But the study area Manianthivu is a site with unique feature along the Nagapattinam, where the area is inundated due to the continues flow of water during the monsoon season, and exposed during the seasons of a year. The present study was carried out to find out the fungal ecology in this seasonally inundated habitat that lies along the southeast coast of Tamil Nadu.

MATERIALS AND METHOD:

The sampling station:

The fungi were isolated from the coastal soils of Manianthivu, Nagapattinam districts, it is one of the coastal districts of Tamil Nadu.This station is located at a distance of 3 km from Vedaranyam. Salt pans are located in close proximity to the station. The site has no vegetation. Flooding is noticed only during the monsoon season. During rest of the seasons salt deposition is seen on the surface. The soil is clay in nature.

Analysis of Mycoflora:

Soil samples were collected from 10 different locations seasonally for a period of two years from January 2007 to December 2008, dividing a calendar year into four seasons viz., Post monsoon (January – March), Summer (April – June), Pre-monsoon (July – September) and Monsoon (October – December), based on the north east monsoon, which is prevailing in the study area.

In each station, the soil samples were collected up to a depth within 10 cm using a metal spatula sterilized every time with 70 per cent alcohol. The samples were kept in new polythene bags, sealed and transported to the laboratory immediately for the mycological examination. For the analysis of soil nutrients, one kg of soil was separately collected in polythene bags from each station.

Dilution plating technique described by Warcup (1950) was used to isolate the fungi from soils. Soil sample weighting 1g was diluted in 10 ml of 50% seawater (1:1 v/v seawater (30 ppt): distilled water). One ml of the diluted sample was poured and spread on Petri plates containing sterilized PDA medium (Himedia) supplemented with streptopencillin antibiotic solution (1%@16/L) in replicates. The inoculated plates were incubated in a dust free cupboard at the room temperature (24±2°C) for 7 days.

The colonies growing on PDA plates with different morphology were counted separately. Semipermanent mounts ware prepared using lactophenol cotton blue mountant and examined microscopically.

Their characters were analyzed and were compared with the standard works of Raper and Thom (1949), Von Arx (1974), Ainsworth et al. (1973); Raper and Fennell (1965) and Ellis (1976) for their identification.

Number of species is referred as species diversity and Population density is expressed in terms of Colony Forming Unit (CFU) per gram of soil with dilution factor. Percentage contribution of individual species to the total population was worked out as follows.

In order to assess the dominance of individual species in each site percentage contribution was worked out as follows.

No. of colonies of a fungus in a sample

% contribution = -------------------------------------------x 100

Total number all colonies of all the

species in a sample

Analysis of physico-chemical characteristics of the soil:

Moisture content was estimated by finding the weight difference of known quantity of soil before and after drying in a hot air oven at 60°C for 6 hours. Soil samples after removing the debris were suspended in distilled water (1:2 w/v) and allowed to settle down the sand particles. The pH of the suspension was read using pH meter (Systronics, India), to find out the soil pH. Electrical conductivity of soil was determined in the filtrate of the water extract using Conductivity Bridge as described by Jackson (1973), Cation exchange capacity (CEC) of the soil was determined by using 1 N ammonium acetate solution as described by Jackson (1973).

Organic carbon content was determined by adopting chromic acid wet digestion method as described by Walkley and Black (1934); available nitrogen was estimated by alkaline permanganate method as described by Subbiah and Asija (1956) and available phosphorus by Brayl method as described by Bray and Kutz (1945). Available potassium was extracted from soil with neutral 1 N ammonium acetate (1:5) and the potassium content in the extract was determined by using flame photometer (Standfold and English, 1949). Calcium (Neutral 1 N NH₄ OAC extractable 1:5) was extracted with neutral 1 N ammonium acetate and the available calcium in the extract was determined by versenate method (Jackson, 1973). Available micronutrients such as Zn, Cu and Mn were determined in the diethylene triamine pentaacetic extract of soil using Perkin-Elmer (model 2280) Atomic Absorption Spectrophotometer (Lindsay and Norvell, 1978). Other nutrients such as magnesium, sodium and available iron were analysed following the method of Barnes (1959) and Muthuvel and Udayasoorian (1999).

RESULT AND DISCUSSION:

The present study revealed the existence of 24 species of fungi belonging to 5 genera, which includes large members of the Deuteromycetes (23 species), and a Phycomycete. All these fungal species were reported earlier from soils and a variety of substrates in the terrestrial environment (Gilman, 1965) and also reported from oceans and estuaries (Johnson and Sparrow, 1961), as facultative forms to marine habitats.

Table 1. Total number of colonies, mean density (CFU/g) and percentage contribution of fungi recorded during different season from Manianthivu

S. No	Name of the organism	2007								2008								Total no. of colonies	% contribution
		Post monsoon		Summer		Premonsoon		Monsoon		Post monsoon		Summer		Premonsoon		Mosoon
		TNC	MD0	TNC	MD0	TNC	MD0	TNC	MD0	TNC	MD0	TNC	MD0	TNC	MD0	TNC	MD0
1.	Absidia glauca	-	-	2	0.66	3	1	-	-	7	2.33	8	2.66	5	1.66	-	-	25	6.88
3.	Aspergillus albicans	3	1	-	-	2	0.66	3	1	-	-	-	-	-	-	3	1	11	3.03
2.	A. awamori	4	1.33	4	1.33	4	1.33	-	-	4	1.33	5	1.66	2	0.66	2	0.66	25	6.88
4.	A. candidus	-	-	2	0.66	-	-	-	-	-	-	4	1.33	3	1	-	-	9	2.47
5.	A. conicus	-	-	-	-	5	1.66	-	-	-	-	-	-	4	1.33	-	-	9	2.47
6.	A. flavipes	2	0.66	-	-	-	-	7	2.33	8	2.66	-	-	-	-	-	-	17	4.68
7.	A. fumigatus	7	2.33	5	1.66	-	-	-	-	4	1.33	3	1	-	-	7	2.33	26	7.16
8.	A. humicola	5	1.66	-	-	7	2.33	4	1.33	-	-	4	1.33	-	-	8	2.66	28	7.71
9.	A. luchuensis	-	-	-	-	4	1.33	-	-	-	-	-	-	-	-	-	-	4	1.10
10.	A. nidulans	-	-	7	2.33	-	-	-	-	-	-	2	0.66	-	-	-	-	9	2.47
11.	A. ochraceous	2	0.66	-	-	-	-	5	1.66	-	-	-	-	-	-	-	-	7	1.92
12.	A. oryzae	-	-	3	1	-	-	-	-	-	-	-	-	4	1.33	-	-	7	1.92
13.	A. phoenicis	1	0.33	4	1.33	-	-	-	-	5	1.66	4	1.33	5	1.66	9	3	28	7.71
s	A. rubber	-	-	-	-	5	1.66	7	2.33	6	2	-	-	3	1	8	2.66	29	7.98
15.	A. rugulosus	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6	2	6	1.65
16.	A. tamari	4	1.33	3	1	-	-	-	-	-	-	-	-	-	-	-	-	7	1.92
17.	A. terricola	-	-	-	-	2	0.66	-	-	-	-	3	1	-	-	-	-	5	1.37
18.	A. ustus	-	-	-	-	3	1	4	1.33	-	-	-	-	7	2.33	-	-	14	3.85
19.	A. variecolor	3	1	5	1.66	-	-	-	-	4	1.33	-	-	-	-	6	2	18	4.95
20.	A. wentii	3	1	-	-	-	-	-	-	-	-	4	1.33	-	-	4	1.33	11	3.03
21.	Bortrytis cinerea	2	0.66	7	2.33	8	2.66	-	-	-	-	5	1.66	6	2	-	-	28	7.71
22.	Fusarium semitectum	4	1.33	-	-	-	-	7	2.33	-	-	3	1	5	1.66	3	1	22	6.06
23.	Trichoderma harzianum	3	1	-	-	-	-	-	-	-	-	4	1.33	-	-	-	-	7	1.92
24.	T. koeningii	-	-	8	2.66	-	-	-	-	-	-	3	1	-	-	-	-	11	3.03
	Total	43	14.3	50	16.7	43	14.3	37	12.3	38	12.7	52	17.3	44	14.7	56	18.7	363

TNC – Total Number of colonies, MD – Mean density

Table 2. Physico-chemical characteristics of soil collected from Manianthivu during different occasions

Parameters	Postmonsoon – 07	Summer – 07	Premonsoon – 07	Monsoon – 07	Postmonsoon – 08	Summer – 08	Premonsoon – 08	Monsoon – 08
pH	8.1	8.3	8.7	8.3	8.2	8.2	8.6	8.9
Electrical conductivity (dSm^-1)	1.28	1.08	0.13	0.12	1.26	1.09	0.11	0.15
Cation exchange capacity (c.mol proton⁺/kg)	8.78	8.82	9.5	8.7	8.62	8.01	9.3	8.4
Organic Carbon (%)	0.05	0.15	0.07	0.16	0.18	0.06	0.08	0.14
Available nitrogen (%)	0.018	0.015	0.013	0.016	0.017	0.012	0.013	0.015
Available phosphorus (%)	0.004	0.004	0.002	0.003	0.003	0.002	0.003	0.005
Available potassium (ppm)	0.013	0.047	0.038	0.027	0.029	0.034	0.045	0.027
Available zinc (ppm)	0.51	0.46	0.48	0.52	0.53	0.42	0.39	0.51
Available iron (ppm)	2.83	2.71	2.12	2.14	2.65	2.52	2.49	2.51
Available copper (ppm)	0.25	0.25	0.31	0.29	0.30	0.28	0.20	0.19
Available manganese (ppm)	1.49	1.47	1.42	1.47	1.50	1.49	1.52	1.41
Calcium (mg/kg)	5.2	5.1	3.2	4.5	4.3	4.1	5.1	3.2
Magnesium (mg/kg)	3.2	3.7	3.9	3.2	3.4	3.5	3.2	3.6
Sodium (mg/kg)	1.08	1.07	0.76	1.22	0.52	1.25	1.01	0.97
Potassium (mg/kg)	0.02	0.03	0.04	0.05	0.07	0.06	0.02	0.02

The species diversity (number of species) spelled variation during different seasons. It was narrow in the range from 7 to 13 species. Thirteen species was recorded during post monsoon season in 2007 and summer season in 2008, 11 species during summer season in 2007, 10 species during pre monsoon in 2007 and premonsoon and monsoon seasons in 2008 and 7 species during monsoon season in 2007 and post monsoon season in 2008. In the general monsoon and postmonsoon seasons recorded the less diversity than the summer seasons. It was because of inundation of sampling station during monsoon seasons, and the fungi isolated are terrestrial in nature.

Mean population density of fungi varied from 12.3 to 18.7 ´ 10² CFU/g with the minimum in the samples collected during monsoon season in 2007 and maximum in the samples collected during monsoon season in 2008. Of 24 species belonged to 5 genera, the genus Aspergillus was constituted by the maximum of 19 species followed by Trichoderma (2 species) and all other genera (Absidia, Botrytis and Fusarium) were represented by one species each (Table 1).

Percentage contribution of the individual species to the total fungal population at all the seasons showed variation. The maximum percentage contribution of 7.98% was foemed with Aspergillus rubber. This was followed by A. humicola, A. phoenicis and Botrytis cinerea (7.71% each); A. fumigatus (7.16%);Absidia glauca and A. awamori (6.88% each); Fusarium semitectum (6.06%), Aspergillus variecolor (4.95%), A. flavipes (4.68%), A. ustus (3.85%), A. albicans, A. wentii and Trichoderma koeningii (3.03% each), A. candidus, A. conicus and A. nidulans (2.47% each), A. ocharaceous, A. oryzae, A. tamari and T. harzianum (1.92% each), A. rugulosus (1.65%) and A. terricola (1.37%) and A. luchuensis (1.10%) (Table 1)

Aspergilli formed the bulk which together contributed 67.56%. The dominance of Aspergilli in all kind of coastal – marine soils was reported as unique feature but different investigations have identified different species of Aspergilli as dominant one in different regions. Evidently, Prabhu et al. (1991) identified A. niger as dominant in the sediments of Madras Coast, Upadhyay et al. (1978) have identified A. terreus as dominant in sand dune samples and Nadimuthu (1998) identified A. terreus and A. niger as dominant fungi in coastal soils of Gulf of Mannar Biosphere Reserve.

Edaphic characteristics are believed to be responsible for the establishment of biotic community of any of the soil ecosystem. Hence, the soil characteristics were analysed along with the fungal community structure.

Soil characteristics such as pH (8.1 to 8.9), electrical conductivity (0.11 to 1.28 dSm^-1), cation exchange capacity (8.01 to 9.5 c.mol proton⁺/kg), organic carbon (0.05 to 0.18%), available nitrogen (0.012 to 0.018%), available phosphorus (0.002 to 0.005%), available potassium (0.013 to 0.047 ppm), available zinc (0.39 to 0.57 ppm), available iron (2.12 to 2.83 ppm), available copper (0.19 to 0.31 ppm), available manganese (1.41 to 1.52 ppm), calcium (3.2 to 5.2 mg/kg), magnesium(3.2 to 3.9 mg/kg), sodium (0.52 to 1.22 mg/kg) and potassium (0.02 to 0.07 mg/kg) showed variation during different seasons. These values represent the marine characteristics and are comparable with other marine habitats (Nadimuthu, 1998; Chandhuri et al., 2009; Madhanraj et al., 2010) (Table-2).

Correlation between the physico-chemical characteristics and total fungal colony:

No correlation could be derived between the fungal population density and physico chemical characteristics, though there is significant positive correlation between electrical conductivity and available iron (r=0.784; P<0.05), and a available copper and potassium (r=0.778; P<0.05) and significant negative correlations were observed between pH and electrical conductivity (r=-0.800; P<0.05) and available manganese and magnesium (r=0.707; P<0.05). Thus in the study area, the submergence and exposure of the sediment during different seasons may be a factor responsible for fungal diversity than the other physic-chemical factor.

ACKNOWLEDGEMENT:

The authors thank the Secretary and Correspondent A.V.V.M. Sri Pushpam College, Poondi – 615 503, Thanjavur Dt. for providing laboratory facilities.

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Received on 16.02.2011

Modified on 25.02.2011

Accepted on 15.05.2011

Research J. Science and Tech. 3(4): July-August. 2011: 175-179