Agriculture Reference
In-Depth Information
the specific thermal conditions lead to a great accumulation of organic material deposited on
the block substrate (Kneisel et al., 2000; Freppaz et al., 2003; Gobat et al., 2004).
In cold regions, such as arctic ecosystems, the reduced organic matter decomposition rate
is a key factor for the control of plant productivity, because plant biomass production
generally is limited by low availability of N and P (Schmidt et al., 1999). Sveinbjornsson
(1993) for example found that in
Betula pubescens
N availability was more important than
soil temperature, in large part due to slow organic matter mineralization. The decomposition
of organic matter and the nutrient dynamics in those environments are strongly affected by
seasonal changes. In the winter time the lack of plant activity and the proliferation of a cold
adapted microbial community may cause a relatively great nutrient immobilization (Schmidt
and Lipson, 2004) by changing the quality itself of the organic matter (Dalias et al., 2001).
During the snow melting and the starting of the plant growing season the nutrients become
available through microbial lysis and mineralization of the easily degradable material and are
rapidly up taken and consumed by plants during the short summer season (Lipson et al.,
1999). Soil N mineralization during the nongrowing season represents an important portion of
annual N cycle, and the accumulation of inorganic N in winter supply a large pulse of mobile
and available N during the early growing season (Schimel at al., 2004).
In low elevation permafrost affected sites, where soil frost conditions are not directly
connected to air temperature, the link between seasonal fluctuation of nutrient availability and
plant growth may be more complex and is still unknown.
In this work we aimed to explore the soil nutrient dynamics and plant characteristics in a
well-known cold site located below the limit of discontinuous alpine permafrost in the Jura
Range, in north-western Switzerland (Lesquereux, 1844, Duchafour, 1976, 1983). In this site
peculiarly dwarfed Norway spruce trees inside a semicircular escarpment are present. The
limited plant growth has been associated for many years with permafrost (Richard, 1961) and
recently Delaloye et al. (2003) revealed that ground temperatures are low and are clearly
associated with permafrost. Previous works have attributed the reduced plant growth mainly
to plant physiological stresses,
since roots are cold but not shoots
(Korner and Hoch, 2006),
but they invoked soil N and P limitation as potential and additional causes.
This paper is aimed to describe and estimate the contribution of soil nutrient availability
to the limited plant growth by evaluating the seasonal cycles of nutrients during the winter
and the early spring season.
M
ATERIALS AND
M
ETHODS
Study Site
This research was conducted in Creux du Van, Swiss Jura (46°56'N, 6°44'E). The talus
slope is located at the bottom of a cirque facing east-northeast between 1170 and 1300 m ASL
(Figure 1). The cirque is closed from its southern to western rim by a 100-150 m high cliff of
hard limestone. The fallen blocks build up a well-sorted talus slope at the base of the cliff.
The mean annual air temperature (MAAT) measured over the period 1998-2001 is +5.5°C
(Delaloye and Reynard, 2001). The annual precipitation is estimated to be 1600 mm.
