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Case Study: Plant-soil interactions in the South Puget Sound Prairies

Case Study: Plant-soil interactions in the South Puget Sound Prairies. Persistence of prairie vegetation attributed to: Low summer precipitation Excessively drained gravelly soils Historically they frequently burned Strong interspecies competition

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Case Study: Plant-soil interactions in the South Puget Sound Prairies

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  1. Case Study: Plant-soil interactions in the South Puget Sound Prairies

  2. Persistence of prairie vegetation attributed to: • Low summer precipitation • Excessively drained gravelly soils • Historically they frequently burned • Strong interspecies competition • Lang 1961; del Moral and Deardoff 1976

  3. Scot’s Broom (Cytisus scoparius) • Shrub that grows to 2 m • Native to Europe • Nitrogen fixer • Accumulates quinolizidine alkaloids in its leaves

  4. Study Site: Glacial Heritage Preserve

  5. Does the legacy of Scot’s broom increase the growth and competitiveness of invasive plants? Hypochaeris radicata Widely distributed invasive plant that is very common in the prairies Festuca roemeri Dominant native vascular plant Microseris laciniata Common native forb

  6. Greenhouse Experiment • Three soil treatments • LB: Soils from areas with historically low cover of Scot’s broom • HB: Soils from areas with historically high cover of Scot’s broom • HB+N: HB soils with nitrogen added as 5 g/m2 of N as NH4-NO3 • Five species combinations: • Monocultures of each species (3 total) • Festuca grown in competition with Hypochaeris • Festuca grown in competition with Microseris • Measurements: • Total Biomass • Leaf chlorophyll level (Hypochaeris only) • Competition • RCI: Difference in biomass between monoculture and competition treatments divided by the biomass in monoculture treatment

  7. Mean (+/- SE) values for surface soils (0 - 15 cm depth) at Glacial Heritage Preserve

  8. Growth after 20 weeks High-broom Soils (HB) Low-broom Soils (LB) Festuca roemeri Hypochaeris radicata Microseris laciniata

  9. Festuca roemeri Hypochaeris radicata Microseris laciniata

  10. Hypochaeris radicata

  11. Species competition and N-enrichment Competition between Festuca and Hypochaeris Competition between Festuca and Microseris RCIs for Festuca vary significant by competitor identity (2x3 ANOVA, d.f. error = 28, P < 0.0001) LB soils HB soils HB+N soils

  12. Questions raised by the experiment • What possible explanations are there for the higher total N found in the low broom (LB) soils? • Is there a plausible explanation for the lower chlorophyll levels measured in Hypochaeris leaves in LB soils? • What possible mechanisms can explain the 2 to 3 times biomass accumulation in the native species Festuca and Microseris in LB soils?

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