Effects of Simulated Climate Change On Plant Seedling Counts

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Effects of Simulated Climate Change On Plant
Seedling Counts

• Ben Gutzler

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Background

• Global climate change is predicted to increase
  temperatures and nitrogen deposition, as well as
  changing precipitation patterns over the next
  century.
• The warming plot experiment is designed to
  replicate these changes with nighttime warming
  shelters, added precipitation, and nitrogen
  addition.
• There are 40 plots, with 5 replicates of each
  treatment (nighttime warming, nitrogen addition,
  precipitation addition, combinations of the
  above, and control).

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The Plants

• Black grama (Bouteloua eriapoda) dominates the
  site, with blue grama (B. gracilis) also present.
  Snakeweed (Gutierrezia sp.), silverleaf
  nightshade (Solanum elaeagnifolium), several
  other grasses, and assorted non-grass species
  also appear.

• As blue and black grama were most prevalent, they
  formed the main focus of the study.

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Questions

• Will the experimental treatments affect the
  carbon and nitrogen content of the plants?
• What effects will the nighttime warming and
  nitrogen addition treatments have on the growth
  of new plants, especially blue and black grama?
• Will there be noticeable changes in the ratios of
  blue versus black grama seedling growth between
  treatments?

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Experimental Design

• CN Analysis
• Done at John Craigs lab, UNM
• Blue and black grama collected
• 12 plots analyzed
• Plant Counts
• Young individuals counted
• Seven species counted,
• with focus on blue and black grama
• 20 plots counted

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Methods

• CN Analysis
• Handfuls of blue and black grama were collected.
• Samples were dried, ground, and analyzed in a
  Carlo Erba NC 2100 Soil Analyzer (a gas
  chromatograph to determine carbon and nitrogen
  content).
• Plant Count
• Young grass individuals were identified as small
  plants not encompassed by a large clump.
• Black grama seedlings attached to larger plants
  (growing from stolons) were counted.
• Young forbs were identified as those who were
  significantly smaller than other specimens of the
  species and appeared to be new growth.
• Plants were tallied by species.
• Sample mean differences between treatments were
  assessed with a t-test

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CN Analysis Results

• The sample was too small for statistically
  significant results, but trends were observed.
• Blue grama responds more positively to warming
  than does black grama in terms of tissue
  nitrogen.
• Black grama responds more positively to nitrogen
  than does blue grama in terms of tissue nitrogen.
• Carbon content showed no distinct trends.

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Plant Count Results

• Black grama growth is suppressed by nitrogen
  addition (P.063). Blue grama growth is
  suppressed by nighttime warming (P.15).
• The combination of nighttime warming and nitrogen
  addition suppresses young plant growth in both
  species. (P.12)
• Nighttime warming alone favors black grama,
  nitrogen addition alone favors blue grama, and
  the combination of the two inhibits both species.

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Further Results

• Comparing the results from the CN analysis with
  the plant count data, tissue nitrogen for blue
  and black grama increases in the treatments that
  suppress seedling growth.
• I hypothesize that in these treatments, more
  energy is devoted to growth and less to
  reproduction.
• Silverleaf nightshade growth is aided by warming.
  (P.14)

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Summary

• Will the experimental treatments affect the
  carbon and nitrogen content of the plants?
• Tissue nitrogen content showed changes depending
  upon the treatment applied to the plot.
• What effects will the warming and nitrogen
  addition treatments have on the growth of new
  plants, especially blue and black grama?
• Addition of nighttime warming favored black grama
  growth, while addition of nitrogen favored blue
  grama growth. Nighttime warming and nitrogen
  addition combined suppressed growth of both
  species.
• Will there be noticeable changes in the ratios of
  blue versus black grama seedling growth?
• The ratios changed according to the treatment
  given.

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Further Questions

• What effect would the treatments have upon
  creosote growth?
• Are these mean changes robust?
• What effects might the change in the growth of
  blue or black grama have on animal populations?

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Acknowledgements

• Will Pockman, Joe Fargione, and Scott Collins
  (mentors)
• Eric Toolson (idea for final study)
• Jennifer Johnson (incalculable patience)
• Cathy McQueen (tasty food)
• Dave Gutzler (statistics help)
• National Science Foundation (threw money at me)
• University of New Mexico Sevilleta LTER (a
  place to sleep a lot)
• US Fish Wildlife Service (a place to study)
• Everyone else (tolerance, assistance,
  understanding you know who you are)