Fjölrit RALA - 15.06.2004, Síða 114

Biophysical characterization of soils on the island of Santorini (Greece)
E. Vavoulidou1, M. Wood2 and E.J. Avramides1
1 NAGREF, Soil Science Institute of Athens, 2 University ofReading, Department of Soil Science
The island of Santorini is located in the southem part of the Cyclades islands and was formed
by consecutive volcanic eruptions. The most recent eruption, approximately 3,500 years ago,
resulted in the deposition of a layer of volcanic ash and pumice 30-40 m deep. This is the
parent material for the soils of Santorini, which have developed in a Mediterranean climate
with a mean annual precipitation of 375 mm and mean annual temperature of 17 °C. The soils
have been characterized previously as Andisols, suborder Xerands mainly belonging to the
large group Vitric Andisols (Misopolinos et al, 1994). Despite the dry summer, the soils are
widely used to cultivate mainly vines and other crops such as tomato. It is believed that dew
is trapped by the highly porous pumice thereby increasing the amount of water available for
plants in the soil.
No information is available on the biological characteristics of soils of Santorini, therefore
the aim of this work was to obtain integrated physical and biological data on these soils using
a combination of conventional parameters such as particle size analysis, organic matter
content and earthworm population size, together with novel biological characterization based
on enchytreid populations and hydrolytic enzyme activity. Enchytreids are small worms, 1-50
mm long, which feed upon microorganisms, nematodes and plant Htter, and are likely to play
a role in nutrient cycling. Hydrolytic enzymes such as cellulase and phosphatase are
produced by organisms in soil in order to catalyse the decomposition of large organic
molecules such as cellulose and inositol phosphate into smaller monomers such as glucose
and phosphate. These enzymes are likely to control the rate of biogeochemical cycling of
elements such as C, N, P and S in soil and are therefore good indicators of soil biological
quality (Dick, 1994).
47 soil samples were taken from a number of sites which were divided into two categories
(a) cultivated soils (vineyards and other crops such as tomato, faba bean, pistachio nuts) and
(b) natural sites (Cost 622). Sampling was carried out using a riverside auger to a depth of
20-30 cm. Each sample consisted of five or ten well-mixed cores, which were collected from
different points on the site. Sampling of earthworms (Lumbricidae) and enchytreids was
performed in the most humid period (at the beginning of spring in 2000, 2001 and 2002). At
each site, two areas 50 x 50 cm were treated with a 0.1 % formalin solution to extract the
earthworms. A cylindrical core (100 cm3 volume) was used to collect samples for enchytreid
abundance studies. Extraction was carried out in the laboratory after 5 weeks of incubation at
20 °C by means of a wet extraction method and their abundance measured using a
stereomicroscope.
Enzyme activity was measured according to the method of Marx et al. (2001), based on the
use of fluorogenic MUB-substrates and microplates. The soil samples were analysed for
cellobiohydrolase (EC 3.2.1.91), N-acetyl-(3-glucosaminidase (EC 3.2.1.30), (3-glucosidase
(EC 3.2.1.21), acid phosphatase (EC 3.1.3.2), P-xylosidase (EC 3.2.2.27) and leucine-
peptidase (EC 3.4.11.1) using 4-methylumbelliferone-p-D-cellobioside, 4-
methylumbelliferone-N-acetyl-P-glucosaminide, 4-methylumbelliferone-P-D-glucoside, 4-
methylumbelhferone-phosphate, 4-methylumbelliferone-7-P-D-xyloside and L-leucine-7-
amino-4 methyl coumarin as substrates, respectively. All enzyme measurements were made
under standard conditions of pH, temperature and soil preparation.
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