants. In the second season, I will also follow the original plant to examine survivorship across seasons, and at the end of the growing season, I will harvest the plants for biomass measures. This research may provide important insight for restoration and management work. Because grasses are often the ?workhorses? of restoration and a large component of many ecosystems, understanding the role of these common fungal symbionts in the persistence of grass populations may be critical for practitioners. Additional Relevant Points 1) I will cut all inflorescences from experimental plants prior to seeds dropping such that no seeds from the experiment will enter the ecosystem. Collecting seeds prior to their dropping should be very feasible because this grass species holds its seeds for an extended period (even well into summer and next growing season). 2) This is a native symbiosis that occurs throughout California: the endophyte is a natural, native symbiont of a native grass. Further, the endophyte is exclusively vertically-transmitted from parent to offspring and does not spread contagiously. 3) Each plant in the experiment will be marked and watched throughout the entire experiment. At the end of the project, they will be removed. 4) Germination data will be collected by attaching seeds to toothpicks, which allows me to monitor each seed placed at the site. I will remove any non-geminating seeds and seedlings after data is collected. 5) Weeding will have a minimal effect on the local ecosystem. I will only remove competitors within 15-20 cm (~6-8in) from the focal individuals and all thatch removed from the weeding will be replaced around the base of the experimental plants to maintain natural soil moisture and other properties. 6) In total, there will be 360 to 540 plants in the entire experiment. I am estimating the plot will be between 2mX4m and 4mX5m depending on the exact number of plants and space per plant. If size is a concern, we can discuss how to adjust accordingly.

Visit #19843 @Angelo Coast Range Reserve

Approved

Under Project # 20873 | Research

Endophyte-mediated niche expansion of native bunchgrass, Bromus laevipes

faculty - University of Miami

Reservation Members(s)

Michelle Afkhami Nov 22, 2009 (1 days)

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Day use 1 Nov 22 (6 hours)