Agriculture Reference
In-Depth Information
Statistical Analysis
All results were expressed as mg N, or P, or C kg
-1
oven dry soil. Statistical analysis of
the data was carried out using SPSS (SPSS Inc., Chicago, IL) software.
R
ESULTS
Vegetation Characteristics
The analysis of tree ring pattern revealed that the smallest trees of stratum I exhibited
ages around 90 years, despite their small size (Table 1). Trees in stratum II at the edge of the
site show distinctly taller size, higher ages and faster growth.
Soil Characteristics
The two soil profiles exhibited unaltered (OL) and emialtered (OF) organic horizons
above a OH horizon which filled the interstices between blocks of hard limestone. The
permafrost body was 15-20 m thick. The dwarf spruce stratum was restricted to the area
where the active layer remained thin reaching the maximal thickness of about 2 m in October
(Delaloye et al., 2003). The organic soil consisted of a hydromor with sphagnum moss rests
on the hard limestone blocks. In the dwarf tree stands, raw humus was overlaying blockfields,
with pockets of sphagnum peat accumulating in the gaps between boulders.
Soil characteristics recorded in the late fall are reported in Table 2. Moisture content was
equal to 75 and 60% in the OH horizon of stratum I and II, respectively. The pH of the OL
and OF horizons was around 4.2 in both sites due to the acidifying effect of spruce litter and
of
Sphagnum
in stratum I. The higher pH (6.2-7.2) in the OH horizon was related to the
limited weathering of limestone blocks (Gobat et al., 2004) and consequent incorporation of
CaCO
3
. Electrical conductivity was generally low and strongly decreased with depth in the
stratum I while it remained constant in the reference site. The organic C content decreased
from the OL to the OH horizons in both sites (Table 2). The total nitrogen increased along the
profile in stratum I from 12.8 to 16.0 g kg
-1
causing a C/N ratio reduction in the deeper
horizons. In stratum II the total N decreased as the C trend resulting in a constant C/N ratio.
The different forms of N, C and P are reported only for the OF and OH horizons (Table
3). The ammonium content was lower in the stratum I than in stratum II with a great depletion
from the OF to the OH horizons. This trend was observed also for nitrate in the Stratum II,
whereas low and comparable values were found in the two horizons of stratum I. The
microbial C was lower in stratum I and generally higher in the upper horizons. The microbial
C/N ratio ranged from 28 in the OF of stratum I to 4 in the OH of stratum II. The highest
DON content was found in the OH of stratum I, but was represented by a low amount of
mineralizable material (NPot). The DOC content as well was more present in the stratum I, in
both horizons.
