Original article
Influence of slope aspects on soil chemical and biochemical
properties in a
Pinus laricio
forest ecosystem
of Aspromonte (Southern Italy)
Maria Sidari
a, Giuliana Ronzello
a, Giuseppe Vecchio
b, Adele Muscolo
a,*
aDepartment of Agricultural and Forest Systems Management, Faculty of Agriculture, University ‘‘Mediterranea’’ of Reggio Calabria,
Piazza San Francesco, 4-89061 Gallina di Reggio Calabria, Italy
bExperimental Institute of Study and Defence of Soil. Department ‘‘Technologies of Soil’’,
via Cagliari, 15, 88063 Catanzaro Lido (Cz), Italy
a r t i c l e
i n f o
Article history:
Received 14 November 2007 Accepted 14 May 2008 Published online 9 June 2008
Keywords:
Chemical properties Enzyme activity Pinus laricio Organic matter Slope aspect
Soil microbial biomass
a b s t r a c t
The study assesses the influence of soil aspect on differences in soil chemical and bio-chemical properties. We examined soils on contiguous south- and north-facing slopes of the Aspromonte Mountains (Calabria, Southern Italy), influenced by the same climate, vegetation and parent material. In each of the two topographic aspects, six study sites were described. The investigated variables were air temperature, soil temperature, soil water content, photosynthetically active radiation, soil microbial biomass C, organic mat-ter content, total nitrogen, total wamat-ter-soluble phenols, humic and fulvic acids. Fluorescein diacetate hydrolytic activity, dehydrogenase, protease urease, alkaline and acid phospha-tases, enzymes related to soil microbiological activity and hydrolysing coefficient, an empiric indicator of soil quality, were analyzed and interpreted. Except in few cases, all considered soil properties and microclimate variables showed significant differences between topographic aspects. In the soil on the north-facing slope, a lower content of organic matter and microorganisms and a lower activity of the enzymes related to soil microbiological activity were observed. The differences may be attributed to topographic aspect-induced microclimatic differences, which causing differences in the biotic soil component and organic matter trend, affect soil fertility.
ª2008 Elsevier Masson SAS. All rights reserved.
1.
Introduction
The spatial variation of soil properties is significantly influenced by some environmental factors such as climate, landscape features, including landscape position, topography, slope gradient and evolution, parent material, and vegetation
[1–3]. It is common knowledge that topography, in the forest
ecosystem, influences local microclimates by changing the pattern of precipitation, temperature and relative humidity
[4,5] and significantly affects soil texture and soil organic
matter trend, which are acknowledged to be among the most important soil physiochemical properties, influencing
*Corresponding author.Tel.:þ39 0965/689012; fax:þ39 0965/312827.
E-mail address:[email protected](A. Muscolo).
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : h t t p : / / w w w . e l s e v i e r . c o m / l o c a t e / e j s o b i
1164-5563/$ – see front matterª2008 Elsevier Masson SAS. All rights reserved.
microbial population activity, dynamic, and ecology of the soil
microbiota[6]. It is generally accepted that microbial
popula-tion is positively related to organic matter content[7–9]and
its activity plays a central role in organic matter trend and nutrient cycling in the forest ecosystem. Fluctuation in the size and turnover of soil microbial biomass is very important
in controlling the turnover of carbon (C) [10] associated
nutrients nitrogen (N), phosphorous (P) and sulphur (S), which
in turn regulate plant availability of N, P, S[11].
Nutrient mineralization from fresh plant litter occurs via the enzymatic activities of the microbial communities. Trend in soil microbial biomass and enzyme activity varies with plant species
[12], and it is dependent on the combination of soil moisture,
temperature, root activity, and organic matter return to soils
via litter fall[13]. Each change in soil chemistry and litter quality
can result in different enzyme activities into the decomposing litter, which in turn can result in increased rate of litter
decom-position [14]. A considerable number of studies have been
conducted to relate organic matter decomposition to climate conditions (temperature, moisture) or litter quality under
Medi-terranean climate[15,16]. In general, effects of topography on
litter quality and decomposition have received little attention.
Sariyildiz and Anderson[17]and Sariyildiz et al.[18]showed
that aspect and slope position within an ecosystem affect the soil chemistry, litter quality and nutrient cycling. Boerner and
Le Blanc[19]and Sariyildiz et al.[18]showed that slope position
exerted greater effects on soil chemical properties and organic N turnover than does bedrock type. Topography, which generally is considered an ultimate control of many biotic and physical factors, seldom can operate as the mechanism directly responsi-ble for such processes as humification.
Studies on topographic characteristics, on slope aspect in particular, have produced contrasting results; foresters have traditionally viewed south aspects as less productive than north aspects, yet there is substantial evidence that the assumption of lower site productivity on south aspects may
be incorrect [20]. Therefore, the study reported here was
conducted to evaluate the influence of south or north aspect on soil biochemical properties and organic matter trend within
a naturally regenerated 80 years oldPinus laricioPoiret
popula-tion forest of Aspromonte Mountains, in Calabria (Southern Italy). We hypothesise that soil aspect could be of relative importance in controlling variability in soil chemical and bio-chemical properties which in turn influence soil productivity. The microbial activity and the organic matter trend, consid-ered early and sensitive indicators of environmental changes, were evaluated by determining the microbial biomass C and organic matter content. In this paper, we decided to measure urease, alkaline and acid phosphatases, dehydrogenase, FDA hydrolysis, and protease enzyme activities, because they are related to soil microbiological activities and thus may be used
as indicators of soil ecosystem functioning[21].
2.
Materials and methods
2.1. Study area
The study area was located in the Peripoli Mountain (San Lorenzo) of Aspromonte Mountains (Calabria, Southern Italy),
1270 m above sea level. Coordinates: Lat. 380300000N, Long.
155100400E. The climate in this area is predominantly
Mediterranean, with dry hot summers and cold winters. The
annual mean temperature is 12C, with a mean rainfall of
about 1250 mm. Rainfall in the study region is typically high-est during the winter (1100) and autumn (1500) compared to spring (900) and summer (600). Snow usually contributes little
(<10%) precipitation in winter. The soils in this zone are
devel-oped from high rank metamorphic rocks, such as schists and biotite gneisses. The predominant soils are Humic Cambisols
[22], with a xeric soil regime moisture and a vegetal cover of
Pinus laricioPoiret, ssp. Calabrica. We selected 12 study sites:
six on the north-facing slope (5–10) and six on the
south-facing slope (182–190). In order to maximise comparability
among sites, sites that had the following qualities were
chosen: (1) had uniform tree layer dominance byPinus laricio;
(2) had an age of the tree stand of 80 years; (3) had a uniform
forest story (Erica arborea, Cytisus scoparius, Anemone apennina,
Euphorbia amygdaloides, Lathyrus pratensis)over a rectangular
area, at least 40 m and 0.5 ha; (4) lacked signs of extensive natural disturbance; and (5) were gently sloping (range incli-nation: 8–22%).
2.2. Sampling procedure
In this study, the change in soil chemistry and biochemistry was evaluated in May 2006, because soil microbial activity, in mountains of Southern Italy, is higher after snow and heavy
rains[23]and the differences in soil biochemical properties
between north- and south-slope aspects are more
pronounced. Similar findings were reported by Garcia et al.
[24]for others Mediterranean regions. At each site, soil profiles
were carefully excavated with as little disturbance as possible. Different layers (horizons) were thoroughly separated from the top to the bottom of the profile on the basis of morpholog-ical differences which could be perceived by the naked eye. Soil samples (1 kg) were taken from each horizon for each soil profile and analyzed separately. The samples were brought to the laboratory on the same day and kept in the
refrigerator at 4C for up to 24 h until processing. Prior to
the soil analysis, except for soil water content (SWC) and microbial biomass, all the soil samples were air-dried, sieved
(<2 mm), and visible roots were removed.
2.3. Measurement of microclimatic variables
The microclimate was assessed by measuring air temperature, soil temperature, soil water content and photosynthetically active radiation (PAR, measured at 400–700 nm) in May 2006.
PAR was determined on bright sunny days, at 12.00 h, four times in a month, during the study period. Measurements were taken in the full open area, a large clearing near the exper-imental area, and in correspondence of soil profiles inside each area of study. PAR levels were measured using a Ceptometer (AccuPAR, Degagon Devices Inc., Pullman, WA, USA). The PAR transmittance was calculated using the following formula:
PARtramsmittance¼ ðPARforest site=PARfull openÞ 100
were taken every 2 h. Air temperature was measured in the study area using an air thermometer. It was monitored and recorded from 1 to 31 May 2006. Records were taken every 2 h, from 8:00 to 20:00 h including the minimum night air tem-perature. Soil water content was determined gravimetrically.
2.4. Physical and chemical analysis
Particle size analysis was carried out by the hydrometer method, using sodium hexametaphosphate as a dispersant
[25]; pH was measured in distilled water and 1 M KCl using
a 1:2.5 (soil:water) suspension; organic carbon was determined
by dichromate oxidation[26], and it was converted to organic
matter by multiplying the percentage of carbon by 1,72; soil
total nitrogen was measured by the Kjeldahl method[27], and
cation exchange capacity (CEC) was measured by using the
bar-ium chloride–triethanolamine method[28]. Available P was
determined by the Bray II method[29]. Exchangeable Kþwas
extracted with 1 M NH4OAc, and determined using a flame
pho-tometer. Soil was classified according to FAO system criteria
[22]. Humic substances were extracted with 0.1 M NaOH (1:10
w/v); the suspension was shaken for 16 h at room temperature, centrifuged at 5000 rpm for 30 min, and the extract was dialysed in Wisking tubes against distilled water to pH 6.0. Subsequently, the solution was filtered through a column of Amberlite IR 120
Hþ. The fractionation of humic substances was carried out as
follows: aliquots of extract were acidified to pH 2.0 with dilute
H2SO4; the humic acids were precipitated and removed by
cen-trifugation, while the fulvic acids corresponded to the
superna-tants [30]. The C content of humic and fulvic acids was
determined by dichromate oxidation[26]and was expressed
as % of OM extractable in NaOH. Phenols were extracted with
distilled water, 1:10 (w/v)[31]. Soil samples were shaken at
75 rev min1for 20 h at room temperature and solutions were
filtered through Whatman’s no 1 paper. Total water-soluble phenols were measured by using the Folin–Ciocalteau reagent,
following the Box method[32]. Tannic acid was used as a
stan-dard and the concentration of water-soluble phenols was
expressed as tannic acid equivalents (mg TAE/g d.w.)[33].
2.5. Microbial biomass determination
Microbial C concentration was determined in fresh soil
sam-ples, by the chloroform-fumigation–extraction methods[34].
Fifteen grams of soil was fumigated with alcohol-free CHCl3
for 24 h at 24C. Both fumigated and non-fumigated samples
were extracted with 0.5 M K2SO4and filtered with Whatman’s
no. 42 paper. The filtered soil extracts of both fumigated and non-fumigated samples were analyzed for soluble organic C
using the method of Walkley and Black [26]. MBC was
estimated on the basis of the differences between the organic C extracted from the fumigated soil and that from the non-fumigated soil, and an extraction efficiency coefficient of
0.38 was used to convert soluble C in biomass C[34].
2.6. Enzymatic assay
Dehydrogenase (DH) activity was determined by the method of
von Mersi and Schinner[35]. Briefly, to a sample of fresh soil
equivalent to 1 g of oven dried (105C) soil were added 1.5 ml
of 1 M Tris–HCl buffer of pH 7.5 followed by 2 ml of 0.5% INT solution (Sigma product No I 8377), and the suspension was
kept at 40C for 1 h. Then 10 ml of extractant (methanol)
was added and the samples were mixed using a vortex mixer, and then left in the dark for 10 min. Finally, the solids were filtered out (Whatman’s no 40 paper), and the absorbance of the filtrate was determined at 490 nm.
Alkaline and acid phosphatase (AlPh, AcPh) activities were determined on 1 g (fresh weight) aliquots of soil, according to
the method of Tabatabai[36]. Enzyme activities are expressed
asmgp-nitrophenol produced by 1 g of dry soil in one hour (mg
p-nitrophenol g1h1).
FDA hydrolysis reaction was determined according to the
methods of Adam and Duncan[37]. Briefly, to 2 g of soil (fresh
weight, sieved<2 mm) 15 ml of 60 mM potassium phosphate
pH 7.6 and 0.2 ml 1000mg FDA ml1 were added. The flask
was then placed in an orbital incubator at 30C for 20 min.
Once removed from the incubator, 15 ml of chloroform/meth-anol (2:1 v/v) was added to terminate the reaction. The content of the flask was centrifuged at 2000 rpm for 3 min. The supernatant was filtered and the filtrates measured at 490 nm on a spectrophotometer (Shimadzu UV–Vis 2100, Japan).
Hydrolysing coefficient (Hc):mmol of fluorescein diacetate
hydrolysed/mmol of total fluorescein diacetate before
hydroly-sis[38].
Protease (PRO) activity was determined on 1 g (fresh
weight) according to the method of Nannipieri et al.[39]. In
short, to a sample of wet soil was added 2 ml of phosphate
buffer (0.1 M, pH 7.1) and 0.5 ml of 0.03 M N-a-benzoyl-L
-argininamide (BAA). The mixture was incubated at 37C for
90 min and then diluted to 10 ml with distilled water. The ammonium concentration was measured by using an ammonium selective electrode (CRISON, micro-pH 2002).
Urease (URE) was determined according to the method of
Kandeler and Gerber [40]. Soil (5 g fresh weight) was mixed
with 2.5 ml of urea (80 mM) and 20 ml 0.1 M borate buffer pH (10.0). The mixture was allowed to react for 2 h in an orbital
shaker at 37C. After incubation, pipette 2.5 ml of urea to
the control, add 30 ml of KCl (2 M) to both sample and control, and shake for 30 min. Filter the contents of the flasks through folded filters. Aliquots of 1 ml of the filtered solution were mixed with 9 ml of distilled water, 5 ml of sodium/salicylate
solution, and 2 ml of dichloroisocyanuric acid (Naþsalt). The
colour intensity of the solution was measured at 690 nm. Ammonium concentrations were determined by using a cali-bration curve of ammonium chloride standard solution.
2.7. Statistical analysis
A two way repeated measures ANOVA (analyses of variance) was applied for analysing the effects of aspects on soil properties and
treatment means were compared using Tukey’s test[41].
3.
Results
3.1. Environmental variables
differences were instead observed in the values of PAR trans-mittance between north- and south-facing slopes. Inside the forest area, PAR transmittance was significantly higher in
the north (18%) compared to south-facing slope (8%) (Table
1). Tree density was higher in the south- (880 plants/ha)
compared to the north-facing slope (550 plants/ha) (Table 1).
The differences detected in the microclimate variables between north- and south aspects were maintained during the year (data not shown).
3.2. Physical and chemical properties
Tables 2 and 3 summarize the soil physical and chemical
properties of the north-facing slope (N) and the south-facing slope (S). Soil temperature was higher in the north- compared to the south-facing slope; the highest soil water content was instead detected in the soil profile of the south-facing slope
(Table 2).
In all samples, pH was greater at the soil surface than at the
depth. Soil pH (H2O) ranged from 6.75 to 5.97 for the north, and
from 6.14 to 5.35 for the south, respectively. Soil pH (KCl) ranged from 5.55 to 4.45 and from 5.05 to 3.45 for the sites N and S, respectively, and it was consistently less than that
measured in H2O.
A different mineral soil texture between the soils on the north- (N) and south- (S) facing slope was observed. The north was typified by loamy-sand texture; on the contrary, the south resulted in a sandy-loam textural class.
The amount of exchangeable Kþdecreased with increasing
soil depths in both north- and south-facing slope aspects.
Available P (mg kg1) was consistently higher in the soils in
the south aspect.
The soil on the south-facing slope contained a greater amount of organic matter as demonstrated by an eluvial Ah
horizon with 7.8% of organic matter and the two B (w1and
w2) horizons with 9.00% and 3.7% of OM, respectively. In
addition, a greater amount of total nitrogen on the south-facing slope was detected.
The C/N ratio decreased, along the profile, with increasing soil depths in the soil on the north-facing slope. No significant variation in the C/N ratio between the surface and the illuvial horizons of the S aspect was observed. Higher cation exchange capacity values were found in the S aspect with higher clay and organic contents. The amount of humic and fulvic carbon was the highest in the soil on the south-facing slope. HC decreased with depth in both aspects. The value of the HC/FC ratio was the highest in the south-facing slope
(Table 3).
The amount of water-soluble phenols (WSP) in both aspects was higher in the surface horizon and then decreased with increasing soil depths. In the soil of the north-facing slope, the amount of WSP was significantly lower than that
found in the soil of the south-facing slope (Table 3).
All soil physical and chemical properties were significantly
(P<0.05) affected by both factors (aspect and depth), and the
interaction of the two factors was also significant except for
clay content (P¼0.12) (Tables 2 and 3).
3.3. Microbial biomass
Microbial Biomass C, as expected, declined with depth, and differed considerably between the north and south aspects. In the soils on the south-facing slope the microbial biomass C was three times higher than on the soils on north-facing slope. The MBC detected along the soil profile on the
south-facing slope mountain ranged from 3673.2 to 75.1mg C g1
soil in the surface horizon and in the Bw2horizon,
respec-tively. In the litter layer and in the Bw2horizon of soils on
the north-facing slope the MBC was 1054.5 and 29.7mg C g1
soil, respectively (Table 4). These significant differences
(P0.05) indicate a strong stimulation of the microbial
community in the forest soil on the south-facing slope. The differences in the microbial biomass amount between north- and south aspects were maintained during the year even if with different values (data not shown).
3.4. Enzyme activities
In general, all the hydrolytic enzymes showed the highest activity levels in the soil on the south-facing slope (S).
The acid phosphatase activity was significantly (P0.05)
higher than the alkaline phosphatase in the soils sampled. The activity of acid phosphatase was highest in the horizons of the soils on the south-facing slope (S), with values ranging
from 2936 to 170mgp-nitrophenol g1h1. Alkaline
phospha-tase activity was higher in the soils on the south aspect with the exception of the two deepest horizons, where no signifi-cant differences, compared to the north aspect, were detected. Protease activity decreased down along the profile of both aspects studied. In the litter layer and in the Ah horizon of the soil on the south-facing slope (S) the level of the protease activity was 2.2-fold greater than in the same horizons of the
north aspect. The protease values ranged from 126.0 to 4.3mg
tyrosine g1soil 2 h1and from 57.3 to 2.3mg tyrosine g1soil
2 h1in the S and N aspects, respectively (Table 4).
The dehydrogenase activity in both soils decreased with depth. The lowest levels of dehydrogenase activity were
Table 1 – Environmental variables ofPinus laricioforests on the north- (N) and south-facing (S) slope aspects of Peripoli
Mountain
Site Air temperature (C) PAR transmittance:
inside the stands (%)
observed in the soils on the north-facing slope (N), where the
values of this activity ranged from 93.5 to 5.4mg INTF g1soil
h1(Table 4).
Hydrolysing coefficient (Hc) decreased in both aspects with increasing soil depths. The highest levels of the Hc were observed in the horizons of the south-facing slope
(Table 4).
The highest urease activity was observed in the soils on the south-facing slope, and this activity strongly decreased from the O to Ah horizons. All enzymatic activities were influenced
by aspect (P<0.05) and depth (P<0.05), with significant
interaction effect.
The differences observed in the enzymatic activities between north- and south aspects were maintained during the year (data not shown).
5.
Discussion
Our results clearly demonstrate that soils developed on the same parent material, with the same vegetal cover and climate, differing only for the position in the landscape, had diverse microclimatic conditions (PAR transmittance, soil temperature and water content). In the northern temperate zone, slope aspect is an important topographic factor
influ-encing local site microclimate [18], mainly because it
deter-mines the amount of solar radiation received. The amount of insolation governs soil temperature and water availability
which in turn affects soil properties. Inside thePinus laricio
forest of the north-facing slope a higher insolation and conse-quently lower moisture content were detected, closely connected to the scanty shading and insolating effects of low vegetation. Investigation of other regions in the temperate zones showed that shade tolerance as an adaptation to differ-ent levels of canopy cover decisively determines the natural
regeneration strategy of the tree species [42]. According to
this, the density of regeneration of Pinus laricio increases
strongly on the south-facing slope caused probably by a differ-ent incidence angle of radiation in the open field of south aspect compared to the north aspect. A pre-requisite for a change in microbial activity is if the chemical, physical or microclimatological properties of the soil are altered in some
way [43]. Soils on the south-facing slopein the Pinus laricio
forest ecosystem of Aspromonte, are more moist and thus subject to slow change in daily microclimate (data not shown). Soil biochemical properties are very sensitive to small changes in soil conditions, and thereby give accurate informa-tion on soil quality because the major part of organic matter and nutrient transformations in soil are microbially mediated
[44]. In our study, organic matter content showed differences
according to soil aspects.
Soil organic matter decomposition by soil microorganisms
is regulated by the synthesis of extracellular enzymes[45]. Soil
enzymes are biological catalysts of specific biochemical reac-tions, fundamental to maintain soil fertility, which in turn are
modified by a variety of factors[46]. Soil enzyme activities are
‘‘sensor’’ of soil status since they integrate information about microbial biomass and soil physico-chemical conditions. En-zymes released extracellularly by micoorganisms constitute an important part of the soil matrix as they are linked to
clay particles[46]. Factors influencing soil microbial activity exert control over soil enzyme production and nutrient
avail-ability and soil fertility[47].
Numerous studies on enzymes exist and comparisons have been made in various soils subjected to different climatic
conditions and management practices [48], but the effects
relative to landscape factors, such as soil aspects and microcli-mate, on the microbial biomass, enzyme activities and organic matter in the Mediterranean region of southern Italy have been less investigated. The trend observed in this study showed a different sensitivity of the organic matter to mineralization or humification processes between the south- and
north-facing slopes. The C to N ratio, index used to monitor the
decomposition of litter and to predict weight loss [49],
confirmed this finding. In fact, the greatest reduction of C/N ratio, along the profile, observed in the soil on the north-facing slope depends on different rates of loss of organic C and N. In addition, the lower content of C in the humic acid fraction suggests also that in this site the mineralization process is
more rapid than in the south-facing slope[50]. In the soils on
the south-facing slope, the higher content of humic carbon with respect to the amount of organic matter and the constant value of the C to N ratio along the soil profile indicated that in these sites the humification process prevailed. Changes in Table 3 – Organic matter (OM, %), total nitrogen (N, %), total organic C: total N ratio (C/N), cation exchange capacity (CEC,
cmol kgL1
), total water-soluble phenols (WSP,mg TAE gL1d.w.), humic (HC, %) and fulvic (FC, %) carbon, HC/FC ratio detected
inPinus laricioforest soils (Humic Cambisols) on the north- (N) and south-facing (S) slope aspects of Peripoli Mountain
Aspect Horizon Depth
(cm)
OM N C/N CEC WSP HC FC HC/FC
N (5–10) O 0–4 32.4a* 0.63b 30 13.9d 100b 3.90b 0.98c 3.97
Ah 4–22 4.8c 0.12d 23 11.2e 95b 1.15e 0.83d 1.39
Bw1 22–38 2.3e 0.08e 17 9.1f 72c 0.88e 0.51f 1.75
Bw2 >38 0.9f 0.05f 10 6.1g 50d 0.53f 0.32g 1.30
S (182–190) O 0–3.5 34.4a 0.87a 23 29.4a 217a 6.15a 1.97a 3.12
Ah 3.5–20 7.8b 0.25c 18 21.5b 105b 2.61c 0.87d 3.00
Bw1 20–36 9.0b 0.24c 21 19.8bc 95b 2.73c 0.62e 4.40
Bw2 >36 3.7d 0.09e 24 18.0c 80bc 1.65d 1.60b 2.75
Replicates 36 36 36 36 36 36
Factors P-value P-value P-value P-value P-value P-value
Results of ANOVA
Effects of aspect <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
Effects of depth <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
Interactions <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
*Means with the same letter are not significantly different (Tukey’s test,P0.05).
Table 4 – Microbial biomass C (MBC,mg C gL1soil), hydrolysing coefficient (Hc), acid phosphatase (AcPh,mgp-nitrophenol
gL1
hL1
), alkaline phosphatase (AlPh,mgp-nitrophenol gL1hL1), dehydrogenase (DH,mg INTF gL1soil hL1), protease (PRO,
mg tyrosine gL1dry soil 2 hL1), urease (URE,mg NH4
D
N gL1dry soil 2 hL1) activities inPinus laricioforest soils (Humic
Cambisols) on the north- (N) and south- (S) facing slope aspects of Peripoli Mountain
Aspect Horizon Depth
(cm)
MBC Hc AcPh AlPh DH PRO URE
N (5–10) O 0–4 1054.5b* 0.67c 1204b 864b 93.5b 57.3b 102.7b
Ah 4–22 69.2e 0.63c 207c 103d 21.5d 9.3d 25.2d
Bw1 22–38 53.1f 0.54d 154e 103d 8.4e 8.4d 23.7d
Bw2 >38 29.7g 0.30g 99f 98d 5.4f 2.3f 26.2d
S (182–190) O 0–3.5 3673.2a 1.10a 2936a 2771a 113.2a 126.0a 147.9a
Ah 3.5-20 266.1c 0.82b 1247b 212c 35.3c 22.2c 49.2c
Bw1 20-36 114.2d 0.39e 184d 99d 21.9d 5.0e 46.7c
Bw2 >36 75.1e 0.35f 170d 95d 17.9d 4.3e 46.5c
Replicates 36 36 36 36 36 36 36
Factors P-value P-value P-value P-value P-value P-value P-value
Results of ANOVA
Effects of aspect <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
Effects of depth <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
Interactions <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05
the concentration of water-soluble phenolic compounds between north- and south-facing slopes could be explained
not only by the variation of microbial biomass[51], but also
by the differences observed in the humication process, as wa-ter-soluble phenols are considered intermediates in the humus
formation[52]. These variations were highly related to the
amount of microbial biomass and enzyme activities. In the soil on the south-facing slope we found that the amount of MBC was threefold greater than in the soil on the north-facing
slope. According to Dick[53]and Arunachalam and Pandey[54],
who observed a close relationship between content of micro-bial biomass, soil organic matter and enzyme activities, the soil enzymes investigated in our study exhibited activities that were related to the MBC amount. The level of the dehydro-genase, enzyme with an essential role in the initial stages of ox-idation of soil organic matter and present in all microrganisms
[55], was three times higher in the soils on the south-facing
slope. The activity of the dehydrogenase serves as an indicator of microbial activity in soils of semiarid Mediterranean areas
[56], and it has been widely used to compare soils under crop
as well as natural and cultivated soils[57]. The higher value
of hydrolysing coefficient (Hc) observed in the S aspect indi-cated a much higher hydrolysing capacity and, consequently, a greater concentration of plant-available nutrients and an increase in fertility of the soil on the south-facing slope. FDA hydrolysis, like dehydrogenase activity, is regarded by some
as a reliable measure of total microbial activity[37]although,
unlike dehydrogenase, these enzymes can function outside
of the cell and form a stable complex with soil colloids[58].
We found higher levels of protease, urease and phospha-tases (alkaline and acid) in the soil on the south-facing slope.
Our data are in agreement with those of Jha et al.[59]and
Renella et al.[60], in which low hydrolase values correspond
to low values of microbial biomass. In our study, the enzy-matic activities tended to increase in the soils of the south aspect, where the MBC and the organic matter content were higher. The existence of a positive relationship between the enzymatic activity and microbial biomass suggests that a part of enzymatic activity could be endocellular as already
demonstrated by Garcia et al.[61]. However, the existence of
very stable extracellular enzymatic activity is clear, since the high content of organic matter and humic acid would also in-crease the amounts of enzyme–humus complex, which would explain the increased activity accompanying accumulation of organic matter. The capacity of soils to protect organic matter against microbial decomposition and microbial biomass against predation seems to depend also on the clay content
[62]. The higher clay content found in the soils on the
south-facing slope may be directly related to weathering agents, in particular temperature and moisture that may have increased clay amount during pedogenesis on the south aspect. Under identical organic matter input, a larger microbial biomass, more organic matter and a slower organic matter mineraliza-tion are expected in soil with a high clay content compared to soil with a low clay content. High clay content could impede mineralization of soil organic matter possibly by two mecha-nisms: (i) physically confining microorganisms in small pores, which makes them less active; (ii) protecting nonliving soil or-ganic matter from decomposition by surface adsorption and/
or entrapment in small pores of soil aggregates [63]. In
classical concepts, stable clay organic complexes are assumed to be responsible for an increased formation of stabilized
or-ganic matter in clay rich soil[64]. Tiny differences in clay are
able to cause a change in the microbial biomass, in fact by in-creasing the clay content it is possible to observe an increase in MBC per unit clay, suggesting a positive relationship be-tween MBC and clay and also a protective effect of clay.
From our results, we can infer a positive relationship be-tween the organic matter, microbial biomass, enzymes and clay contents, because, in the south aspect a higher content of clay was joined in an increase of MBC, organic matter and enzyme activities. This suggests that the higher clay content in the south-facing slope has the capacity to retain and protect the enzymes and microbial biomass, playing an important role in the turnover of organic substrate, as already reported
by Saggar et al.[65]and McLauchlan[66].
On the basis of the differences found in the examined soils on the south- and north-facing slopes, we can suggest that soil aspects significantly affected microclimate variables and clay content leading to a variation of MBC, organic matter trend and enzyme activities, factors responsible for soil fertility; thus soil aspect should also be carefully considered as a key factor to study and experiment scientifically forest ecosystem development, productivity, conservation strategies and sus-tainable management of the regional forest.
Acknowledgements
This research was supported by the University of Study ‘‘Med-iterranea’’ di Reggio Calabria. Programmi di Ricerca Scientifica (ex Quota 60%). The authors thank Ms. Aileen Cummins for re-vising the language.
r e f e r e n c e s
[1] Z.S. Chen, C.F. Hsieh, F.Y. Jiang, T.H. Hsieh, I.F. Sun, Relationship of soil properties to topography and vegetation in a subtropical rain forest in southern Taiwan, Plant Ecol. 132 (1997) 229–241.
[2] N.J. McKenzie, P.J. Ryan, Spatial prediction of soil properties using environmental correlation, Geoderma 89 (1999) 67–94. [3] S.V. Ollinger, M.L. Smith, M.E. Martin, R.A. Hallett, C.L.
Goodale, J.D. Aber, Regional variation in foliar chemistry and N cycling among forests of diverse history and composition, Ecology 83 (2002) 339–355.
[4] C.C. Tsui, Z.S. Chen, C.F. Hsieh, Relationships between soil properties and slope position in a lowland rain forest of southern Taiwan, Geoderma 123 (2004) 131–142.
[5] F. Yimer, L. Sting, A. Adelkadir, Soil property variations in relation to topographic aspect and vegetation community in the south-eastern highlands of Ethiopia, For. Ecol. Manage. 232 (2006) 90–99.
[6] G. Stotzky, Soil as an environment for microbial life, in: J.D. Van Elsas, J.T. Trevors, E.M.H. Wellington (Eds.), Modern Soil Microbiology, Marcel Dekker, New York, 1997, pp. 1–20. [7] E.D. Vance, N.M. Nadkarni, Microbial biomass and activity in
[8] G.P. Sparling, P.B.S. Hart, J.A. August, D.M. Leslie, A comparison of soil and microbial carbon, nitrogen, and phosphorus contents, and macro-aggregate stability of a soil under native forest and after clearance for pastures and plantation forest, Biol. Fert. Soils 17 (1994) 91–100. [9] A.S. Allen, W.H. Schlesinger, Nutrient limitations to soil
microbial biomass and activity in loblolly pine forests, Soil Biol. Biochem. 36 (2004) 581–589.
[10] S. Melero, J.C.R. Porrai, J.F. Herencia, E. Madejon, Chemical and biochemical properties in a silty loam soil under conventional and organic management, Soil Till. Res. 90 (2006) 162–170.
[11] Z.L. He, J. Wu, A.G. O’Donnell, J.K. Syers, Seasonal responses in microbial biomass carbon, phosphorous and sulphur in soil under pasture, Biol. Fert. Soils 24 (1997) 421–428. [12] S.J. Grayston, C.E. Prescott, Microbial communities in forest
floors under four tree species in coastal British Columbia, Soil Biol. Biochem. 37 (2005) 1157–1167.
[13] S. Kramer, D.M. Green, Acid and alkaline phosphatase dynamics and their relationship to soil microclimate in a semiarid woodland, Soil Biol. Biochem. 32 (2000) 179–188. [14] M. Carreiro, R. Sinsabaugh, D. Repert, D. Parkhurst, Microbial
enzyme shifts explain litter decay responses to stimulated nitrogen deposition, Ecology 81 (2000) 2359–2365.
[15] C. Garcia, T. Hernandez, A. Roldan, A. Martin, Effect of plant cover decline on chemical and microbiological parameters under Mediterranean climate, Soil Biol. Biochem. 34 (2002) 635–642.
[16] F. Bastida, J.L. Moreno, T. Herna´ndez, C. Garcı´a, The long-term effects of the management of a forest soil on its carbon content, microbial biomass and activity under a semi-arid climate, Appl. Soil Ecol. 37 (2007) 53–62.
[17] T. Sariyildiz, J.M. Anderson, Decomposition of sun and shade leaves from three deciduous tree species, as affected by their chemical composition, Biol. Fert. Soils 37 (2003) 137–146. [18] T. Sariyildiz, J.M. Anderson, M. Kucuk, Effects of tree species
and topography on soil chemistry, litter quality, and decomposition in Northeast Turkey, Soil Biol. Biochem. 37 (2005) 1695–1706.
[19] R.E.J. Boerner, D.C. Le Blanc, Landscape position, substrate quality, and nitrate deposition effects on forest soil nitrogen dynamics in the Hoosier National Forest, Appl. Soil Ecol. 2 (1995) 243–251.
[20] D.W. Coble, K.S. Milner, J.D. Marshall, Above- and below-ground production of trees and other vegetation on contrasting aspects in western Montana: a case study, For. Ecol. Manage. 42 (2001) 231–241.
[21] P. Nannipieri, J. Ascher, M.T. Ceccherini, L. Landi, G. Pietramellara, G. Renella, Microbial diversity and soil function, Eur. J. Soil Sci. 54 (2003) 655–670.
[22] FAO–UNESCO World Soil Map, revised legend, Rome, 1999. [23] A. Muscolo, M. Sidari, Seasonal fluctuations in soil phenolics
of a coniferous forest: effects on seed germination of different coniferous species, Plant Soil 284 (2006) 305–318. [24] C. Garcia, A. Roldan, T. Hernandez, Changes in microbial activity
after abandonment of cultivation in a semiarid Mediterranean environment, J. Environ. Qual. 26 (1997a) 285–291.
[25] G.J. Bouyoucos, Hydrometer method improved for making particle-size analyses of soils, Agron. J. 54 (1962) 464–465. [26] A. Walkley, I.A. Black, An examination of the Degtjareff
method for determining soil organic matter and a proposed modification of the chromic acid titration method, Soil Sci. 37 (1934) 29–38.
[27] J. Kjeldahl, Neue methode zurestimmung des stickstoffs in organischen ko¨rpen, Z. Anal. Chem. 22 (1883) 366–382. [28] A. Mehlich, Rapid determination of cation and anion
exchange properties and pH of soils, J. Ass. Agric. Chem. 36 (1953) 445–457.
[29] R.H. Bray, T. Kurtz, Determination of total, organic and available forms of phosphorous in soils, Soil Sci. 59 (1945) 39–45. [30] J.R. Bettany, S. Saggar, J.W.B. Stewart, Comparison of the
amount and forms of sulphur in soil organic matter fractions after 65 years of cultivation, Soil Sci. Soc. Am. J. 44 (1980) 70–75. [31] R. Kaminsky, W.H. Muller, A recommendation against the
use of alkaline soil extractions in the study of allelopathy, Plant Soil 49 (1978) 641–645.
[32] J.D. Box, Investigation of the Folin–Ciocalteau reagent for the determination of polyphenolic substances in natural waters, Water Res. 17 (1983) 511–525.
[33] A.T. Kuiters, C.A.J. Denneman, Water-soluble phenolic substances in soils under several coniferous and deciduous tree species, Soil Biol. Biochem. 19 (1987) 765–769.
[34] E.D. Vance, P.C. Brookes, D. Jenkinson, An extraction method for measuring microbial biomass carbon, Soil Biol. Biochem. 19 (1987) 703–707.
[35] W. von Mersi, F. Schinner, An improved and accurate method for determining the dehydrogenase activity of soils with iodonitrotetrazolium chloride, Biol. Fert. Soils 11 (1991) 216–220.
[36] M.A. Tabatabai, Soil enzymes, in: A.L. Page, R.H. Miller, D.R. Kneeney (Eds.), Methods of Soil Analyses, Part 2, Chemical and Microbiological Properties, American Society of Agronomy, Madison, WI, 1982, pp. 491–515.
[37] G. Adam, H. Duncan, Development of a sensitive and rapid method for the measurement of total microbial activity using fluorescein diacetate (FDA) in a range of soils, Soil Biol. Biochem. 33 (2001) 943–951.
[38] P. Perucci, Enzyme activity and microbial biomass in a field soil amended with municipal refuse, Biol. Fert. Soils 14 (1992) 54–60.
[39] P. Nannipieri, B. Ceccanti, S. Cervelli, E. Matarese, Extraction of phosphatase, urease, proteases, organic carbon, and nitrogen from soil, Soil Sci. Soc. Am. J. 44 (1980) 1011–1016. [40] E. Kandeler, H. Gerber, Short-term assay of soil urease
activity using colorimetric determination of ammonium, Biol. Fert. Soils 6 (1988) 68–72.
[41] R.R. Sokal, F.J. Rohlf, Biometry, second ed. Freeman & Co, San Francisco, 1981.
[42] N.T. Welander, B. Ottoson, The influence of shading on
growth and morphology in seedlings ofQuercus roburL. and
Fagus sylvaticaL, For. Ecol. Manage. 107 (1998) 117–126.
[43] S. Zimmermann, B. Frey, Soil respiration and microbial properties in an acid forest soil: effects of wood ash, Soil Biol. Biochem. 34 (2002) 1727–1737.
[44] M.J. Swift, O.W. Heal, J.M. Andersonm, Decomposition in Terrestrial Ecosystems, Blackwell Scientific Publications, Oxford, 1979.
[45] D.S. Allison, P.M. Vitousek, Responses of extracellular enzymes to simple and complex nutrient inputs, Soil Biol. Biochem. 37 (2005) 937–944.
[46] R.L. Sinsabaugh, Enzymatic analysis of microbial pattern and processes, Biol. Fert. Soils 17 (1994) 69–74.
[47] V. Acosta-Martinez, L. Cruz, D. Sotomayor-Ramirez, L. Pe¨rez-Alegria, Enzyme activities as affected by soil properties and land use in a tropical watershed, Appl. Soil Ecol. 35 (2007) 35–45.
[48] J. Sardans, J. Penuelas, Drought decreases soil enzyme
activity in a Mediterranean Quercus Ilex forest, Soil Biol. Biochem. 37 (2005) 455–461.
[49] B. Nicolardot, S. Recous, B. Mary, Simulation of C and N mineralization during crop residue decomposition: a simple dynamic model based on the C/N ratio of residues, Plant Soil 228 (2001) 83–103.
[50] F.J. Stevenson, Humus Chemistry Genesis, Composition, Reaction, Wiley Interscience Publication, New York, 1994. [51] Inderjit, Soil microorganisms: an important determinant of
[52] C. Gallet, F. Pellissier, Phenolic compounds in natural solutions of coniferous forest, J. Chem. Ecol. 23 (1997) 2401–2412. [53] W.A. Dick, Influence of long-term tillage and crop rotation
combinations on soil enzyme activities, Soil Sci. Soc. Am. J. 48 (1984) 569–574.
[54] A. Arunachalam, H.N. Pandey, Ecosystem restoration of jhum fallows in northeast India: microbial C and N along altitudinal and successional gradients, Restor. Ecol. 11 (2003) 168–173. [55] R.P. Dick, Soil enzyme activities as integrative indicators of
soil health, in: C.E. Pankhurst, B.M. Boube, V.V.S.R. Gupta (Eds.), Biological Indicators of Soil Health, CAB International, Wallingford, 1997, pp. 121–156.
[56] C. Garcia, T. Hernandez, F. Costa, Potential use of
dehydrogenase activity as an index of microbial activity in degraded soils, Soil. Sci. Plant Anal 1-2 (1997c) 123–134. [57] G. Masciandaro, B. Ceccanti, J.F. Gallardo-Lancho, Organic
matter properties in cultivated versus set-aside arable soils, Agric. Ecos. Environ. 67 (1998) 267–274.
[58] J. Schnu¨rer, T. Rosswall, Fluorescein diacetate hydrolysis as a measure of total microbial activity in soil and litter, Appl. Environ. Microbiol. 43 (1982) 1256–1261.
[59] D.K. Jha, G.D. Shanna, R.R. Mishra, Soil microbial population number and enzyme activities in relation to altitude and forest degradation, Soil Biol. Biochem. 24 (1992) 761–767.
[60] G. Renella, L. Landi, F. Valori, P. Nannipieri, Microbial and hydrolase activity after release of low molecular weight organic compounds by a model root surface in a clay and a sandy soil, Appl. Soil Ecol. 36 (2007) 124–129.
[61] C. Garcia, T. Hernandez, F. Costa, Microbial activity in soils under Mediterranean environmental conditions, Soil Biol. Biochem. 26 (1994) 1185–1191.
[62] C.L.S. Wiseman, W. Pu¨ttmann, Interactions between mineral phases in the preservation of soil organic matter, Geoderma 134 (2006) 109–118.
[63] W.J. Wang, R.C. Dalal, P.W. Moody, C.J. Smith, Relationships of soil respiration to microbial biomass, substrate availability and clay content, Soil Biol. Biochem. 35 (2003) 273–284.
[64] T. Mu¨ller, H. Ho¨per, Soil organic matter turnover as a function of the soil clay content: consequences for model applications, Soil Biol. Biochem. 36 (2004) 877–888.
[65] S. Saggar, A. Parshotam, C. Hedley, G. Salt,14C-labelled
glucose turnover in New Zealand soils, Soil Biol. Biochem. 31 (1999) 2025–2037.
