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cushion plant effects on seed germination of alpine plants
- 1. Cushion plant effects on seed germination in an alpine environment Amanda Liczner MSc. candidate
- 2. Presentation topics Introduction What is facilitation Purpose, hypothesis Methods Field collection Germination trials Results Implications
- 3. Introduction: facilitation is positive interactions between species A B A B Bruno et al. 2003, Brooker et al. 2008
- 4. Introduction: nurse effects on beneficiary species Temperature Soil moisture Soil nutrients Wind UV radiation Cavieres et al. 2008; le Roux and McGeoch 2010; Anthelme et al 2012; Molenda et al 2012; Schoeb et al 2012
- 5. Purpose: to determine the influence of cushions on germination
- 6. Question: do seeds from open plants have greater germination in cushions?
- 7. Hypothesis: seeds from species in the open will benefit from decreased abiotic stress and thus will have greater germination within the cushion Predictions: 1. Plant height will be greater in the cushion 2. Seed germination will be greater in the cushion 3. Seeds will germinate faster in the open
- 8. Methods: surveyed cushion-open paired sites Plant density of beneficiaries in cushion and open Measured average plant height of beneficiaries
- 9. Methods: seeds were collected for germination trials Seeds (10/species) cushion chambers open chambers
- 10. Methods: germination trials were conducted for 14d
- 11. Methods: germination trials were conducted for 14d
- 12. Results: plant density is greater in the open *** * *
- 13. Results: plant height is greater in the open *** *** *
- 14. Results: there is no difference in germination between microsites
- 15. Results: no difference between microsites for days to 50% germination
- 16. Implications: competition may prevent establishment on cushions Although density is higher in the open there is no difference in germination between microsites
- 17. Implications: competition may prevent establishment on cushions Environmental stress Michalet et al. 2006; Brooker et al. 2008; He et al 2013; McIntire et al. 2013 Strength of facilitation
- 18. Conclusions Seeds from plants found primarily in the open germinate equally well in both microsites These plants may be competitively excluded at another life stage
- 19. Thank you! Ron Long Christopher Lortie Rick Bello
- 20. R2= 0.224
- 21. R2= 0.021
- 22. Purpose: some previous studies had conflicting results shrub open
Editor's Notes
- Hello everyone, my name is amanda liczner and I will be presenting my early findings from my research on pink mountain in british columbia which looked at the effects on cushion plants on the seed germination of other beneficiary plants
- I will start off my presentation giving some background information on facilitation and seed germination. I will then get into the purpose of my study, how I conducted the study and show my results and give you some of the early implications I have so far
- Facilitative interactions are positive interactions between species in which at least one species benefits so here we can have both species A and species B benefiting or here we can have species B benefiting and no negative effect on species A. Positive interactions have been incresingly shown to influence plant community composition as well as competition which has previously been the dominant interaction used to explain community structure
- Facilitation is more frequently observed in stressful ecosystems including arctic, alpine, salt marshes, and the desert and in these environments facilitation is commonly studied using a dominant plant species which is commonly referred to as a nurse plant. In my study the dominant or nurse plant is a cushion plant. Cushion plants can positively affect other plant species by decreasing abiotic stresses. For example they can provide a warmer habitat by trapping heat, increase soil moisture by preventing evaporation, and increase soil nutrients by increasing litter accululation. They can also provide protection from wind and UV damage.
- The ecological consequences of nurse plant facilitation on plants has been well studied. But what has not been studied frequently, especially not in alpine or tundra ecosystems, is the potential for facilitative interactions to influence seed germination. Germination is a very important stage as this is the only link between generations and germination is highly dependent on environmental conditons. In highly stressful environments, it can be very difficult to time germination as conditions can rapidly change. Seeds use dormancy as a strategy to help time germination to optimal environmental conditions. As cushions are able to modify microclimatic conditions, cushions may also be able to influence seed germination and it may be expected that seeds would preferentially germinate within cushions due to decreased abiotic stress
- As mentioned previously, cushions reduce abiotic stress and one might expect seeds to preferentially germinate in cushion microhabitats. As these sites are expected to have a higher density of species, it is expected that competition will be higher within cushion microsites and thus some species may not be found more commonly on cushions due to competitive exclusion even though these species may benefit if given the chance to grow within the cushion environment. So the question we are asking is would seeds from plant species found more commonly in the open benefit from the facilitative effects of cushions and germinate preferentially within the cushion
- It was hypothesized that seeds from plants that are found more commonly in the open compared to the cushion microsite would benefit from decreased abiotic stress within the cushion microhabitat and would germinate higher in the cushion microhabitat compared to seeds in the open microhabitat. Which leads me to my predictions that these plant species, although found more commonly in the open, would have greater heights in the cushion as the plants benefited from the facilitative effect of the cushion, and seed germination will be greater in the open for this same reason and finally seeds will germinate faster in the open then the cushion. Early emergence has been associated with competitive ability with earlier emergence being associated with higher competitive ability. So one reason these species are not found on cushions more frequently is that they have a poor competitive ability when compared to other species
- The study took place on Pink mountain in northern BC. Here I surveyed cushion and open paired sites for species abundance, and the height of plant species. I also set up hobo loggers to track environmental data to program growth chambers for germination trials. I collected seed from five target species that were more common in the open
- The seeds were then germinated in growth chambers that were programmed to simulate cushion and open conditions. 10 seeds per species were placed in petri dishes. 30 of these petri dishes per species were then placed in both cushion and open chambers.
- Here is a picture of some of the seeds in the growth chambers. The germination trials were run for 14days and germination was surveyed every other day to help get an estimate of the speed of germination
- Here is an example of a seed that is germinated which is just a zoomed in picture from the last slide. A seed was considered germinated with the coleoptile or radicle is visible and the seed was removed
- Although visually all four target species appeared more frequently in the open I tested this statistically using a GLM and found that three of the five species were found significantly more often in the open compared to the shrub while the other two species were found equally in both cushion and open sites.
- the plant heights for the same three species that had a significantly higher density in the open also had significantly greater heights in the open. And the same two species that were found equally in both sites also had no signifcant difference between heights in either the cushion or the open
- There was a significant difference among species with the same three species that preferred the open germinating more extensively but no differences within species between chamber treatments
- There was a significant difference among species for the number of days to 50% germination which was used to estimate the speed of germination but there was no difference among chamber treatments so the seeds from these species are not changing their germination rate based on microclimatic conditions
- Even though the five target species were found more frequently in the open, there was no difference in the total germination of these five species between cushion and open so both this microhabitats are appropriate for these species. However, they are present at greater densities and grow taller in the open so it is possible that these species get outcompeted at a later life stage and that is why they are found less frequently and are shorter on cushions. As mentioned prevously faster germination is associated with greater competitive ability. As there was no difference in germination timing between sites this may give some indication towards these species having a lower competitive ability. It suggests that species that 'prefer' the open have a different life-history strategy and this persists regardless of the conditions Dyer et al 2000 finch savage et al 2006 espeland and rice 2007 days 50 May be limited by the HOBO data which was not for the growing season and was only significantly different with humidity
- Another study that looked at plant abundance on the same cushion species found that species were found at a higher density on cushions compared to the open. This may be due to the fact that this study took place at a higher elevation (2000 vs 1500). Higher elevation is associated with higher stress and faciliative interactions are expected to increase with environmental stress so it is possible that we are at the lower end of stress so the strength of facilitation is low. Facilitative interactions have also been shown to be species specific, and these species may have a different life history strategy that does not require stress amelioration by cushions. Molenda et al 2012 same cushion but at a higher elevation limitations
- I found no difference in the germination or the rate of germination between cushion and open sites for species that are found primarily in the open. These results may be attributed to higher competition excluding these species from the cushion. Facilitative interactions have also been shown to be species specific so these species may not benefit from cushions.
- There has been conflicting results in two studies looking at this topic but in deserts and with shrub species. One paper found that seeds preferentially germinated in the open, and the other found that seeds preferentially germinated in the shrub. This may be attributed to species specific differences in optimal habitats and thus seeds may preferentially germinate in this microhabitat. Here some species prefer the shrub to the open and are thus found more frequently in the shrub, and converely some species may prefer the open. Finally some species may do equally well and may be found equally in both micosites.