Title: Successional processes Hypothesis: Climate influences the rate and trajectory of succession by alter
1Successional 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.
2Studying 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
3Microbial 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.
5PLFA
- 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
6Taxonomic groups
7Experimental 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??
8Predictions
- 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.
9Successional 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.
10Physiological 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?
11Objectives
- 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.
12Hypothesis
- 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.
13Objective 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.
14Objective 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
-
16Results (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