Soil enzyme activities in dependence on tree litter and season of a social forest, Burdwan, India

Soil enzyme activities in dependence on tree litter and season ofa social forest, Burdwan, India

Chittaranjan Das, Papia Aditya, Jayanta Kumar Datta and Naba Kumar Mondal*

Department of Environmental Science, The University of Burdwan, Rajbati, Burdwan, India

(Received 9 October 2012; final version received 16 March 2013)

The study was done to evaluate enzyme activities (amylase, cellulase and invertase)from the soils of different vegetation sites, with seasonal variation, of social forest,Burdwan, India. Study results showed significant lower enzymatic activities in thesubsoil compared to those of the topsoil. The seasonal variations indicated thatamylase, cellulase and invertase enzyme activities had reached peaks during therainy seasons in different soil depths. Amylase activity was highest in Tectona littercontaining soil in all seasons in both the soil layers. All the three enzyme activitieshave shown significant positive correlation with available nitrogen (p < 0.05) andavailable phosphorous (p < 0.05) during rainy season in both the soil depths.Correlation study revealed that soil organic carbon was positively correlated withcellulase and invertase activities except in the Anacardium vegetation site in the topsoilduring rainy season. Irrespective of the seasons and the depths of soil, control sitewithout vegetation showed much lower levels of organic carbon and enzyme activitycompared to those of the experimental sites. Therefore, it is concluded that carbontransformation will be higher during rainy season in the vegetation sites of forest soilunder such agroclimatic conditions.

Keywords: agroforestry; decomposition; carbon transformation; exocellular enzymes(amylase, cellulase, invertase)

Introduction

All biological and chemical processes of soils almost depend on soil enzyme activities.Knowledge of enzyme activities can be used to describe changes in soil quality due toland-use management and for the understanding of the functioning of soil ecosystem. Soilenzymes are continuously playing an important role in maintaining soil ecology, physicaland chemical properties, fertility and soil health. The enzymes play a key role inbiochemical functions, in the overall process of organic matter decomposition(Sinsabaugh et al. 1993) and for the maintenance of concentration of soil ions and climate(Jimenez et al. 2002) in the soil system. They are important for catalysing several vitalreactions necessary for the life processes of microorganisms in soils and are also importantfor the stabilization of soil structure, formation of organic matter, nutrient cycling anddecomposition of organic wastes, hence playing an important role in agriculture andagroforestry (Dick et al. 1994; Dick 1997; Dilly et al. 2007; Trasar-Cepeda et al. 2008;Sinsabaugh et al. 2009; Ulrich et al. 2010; Garcia & Nahas 2012). Soil quality is alwaysdetermined by several factors and soil enzymes are key factors for maintaining soilfertility. Soil enzyme activities have been suggested as suitable indicators of soil quality

*Corresponding author. Email: [email protected]

Archives of Agronomy and Soil Science, 2014Vol. 60, No. 3, 405–422, http://dx.doi.org/10.1080/03650340.2013.789869

© 2013 Taylor & Francis

mailto:[email protected]

and mainly originate from microorganisms (Ladd 1978; Zimmermann & Frey 2002),animals and plants (Tabatabai 1994) as well as from the decomposition of plants andanimal residues (Shan et al. 2008). Soil microbes serve both as the source and sink ofplant nutrients and as a driving force for nutrient availability in agroforestry ecosystems(Wang et al. 2005). Soil enzymes can be excreted from living cells or can be released intosoil solution from dead cells (Tabatabai 1994). According to Dilly and Munch (1996),plant litter is the major source of energy for soil microbes, and these microbes releaseexocellular enzymes during litter decomposition. Litter decomposition and mineralizationare affected by physicochemical factors like soil temperature, moisture, pH, litter qualityand decomposer organisms (Liu et al. 2006). Graham and Haynes (2005) noted that majorindicators of microbial functional pool include microbial biomass carbon (MBC) andactivity of exocellular enzymes involved in the transformations of carbon (i.e. amylase,cellulase and invertase), nitrogen (i.e. protease) and phosphorus (i.e. phosphatases). Sincelitter degradation requires concurrent enzymatic diversity, the microbial biomass andassociated enzymatic activities are essential for humus turnover and nutrient release orimmobilization (Dilly et al. 2007). Several workers have observed the importance ofseason on the rates of litter production and decomposition. According to Singh andAmbasht (1980), the rate of litter production in deciduous tropical forests followed aseasonal trend, with a peak in summer and minimum in rainy season. The decompositionof soil carbon depends on the microbial production of exocellular enzymes that convertcomplex compounds into smaller products (Ratledge 1994; Kögel-Knabner 2002;Nannipieri et al. 2002). Satchell (1974) proposed that in tropical forests, the litterdeposited in dry season undergoes rapid mineralization in the following wet season, andLambert et al. (1980) attributed predominant control of litter decomposition to tempera-ture and moisture limitations. However, according to Loranger et al. (2002), in someclimatic regions, litter quality parameters are the best predictors of decomposition rates.Carbon-degrading microbes must also produce nutrient-acquiring enzymes (Sinsabaughet al. 1993; Asmar et al. 1994) such as amylase, invertase and cellulase to obtain growthand enzyme synthesis. In discussing soil quality indicators, Karlen et al. (1997) includedsoil MBC and exocellular enzyme activity as biological indicators. Exocellular enzymescatalyse the decomposition of organic carbon, and enzyme activities would be greater insoil fractions with rapid carbon transformation. Thus, knowledge of several soil enzymeactivities can provide information on the soil degradation potential (Trasar-Cepeda et al.2000). These studies have noted the importance of soil enzyme activities, in relation tolitter decomposition, in various vegetation sites. However, not much work has been doneon carbon transformation by exocellular enzymes in the subtropical region influenced bydifferent litter types. In keeping with this information deficit, the present study wasundertaken to (1) evaluate the effect of major seasons (summer, rainy and winter), littertypes and quality as well as soil physicochemical properties on selected soil enzymeactivities of amylase, cellulase and invertase in different vegetation sites and (2) find outcorrelations between soil enzyme activities and soil physicochemical parameters indifferent depths of soil.

Materials and methods

Study site

The study took place at a social forest situated very near to the Burdwan University(23° 15′ 5.44″ N and 87° 51′ 1.92″ E and elevation 53 metre) academic campus. This areahas a monsoon of subtropical climate with three distinct seasons, viz. rainy (July to

406 C. Das et al.

October), winter (November to February) and summer (March to June). Site character-istics are summarized in Table 1. The study site of soil samples were characterized by pH(6.70 ± 0.20), approximately 2.16% organic matter and a cation-exchange capacity of10.73 meq (100 g soil)−1; available nitrogen (AN) and available phosphorous (AP)(Olsen-P) range from 59.9 to 48.06 kg ha−1 and 30.66 to 30.56 kg ha−1, respectively.The average ambient temperature ranged from a minimum of 9.1°C to a maximum of36.8°C and the mean annual precipitation is about 1141.7 mm. According to United StatesDepartment of Agriculture (2003), the soils were classified as Alfisol soils with sandyloam texture (88.3% sand, 4.7% silt and 7.0% clay). Control site was situated very near tothe social forest (23° 15′ 5.45″ N and 87° 51′ 1.93″ E) and was without any vegetation.The present investigation samples were collected from the experimental sites underdifferent vegetation types, such as

Tectona grandis L. F. (Indian oak) (S1),Albizia lebbeck (L) Benth var. pubescens Haines (Lebbek tree) (S2),Shorea robusta Gaertn. F (Shala tree) (S3),Anacardium occidentale L. (Cashew tree) (S4),Phyllanthus emblica L. (syn. Emblica officinalis) (Indian gooseberry) (S5),Corymbia citriodora (Hook) K.D. Hill & L.A.S. Johnson (syn. Eucalyptus citriodora)

(Lemon scented gum) (S6) andAcacia auriculiformis A. Cunn ex. Benth (Earleaf acacia) (S7).

Table 1. Site characterization of the Ramona forest.

Parameters Value

LocationAltitude (at sea level) m 53Latitude (N) 23° 15′ 5.44″Longitude (E) 87° 51′ 1.92″Precipitation (mm) annually about 1141.7

Temperature (°C) annuallyMinimum 09.1 to 26.4Maximum 23.8 to 36.8

Soil properties of control siteMoisture (%) 11.73 ± 0.19Particle density (g cm−3) 1.36 ± 0.00Bulk density (g cm−3) 1.22 ± 0.00Specific gravity (g cm−3) 1.24 ± 0.02Porosity (%) 10.80 ± 0.10Sand (%) 88.30 ± 0.26Silt (%) 4.70 ± 0.10Clay (%) 7.00 ± 2.00pH 6.70 ± 0.20Electrical conductivity (mS cm−1) 21.33 ± 2.31Available nitrogen (kg ha−1) 53.98 ± 1.92Available phosphorous (kg ha−1) 30.61 ± 0.05Organic carbon (%) 2.16 ± 0.01Cation-exchange capacity (meq (100 g soil)−1) 10.73 ± 0.20

Soil enzyme activity (μg GE g−1 soil h−1) of control siteAmylase 0.150 ± 0.01Cellulase 0.152 ± 0.01Invertase 0.269 ± 0.02

Note: Values are mean ± standard deviation (n = 3).

Archives of Agronomy and Soil Science 407

Soil sampling

Soil samples were collected from different depths (0–5 cm (topsoil) and 5–10 cm (sub-soil)) of canopy-covered tree species during summer (March), rainy (August) and winter(November) seasons of 2010, using a 4.5 cm diameter corer, after removing undecom-posed surface litter. The soil sample collected from adjacent site served as control, i.e.without tree species. Cores were taken randomly at four locations in each tree species andapproximately 1.5 m from the stem to avoid the impacts of stem flow. Samples were takenimmediately to the laboratory and roots were removed by hand and transferred in sealedplastic bags. All the randomly collected soil samples were subsequently combined andsieved with <2 mm sieve and homogenized. Half of each sample was kept field moist in acooler stored at 4°C until analyses, so that soil biological properties can be tested. Theother half of each sample was air-dried and stored at room temperature, to be used for thedetermination of soil physicochemical properties.

Analyses of physicochemical characteristics of soil

Soil pH was determined in a soil–water suspension of 1:2.5 (weight/volume) by dipping adigital pH meter (SYSTRONICS-335, Systronics Pvt. Limited, Ahmedabad, India). Thesame suspension was used to measure electrical conductivity in a digital conductivitymeter (Model 304-Systronics Pvt. Limited). Soil organic carbon content was estimatedfollowing Walkley–Black’s (1934) rapid titration method, AN by Subbiah and Asija’smethod (1956), AP by Olsen’s method (1954) and soil cation-exchange capacity (CEC)by Schollenberger and Dreibelbis’s method (1930) using spectrophotometer (Model 1203-Systronics Pvt. Limited). Soil physical properties, i.e. particle density (PD), porosity(PORO) and bulk density (BD), were determined by Black’s method (1965), soil texturewas estimated by hydrometer method and soil moisture by gravimetric method. Soilmoisture was measured in all soil samples by weighing 5 g of field moist soil, dryingthe soil for 24 hours at 60°C and then reweighing.

Measurement of soil enzyme activity

Carbohydrate-reducing enzymes, namely amylase (EC 3.2.1.1), cellulase (EC 3.2.1.4) andinvertase (EC 3.2.1.26), were estimated by the DNSA (3,5 dinitrosalicylic acid) method(Mishra et al. 1979) using the respective substrates, namely starch, carboxymethylcellulose and sucrose. Three grams of moist soil was incubated with Sorensen’s buffer(0.06 M, pH 5.5) and substrate solution at 30°C for 24 hours. After incubation, thesupernatant was reacted with the DNSA reagent and heated in a boiling water bath. Theoptical density was taken at λ = 540 nm and the result was compared against standardcurve for D-glucose. The results for this group of enzyme activities were expressed in µgglucose equivalent g−1 soil h−1(µg GE g−1 soil h−1).

Analysis of leaf litter

Analysis of the leaf litter of tree species was performed in the laboratory by standardmethods. Total nitrogen was determined by the micro-Kjeldahl procedure as described byJackson (1973). Total phosphorus was determined colorimetrically by tri-acid digestion(nitric acid, perchloric acid and sulphuric acid, 10:4:1) followed by ammonium molybdatestannous chloride blue colour method and potassium (Jackson 1958) was determined with aflame photometer (Systronics-128, Systronics Pvt. Limited). Lignin content was determined

408 C. Das et al.

by acid detergent fibre method (Goering & Van Soest 1975) and organic carbon content byWalkley–Black method (1934).

Statistical analysis

Microsoft excel (windows 2007, Microsoft), Origin pro (version 8.0, Northampton,MA, USA) and Minitab (version 8.0, Inc., Des Moines, IA, USA) software programswere used for the statistical evaluation. One-way ANOVA was used to indicatesignificant differences in soil organic carbon and enzyme activities between littertypes and seasons. Correlation coefficient (r) was determined to find statisticallysignificant relationship between soil physicochemical parameters and enzyme activitiesin experimental soils in different seasons. The significant difference between the littertypes and enzyme activity were compared through DMRT (Duncan’s multiple rangetest) (Panse & Sukhatme 1967; Gomez & Gomez 1984).

Results and discussion

Influence of litter types and quality on enzyme activities

Soil enzyme activities have been suggested as appropriate indicators of soil qualityand functional microbial diversity because they control key metabolic pathways insoil. The chemical status revealed higher levels of nitrogen and organic carbon andmoderate levels of lignin to nitrogen ratio for Anacardium litter (Table 2). Theamylase activity from Anacardium litter containing soil was found to be significantlydifferent (p < 0.05) from other varieties of litter at the top- and subsoil (Tables 3 and4) during summer and rainy seasons. On the other hand, Tectona litter showed higherlignin content but moderate levels of nitrogen, phosphorous and lignin to nitrogenratio (Table 2). Anacardium and Tectona litter showed higher levels of amylaseactivity in both the top- and subsoil during the three experimental seasons, and it issignificantly different from other litter containing soils (Tables 2–5). The litter ofAlbizia and Acacia showed very high levels of carbon to nitrogen and carbon tophosphorous ratios, respectively. The enzyme activity results showed that Albizia andAcacia litter containing soils have higher cellulase and invertase activities at the top-and subsoil, respectively, during summer season (Table 3). The different enzymeactivities in different litter containing soils are probably due to changes in the speciescomposition of plant communities and the subsequent enzyme activities of the micro-biota (Kourtev et al. 2002). Higher level of Albizia litter decomposition rate enhancedthe cellulase activity in the soil, which seems to be greatly influenced by the litterchemistry (Kourtev et al. 2002). Similar changes in enzyme activities with litter typesand soil depths were reported by Mukhopadhyay and Joy (2010) and Chhotaray et al.(2011). The decomposers, such as fungivorous and detrivorous soil microbes, showeddifferent decomposition rates (Baldock 2007). High nitrogen content and low carbonto nitrogen ratio might be the main causes for the differences in enzyme activities indifferent vegetation sites (Sinsabaugh & Linkins 1988). From the experimental results,it was found that Tectona grandis litter containing soil showed higher amylase activityin all seasons, perhaps due to its both moderate lignin and nitrogen content along withcarbon to nitrogen ratio. Similar variations in soil enzymes were reported byQuilchano and Maranon (2002). Moreover, different levels of invertase activity wererecorded in the experimental sites, probably due to variability in plant litter quality(Luxhoi et al. 2002). It is well documented that the available nitrogen content in litter


Table

2.Initial

litterchem

ical

compo

sitio

nof

differenttree

species.

Param

eter

S1

S2

S3

S4

S5

S6

S7

N(%

)0.39

±0.01

0.29

±0.01

0.38

±0.01

0.41

±0.01

0.33

±0.01

0.37

±0.3

0.27

±0.04

P(%

)0.89

±0.01

0.61

±0.05

0.92

±0.02

0.85

±0.02

0.38

±0.01

0.54

±0.04

0.31

±0.02

K(%

)1.45

±0.02

1.88

±0.01

1.34

±0.01

1.63

±0.03

1.39

±0.02

1.59

±0.02

1.30

±0.02

C(%

)2.42

±0.02

2.61

±0.02

2.90

±0.01

3.20

±0.02

1.80

±0.05

2.29

±0.02

1.79

±0.02

L(%

)3.24

±0.02

1.90

±0.04

2.70

±0.01

3.20

±0.02

1.82

±0.02

2.39

±0.02

2.59

±0.02

C/N

6.20

±0.02

9.00

±0.03

7.63

±0.02

7.80

±0.02

5.45

±0.17

6.18

±0.02

7.29

±0.02

C/P

2.71

±0.08

4.27

±0.02

3.15

±0.02

3.76

±0.13

4.73

±0.21

4.24

±0.08

5.77

±0.08

L/N

8.30

±0.02

6.55

±0.04

7.10

±0.02

7.80

±0.02

5.51

±0.02

6.45

±0.02

9.59

±0.03

Notes:Valuesaremeans

(n=3)

with

±standard

deviation.

N,K,L,PandCdenote

totalnitrogen,po

tassium,lig

nin,

phosph

orou

sandorganiccarbon

,respectiv

ely.

Sam

pleno

.S1

(Tectona

grandis),S2(Albizia

lebb

eck),S3(Sho

rearobu

sta),S4(Ana

cardium

occidentale),S5(Phylla

nthu

sem

blica),S6(Corym

biacitriodo

ra)andS7(Acaciaauriculiformis).

410 C. Das et al.

Table

3.Activity

ofsoilenzymes

insummer

season

(enzym

eactiv

ityratesno

rmalized

tothesametim

eun

it,i.e.perho

ur).

Enzym

esof

topsoil(0–5)cm

depth

Enzym

esof

subsoil(5–1

0)cm

depth

Amylase

Cellulase

Invertase

Amylase

Cellulase

Invertase

SN

(μgGEg−

1soilh−

1)

S1

0.48

8a±0.08

0.17

5c±0.00

0.45

0abc±0.09

0.42

5a±0.09

0.09

8g±0.00

0.43

2bc±0.05

S2

0.44

7b±0.04

0.30

8a±0.05

0.43

6cd±0.12

0.33

9f±0.03

0.23

0a±0.01

0.42

7bcdef±0.10

S3

0.34

6f±0.16

0.15

9ef±0.00

0.43

4cdef±0.1

0.34

5f±0.04

0.15

6ef±0.01

0.43

2bcd

±0.06

S4

0.37

7d±0.10

0.15

7ef±0.01

0.43

6cde±0.08

0.37

6c±0.03

0.16

2c±0.01

0.42

7bcdef±0.02

S5

0.35

7def±0.08

0.21

9b±0.00

0.46

1a±0.04

0.35

7e±0.03

0.19

9b±0.01

0.46

1a±0.03

S6

0.37

7de±0.10

0.17

3cd±0.01

0.43

4cdef±0.11

0.36

7d±0.01

0.15

9cde±0.01

0.43

1bcde±0.03

S7

0.43

4bc±0.08

0.16

1e±0.02

0.45

6ab±0.14

0.38

7b±0.01

0.16

1cd±0.00

0.43

2a±0.01

Notes:The

values

aremean±standard

deviationwith

four

replicates

foreach

interval.

Means

follo

wed

bythesameletter(a,b,

c,d,

eandf)with

intreatm

entarenotsignificantly

differentat

5%usingDuncan’smultip

lerangetest(D

MRT).Means

ofsixreplicates

are

taken.

Sam

pleno

.S1(Tectona

grandis),S2(Albizia

lebbeck),S3(Sho

rearobu

sta),S4(Anacardium


nthusem

blica),S6(Corym

biacitriodo

ra)andS7(Acacia

auriculiformis).


Table

4.Activity

ofsoilenzymes

inrainyseason

(enzym

eactiv

ityratesno

rmalized

tothesametim

eun

it,i.e.perho

ur).

Enzym

esof

topsoil(0–5

)cm

depth

Enzym

esof

subsoil(5–1

0)cm

depth

Amylase

Cellulase

Invertase

Amylase

Cellulase

Invertase

SN

(μgGEg−

1soilh−

1)

S1

0.89

3a±0.04

0.24

9f±0.00

1.36

2d±0.03

0.45

8a±0.01

0.04

9c±0.00

0.52

8c±0.01

S2

0.76

8c±0.01

0.35

6b±0.03

1.45

2b±0.01

0.41

2b±0.02

0.29

6a±0.01

0.63

3ab±0.00

S3

0.73

1de±0.01

0.38

9a±0.03

1.63

1a±0.01

0.36

1g±0.01

0.12

8b±0.00

0.24

0def±0.02

S4

0.82

1b±0.02

0.32

1c±0.02

1.25

3ef±0.01

0.37

5d±0.01

0.02

7cde±0.00

0.25

3de±0.01

S5

0.63

1g±0.02

0.26

1e±0.02

1.43

6bc±0.01

0.36

4f±0.00

0.02

3def±0.00

0.63

4a±0.00

S6

0.73

4d±0.00

0.28

3d±0.02

1.27

1e±0.02

0.37

2e±0.00

0.02

6def±0.00

0.27

1d±0.01

S7

0.66

1f±0.01

0.23

2g±0.06

1.10

3g±0.03

0.39

7c±0.02

0.03

1cd±0.00

0.23

1def±0.01

Notes:The

values

aremean±standard

deviationwith

four

replicates

foreach

interval.

Means

follo

wed


c,d,

eandf)with

intreatm

entareno

tsign

ificantly

differentat

5%usingDun

can’smultip

lerangetest(D

MRT).Means

ofsixreplicates

are

taken.

Sam

pleno

.S1(Tectona

gran

dis),S2(Albizia

lebb

eck),S3(Sho

rearobu

sta),S4(Anacardium


nthu

sem

blica),S6(Corym

biacitriodo

ra)andS7(Acacia

auriculiformis).

412 C. Das et al.

Table

5.Activity

ofsoilenzymes

inwinterseason

(enzym

esactiv

ityratesno

rmalized

tothesametim

eun

it,i.e.perho

ur).

Enzym

esof

topsoil(0–5

)cm

depth

Enzym

esof

subsoil(5–10)

cmdepth

Amylase

Cellulase

Invertase

Amylase

Cellulase

Invertase

SN

(μgGEg−

1soilh−

1)

S1

0.46

9a±0.01

0.14

6de±0.00

0.43

2e±0.01

0.12

4b±0.00

0.09

2f±0.00

0.31

5c±0.00

S2

0.33

2b±0.01

0.13

5f±0.00

0.48

2cd±0.01

0.42

1a±0.00

0.09

5f±0.00

0.27

5e±0.01

S3

0.33

2bc±0.01

0.24

1a±0.01

0.39

1g±0.04

0.09

2bcd

±0.00

0.20

1b±0.00

0.23

9f±0.00

S4

0.25

3ef±0.01

0.13

8f±0.01

0.42

0f±0.01

0.04

7g±0.00

0.12

7e±0.00

0.22

0g±0.00

S5

0.28

1d±0.01

0.14

6d±0.01

0.49

8a±0.05

0.08

4cde±0.00

0.14

5d±0.01

0.38

4b±0.00

S6

0.26

4de±0.00

0.16

9c±0.01

0.48

4bc±0.01

0.06

7cdef±0.00

0.16

8c±0.00

0.29

3d±0.01

S7

0.19

6g±0.00

0.23

4b±0.03

0.48

9b±0.02

0.09

5bc±0.00

0.22

8a±0.03

0.47

6a±0.00

Notes:The

values

aremean±standard

deviationwith

four

replicates

foreach

interval.

Means

follo

wed


c,d,

eandf)with

intreatm

entareno

tsign

ificantly

differentat

5%usingDun

can’smultip

lerangetest(D

MRT).Means

ofsixreplicates

are

taken.

Sam

pleno

.S1(Tectona

grandis),S2(Albizia

lebb

eck),S3(Sho

rearobu

sta),S4(Ana

cardium


nthu

sem

blica),S6(Corym

biacitriodo

ra)andS7(Acacia

auriculiformis).


has a positive correlation with enzyme activity (Deng & Tabatabai 1997; Acosta-Martinez & Tabatabai 2000; Dodor & Tabatabai 2002; Taylor et al. 2002).

Influence of season on enzyme activities

At the topsoil, the highest amylase activity was recorded in rainy season followed bywinter and lowest in summer. But at the subsoil, a reduced level of amylase activity wasfound in different seasons (Tables 3–5). The variation of soil enzyme activities withrespect to seasons and soil types is well documented (Kerstin & Egbert 2003; Boerneret al. 2005; Mukhopadhyay & Joy 2010). On the other hand, higher level of cellulaseand invertase activities were recorded in rainy season followed by summer and lowest inwinter at the topsoil (Table 3–5). With respect to the topsoil, the subsoil showed thehighest reduction of mean activity of cellulase (291.55%) and invertase (240.79%)during rainy season. But, the highest reduction of mean amylase activity (128.71%)was obtained in winter season. The main reason for higher enzyme activities in theupper soil layer was correlated with a higher concentration of soil organic matter (Huet al. 2005). Although, during summer season, invertase activity did not show depthvariation, cellulase activity showed substantial reduction in the subsoil with respect totop soil (16.05%). Similar results of non-significant changes of enzymatic activitieswith depth are reflected in findings of Chhotaray et al. (2011). Irrespective of theseasons, the activities of amylase, cellulase and invertase enzymes progressivelydeclined with increasing soil depth. Innermost soil layer exhibited minimum amylase,cellulase and invertase activity in winter and rainy season, but a reverse trend wasobserved in summer (Chhotaray et al. 2011).

Influence of soil organic carbon on enzyme activities

Dead plant material is the main source of organic matter in soils and its decompositionby soil organisms ensures the recycling of nutrients, which can be reused by plants(Couteaux et al. 1995). In this study, the enzyme activities (amylase, cellulase andinvertase) were higher at different vegetation sites compared with those at the controlsite due to the higher organic carbon content in the vegetation sites. Similar observa-tion was reported by Fernandes et al. (2005) and Ge et al. (2009). This may again beattributed to higher level of organic sources which accelerate the growth and activityof microorganisms. The declining trend of all selected enzymes with increasing soildepth indicates a gradual depth-dependent reduction in the microbial activity(Chhotaray et al. 2011). On the other hand, Figure 1(a–f) reveals that none of theenzyme activity showed significant relationship with organic carbon content in bothtop- and subsoil except invertase in the subsoil during winter season. However,species of Corymbia and Acacia did not influence the soil organic carbon content.Moreover, the subsoil from Shorea litter showed higher soil organic carbon contentduring summer than during rainy and winter season. Such higher level of organiccarbon was also reported from teak litter (Potvin et al. 2004). During rainy season, apositive correlation was observed between organic carbon content and enzyme activity(invertase and cellulase) in all experimental soils except Anacardium vegetation site inthe topsoil. Organic carbon showed positive relationship with cellulase and amylaseactivity from Tectona, Albizia, Shorea, Acacia, and Corymbia litter containing soils,but invertase activity did not show any relationship with organic carbon during winterseason. Similar significant relationship between organic carbon content and different

414 C. Das et al.

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

5.2

5.4Organic carbonAmylaseCellulaseInvertase

Sample

Org

anic

car

bo

n (%

)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

cdefacd

bef

a

Enz

yme

activ

ity (

µg G

E g

–1 s

oil h

–1)

ab

fd def

bcde

c ef

cd

e

abc cdef cde ab

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3.0

3.1

3.2Organic carbonAmylaseCellulaseInvertase

Sample

Org

anic

car

bon

(%)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

ge

ab

d

gdca

b

f

Enz

yme

activ

ity (

µg G

E g

–1 s

oil h

–1)

ac de

b

gd

f e

efbc

S1 S2 S3 S4 S5 S6 S7

S1 S2 S3 S4 S5 S6 S7

S1 S2 S3 S4 S5 S6 S7

2.12.22.32.42.52.62.72.82.93.03.13.23.3

bb caf

g

b

dfa

d e

Organic carbonAmylaseCellulaseInvertase

Sample

Org

anic

car

bon

(%)

a

b b ce f

d d eg

f c

e

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0E

nzym

e ac

tivity

(µg

GE

g–1

soi

l h–1

)

c d

(a)

(b)

(c)

Figure 1. Relationship between soil enzymes and organic carbon at 0–5 cm depth during (a)summer, (b) rainy and (c) winter season and at 5–10 cm depth during (d) summer, (e) rainy and (f)winter season, respectively. Unit of enzyme activity (EA) expressed as µg GE (Glucose Equivalent)g−1 soil h−1. Bars indicate standard error of mean (n = 3). S1 (Tectona grandis), S2 (Albizia lebbeck),S3 (Shorea robusta), S4 (Anacardium occidentale), S5 (Phyllanthus emblica), S6 (Corymbia citrio-dora) and S7 (Acacia auriculiformis).


enzyme activities was also recorded in subsoil. In summer season, Tectona, Albizia,Anacardium and Corymbia soils were positively correlated to cellulase activity, butinvertase activity showed positive correlation for Tectona, Albizia, Shorea,Anacardium and Phyllanthus litter containing soils in rainy season and Albizia,Shorea and Anacardium for cellulase during the same season. Similar positive rela-tionship between enzyme activity and soil organic matter was recorded by Deng andTabatabai (1996, 1997). A non-significant correlation was observed in the enzymeactivity of amylase, invertase and cellulase with organic carbon content of the subsoilin all the three seasons (Figure 1(a–f)). Soil organic matter is also a good indicator for

3.23.43.63.84.04.24.44.64.85.05.25.4

a


Sample

Org

anic

car

bon

(%)

e fc d e

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

aab c d e f

bc

f

Enz

yme

activ

ity (

µg G

E g

–1 s

oil h

–1)

af

c e db

g c d

b c b c d e f b c d b c d e

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4 Organic carbonAmylaseCellulaseInvertase

Sample

Org

anic

car

bon

(%)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

d e fd

a

d e f

c

d e f

b

a

c

Enz

yme

activ

ity (

µg G

E g

–1 s

oil h

–1)

ab

g d f e c

c d ed e f c d

a b

de

S1 S2 S3 S4 S5 S6 S7

S1 S2 S3 S4 S5 S6 S7

S1 S2 S3 S4 S5 S6 S7

1.4

1.6

1.8

2.0

2.2

2.4

2.6

dg

ec

b


Sample

Org

anic

car

bon

(%)

e dc

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

a

b

f a

f

Enz

yme

activ

ity (

µg G

E g

–1 s

oil h

–1)

a

bb c d

g c d e c d e f b cf

(d)

(e)

(f)

Figure 1. Continued.

416 C. Das et al.

understanding the activity of soil organisms (Couteaux et al. 1995). Non-significant(p < 0.05) positive correlation was observed in the case of cellulase and invertaseactivity with soil organic carbon content during rainy season. Such low level oforganic carbon may be due to high percentage of lignin as well as high lignin tonitrogen ratio of the experimental litter. On the other hand, in all cases, irrespective ofseason and depth of soil, control sites showed much lower levels of organic carbonand enzymatic activities compared with those of the experimental sites. This isperhaps due to the decomposition of litter by soil microbes, which enhances theorganic carbon and soil enzymes (Li et al. 2010; Mukhopadhayay & Joy 2010). It isnoteworthy mentioning that enzyme activities are correlated to soil organic mattercontent because the litter plays a key role as a precursor for enzyme synthesis and inenzyme physical stabilization (Sinsabaugh et al. 1991; Tabatabai 1994). Severalworkers have showed that amylase activity is a sensitive biological indicator of soilmanagement practice because it increased with organic carbon content of soil (Miller& Dick 1995; Falih & Wainwrisht 1996; Crecchio et al. 2001).

Influence of soil physicochemical parameters on enzyme activities

Correlation study revealed that soil amylase activity was positive and significantlycorrelated with AN, AP and porosity at the topsoil and soil pH and AN during rainyseason at the subsoil. Silt and clay content showed positive correlation with cellu-lase activity in both the soil layers during winter season. However, in the topsoil,invertase activity showed positive relationship with AP (p < 0.05) during winter andwith AN (p < 0.05) and AP (p < 0.01) during rainy season at the subsoil (Tables 6and 7). Moreover, in rainy season, specific enzyme activity is attributed to availablesoil nitrogen, phosphorous and other edaphic characteristics of soil because theseare greatly influenced by microorganisms during the decomposition of litter(Sinsabaugh et al. 1981; Sinsabaugh & Linkins 1987; Sinsabaugh 1994). Duringrainy season, all the enzymes did not show similar activity, which is probably dueto soil chemistry (e.g. pH), nutrient availability and litter quality (Carreiro et al.2000). According to Spalding (1980), different amounts of amylase, cellulase andinvertase enzymes extracted from different litter-exposed soils are attributed to litterchemistry.

Conclusion

In conclusion, forest soil is highly influenced by both litter types and seasons. Among thestudied species, Shorea robusta litter contributed to a maximum increase in organiccarbon content in the topsoil in all seasons. However, at the subsoil, similar high levelof organic carbon was recorded only in summer. Furthermore, the results revealed thatcellulase and invertase activities were significantly influenced by soil texture. It canfurther be inferred that enhancement of soil fertility, such as organic matter content, soilsustainability, productivity, and consequently soil enzyme activity depend on litter typesand litter chemistry. Therefore, present investigation suggests that litter of all the treespecies was not equal in contribution towards carbon transformation in forest soil undersuch agroclimatic conditions.


Table6.

Correlatio

ncoefficientof

soilenzymeactiv

ities

andsoilparameters(0–5

cmdepth)

(degreeof

freedo

m=15

).

Amylase

Cellulase

Invertase

Param

eter

Sum

mer

Rainy

Winter

Sum

mer

Rainy

Winter

Sum

mer

Rainy

Winter

pH0.43

80.48

70.05

80.10

2−0.36

3−0.48

9−0

.272

0.05

70.42

3EC

0.51

40.64

8*−0.25

0−0.38

0−0.30

3−0.37

00.00

20.13

80.22

3OC

−0.23

7−0.07

4−0.32

2−0.20

80.36

70.08

6−0

.135

0.39

1−0.31

2AN

0.12

10.61

4*0.29

50.39

00.34

2−0.56

4−0

.383

0.37

80.06

9AP

0.02

80.64

4*0.21

80.20

80.26

0−0.81

8−0

.417

0.42

40.62

9*CEC

0.38

40.46

20.18

40.48

50.03

8−0.65

5−0

.380

0.34

8−0.43

0MOIS

−0.46

9−0.07

40.59

3*0.16

6−0.12

6−0.41

2−0

.608

−0.32

6−0.42

2BD

0.14

20.03

30.40

50.41

8−0.17

8−0.59

60.211

0.02

0−0.10

0PORO

−0.06

70.86

0**

0.74

2**

−0.54

90.45

7−0.33

7−0

.013

0.41

6−0.61

0PD

0.17

20.40

40.62

4*0.15

10.00

6−0.50

00.26

50.19

1−0.37

8SPG

0.14

7−0.07

30.60

4*0.41

7−0.01

8−0.15

10.21

30.35

9−0.26

2SAND

0.49

30.34

60.54

00.18

9−0.20

8−0.72

90.36

9−0.25

1−0.28

2SILT

−0.44

3−0.14

6−0.62

0−0.10

60.28

60.60

7*−0

.233

0.311

0.36

7CLAY

−0.35

7−0.57

6−0.46

3−0.17

70.09

00.71

7**

−0.354

0.15

20.21

8AMY

__

_0.27

10.14

1−0.32

30.23

00.04

7−0.40

9CEL

0.27

10.14

1−0.32

3_

__

−0.030

0.72

0**

−0.24

0IN

VER

0.23

00.04

7−0.40

9−0.03

00.72

0**

−0.24

0_

__

Notes:*

p<0.05,*

*p<0.01.p

H=soilpH

,EC=electricalconductiv

ity,O

C=organiccarbon,A

N=availablenitrogen,A

P=availablephosphorus,C

EC=catio

n-exchange

capacity,

MOIS

=moisture,

BD

=bulk

density,PORO

=porosity,PD

=particle

density,SPG

=specific

gravity,AMY

=am

ylase,

CEL=cellu

lase

andIN

VER=invertase.

418 C. Das et al.

Table

7.Correlatio

nbetweensoilenzymes

andsoilparameters(5–10cm

depth)

(degreeof

freedo

m=15

).

Amylase

Cellulase

Invertase

Param

eter

Sum

mer

Rainy

Winter

Sum

mer

Rainy

Winter

Sum

mer

Rainy

Winter

pH0.24

60.64

3*0.45

6−0.21

00.46

7−0.03

0−0.85

90.42

30.06

2EC

0.80

30.75

5**

−0.24

7−0.86

4−0.26

0−0.01

8−0.27

60.14

6−0.29

1OC

−0.34

3−0.66

30.07

60.08

70.12

8−0.42

8−0.28

00.45

2−0.16

2AN

−0.21

40.65

0*0.20

40.12

30.76

5**

−0.00

20.07

60.63

3*−0.52

8AP

−0.13

40.55

50.39

10.110

0.63

9*−0.57

8−0.32

00.72

6**

0.08

7CEC

0.02

40.36

3−0.03

70.17

3−0.16

0−0.67

7−0.14

80.49

1−0.70

4MOIS

−0.22

9−0.35

10.35

70.04

1−0.33

6−0.67

5−0.07

5−0.07

3−0.50

9BD

−0.117

−0.17

20.26

80.01

2−0.64

6−0.67

4−0.18

5−0.14

1−0.30

8PORO

0.06

20.52

50.52

4−0.07

20.65

7*−0.56

80.34

90.02

8−0.86

5PD

0.01

00.05

40.41

9−0.05

80.38

8−0.73

10.29

4−0.05

5−0.56

1SPG

−0.17

00.38

80.45

70.10

7−0.53

2−0.63

70.44

6−0.05

0−0.30

6SAND

−0.00

90.80

20.26

50.02

30.21

3−0.80

00.05

6−0.18

9−0.79

3SILT

−0.02

6−0.70

1−0.36

90.01

5−0.62

80.84

4**

0.01

3−0.73

30.65

1*CLAY

0.05

5−0.86

7−0.22

5−0.07

00.09

40.71

5**

−0.14

1−0.26

10.78

4**

AMY

__

_−0.83

90.19

9−0.48

3−0.12

20.40

1−0.12

3CEL

−0.83

90.19

9−0.48

3_

__

0.23

20.42

10.44

8IN

VER

−0.12

20.40

1−0.12

30.23

20.42

10.44

8_

__

Note:*p

<0.05

,**p

<0.01.p

H=soilpH

,EC=electricalconductiv

ity,O

C=organiccarbon,A

N=availablenitrogen,A

P=availablephosphorus,C

EC=catio

n-exchange

capacity,

MOIS

=moisture,

BD

=bulk

density,PORO

=porosity,PD

=particle

density,SPG

=specific

gravity,AMY

=am

ylase,

CEL=cellu

lase

andIN

VER=invertase.


AcknowledgementsAuthors express their sincere thanks to the Forest Officer of Ramona forest, Burdwan. They alsoexpress their gratitude to all faculty members of the Department of Environmental Science, BurdwanUniversity.

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Soil enzyme activities in dependence on tree litter and season of a social forest, Burdwan, India