WINTER SOIL BIOLOGY
FIELD DAY RETURN TO SYLLABUS (Schedules etc. subject
to modification)
Results - Winter Soil
Biology
2019
Soil Respiration exercise:
"What is the question?":
State the question and concepts behind it
(why did we do this?)
Graph (image to the right)
y-axis is CO2 flux, units = [CO2] * sec-1
* 78cm-2
x-axis:
Lodgepole -
Snow Depth (red
data points, axis labels)
Soil Temperature degC at 0 cm (blue data points, axis labels)
Aspen grove -
Snow Depth (green
data points, red axis labels)
Plotted plots are means mean
+/- 1 SE bars (standard error of the
mean)
What is the standard error of the
mean (define; write equation)?
How does it help you interpret the
results?
Interpretation
--
There was a
more consistent relationship of Soil R
with Snow Depth (red points)
than with Surface Soil Temperature (blue
points).
The former
showed a
statistically-significant sharp increase
in Soil R between Snow
Depths of 40 & 60
cm (red line).
This was statistically
significant at roughly 95% confidence
level -- shown by that doubled SE bars
do not overlap.
The lack of
a relationship with 0-cm Soil Temperature
may have been because soil
temperature at the surface poorly
represents the temperature of the
microbe-active soil layer.
Soil was frozen solid under 40 cmsnowpack,
as it was under 10 cm
pack, suggesting that the -1C for 40-cm
reading
"misplaced"
to
the right the
(blue) data point.
There was
no significant difference between
Aspen and Lodgepole sites in the
pattern of Soil R vs. Snow
Depth.
This
was counter to expectations, given
that Aspen produce organic matter in
greater amounts and of higher
quality (higher N:lignin ratio) than
Lodgepole Pines.
Discussion:
a review of results --
For Lodgepole - What do you
infer from these Results?
That is, what environmental
factors are at play in your experiment
and what do your results say about
winter soil respiration rates ...
... in space
(across the landscape)?
... and in time (e.g.,
diurnally and across the season)?
Seasonally - When
is the
more stable vs. more variable
environment?
In each case, what are
the consequences for the microbial
biota?
Why does there appear to be a
strong
difference
response at temperatures (blue line)
between -3 and -1șC?
What other factors did you
attempt to control for? How might
they may determine different winter soil
respiration rates across the landscape?
(see *)
For previous results
with Aspen, showing an
Aspen
site with greater
Soil R than a Lodgepole
site, see
results
for 2010
In the small diagram at
the top of the whiteboard image to the
right, explain by soil respiration has
this relationship with soil moisture?
Soil respiration under Lodgepole
pine
vs. soil temperature at 0 cm (blue) and
snow depth (red).
And vs. snow depth under
Aspen (green). Data points are means +/- 1
SE bars
40 cm Lodgepole site
63 cm
Aspen site
Photos
(c)T Kittel
Previous Years
2018
Soil Respiration exercise:
"What is the question?":
State the question and concepts behind it
(why do this?)
Graph (image to the right, click to
enlarge)
y-axis is CO2 flux, units = [CO2] * sec-1
* 78cm-2
x-axis:
Snow Depth (Left graph, green data
points)
The rightmost green data point is
hypothetical )not from our data), to
illustrate that flux levels off under
yet deeper snowpack.
Soil Temperature degC at 10 cm - Right
graph: blue
data points = mean & red =
+/- 1 SE (standard error of the mean)
What is the standard error of the mean
(define; write equation [hint: it's in the
image])?
How does it help you interpret the
results?
Discussion --
What do you infer from these
Results?
That is, what environmental
factors are at play in your experiment
and what do your results say about
winter soil respiration rates ...
... in space
(across the landscape)?
... and in time (e.g.,
diurnally and across the season)?
Seasonally - When
is the
more stable vs. more variable
environment?
In each case, what are
the consequences for the microbial
biota?
Why does there appear to be a
strong, nearly threshold response at
temperatures in the vicinity of 0șC?
We sampled two sites with shallow
snowdepths
of 10cm.
Why were the results so different (Note
the 2 data points for 10cm in
the left
graph)?
Giveaway answer - see
note on the very right
of the image.
What other factors did you
attempt to control for? How might
they may determine different winter soil
respiration rates across the landscape?
(see *)
High flux value (0.23+/-0.04) at SnowZ=0
cm is pulled into a tighter relationship
with other points when fluxes are plotted
against T(0 cm) rather than vs. SnowZ
Other questions -
Is there Dependence on Vegetation Type?
and Soil Organic Matter Quality?-
See results for
2010 and other years
click image to enlarge
2014
Soil Respiration exercise:
"What is the question?":
State the question and concepts behind it
(why do this?)
Graph (image to the right, click to enlarge)
see Notes in 2013
SE's are usually given in parentheses
Green x-axis,
green data points, and red line are for
Fluxes plotted vs. Snow Depth (Z, cm)
What do you think might be a good
estimate for a snow depth threshold for
Soil Respiration?
Blue x-axis,
blue data points, and black line are for
Fluxes plotted vs. Soil Temperature (deg C
at soil surface)
Black vertical & horizontal lines
(with "?") are to suggest a location for a
Temperature Threshold for Soil
Respiration.
Interpretation - See Results
& Discussion for 2013
Other questions -
Dependence on Vegetation Type?
and Soil Organic Matter Quality?-
See results for 2010 and other years
Error
bars on plots are +/- 1 standard error
(SE).
Samples
are however not true replicates
(=pseudoreplicates), so the SE's are
underestimated.
Hand-drawn
(solid green) curves are an idealized
summary of results.
Dashed
curves are excel-generated polynomial
fits. R2's
(regression coefficients) and
corresponding p's (1-significance
level) can be used to evaluate the
strength of the observed pattern.
Results
--
3 flux
results are significantly different from
-0- at the 95% confidence level (based on
2SE).
With
snowcover (blue points),
respiration depends on depth of snowcover
(Fig. 1)
Without
snowcover (red points),
respiration rates vary strongly in spite
of snow Z=0 (Fig. 1), suggesting
that another factor is also having an
effect.
Replotting
against soil temperature appears to
brings all data points into one
relationship (Fig. 2, plotted with average
upper layer soil T).
This
is most obvious in the case of the
no-snowcover site (red point)
with
a significantly strong flux of 0.18 (and
very small SE) that shifts from the left
side of Fig 1 to the right in Fig 2,
and so bringing it more in line with the
exponential pattern of other datapoints
(this is site 3 in the results table xls).
Discussion --
What do you infer from these
Results?
That is, what environmental
factors are at play in your experiment
and what do your results say about
winter soil respiration rates ...
in space (across the
landscape)?
and in time (e.g.,
diurnally and across the season)?
Which is the more stable
vs. more variable environment? In each
case, with what consequences for the
microbial biota?
Why does there appear to be a
strong, nearly threshold response at
temperatures in the vicinity of 0șC?
What other controlling
factor is changing?
What other factors did you attempt to control for? How might
they may determine winter soil respiration
rates across the landscape?
Winter Ecology
Field Results
