دانلود رایگان مقاله بوم شناسی میکروب های خاک در یک جنگل گرمسیری

abstract

Present work enumerated nine groups of microorganisms in the soil samples drawn at 10depths from two mangrove sites for four seasons in two years, along with 23 physicochemical characteristics in a mangrove forest. The microbial density was higher in dense mangrove sediments than that in sparse ones. Among the microorganisms, actinobacteria, total heterotrophic bacteria (THB), thraustochytrids, yeasts and fungi were high in dense mangrove sediments. Microbial counts reduced with increasing soil depth. Physical factors displayed profound effect on microbes than chemical factors did. Among the physical factors, the dense mangrove sediment exhibited many fold higher silt, clay, redox potential, lower sand and higher pore water salinity than sparse mangrove sediment did. Among the chemical factors, total organic carbon (TOC) was 52% and soil nitrogen was 4.5% higher in dense mangrove sediment than that in sparse mangrove sediment. This work reiterated significance of mangrove forest for conserving marine microbiota for maintaining carbon and nutrients in coastal sediment.

.7. Discussion

Mangroves provide a unique ecological environment for diverse microbial communities, which are fundamental to the functioning of the habitats. In the mangrove system, activities of microbes are predominant in decomposing organic matter, making protein rich detritus food for fishes, recycling of nutrients, carbon fluxes as well as climate change. A variety of abiotic and biotic factors influenced the density of microorganisms. All these factors change with time and spatial heterogeneity. The microbes areadapted to varied physical and chemical conditions of mangrove systems (Kathiresan, 2000; Holguin et al., 2001a, 2001b; Kathiresan and Bingham, 2001; Kathiresan and Qasim, 2005; Rajendran and Kathiresan, 2007; Sahoo and Dhal, 2009; Kathiresan, 2011). Microbial density in relation to soil depth and type of mangrove forests are largely unknown for mangrove sediment, although it is known for seasonal changes. Bearing this in mind the present study was undertaken to analyze the microbial density in relation to the soil physical and chemical characteristics in a mangrove forest, located in southeast coast of India. Mangrove is a detritus-based ecosystem and hence is colonized with a rich population of saprophytic microorganisms, distributed all through the seasons in order to decompose the organic matter, available in the biotope. For instance, the highest counts of azotobacters or fungi were recorded in premonsoon, yeasts or thraustochytrids in monsoon, Trichoderma in summer, and THB or lactobacilli in postmonsoon. The counts of nitrogen fixing autotrophic cyanobacteria were recorded maximum in postmonsoon and the nitrogen fixing azotobacters in monsoon (Table 1). In general wet seasons appeared to be favourable for microbial colonization. This is accordance with the fact that the degree of wetness is an important factor regulating microbial cycling of organic matter in the mangrove soil (Alongi et al., 1993, 2005a, 2005b).