Oak phenology changes the contribution of respiration from the forest floor and soil

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Oak phenology changes the contribution of
respiration from the forest floor and
soil Jared L. DeForest Earth, Ecological and
Environmental Sciences University of Toledo
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The canopy, organic horizon, roots and soil
release CO2 into the atmosphere
Determining the flow of carbon from these pools
gains insight into how ecosystems cycle store
carbon
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Measurements of soil respiration often include
respiration from the organic horizon (i.e. forest
floor). The combination from these two pools
into one measurement adds uncertainty when
scaling-up measurements spatially or temporally
These two pools likely have different
sensitivities to environmental conditions
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How much does the forest floor contribute to
ground respiration and is this value consistent
seasonally?
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The contribution of CO2 from the forest floor is
likely to change seasonally
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Why focus on forest floor respiration?
An accurate estimation of forest floor
respiration combined with Inputs of litter
(litter traps) Outputs through decomposition
(litter bags) Soil carbon sequestration Can be
used to understand the cycling storages of
carbon at multiple temporal and spatial scales.
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Objectives To determine the CO2 contribution of
the organic horizon (i.e. forest floor) to ground
respiration. To quantify how forest floor
respiration changes seasonally based on tree
phenology.
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The Oak Opening Region
Oak Openings Preserve Metropark
Image 3600 ha (6 km x 6 km) Inset Study site
(100 ha) Dot Satellite Site
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The four phenophases
Pre-Growth 5 Bud break Growth 95 leaf
flush Pre-Dormancy 5 leaf discoloration Dorman
cy 95 leaf drop
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Litter exclusion experiment
Litter Soil
Soil
Litter horizon was removed replaced with
rubberized mulch
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The forest floor represents a major source of
variation in carbon efflux
Growth
Dormancy
Pre-Growth
Pre-Dormancy
mmol CO2 m-2 s-1
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The relative contribution of litter to ground
respiration is influenced by temperature,
moisture, and plant phenology
DOY (2005-2006)
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Temperature influence on respiration is weaker
for litter than soil
mmol CO2 m-2 s-1
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When trees are dormant, soil respiration
decreases consistently until plants start to grow
SR -0.31ln(days)
mmol CO2 m-2 s-1
DOY (2005-2006)
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Temperature can explain the most variation in
respiration, followed by moisture
0.013 increase
0.287 increase
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Temperature was used to estimate annual
respiration from soil and litter
An Arrhenius type equation was used to estimate
respiration at larger temporal scales. While
moisture is important in forest floor
respiration, I had no useful means to gap-fill
litter moisture. Ground respiration was
calculated by adding soil and litter respiration
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The relationship between soil forest floor
respiration is tightly coupled within phenophases
Soil Dominates
Forest Floor Dominates
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Seasonally respiration carbon budget
Seasonal Budget (g C m-2) Summer 772 Fall
55 Winter 171
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Respiration estimates from forest floor are
reasonable in the winter, but not in the summer
Winter 90 day mass loss (g C m-2) Forest floor
137 Litter bags (2 yr classes) 35 Estimated 90
day Litter Respiration Forest floor 65.9
Summer mass loss (g C m-2) Forest floor
101 Litter bags (1 yr age class) 76 Estimated
Summer Litter Respiration Forest floor 334
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Possible reasons why forest floor respiration is
overestimated
No incorporation of litter moisture 200 - 160 -
Possibly Stimulates 160 100 - No
noticeable effect 100- 50 - Suppresses

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Accounting for temperature, litter moisture is
important in estimating respiration
Suppression
No Effect
Stimulation
Below 0oC or Summer
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Possible reasons why forest floor respiration is
overestimated
No incorporation of litter moisture 200 - 160 -
Possibly Stimulates 160 100 - No
noticeable effect 100- 50 - Suppresses
False to assume that ground respiration
soil respiration litter respiration Roots or
mycorrhiza may be present in the forest floor,
though none was observed The presences of the
forest floor likely stimulates soil respiration
through the leaching of nutrients
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Future direction of litter exclusion experiment
Gap-fill forest floor moisture content Continuous
measurements to gain insight into biophysical
mechanisms Scale-up How does the influence of
litter C efflux change through space time?
Compare in tandem with decomposition
experiments
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Preliminary Conclusions
The relationship between soil and litter
respiration are tightly coupled within a
phenophase Variation in ground respiration can
be largely explained forest floor
respiration. The environmental factors
regulating ground respiration changes seasonally.