Dynamics of humus forms and soil characteristics along a forest altitudinal gradient in Hyrcanian forest - SISEF ...
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iForest Research Article
doi: 10.3832/ifor3444-013
vol. 14, pp. 26-33
Biogeosciences and Forestry
Dynamics of humus forms and soil characteristics along a forest
altitudinal gradient in Hyrcanian forest
Mohammad Bayranvand (1), Humus forms are good indicators of environmental conditions and thus impor-
tant in forest ecological processes. Altitudinal gradients are considered as nat-
Moslem Akbarinia (1), ural laboratory for evaluating soil ecological processes and humus form distri-
Gholamreza Salehi Jouzani (2), bution. The objective of this study was to evaluate the macromorphology of
Javad Gharechahi (3), humus forms along an altitudinal gradient (0-2000 m a.s.l.) covered with plain
Giorgio Alberti (4) forest, mixed and pure forests and forest-grassland ecotone, in Alborz Moun-
tains in northern Iran. In total, 225 humus profiles were evaluated. Forest
stand variables including tree density, basal area, crown density, and height,
forest floor and soil physico-chemical properties along with biological features
were measured. We found that altitudinal gradients influence both humus
forms distribution and soil properties but with different mechanisms. While
soil properties (i.e., temperature, pH, CaCO3, soil N content, soil C/N and mi-
crobial biomass N) were significantly correlated with altitude, the forest floor
properties were more influenced by tree species composition. Particularly, the
abundance of Mull was decreased in plain mixed forests compared to mountain
pure forests, whereas the frequency of Amphi was increased. Moreover, Oligo-
mull and Leptoamphi were abundant in mixed beech forests, while Eumacro-
amphi, Eumesoamphi and Pachyamphi were only observed in pure beech for-
ests. Such a distribution influenced soil fertility where higher values of nitro-
gen (N), microbial biomass nitrogen (MBN) and pH were observed at lower alti-
tudes under mixed forests compared to pure forests at higher altitudes.
Keywords: Altitude Gradient, Plant-humus-soil Relationships, Humus Systems,
Soil Microbial Biomass
Introduction soil fertility (Salmon 2018). of different humus forms. On the other
Forest humus is an indicator of the exist- The current classification systems en- hand, altitude through changes in tempera-
ing environmental conditions (Ponge 2013), abled to distinguish five humus systems ture and precipitation, affects the distribu-
because it is the result of complex interac- and sixteen humus forms in terrestrial eco- tion of forest species, forest floor quality
tions between stand species composition systems (Jabiol et al. 2013, Zanella et al. and quantity (Bayranvand et al. 2017b), soil
(Labaz et al. 2014), soil properties (Ponge 2018). Humus forms can be directly identi- characteristics (Ponge et al. 2011), micro-
et al. 2011), soil micro- and macro-organ- fied in field without the need for expensive organism types and activities (Zhang et al.
isms’ activities and environmental factors laboratory tools (Zanella et al. 2018). 2013, Xu et al. 2015), thus contributing in
(Badía-Villas & Girona-García 2018). Since According to Zanella et al. (2011), temper- humus forms (Ascher et al. 2012, Salmon
humus forms show specific morphological ature, precipitation and vegetation compo- 2018). Altitudinal gradients are considered
patterns (layering and structure – Jabiol et sition are the three most important factors as natural laboratories for evaluating soil
al. 2013), they are useful tool for assessing affecting biological degradation of organic ecological processes (Labaz et al. 2014, Bo-
the health status of forests and the overall residues and contributing in the formation jko & Kabala 2017). Understanding the
complex interactions between soil and
plant communities along altitude gradients
(1) Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, 46417- can be used for the prediction of soil micro-
76489, Noor, Mazandaran (Iran); (2) Microbial Biotechnology Department, Agricultural bial activity and forest floor decomposition
Biotechnology Research Institute of Iran (ABRII), Agricultural Research, Education and Exten- (Bojko & Kabala 2017, Xu et al. 2015).
sion Organization (AREEO), Fahmideh Blvd., P.O. Box:31535-1897, Karaj (Iran); (3) Human The natural broadleaf forests in northern
Genetics Research Center, Baqiyatallah University of Medical Sciences, Tehran (Iran); (4) De- Iran are similar to those in central Europe,
partment of Agri-food, Environmental and Animal Sciences, University of Udine, v. delle northern Turkey and the Caucasus. In these
Scienze 206, 33100 Udine (Italy) forest ecosystems, composition of tree
species changes with elevation (Bayran-
@ Gholamreza Salehi Jouzani (gsalehi@abrii.ac.ir) vand et al. 2017a). Due to their unique
topographical conditions compared to the
Received: Apr 09, 2020 - Accepted: Nov 02, 2020 oldest forest in Asia, Alborz mountains of-
fers the potential to assess changes in for-
Citation: Bayranvand M, Akbarinia M, Salehi Jouzani G, Gharechahi J, Alberti G (2021). est types and humus forms with altitude
Dynamics of humus forms and soil characteristics along a forest altitudinal gradient in (Naqinezhad et al. 2013). So far, few stud-
Hyrcanian forest. iForest 14: 26-33. – doi: 10.3832/ifor3444-013 [online 2021-01-10] ies investigated the pattern of humus
forms, forest floor features and soil micro-
Communicated by: Maurizio Ventura bial biomass along altitudinal gradients
(Bayranvand et al. 2017b, Waez-Mousavi
© SISEF https://iforest.sisef.org/ 26 iForest 14: 26-33
Bayranvand M et al. - iForest 14: 26-33
2018). m a.s.l.): Beech (Fagus orientalis Lipsky), Jurassic and lower Cretaceous period (Kha-
iForest – Biogeosciences and Forestry
In this study, we described humus mor- Ash (Fraxinus excelsior L.), Parrotia persica leghi et al. 1997, IUSS Working Group 2015).
phology, forest floor, soil quality, microbial C. A. Meyer, Acer (Acer velutinum Boiss)
biomass carbon (MBC) and nitrogen (MBN) and Carpinus betulus; (3) middle mountain- Experimental design, tree investigation,
in five different forest types along an altitu- ous mixed forests (MMMF – 1000 m a.s.l.): humus identification, forest floor and
dinal gradient from 0 to 2000 m a.s.l. (i.e., Beech (Fagus orientalis Lipsky), Ash (Fraxi- soil sampling
plain forest, low, medium and high moun- nus excelsior L.), Parrotia persica C. A. At each altitude (0, 500, 1000, 1500 and
tainous mixed and pure forests, and forest- Meyer, Acer (Acer velutinum Boiss) and 2000 m a.s.l.), three 1-ha plots with at least
grassland ecotone). We hypothesized that: Carpinus betulus; (4) high mountainous 1500 m distance were delimited. Elevation
(1) increased beech species abundance and pure forests (HMPF – 1500 m a.s.l.): Fagus at each plot was recorded using a Garmin™
decreased soil temperature along altitudi- orientalis Lipsky; (6) forest-grassland eco- model GPSMAP® 60Cx (Olathe, KS, USA).
nal gradient strongly affect the pattern of tone (F-GE – 2000 m a.s.l.): Hawthorn (Cra- Aspect values were assigned using angles
humus forms and organic layer thickness; taegus sp.), Pear (Pyrus communis L.), Ap- from 0 to 360° given by a pocket compass.
(2) forest floor and soil characteristics ple (Malus communis L.), Barberry (Berberis In each plot, three random subplots (400
change with altitude and soil fertility; (3) crataegina), Maple-AC (Acer campestre L.). m2) were chosen for sampling. All living
specific soil chemical and biological fea- The mean annual temperature at PMF, trees were counted at each subplot. The di-
tures correlate with humus forms and veg- LMMF, MMMF, HMPF and F-GE are 19.2, ameter at breast-height (DBH, 1.3 m) and
etation characteristics. 16.3, 14, 11.6, and 8 °C, respectively. For ev- total height (> 1.3 m) of all living trees were
ery 1000 m increase in altitude, an average measured with a diameter tape and Im-
Material and methods 3-5 °C decrease in temperature has been pulse® 200 Laser Hypsometer (Laser Tech-
recorded. The mean annual precipitations nology Inc., Centennial, CO, USA), respec-
Site description are 898, 843, 805, 746 and 844 mm in PMF, tively (Tab. 1).
With an area of about 14,000 hectares, LMMF, MMMF, HMPF and F-GE, respec- The experiment was conducted during
the Vaz catchment forests are located in tively (Karger et al. 2017). About 35-45% of April 2018. Humus profiles (Organic: OL,
the northern Alborz mountain, beside the the rainfall occurs in autumn (from Sep- OF, OH; and organic-mineral: AH) and diag-
Caspian Sea, in northern Iran (36° 16′ N, 52° tember to November), 18-35% in winter nostic horizons were described and sam-
48′ E – Fig. S1 in Supplementary material). (December to February), and the rest (10- pled at the corners and at the center of
The study area was located along an alti- 20%) in summer (June to August; Noushahr each sub-plot using a metal frame (30×30
tude gradient 0-2000 m a.s.l. Forest vege- city meteorological station, 1977-2010 – Fig. cm). The morphological characteristics of
tation in this area largely depends on alti- S2 in Supplementary material). Based on each humus profile were described accord-
tude and therefore five different forest World Reference Basis (WRB) and USDA ing to Zanella et al. (2018). The basilar ele-
types could be distinguished (Khaleghi et Soil Taxonomies, plain forest soils were ments of the adopted humus classifications
al. 1997): (1) plain mixed forests (PMF – 0 m classified as Cambisols (Inceptisol), low are reported in Tab. S1 (Supplementary ma-
a.s.l.): Ironwood (Parrotia persica C.A. Mey- and medium altitudes as Luvisols (Alfisols), terial). Humus layer thickness (HLT) was
er), Oak (Quercus castaneifolia C. A. M.) and and higher altitudes as Phaeozems (Mol- also measured with a tape from the forest
Hornbeam (Carpinus betulus L.); (2) low lisols) and Cambisols, developed on dolo- floor surface to the top of the mineral soil.
mountainous mixed forests (LMMF – 500 mite limestones belonging to the upper The earthworm ecological groups (i.e., Epi-
Tab. 1 - Mean ± standard error (n=9) and Pearson’s correlation coefficients (R cor) of vegetation characteristics along the altitudinal
gradient in Hyrcanian forests. (PMF): plain mixed forests; (LMMF): low mountainous mixed forests; (MMMF): middle mountainous
mixed forests; (HMPF): high mountainous pure forests; (F-GE): forest-grassland ecotone. Different letters indicate significant differ-
ences (p
Humus and soil dynamics along a forest altitudinal gradient
geic, Anecic and Endogeic) were also iden-
iForest – Biogeosciences and Forestry
Tab. 2 - Correlation of vegetation, humus forms and soil features with PCA compo-
tified (Bohlen 2002). Forest floor samples
nents. (*): p < 0.05; (**): p < 0.01.
including OL and OF layers were finely
mixed before sampling. To remove soil, the
forest floor samples were soaked gently in Features PC1 PC2 Features PC1 PC2
tap water for a few seconds (this is not rec- Tree density -0.56 ** 0.25 Eumacroamphi -0.33 -0.20
ommended for samples dominated by OH Tree basal area 0.39 * -0.40 Eumesoamphi -0.35 * -0.37 *
layers) and then dried at 70 °C for 48 h.
Tree crown density 0.60 ** -0.67 ** Pachyamphi -0.38 * -0.25
Dried forest floor samples were finely
grounded/homogenized with an electric Mean tree height 0.34 * -0.76 ** FFC -0.32 -0.50 **
mixer and analyzed. OL -0.65 ** -0.63 ** FFN 0.16 0.07
Top mineral soil samples (depth 0-10 cm) OF -0.75 ** -0.32 FFC/N -0.24 -0.23
were collected after removal of the or-
ganic layers. Using a standard soil auger (5 OH -0.67 ** -0.50 ** SM -0.35 * -0.26
cm inner diameter). Soil temperature (ST) AH 0.57 ** -0.43 * ST 0.89 ** -0.25
was measured at a depth 0-10 cm with a Eumull 0.33 0.04 pH 0.23 -0.61**
portable temperature probe (model TA-
Mesomull 0.25 0.03 CaCO3 0.20 -0.32
288). Since no rainfall occurred during the
sampling time, temperature was quite con- Oligomull 0.54 ** -0.09 SOC -0.42 * -0.75 **
stant during the day. Rhizo Mesomull -0.12 0.25 SN 0.24 -0.55 **
To determine microbial biomass, the soil Rhizo Oligomull -0.24 0.54 ** SC/N -0.63 ** -0.23
samples were immediately transferred to
sterile bags, placed in a cooled and insu- Rhizo Dysmull -0.24 0.54 ** MBC -0.004 -0.47 **
lated container, transferred to the labora- Leptoamphi -0.04 -0.22 MBN 0.70 ** -0.02
tory and stored at 4 °C. Soil samples used
for physico-chemical analyses were air-
dried and passed through a 2-mm sieve. In meter (ThermoFischer Scientific, Waltham, and biological properties along the altitudi-
total, 225 samples were analyzed in this MS, USA). Calcium carbonate (CaCO3) con- nal gradient. Means were compared using
study (5 altitude levels × 3 plots × 3 sub- tent was determined by the neutralization Tukey HSD post-hoc test. Abundance of hu-
plots × 5 profiles). The soils and forest titration method. Soil organic carbon (SOC) mus systems and forms in relation to the
floors collected from five elevation level and soil nitrogen (SN) contents were de- altitudinal gradient was tested by Fisher’s
were mixed and the mean of the humus termined based on the modified Walkley- exact test. Pearson’s correlation analyses
layers and percentage of humus form were Black (Allison 1965) and semi Micro-Kjel- were performed to correlate the vegeta-
used to compute humus layer thickness dahl methods (Bremner & Mulvaney 1982), tion variables and forest floor and soil char-
and humus form classification, respective- respectively. The microbial biomass carbon acteristics across the altitudinal gradient.
ly. (MBC) and microbial biomass nitrogen For non-normally distributed data, the
(MBN) were assessed through the fumiga- Spearman’s correlation analysis was per-
Laboratory analysis of forest floor and tion-extraction method with a conversion formed. All statistical analyses were con-
soil physico-chemical and biological factor of 0.45 for microbial C and 0.54 for ducted using SPSS® v. 16 (IBM Corp., Ar-
properties microbial N (Brookes et al. 1985, Sparling et monk, NY, USA). Multivariate correlations
Forest floor carbon (FFC) and nitrogen al. 1998). were analyzed using factor analysis based
(FFN) contents were determined through on principal components analyses (PCA)
dry combustion and semi micro-Kjeldahl Statistical analysis performed by the software PC-Ord v. 5.0
techniques, respectively (Bremner & Mul- The normality of data was checked by the (McCune & Mefford 1999).
vaney 1982). Soil texture was determined Kolmogorov Smirnov test (P >0.05), and
using the Bouyoucos hydrometer method the homogeneity of variances was tested Results
(Bouyoucos 1962). Soil moisture (SM) was using the Levene’s test (P >0.05). One-way PCA revealed significant changes in all
measured after drying the soil samples in analysis of variance (ANOVA) was per- studied soil and humus characteristics
an oven at 105 °C for 24 h. Soil pH was mea- formed to analyze differences in vegeta- along the altitudinal gradient (Tab. 2, Fig.
sured in a ratio of 1:2.5 (M/V) of soil/water tion properties, humus layer thickness 1A-B), with greater than 45 percent of vari-
using an Orion™ Analyzer Model 901 pH (HLT), forest floor, soil physical, chemical ations being explained. The left side of the
Fig. 1 - Principle compo-
nent analysis (PCA)
based on the correlation
matrix to identify the
relationships between
forest types, humus
forms, forest floor and
soil properties (A-B).
(PMF): plain mixed
forests; (LMMF): low
mountainous mixed
forests; (MMMF): middle
mountainous mixed
forests; (HMPF): high
mountainous pure
forests; (F-GE): forest-
grassland ecotone.
iForest 14: 26-33 28
Bayranvand M et al. - iForest 14: 26-33
tionship with leptoamphi humus and MBC
iForest – Biogeosciences and Forestry
Fig. 2 - Abun- (Fig. 1B). In addition, the forest-grassland
dance of humus ecotone with Rhizo-Mull humus forms did
systems (A) and not show any relationship with soil proper-
forms (B) in rela- ties (Fig. 1B).
tion to altitudi- As expected, canopy composition, stand
nal gradients features, humus forms and their character-
(n=45). istics changed with altitude (Tab. 1, Tab. 2).
In the plain forest, ironwood was the domi-
nant species followed by oak and horn-
beam. However, ironwood density de-
creased with altitude and this species was
totally absent at altitudes above 1500 m
a.s.l. At intermediate altitudes (500 and
1000 m), beech, ash and maple were the
dominant species, while at higher altitude
(1500 m) only beech was present. Above
2000 m a.s.l., hawthorn was the most com-
mon species. Total tree density significantly
increased with altitude (R = 0.54, p < 0.01),
while basal area (R = -0.39, p < 0.01), crown
density (R = -0.79, p < 0.01) and mean tree
height (R = -0.52, p < 0.01) decreased.
Altitudinal gradient significantly affected
the abundance of the humus systems (p <
0.001) and humus forms (p < 0.001 – Fig.
2A). Mull was the dominant system below
1000 m a.s.l.; Amphi appeared at 1000 m
and dominated at 1500 m; Rhizo Mull was
dominant under F-GE at 2000 m a.s.l. Oligo-
mull was the most common form at 0 and
PC axis 1 reflects low quality of forest floor height), improved forest floor (i.e., N) and 1000 m and Eumull at 500 m (Fig. 2B). At
(i.e., high FFC, FFC/N and thickness), and soil characteristics (N content, MBN, pH higher altitudes, no dominant humus form
soil (i.e., higher values of SOC and C/N) and CaCO3). In these conditions, the fre- was detected. In fact, Eumacro, Eumeso
which resulted in the formation of Amphi quency of the mull humus forms was and Pachyamphi humus forms were equal-
humus forms under high mountainous higher (plain mixed and low mountainous ly represented at 1500 m, while at 2000 m
pure forests (Fig. 1B). The right side of PC mixed forests – Fig. 1B). Middle mountain- Rhizo Mesomull, Rhizo Oligomull and Rhizo
axis 1, instead, corresponds to conditions ous mixed forests showed intermediate Dysmull were equally abundant (Fig. 2B).
with higher forest productivity (tree basal conditions with regard to the forest floor The thickness of the organic layers includ-
area, tree crown density and mean tree and soil properties and thus a strong rela- ing OL, OF, OH significantly increased with
altitude (R = 0.36, p < 0.05; R = 0.53, p <
0.01; R = 0.36, p < 0.05; respectively),
Tab. 3 - One-way analysis of variance (ANOVA) and Pearson’s correlation coefficients whereas the organic-mineral thickness
(Rcor) of forest floor and soil characteristics along the altitudinal gradients. (*): p < (AH) decreased (R = -0.62, p < 0.01 – Tab. 3,
0.05; (**): p < 0.01. Fig. 3). The thickness of OL and OF at 1500
m was approximately 2.5 times greater
Humus and than that at the other altitudes (p < 0.001);
Variables Abbr. F test P value Rcor
soil properties the highest thickness of OH was recorded
Organic litter (cm) OL 81.86
Humus and soil dynamics along a forest altitudinal gradient
est was recorded in high mountainous pure
iForest – Biogeosciences and Forestry
Fig. 3 - Organic
forests (Fig. 5A, Tab. 3). On the contrary,
(OL, OF and OH)
soil pH (R= -0.51, p < 0.01), calcium carbon-
and organic-min-
ate (R = -0.45, p < 0.01), soil N (R = -0.39, p
eral (AH) humus
< 0.01) and microbial biomass nitrogen (R =
layers thickness
-0.70, p < 0.01) decreased with altitude,
along the altitu-
while soil C/N ratio increased (R = 0.53, p <
dinal gradient.
0.01). The highest soil pH and CaCO 3 con-
Error bars indi-
centration were observed in plain mixed
cate standard
forests and high mountainous pure forests
error (n = 45).
and the lowest in forest-grassland ecotone
(Fig. 5B). The highest concentrations of soil
C, C/N ratios and BMC values were mea-
sured under high and middle mountainous
forests, whereas plain mixed forests
showed the highest soil N concentrations
and BMN values (Fig. 6).
Discussion
We showed that there exist significant as-
sociations between altitudinal gradient and
forest characteristics including tree compo- published (Naqinezhad et al. 2013, Bayran- creased with altitude, while Amphi forms
sition, stem density, tree height in Hyrca- vand et al. 2018). The distribution of humus increased. With respect to the forest type,
nian forest in northern Iran, consistently forms also changed with altitudinal gradi- our results showed that Oligomull and Lep-
with findings of other studies previously ent. Particularly, Mull humus forms de- toamphi were dominant in mixed beech
Fig. 4 - Mean floor carbon (A), nitrogen (B), and C/N ratio (C) among the altitude levels. Different letters indicate significant differ -
ences (p < 0.05) according to the ANOVA and Tukey HSD test. Error bars indicate standard error (n=9). (PMF): plain mixed forests;
(LMMF): low mountainous mixed forests; (MMMF): middle mountainous mixed forests; (HMPF): high mountainous pure forests;
(F-GE): forest-grassland ecotone.
Fig. 5 - Mean soil mois-
ture and soil tempera-
ture (A), pH and CaCO3
(B) among the altitudes.
Different letters indicate
significant differences (p
< 0.05) based on ANOVA
and Tukey HSD test.
Error bars indicate stan-
dard error (n=9). (PMF):
plain mixed forests;
(LMMF): low mountain-
ous mixed forests;
(MMMF): middle moun-
tainous mixed forests;
(HMPF): high mountain-
ous pure forests; (F-GE):
forest-grassland eco-
tone.
iForest 14: 26-33 30
Bayranvand M et al. - iForest 14: 26-33
iForest – Biogeosciences and Forestry
Fig. 6 - Mean soil carbon
(A), nitrogen (B), C/N ratio
(C), BMC (D) and BMN (E)
along the altitude gradient.
Different letters indicate
significant differences (P <
0.05) according to the
ANOVA and Tukey HSD
test. Error bars indicate
standard error (n=9).
(PMF): plain mixed forests;
(LMMF): low mountainous
mixed forests; (MMMF):
middle mountainous mixed
forests; (HMPF): high
mountainous pure forests;
(F-GE): forest-grassland
ecotone.
forests, while in pure beech forests Eu- Amphi humus form under pure beech for- C, and N content), earthworm and micro-
macroamphi, Eumesoamphi and Pachyam- est (1500 m) could likely be due to high soil bial activity were mostly controlled by cli-
phi were the dominant forms. Previous pH (> 7.5) resulted from high CaCO 3concen- mate. Our results support the idea that soil
study by Waez-Mousavi (2018) also re- trations (Li et al. 2018). The CaCO3 concen- properties including temperature, pH,
ported that Mull and Amphi are the most tration has probably a positive impact on CaCO3, soil N content, soil C/N and micro-
dominant humus systems in the Hyrcanian the forest floor decomposition rate and bial biomass N are significantly correlated
forests. In mixed beech stands, Waez-Mou- soil microbial activity (Guo et al. 2019) and with altitude, while most forest floor prop-
savi & Habashi (2012) reported the domi- could likely facilitate the transition from erties are not directly influenced by tem-
nance of Mull and Amphi humus systems. Moder to Amphi form (Labaz et al. 2014, perature, but affected by tree species com-
Both environmental conditions and tree Bonifacio et al. 2018). position. In fact, litter quality influences
species composition influence humus for- Previous studies showed that climatic both decomposition rates and the dynamic
mation and its characteristics. A significant (moisture and temperature) and biotic fac- of nutrient mineralization (Lucas-Borja et
change in soil temperature, moisture and tors (species type and richness) are impor- al. 2019). Previous studies have argued that
species composition was noted in our alti- tant factors influencing humus accumula- higher forest floor N concentrations are as-
tudinal gradient. Previous study revealed tion (Zanella et al. 2011, Labaz et al. 2014, sociated with faster litter decomposition
that a decrease in mean temperature asso- Badía-Villas & Girona-García 2018). In our rates (Kooch & Bayranvand 2017, Lucas-
ciates with a decline in Mull humus form study, the thickness of OL, OF, OH layers Borja et al. 2019). A decrease in forest floor
and an increase in Amphi humus (Ponge et significantly were increased, while that of quality (high C content and high C/N ratio)
al. 2011). In agreement to our finding in AH was decreased. The more favorable was reported to associate with a higher hu-
plain mixed forest, Ponge et al. (2011) conditions for organic matter decomposi- mus layer thickness and a decreased de-
noted that Mull systems are more frequent tion in plain mixed forests (i.e., high tem- composition rate in beech dominated for-
at higher tree species diversity and under perature, good soil moisture and high litter ests at high altitudes (Bayranvand et al.
rich trophic conditions. In contrary, under quality) is likely the cause (Salmon 2018). 2017b). In fact, beech litter is known for
low tree species richness and in colder en- Similarly, Bonifacio et al. (2018) also having a high lignin/N ratio and a relatively
vironments, Moder and Amphi humus sys- showed that the OH layer thickness in low contents of basic cations and N (Boni-
tems with OF and OH layers are dominant beech forests with a low litter quality is facio et al. 2018). In agreement with our
(Badía-Villas & Girona-García 2018). Labaz higher than in hornbeam, maple and ash findings, low humus layer thickness is re-
et al. (2014) showed that Amphi humus forests (Labaz et al. 2014). Thus, the higher lated to high quality floors in maple, iron-
forms can be found in cold conditions OH layer thickness at 1500 m a.s.l. found in wood, alder and hornbeam (Kooch & Bay-
where organic matter decomposition is this study can be attributed to the low ranvand 2017, Bayranvand et al. 2017b).
slower. Previous study by Waez-Mousavi & temperature in this elevation level, which Forest floor C/N ratio and N content are
Habashi (2012) indicated that Mull humus slow down mineralization rates (Badía-Vil- the two most important factors influencing
forms are abundant under forest types las & Girona-García 2018), decrease litter litter decomposition and nutrient release
with higher floor quality and decomposi- quality under beech (Bayranvand et al. (Lucas-Borja et al. 2019).
tion rate, while Amphi and Moder humus 2017a) and higher soil moisture (Zanella et Badía-Villas & Girona-García (2018) re-
forms are observed under beech forest al. 2011). ported that forest floor N in mountain for-
type with low floor quality (high C and low The chemical composition of humus and est in Spain is decreased during shift from
N – Bayranvand et al. 2017a). Mull humus soil are the result of the interaction of Mull to Amphi forms with increasing eleva-
forms are biologically active (Endogeic and many factors including topography, cli- tion. Ponge et al. (2011) measured lower C
Anecic with high activity) with fine-granular mate, tree cover and soil microbial commu- content in Mull than in other humus forms.
structure, which have low SOC content nities (Ponge et al. 2011). Shedayi et al. It could be speculated that Mull forms de-
compared to humus forms with OF and OH (2016) showed that altitude has a low im- compose faster and introduce more N into
layers (Jabiol et al. 2013, Labaz et al. 2014). pact on soil organic carbon and nitrogen, the soil. Zanella et al. (2011) argued that
Moder forms are abundant in beech domi- while vegetation cover explains most of forest floor and soil C/N ratios in Mull are
nated forest with low soil pH (≈ 5.5), while the measured variations. Bayranvand et al. usually lower than in Amphi and the C/N is
Mull forms are absent in non-beech stands (2017a) reported that, although tree spe- an important indicator for the decomposi-
(Bayranvand et al. 2018). The increased cies affect soil chemical properties (i.e., pH, tion rate and nutrient cycling in the humus
31 iForest 14: 26-33Humus and soil dynamics along a forest altitudinal gradient
and soil. Forest floor nitrogen; FFC/N: Forest floor C/ 035
iForest – Biogeosciences and Forestry
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levels (i.e., HMPF). This may be the result Author contributions Bojko O, Kabala C (2017). Organic carbon pools
of a greater and a more diverse litter input MB and MA conceived and designed the in mountain soils - Sources of variability and
in stands with a higher species richness or experiment. MB performed the experi- predicted changes in relation to climate and
diversity (Wang & Wang 2011). Many inves- ment. MB, GA and GS-J carried out the sta- land use changes. Catena 149: 209-220. - doi:
tigations have also documented that soil tistical analysis. MB, JG, GA and GS-J con- 10.1016/j.catena.2016.09.022
microbial community structure is primarily tributed to the data analysis and data inter- Bonifacio E, D’Amico M, Catoni M, Stanchi S
driven by soil pH and C/N ratio as the alti- pretation. MB, JG, GS-J and GA wrote and (2018). Humus forms as a synthetic parameter
tude increases. Thus, higher levels of pH, edited the manuscript. for ecological investigations. Some examples in
such as those at low elevations, may be re- the Ligurian Alps (North-Western Italy). Applied
lated to increased microbial biomass and Acknowledgements Soil Ecology 123: 568-571. - doi: 10.1016/j.apsoil.
bacterial diversity (Xu et al. 2015). Higher This research was funded by a grant pro- 2017.04.008
levels of soil temperature and N content, vided by Tarbiat Modares University (TMU) Bouyoucos GJ (1962). Hydrometer method im-
such as those at low elevations, may con- and Iran National Science Foundation proved for making particle size analysis of soils.
tribute to a larger microbial biomass (Xu et (INSF). We would like to thank Mr. J. Es- Agronomy Journal 56: 464-465. - doi: 10.2134/ag
al. 2015, Bojko & Kabala 2017, Guo et al. lamdoust, A. Khodadust, MR Soleimani, E. ronj1962.00021962005400050028x
2019). Sharifi, M. Mohammadi, and A. Daryaei for Bremner JM, Mulvaney CS (1982). Nitrogen-to-
Beech litter quality, FFC accumulation and their assistance during field samplings. We tal. In: “Methods of Soil Analysis, Part 2 (2 nd
lower earthworm activity are main factors also thank M. Naeiji and M. Haghdoust for edn)” (Page AL, Miller RH, Keeney RR eds).
affecting soil quality in this forest system. their assistance during laboratory analysis American Society of Agronomy, Madison WI,
PMF was correlated with Mull humus and of the soil samples. The authors also ex- USA, pp. 595-624.
higher forest floor and soil quality (high press their sincere appreciation to Augusto Brookes PC, Landman A, Pruden G, Jenkinson DS
FFN and SN; low FFC and SN). In this condi- Zanella for helping with morphological (1985). Chloroform fumigation and the release
tion, tree species composition along with identification of humus forms and Björn of soil N: a rapid direct extraction method to
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