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Successional processes Hypothesis: Climate influences the rate and trajectory of succession by alter

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Characterize soil microbial community composition among successional stages and ... Characterize the ecophysiology of host selection for EMF in response to N and P ... – PowerPoint PPT presentation

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Title: Successional processes Hypothesis: Climate influences the rate and trajectory of succession by alter


1
Successional processes Hypothesis Climate
influences the rate and trajectory of succession
by altering disturbance regime and the abundance
of key species.
How do plant, animal and microbial communities
change through succession and what are the
consequences for ecosystem processes?
  • Task S7
  • Characterize soil microbial community
    composition among successional stages and seasons
    in floodplain and upland ecosystems.

2
Studying plant-microbial interactions in the
cycling of soil C and N(The black box approach)
  • Soil C and N levels are determined by the
    balance between organic matter inputs and losses
    due to decomposition, erosion and leaching.
  • Plant inputs
  • Litterfall
  • Root turnover
  • Exudation
  • Soil microbial community
  • Decomposition
  • Formation of organic matter

Schimel et al 2006
3
Microbial contributions to soil C storage
  • What role does microbial
  • community composition play in
  • soil C sequestration?
  • Microbial growth efficiency
  • Recalcitrance of microbially- derived organic
    matter
  • How does community composition change across
    successional development?
  • Substrate availability
  • Substrate quality

Six et al 2006
4
  • Proposed research
  • Assess soil microbial composition and biomass
    along floodplain and upland chronosequences using
    PFLA analysis.
  • WHY?
  • In order to develop and test hypotheses about
    the role of soil microbes in C cycling in
    forested ecosystems of interior Alaska, we need
    to have empirical observations of how community
    structure varies over time and space.

5
PLFA
  • Unlike CF methods, PLFA is useful as a proxy for
    living and possibly active biomass
  • Phosphate group is quickly consumed upon cell
    death
  • Not found in storage products
  • Found in relatively constant proportion of the
    biomass
  • Great structural diversity, coupled with high
    biological specificity

6
Taxonomic groups
7
Experimental design
  • All major stages of succession in FP (n5) and UP
    (n3) communities
  • 3-5 replicate stands per stage
  • 3 sampling periods
  • May
  • Mid July
  • Late September
  • 2 horizons
  • O (integrated organic)
  • A (mineral)
  • 50 cores composited from each 30m x 30m plot
  • 2 years??

8
Predictions
  • Broader patterns
  • Microbial biomass ? along the chronosequence.
  • FP Microbial community shifts from
    bacterial-dominated to fungal-dominated over
    succession. UP ? BF.
  • Potential for vertical stratification in
    community structure as a function of substrate
    availability and water-filled pore space.
  • Seasonal patterns
  • BacterialFungal ? seasonally.

9
Successional processes Hypothesis Climate
influences the rate and trajectory of succession
by altering disturbance regime and the abundance
of key species.
How do plant, animal and microbial communities
change through succession and what are the
consequences for ecosystem processes?
  • Task S8
  • Determine the direct and interactive effects of
    soil resources, microclimate, and microbial
    symbionts on the cumulative nitrogen fixation
    through succession by alder in floodplain and
    upland ecosystems.

10
Physiological ecology of the Alnus-Frankia-EMF
tripartite
  • A. tenuifolia a key player in the N economy of
    floodplain forest ecosystems in interior AK
  • Persists throughout successional development
  • How important are coordinated changes in
    ectomycorrhizal and Frankia associations of alder
    in enabling species persistence and N fixation
    capacity throughout succession?

11
Objectives
  • Identify EMF composition and functional traits in
    Alnus tenuifolia across a 200 year floodplain
    chronosequence
  • Characterize the ecophysiology of host selection
    for EMF in response to N and P fertilization in
    field plots, and in response to controlled
    partner choice experiments in the greenhouse.

12
Hypothesis
  • Alder shifts associations with ectomycorrhizal
    species based on variation in plant demand for N
    and P, combined with the availability and forms
    of these nutrients in soil.

13
Objective 1 Describe EMF community composition
and functional traits across succession
  • Prediction Successional nutrient gradients favor
    selection of different fungal species across
    successional stages.
  • Task 1 - Extract DNAs from randomly subsampled EM
    root tips (control plots) and identify fungal
    associates through PCR and sequence analysis of
    the ITS region
  • Seasonality of mycorrhizal development
  • Task 2 - Determine whether the activities of key
    enzymes related to nutrient acquisition vary
    among fungal associates and successional stages
  • Acid phosphatase and phytase activity in single
    root tips using
  • methylumbelliferone (MU)-labelled fluorescent
    substrate analogues.

14
Objective 2 Characterize host selection of EMF
in response to N and P fertilization
Prediction N fertilization will have the
greatest effect on N-mobilizing EMF species and
enzymes in late succession, while P fertilization
will down-regulate acid phosphatase activity
primarily in early succession Task 1 - Extract
and sequence DNAs from randomly subsampled EM
root tips across N and P ammended plots Task 2
Controlled greenhouse experiment to examine the
capacities of the dominant alder EMF species to
mobilize different forms of P, organic vs.
inorganic.

15
  • Field study
  • 3 successional stages
  • Alder, balsam poplar, white spruce
  • 3 sampling periods
  • June, mid-July, early September
  • 3 stand replications
  • 20m x 20m plot divided into
  • 16 5m x 5m subplots

16
Results (to date)
  • Overall EMF diversity appears low
  • Strong core to core as well as site to site
    variation
  • Most sites appear to be dominated by lt6
    morphotypes with several rare morphotypes mixed
    within.
  • Fine root development delayed in alder relative
    to other taxon
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