Environmental Engineering Reference
In-Depth Information
Fig. 8.5
Percentage of
variation in the organic
carbon pools with the A1b
climatic scenario (2091/2100
mean SOC data vs. 2000)
8.6 Regional Case Study on SOC Fluxes from Trentino
The site “Monte Bondone” (see Sect.
2.2.13
) is equipped with an Eddy Covariance
measurement tower. The meadow is mowed once a year in mid July. Soil CO
2
fluxes were measured at twenty sampling points with a closed dynamic system
(LI-COR 6400, soil chamber LI 6400-09; LI-COR Inc., Lincoln, NE, USA) every
15-20 days. The soil chamber was used with plastic collars inserted for about
1.5 cm into the soil and fixed with iron legs to prevent the collar from moving
when the chamber was placed on it. The collars were systematically positioned
around the eddy flux tower following a cross pattern. The vegetation inside the
collars was cut 1 day prior to measurement. Soil temperature at a depth of 5 cm
was measured with the LI-COR 6400 temperature probe. Soil water content was
recorded on three points around each soil collar with a ThetaProbe ML2x (Delta-T
Devices Ltd, Cambridge, UK). Moreover the soil temperature at a depth of 5 cm
was recorded every 5 min with StowAway TidbiT loggers (Onset Comp. Corp.,
Bourne, MA, USA). An exponential model (Bahn et al.
2008
; Rodeghiero and
Cescatti
2005
) was fitted to the temperature (T
s
), soil respiration (R
s
) data:
R
S
=
R
10
∗
EXP
(
E
0
∗ (
1
/
56.02
− (
1
/
T
S
+
46.02
)))
(8.1)
where R
10
is the soil respiration at 10 °C, E
0
is the activation energy (Lloyd and
Taylor
1994
; Eq.
8.1
). The total soil respiration in a given year was calculated by
summing the fluxes estimated by the model from continuous temperature data.
In this meadow ecosystem temperature resulted to be the main determinant of
soil respiration [the variance explained by the fitting model being 0.77 (Eq.
8.1
;
Fig.
8.6
a)] whereas no evident drought stresses during the growing season were
detected. A reduction of the soil CO
2
flux rates after mowing was observed and
was probably related to a decrease in photosynthetic activity which caused a
consequent decrease in autotrophic respiration (data not shown). As a conse-
quence, the higher level of irradiance lowered the soil water content and possibly
