Investigating the mechanisms by which available nitrogen affects biodiversity of a plant community native to the Indiana Dunes

National Lakeshore

Eric BirdPurdue University Calumet

Flora Richardson Fellowship Recipient

Concern

• Atmospheric deposition of nitrogen is high in the Midwestern and Eastern United States

• The Indiana Dunes receive approximately 15kg ha-1 y-1 nitrogen as wet deposition

• Research has shown that increases in available nitrogen to low nitrogen ecosystems affects species composition and can have an overall negative affect on biodiversity

Preliminary research shows that ammonium nitrate treatment

• Reduces the total biomass of some species

• Alters how species allocate biomass (aboveground vs. belowground)

• Reduces the germination success of some species

Setup

• Use laboratory experiments to determine which species are hindered by nitrogen treatment and…

• Use this information to predict which species will occur less frequently in a constructed native plant community grown in the field against a gradient of available nitrogen

Species investigated• Schizachyrium scoparium – little bluestem grass• Elymus canadensis – Canada wild rye• Panicum virgatum – switchgrass • Sorghastrum nutans – Indiangrass • Rudbeckia hirta – black eyed susan• Echinacea purpurea – purple cone flower• Dalea purpurea – purple prairie clover• Monarda punctata – dotted mint• Liatris aspera – rough blazing star• Lupinus perennis - lupine

Experiments

• Biomass allocation – greenhouse

• Germination – laboratory

• Aboveground biomass production – field

• Biodiversity – field

• Competition – field

Biomass allocationgreenhouse

• Purpose: to determine the relationship between available nitrogen and biomass allocation of ten native species

Biomass allocationgreenhouse

• Hypothesis: if amount of ammonium nitrate increases then some species will allocate more biomass to aboveground growth while others will not.

Biomass allocationgreenhouse

• Four treatment groups (n = 5): – control– 30kg ha-1

– 60kg ha-1 – 120kg ha-1

• Biomass will be harvested after approximately 6 months of growth.

Biomass allocationgreenhouse

• Prediction 1: species that allocate more biomass to aboveground growth will outcompete other species in the field as available nitrogen increases

Competition and biomass allocationfield

• Purpose: to determine whether aboveground or belowground biomass allocation increases the relative dominance of a species in a high nitrogen environment

Preliminary researchbiomass allocation

• Table 1 aboveground and belowground percent biomass for E. canadensis and S. scoparium (n = 5)

BiomassPercentage Schizachyrium scoparium Elymus canadensis

ControlMean (g)

NitrogenMean (g) p-value

ControlMean (g)

NitrogenMean (g) p-value

Aboveground 50.3 ± 4.75 63.8 ± 5.45 0.0990 53.9 ± 2.04 43.7 ± 2.59 0.0149

Belowground 49.7 ± 4.75 36.2 ± 5.45 0.0990 46.1 ± 2.63 56.3 ± 2.59 0.0149

Competition and biomass allocationfield

• Prediction 1: species that allocate more biomass to aboveground growth will outcompete other species in the field as available nitrogen increases

• Hypothesis 1: if biomass allocation determines relative dominance then one of the two species should dominate at increased nitrogen levels

• Hypothesis 2: if preliminary data and prediction 1 are correct then in high treatment groups S. scoparium will allocate more biomass to aboveground growth and will increase in relative dominance over E. canadensis

Competition and biomass allocationfield

• Two species: E. canadensis, and S. scoparium

• Four treatment groups (n = 5): – Control– 30kg ha-1

– 60kg ha-1

– 120kg ha-1

• Rectangular plastic containers are buried at the field site and half seeded with each of the two species. After one growing season the percent coverage by each species is determined

Germination laboratory

• Purpose: to determine the relationship between the concentration of ammonium nitrate and the germination success of ten native species.

• Hypothesis: if ammonium nitrate concentration is increased then the germination success of most species will be reduced

Preliminary research germination

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MEAN RELATIVE GERMINATION OF EACH SPECIES IN CONTROL GROUP

PG

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MEAN RELATIVE GERMINATION OF EACH SPECIES IN LOW GROUP

PGSNLPSSMPEPECPVRHDP

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MEAN RELATIVE GERMINATION OF EACH SPECIES IN HIGH GROUP

PGSNLPSSMPEPECPVRHDP

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GERM

I-N

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Germination laboratory

• Four treatments (n = 7): – Control– 1000ppm– 2000ppm– 4000ppm

• Seeds germinated in petri dishes containing mineral sand at 22°C for 6 weeks

• Number of germinated seeds recorded each week

Germination laboratory

• Prediction 2: Species that are most successful at germinating at higher end of the spectrum should occur more frequently in the field as ammonium nitrate levels increase

Biodiversityfield

• Purpose: to determine whether available nitrogen affects biodiversity of a plant community native to the Indiana dunes

Biodiversityfield

• Prediction 1: species that allocate more biomass to aboveground growth will outcompete other species in the field as available nitrogen increases

• Prediction 2: Species that are most successful at germinating at higher end of the spectrum should occur more frequently in the field as ammonium nitrate levels increase

Biodiversityfield

• Hypothesis 1: if nitrogen levels increase then biodiversity will decrease

• Hypothesis 2: if biodiversity decreases as a result of nitrogen additions then predictions 1 and 2 will be true

Biodiversityfield

• Four treatment groups (n = 5): – Control– 30kg ha-1

– 60kg ha-1

– 120kg ha-1

• Species are seeded in 2x2m plots at field site. Percent coverage and aboveground biomass of each species is determined after two seasons.

Summary

• It is expected that nitrogen additions will– Reduce germination of most species– Cause some species to allocate more biomass

aboveground

• Therefore– As nitrogen levels increase few species with high

germination success and aboveground biomass allocation will begin to dominate and biodiversity will decline as a result