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Relationships Between Soil Physico-chemical Properties and Total Viable Bacterial Counts in Sunderban Mangrove Forests, Bangladesh

MOHAMMAD ZABED HOSSAIN
Department of Botany, University of Dhaka, Dhaka 1000, Bangladesh

CHAMAN BINTA AZIZ
Department of Botany, University of Dhaka, Dhaka 1000, Bangladesh

MIHIR LAL SAHA
Department of Botany, University of Dhaka, Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

Although soil bacterial communities are one of the important biotic components that influence decomposition and nutrient mineralization in the terrestrial ecosystems, factors driving this biotic community in the Sunderban mangrove forests are not well studied. The present study examined the importance of soil physico?chemical properties in driving soil bacterial communities in the Sunderban mangrove forests, Bangladesh. Soils were collected from 12 locations under four sites, namely Koromjal, Kotka, Hironpoint, and Dublarchar of Sunderban forests. Results showed a large range of variation in total bacterial colony counts (7.65 × 104 ? 14.5 × 104 cfu/g soil), soil moisture (9.0 ? 27.0%), total nitrogen (0.057 ? 0.158%), available nitrogen (0.504 ? 2.016 μg/g soil), soil salinity (20.99 ? 34.99 mg chloride/g soil), and organic carbon (0.460 ? 0.885%). Data of the present study revealed that the number of total viable bacterial count was significantly and positively correlated only with total nitrogen content in soil indicating that total nitrogen content is the major driving factor of bacterial communities in the Sunderban mangrove forest soils.

Keywords: Bacterial colony counts, Soil physico-chemical properties, Sunderban mangrove forests

Location: Koromjal, Kotka, Hironpoint, and Dublarchar in the Sunderban mangrove forests of Bangladesh

Start Date: 00-08-2008

End Date: 00-12-2008

Program Area: Resource Development and Management

Commodity: Bio fertilizer

Objectives:

1. To study the bacterial population size by counting total viable bacteria and to examine the relative importance of the various physico?chemical properties in driving bacterial colony counts in the Sunderban mangrove forest soils.

Methodology:

Study site description and soil sampling: In order to ensure a large range of variation in soil physico?chemical properties and bacterial colony counts present in the samples, soils were collected from four distant sites, namely Koromjal (22⁰22´36.24´´N 89⁰36´34.23´´E), Kotka (21⁰54´42.79´´N 89⁰44´20.47´´E), Hironpoint (21⁰50´19.34´´N 89⁰26´33.84´´E), and Dublarchar (21⁰44´06.91´´N 89⁰28´11.21´´E) in the Sunderban mangrove forests of Banglades. Then, from each of the four sites, three locations, 50 m distant from each, were selected to collect soil samples. Thus, soils were collected from a total of 12 locations. Soil samples were collected from 0 ? 10 cm depth and kept in a plastic bag. After collection, soil samples were brought to the laboratory and separated into two subsamples; one for bacteriological analysis that was kept in a refrigerator and the other one for the analysis of soil physico?chemical properties. The collected soils were sieved through a 2 mm mesh screen to remove plant roots, rocks, and macrofauna. After sieving, soil samples were analyzed to characterize their physico?chemical properties. Soil sampling was done in September, 2008. Analysis of soil physico?chemical properties: Soil moisture content (%) was determined by weight loss at 65ºC for 24 h. The pH of the soil was measured in a soil water suspension (1 : 2, soil : water). Total nitrogen (%) was determined by Kjeldahl method following extraction from 2 g soil with conc. H₂SO₄. Available nitrogen content was also determined by Kjeldahl method following extraction from 10 g dry soil using 1N KCl solution. Organic carbon content (%) of the soil was determined by Wakley and Black method using 1 g soil. Organic matter (%) was determined by multiplying the value of organic carbon by 1.724 (Van Bemmelen factor). Soil salinity was determined as chloride content by following methods described elsewhere. Bacteriological analysis: Nutrient agar medium was used for the enumeration of bacteria present in soil samples. The pH was adjusted before addition of agar and sterilization. Serial dilution plate technique was used for the isolation of microorganisms. One gram sample was diluted (1 : 100) with 100 ml distilled water in a sterile conical flask and shaken well. One ml of this suspension was transferred to 9 ml of sterile water for tenfold (1 : 10) dilution and by following serial dilutions further diluted up to 105 times. Plating in duplicate plates was made for each diluted sample. One ml of each of the diluted sample was taken in a sterilized Petri dish by pipette. Then, molten agar medium was poured and mixed thoroughly by rotating the Petri dish, first in one direction and then in the opposite direction. After setting the medium, the plates were inverted and incubated at 37ºC for 48 h in an incubator (Memmert GmbH + Co Kg 8540 Schwabach). After 48 h of incubation, the plates having well discrete colonies were selected for counting. The selected plates were placed on a colony counter (Digital colony counter, DC?8OSK 1000086, Kayagaki, Japan) to count the number of colonies.

Source of Information: Dhaka Univ. J. Biol. Sci. 21(2): 169‐175, 2012 (July)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The results of the present study showed that soil physico?chemical parameters such as soil moisture, total nitrogen, available nitrogen, organic carbon, and salinity measured varied largely among the 12 locations under the four sites of Koromjal, Kotka, Hironpoint and Dublarchar in the Sunderban mangrove forests. Such variation in the soil properties from location to location might be related with the local environmental factors such as micro?climate, vegetation above the ground and disturbances. Number of viable bacterial count was significantly and positively correlated with only the total soil nitrogen content rather than available inorganic nitrogen indicating the importance of the soil total nitrogen in driving the bacterial population in the study area. The result of the present study corresponded with the findings of other study that reported that dissolved organic nitrogen and amino acids were more important than inorganic nitrogen for bacteria in the marine habitats .

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