Agriculture Reference
In-Depth Information
Table 4. Effect of soil incubation in the buried bags (t1b: C and N forms (mg kg
-1
) in the
buried bags in May 2002; t1notb: C and N forms in the undisturbed soil in May 2002).
Asteriscs indicate significant differences between means (p
<
0.05). ns: not significant
differences between means
Stratum I
t1b
t1notb
N-NH
4
+
4.4
4.8
ns
N-NO
3
-
31.4
6.8
*
Nmicr
680.7
580.3
ns
Cmicr
7243
3702
*
DON
11.9
40.60
*
DOC
320
438
ns
Stratum II
t1b
t1notb
N-NH
4
+
2.4
9.4
ns
N-NO
3
-
52.5
10.9
*
Nmicr
569
763.5
ns
Cmicr
5002
4039
*
DON
13.2
15.5
ns
DOC
293
355
ns
D
ISCUSSION
The tree growth was significantly lower in stratum I, where the permafrost active layer
remains thin. Although the size of the dwarf trees was hardly more than 3 m, they were of
similar age to the adjacent reference trees, ranging from 90 to 130 years, with values similar
to those reported by Korner and Hoch (2006).
The winter soil temperature decreased to a mean value of -0.45 °C at the stunted forest,
with the minimum peaks registered during the December-February period, well below the
values recorded during the same months in a forested (
Picea mariana
) peatland in North
Central Minnesota (mean annual air temperature of +3.3°C) (Nichols, 1998). The presence of
the permafrost table seems to reduce the insulation effect due to snow cover and keep the soil
at temperature lower than 0°C, with possible stress or even damages to the root system
(Edwards and Cresser, 1992). In the reference site, even if the greater presence of trees shades
the ground from solar radiation and intercepts some of the snowfall in winter (French, 1996;
Hardy et al., 2001), the soil temperature in the cold season resulted significantly higher. This
is in accord with the data reported by Korner and Hoch (2006), who in the same site, during
the previous winter season (2000-2001), recorded a soil temperature 2-3 °C colder than under
the reference forest canopy, although the air temperature in the two sites was very similar.
The low temperature at the site I determined a greater soil moisture due to the H
2
O
vapour condensation following the cooling of the air during circulation inside the permafrost
lens. This has allowed the development of a particular flora, dominated by a dense layer of
Sphagnum
. Nevertheless the high moisture, the stratum I appeared to be well oxygenated due
to the air flux through the soil.
