Full
Length Research Paper
Role
of Forest Litter on Soil Enzyme Activities
Vasantha Naik.T1[*]
and Prashanth Kumar. C.S2
1-Department
of Botany DRM Science College Davangere, Davangere University, Karnataka, India.
2-Department of Studies
and Research in Botany,
Sahyadri Science College, Shimogga, Karnataka, India.
ARTICLE DETAILS ABSTRACT
- Introduction
Vegetation plays an
important role in soil formation (Chapman and Reiss, 1992). Forest ecosystem
contributes a lot of organic matter in the form of leaves, twigs, branches,
reproductive parts, fruits etc., which after decomposition results in the
formation of organic matter and release of nutrients (Tandel
et al., 2009). Forest trees help improving soil fertility through biological
nitrogen fixation, phosphorus solubilization and decomposition of organic
matter in their Rhizosphere and non Rhizosphere zone. These processes play an important role in
plant nutrition and maintaining soil fertility (Prasad and Mertia,
2005). The fertility of soil improves under the tree cover which checks soil
erosion, adds soil organic matter, available nutrients and replenishes the
nutrients through effective recycling mechanisms (Tripathi
et al., 2009). Decomposition of leaf litter includes leaching, breakup by soil
fauna, and transformation of organic matter by micro
organisms and transfer of organic and mineral compounds. Decomposition
of plant residues is influenced by substrate quality, decomposer community and
environmental factors (Swift et al., 1979; Coleman and Crossley,
1996; Smith and Bradford, 2003). Plant tissues are the main sources of organic
matter which influences physico-chemical characteristics of soil such as pH,
WHC, texture and nutrient availability (Johnston, 1989). Physico-chemical
characteristics of forest soils vary in space and time due to variations in
topography, climate, physical weathering, processes, vegetation cover,
microbial activities and several other biotic and abiotic variables. (Shishirpoudel and Jaysah,
2003).
Various soils exhibits
enzyme activities but differ based on the respective crops and are related to
microbial biomass, therefore changes in enzymes and microbial activities could
alter the availability of nutrients for plants uptake (Dick et al., 1988 a) and
these changes are potential sensitive indicators of soil quality. The term
"soil microbial activity" implies to the overall metabolic activity
of all microorganisms inhabiting soil including bacteria, fungi, actinomycetes,
protozoa, algae and micro fauna (Nannipieri, 1990).
The microbial activity plays a vital role in soil productivity, sustainability
as it underpins a number of fundamental soil properties such as fertility and
structure. The diversity and population of soil microorganisms and the enzymes
produced will depend mainly on the chemical com- position of plant residues.
The soil enzymes are sensor for soil degradation and microbial status (Wick et
al., 1998; Aon and Colaneri, 2001; Baum et al.,
2003).
The objective of the
present investigation is to determine influence of available nutrients (litter)
on soil physico-chemical, biological properties and soil enzyme activities
which in turn represents soil quality.
- Materials
and Methods
2.1 Collection of soil
samples
Soil sample composed
with litter was collected from Thirtharameswara Reserve forest, Honnali, Davangere ,Karnataka
India. The soil sample collected from adjacent site served as control.
It was air dried and mixed thoroughly to in- crease homogeneity and shifted to
< 2mm. sieves for determination of soil texture.
2.2 Analytical methods
for physico-chemical characterization of soil samples
Mineral matter of soil
samples such as sand, silt, clay contents were analyzed with the use of
different sizes of sieves by following method of Alexander (1961). Cent percent
water holding capacity of soil samples were measured by the method of Johnson
and Ulrich (1960). Soil pH was measured in ELICO digital pH meter with Calomel
glass electrode assembly. Electrical conductivity of soil samples were
determined by the conductivity bridge quantified by the method of Chapman and
Pretty (1961). Soluble phosphorus and potassium contents were determined by the
method of Kuprevich and Shcherbakova
(1972). The microbial populations such as bacteria and fungi in both the soil
samples were enumerated by serial dilution technique.
2.3 Enzyme activities in
soils samples with/without litter
Five gm
of soil samples were transferred to test tubes. Samples were maintained at 60%
water holding capacity at room temperature in the laboratory(28±4°C).
Duplicate soil samples (with/without substrate) of test and control were
withdrawn at periodic intervals (0, 7, 14 and 21 days) to determine the cellulase, protease and dehydrogenase activity followed by
the method of Pancholy and Rice (1973), Cole (1977)
and Chandrayan et al., (1980) and Casida
et al., (1964). The soil samples were transferred to 250 ml. Erlenmeyer flasks
and 1mL of toluene was added. After 15 min, 6mL of 0.2 M acetate buffer (pH
5.9) containing 1% carboxymethyl cellulose, 1% casein
was added to the soil samples and flasks were plugged with cotton and incubated
at 30 min, at room temperature. After desired incubation, soil extracts were
passed through what man filter paper and cellulase
and protease activities in the filtrate was measured by the method of Nelson-Somogyi (1944) and Folin-Lowry
(1951) respectively. Dehydrogenase activity was determined by treating soils samples
with 0.1 g calcium carbonate and 1 ml. of 0.18 mM TTC
incubated at 30°C for 24 hours. The triphenyl formazan formed was extracted with methanol from the
reaction mixture and assayed at 485 nm in spectrophotometer (ELICO, SL 171).
- Results
and Discussion
3.1 Physico-chemical
characteristics of soil samples with/without litter
Soil fertility mediated
by microorganisms is dependent on maintenance of physico-chemical properties of
soil. Therefore the soil samples were analyzed for physico-chemical characteristics
and results were represented in Table 1. Analysis of soil samples revealed that
forest litter soil (test) underwent changes in all the measured parameters in
comparison to control.
Table 1. Physico-chemical
characteristics of soil samples with/without litter
|
Properties |
Test (litter) soil |
Control Soil |
|
Colour |
Reddish brown |
Grey |
|
Odour |
Light pungent |
Normal |
|
pH |
4.8 |
5.1 |
|
Water Holding
Capacity(mg/l of soil) |
0.33 |
0.30 |
|
Electrical
conductivity ( uMhos / cm) |
0.10 |
0.09 |
|
Sand (%) |
80.11 |
85.70 |
|
Slit (%) |
14.60 |
9.92 |
|
Clay (%) |
4.94 |
3.90 |
|
Phosphorus (kg /h ) |
9 |
2 |
|
Potassium (kg /h) |
108 |
103 |
Fig:1 Graph
shows the characteristics of soil
samples with/without litter
Soil composed with
forest waste (litter) exhibited texture different from that of corresponding
control. Soil texture in terms of percentage of sand, silt and clay were 80.11,
14.60 and 4.94 in the test; 85.70, 9.92 and 3.90 in control soils (Table 1).
The above results indicated that test sample had lower sand and higher silt and
clay content in comparison to the control. The results of the present study
seem to be in agreement with an earlier study, Oseniet
al., (2007) reported that natural forest and aged plantation soils show similar
particle size characteristics of sand, clay and silt.
Soil pH is one of the
most indicative measurements of soil because it is an important factor for the
survival of microorganisms (Evans et al., 1984). In the present study, the pH
of litter sample was de- creased to 4.8 from 5.1. This change in pH may be due
to the deposition of plant residues in the soil. Similar reports were made by Oseni et al., (2007) that pH of the natural forest soil was
acidic, as acidity was observed to increase with increase in soil depth. The pH
of soil ranged about 4.03 to 4.24 in Pinus densiflora
forest soils and 4.38 to 4.65 in Quercus mongolica
forest soils (Lee et al., 1998). An acidic pH of 5.25and 5.35 was recorded in
oak and pine oriented forests (Prashant, 2010). Water
holding capacity (WHC) and electrical conductivity (EC) of 0.33 ml/g and 0.10 µMhos/Cm was recorded in test soil where
as 0.30 ml/g and 0.09 µ Mhos/Cm was re- corded in control. This
improvement in EC and WHC in the test soil may be due to the long term
deposition of organic manure in the form of plant residues. Phosphorous and
potassium content in the test soil is 9 kg/h and 108 kg/h as against control 2
kg/h and 103 kg/h respectively (Table 1). Similar results were reported by Cavero et al., (1997), Clark et al., (1998), Poudel et al., (2002). Higher levels of total organic
carbon, total nitrogen and soluble phosphorous were found in organic soils.
High con- tent of available phosphorous (11.2 mg/kg) was observed in pine
oriented than oak oriented forest areas (6.3 mg/kg), (Prashant,
2010). Concentrations of C. N and potassium increased significantly with
increasing application rates of organic amendments (Supradip
Saha et al., 2008). Amendment of sewage sludge to the
soil improved total N and P contents (Subbaiah and Sreeramulu, 1979).
3.2 Counting of
microflora in soil samples with/ without litter
Microorganisms are
widely distributed in different types of environments like soil, water and air.
In soil these organisms play an important role in maintaining soil fertility by
recycling of nutrients through their biochemical processes. Amendment of sewage
sludge (litter) to the soil generally raises microbial activity by increasing
the soil organic matter. Be- cause of importance of soil microbial biomass in
breakdown of organic matter in soil and decomposition in soil by proteolytic fungi and bacteria, micro flora of both soil
samples were enumerated. Higher bacterial and fungal populations were observed
in the test soil than the control (Table 2). The fungal populations were
relatively higher in litter decomposed soil by nearly 3 folds than in control
soil. For instance the fungal population in the test soil was 14x10° CFU/g of
soil where as 3x10 CFU/g of soil in control (Table
2). Two folds higher bacterial population with 384x104 CFU/g in test soil was
re- corded than in control soil with 158x10 CFU/g. In-
crease in size of fungal and bacterial population ob
served in the litter soil may be attributed to deposition of organic manure
(mostly lignocellulosic wastes) and lower pH favourable for fungal organ- isms. These findings
corroborate with observation of Oseni et al., (2007).
The natural forest at 0-10Cm depth has the greatest number of both fungi and
bacteria count. Similarly, Narasimha et al., (1999)
and Nagaraj et al., (2009), reported that organic
waste released from agro-based industries improved the microbial populations.
Higher microbial activity (Mader et al., 2002) and
microbial biomass (Mader et al., 2002; Mulder et al.,
2003) were found in organic soils. The higher microbial activities in rhizosphere soil in oak oriented forest soil might be due
to increased supply of carbon and nutrients from dead root cells and rhizodeposition (Huxley, 1999; Kang et al., 2009) and less
forest floor removal (Xiao et al., 2008).
3.3 Enzyme activities in
soil samples with/without litter
1. Cellulase
activity: Soil
cellulase activity was measured by disappear
Table
2. Microbial populations in
soil samples with/ without litter.
|
Parameter |
Test
(litter) soil |
|
|
Bacteria |
384 × 10⁴ |
158× 10⁴ |
|
Fungi |
14 × 10⁴ |
3 × 10⁴ |
Microbial populations in
terms of colony forming units (CFU/g soil)of
substrates like cellulose powder, carboxymethyl
cellulose and appearance of reducing sugars quantitatively measured by
spectrophotometer (Levinson and Reese et al., 1950). Disturbance of micro flora
in soil system due to pollution such as discharge of industrial effluents or
accumulation of vegetative waste (litter) may adversely affect recycling of
nutrients. Therefore cellulase activity was measured
with or without addition of substrate (CMC) and represented in Fig. 1. Cellulase activity was enhanced in soils with/without
litter composition upon inclusion of substrate in the assay systems (Fig. 1).
The enzyme activity was measured in terms of liberation of µg of glucose from
CMC/g of soil. With increase in soil incubation period cellulase
activity was improved by one fold up to 14th day and declined at further
intervals in both soil samples. For instance, the enzyme activity in test soil
(litter) at 0 day interval was 170µg of glucose liberated/g of soil where as 630µg of glucose/g at 14th day interval and
decreased to 320µg/g. Higher levels of enzyme activity were observed in the
test soil than control at all incubations. For instance the cellulase
activity was 170µg/g in test soil were as 140µg/g in control soil at initial
day. Similar pattern was noticed at remaining intervals. A slight variation in
the cellulase activity was observed at all incubation
days in the absence of substrate (CMC) in both soils. For instance, the cellulase activity was 120µg of glucose/g of soil at 0 day where as 180 µg/ g at 14th day interval and reduced to
150µg/g in the test sample. Same trend was observed in control soil (Fig.1).
Higher cellulase activity was observed in test soil
than the control at all incubations. For in- stance the enzyme activity was
120µg/g in test against 110µg/g in control sample. Analogous trend was observed
at remaining soil incubation days. Higher cellulase
activity was observed in the litter soil in the present study could be
attributed to the presence of high organic content and microbial population.
(Table 2)
According to Joshi et
al., (1995) cellulase activity was greatly increased
in soils treated with cellulose as a substrate. Narasimha
et al., (1999) made similar observations in soils discharged with effluents of
cotton ginning industry stimulated the soil cellulase
activity. In contrast, cellulase activity was greater
in mineral fertilized soil than in organically amended soil (Supradip Saha et al., 2008).
Fig. 2 Cellulase activity in
forest litter and control soils
2 . Protease
activity
Protease
enzymes are widely distributed among the soils exhibiting a wide range of
activities and properties (Ladd and Butler, 1972). These enzymes are involved
in the initial hydrolysis of protein com- pounds of organic nitrogen to simple
amino acids. Protease can hydrolyze not only added proteins but also native
soil proteins and peptides. Soil samples with/without litter composition were
incubated with 60% water holding capacity at room temperature. After incubation
two soil samples were supplemented with/without 1% sodium caseinate
in order to determine enzyme activity in litter/control soils. Protease
activity was determined in terms of tyrosine equivalents formed in trichloro acetic acid soluble fraction during 6 hours at
30°C. Protease activity in terms of formation of tyrosine from casein remained
steady over a period of first 14 days and then onwards slightly declined in
further intervals of measurement made in the present study (Fig. 2).
At initial day the
enzyme activity was 160µg of tyrosine/g in test soil; it was increased to
420µg/gat 14th day of incubation and reduced to 160µg/g at 21st day. Similar
trend was observed in control soil. Higher protease activity was recorded in
test sample than control at all incubations. For instance at initial day the
test sample exhibited 160µg/g against 100µg/g in control soil. Same trend was
continued at the rest of incubation days. The protease activity in both soil samples
without supplementation of substrate also shows analogoustrend.
With increase in incubation days the enzyme activity increased up to 14th day
and declined at further incubation. For instance, at 0 day interval the
protease activity was 60µg/g in the test, it was in- creased to 290µg/g at 14th
day and declined to 110µg/g at 21st day of incubation. Similar trend was
observed in control soil. Increase in the protease ac- tivity
was recorded in test soil compared to control at all incubation days (Fig.2).
For instance, at initial day incubation, the casein hydrolyzing enzyme ac- tivity was 60µg/g in test soil where as
30µg/gin control soil. Identical trend was noticed at remaining days.
Increased
proteolytic activity in litter soil may be due to
availability of suitable substrates (Casein), decrease in soil pH and increased
proteolytic micro- organisms in soil. Soil protease
activity was correlated with number of micro flora as reported earlier by Narasimha et al., (1999). Similarly, soils treated with
tomato processing waste (Sarade and Joseph Richard,
1994), effluents of cotton ginning mills (Narasimha,
1997) paper mill (Chinnaiah et al., 2002), improved
soil protease activity than control. The rates of protease activity were higher
with the organic amendments than in mineral fertilizer amended and unamended soils (Supradip saha et al., 2008). In contrast, soil polluted with organic
matter (Ladd and Butler, 1969), cement dust from cement industries (Shanthi, 1993), waste water treatment plant discharge (Montuelle and Volat, 1998; Zdenek Filip et al., 2000),
herbicides (Pahwa and Bajaj, 1999), insecticides
(Omar and Abd-Alla, 2000) ceased the soil protease
activity.
Fig. 3. Protease
activity in forest litter and control soils
3 .
Dehydrogenase activity
Soil dehydrogenase
activity measured in terms of formation of formazan
from triphenyl tetrazolium
chloride was also chosen as good index of microbial activity in soil. The soil
dehydrogenase system is due to rather wide group of soil enzymes which transfer
electrons to available acceptors. Its activity appears to be more dependent on
metabolic state of microbial population of the soil rather than activity of
specific free enzymes. The dehydrogenase activ- ity was maximum at 14th day
interval and there on- wards decline in both samples with/without sub strate. For instance at 0 day incubation, the dehydrogenase
activity was 118ugof formazan /g of soil, it was
increased to 239µg/g at 14th day and later declined to 158µg/g at 21st day. The
control soil also exhibited same trend. Higher dehydrogenase activity was
recorded in test sample in comparison to control. For instance, at initial day
of incubation, the enzyme activity was 118 µg/g in test sample where as 8.05 µg/g was recorded in control. Similar trend
was followed at remaining incubation days (Fig. 3). The dehydrogenase activity
was maximum at 14th day interval in the absence of
substrate in both the soil samples. For instance, the enzyme activity was noted
as 5.3µg/g at 0 day 2.68µg/g control soil. Soil samples with litter always in
the test soil against recorded significantly higher dehydrogenase activ- ity than control soil
samples. But no regular pattern of increments in dehydrogenase activity in test
sample over control soil was observed. Similarly, addition of organic
materials, composts and low metal sludges has been
found to increase soil dehydrogenase activity (Chander
and Brookes, 1991 b; Giusquiani et al., 1994). The
enzyme activity was higher in the rhizosphere soils
than in non-rhizosphere sludge amended soils.
However, the addition of sludges or composts at the
higher rates re- versed this effect causing a decrease in dehydrogenase
activity (Reddy et al., 1987). Dehydrogenase enzyme is high in soils polluted
with pulp and pa- per mill effluents (McCarthy et
al., 1994) but low in soils polluted with flyash (Pitchel and Hayes, 1990). Moreno et al., (1999) and Masciandaro et al., (2000) studied dehydrogenase activity
under the influence of organic matter and reported an increase following the
organic matter amendement. Amendment of sesbania straw to the soil improved dehydrogenase activity
than wheat straw, maize straw amended soils and unamended
soil (Sajjad et al., 2002). The dehydrogenase
activity had ranges of 170.67 to 221.66 µg TPF/g in pinus
densiflora and Quercus mongolica
forest soils that showed lower values than in Kawngneung
site (Lee et al., 1998). Higher dehydrogenase activity of 106.28 nmol/g/2hr was recorded in oak oriented forest area where
as less (66.37 nmol/g/2hr) in pine oriented forest area(prashant, 2010).
Soils discharged with
effluent waste water from pulp and paper mills exhibited relatively higher
dehydrogenase activity than soil without corresponding irrigation (Kannan and Oblisami, 1990).
Increase in soil dehydrogenase activity was attributed to low pH and high
organic content in the effluents. Reddy and Faza
(1989) compared dehydrogenase activity in soil amended with/without industrial
sludge. The activity was more in soils with- out sludge than in soils amended
with sludge.
- Conclusion
Vegetation plays an
important role in soil formation (Chapman and Reiss, 1992). Forest ecosystem
contributes allot of organic matter in
the form of leaves, twigs, branches, reproductive parts, fruits etc., which
after decomposition results in the formation of organic matter and release of
nutrients (Tandel et al., 2009). Forest trees
help improving soil fertility through biological nitrogen fixation, phosphorus
solubilization and decomposition of organic matter in their rhizosphere
and non rhizosphere zone. These processes play an
important role in plant nutrition and maintaining soil fertility (Prasad and Mertia, 2005). Various soils exhibits enzyme activities but
differ based on the respective crops and are related to microbial biomass,
therefore changes in enzymes and microbial activities could alter the
availability of nutrients for plants uptake (Dick et al., 1988 a) and
these changes are potential sensitive indicators of soil quality.
- Acknowledgement
The author is grateful
to the Principal DRM Science College Davangere for
providing information.
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