Bacterial Diversity of Decomposing Leaf Litters of Polyalthia longifolia (Sonner.) Thw. and Rhododendron arboreum Sm. Under Natural Condition

Abstract

The role of microorganisms in the decomposition of plant material is of immense importance. A large amount of plant litter is added annually to the soil through leaf fall and death of plants. As the plant materials fall on the ground, they are immediately attacked by various groups of soil microorganisms and soon after, the process of decomposition is initiated. Microorganisms being heterotrophic in their mode of nutrition are responsible for the decay processes and thereby releasing locked up nutrients from the dead bodies of plants and animals. The result of decomposition is that the building blocks required for life can be recycled. Decomposition is a determining factor for the functioning of ecosystems because litter dynamics (litter fall and decomposition) constitute a key process in the regulation of the recycling of carbon and nutrients. Bacterial diversity of decomposing leaf litter of two selected common tree species Polyalthia longifolia (Sonner) Thw. and Rhododendron arboreum Sm. were studied for a period of one year. For the present investigation, two broad leaved forest stands at different altitudes of Meghalaya were selected. The study sites selected were Upper Shillong at a higher altitude and Mawkyrdep at a lower altitude. The forest stand at a higher altitude is situated at 1861 m above sea level and the other forest stand at a lower altitude is situated at 889 m above sea level. For the isolation of bacteria, Nutrient Agar (Difco-manual, 1953) medium was used. Results showed that bacterial CFU was higher in the decomposing leaf litter of P. longifolia as compared to Rhododendron arboreum. It was also higher in the high altitude forest stand as compared to the low altitude forest stand. Altogether, 11 bacterial species were isolated from both the decomposing leaf litters at the two forest stands. Eleven species were isolated from the high altitude forest stand, of which 9 species were isolated from decomposing leaf litter of P. longifolia and 7 species were isolated from R. arboreum, whereas, at the low altitude forest stand, 9 species were isolated from both the decomposing leaf litters, of which, 8 species were isolated from decomposing leaf litter of P. longifolia and 7 species from R. arboreum. The common bacterial species isolated from both the decomposing leaf litters at the two forest stands were Bacillus mycoides, Pseudomonas aeruginosa and Rhizobium sp. Bacillus cereus and Micrococcus luteus were restricted to P. longifolia at the high altitude forest stand. Moisture content was also higher at the high altitude forest stand as compared to the low altitude forest stand and higher at the decomposing leaf litter of P. longifolia. pH of decomposing leaf litter was slightly more acidic at the high altitude forest stand than at the low altitude forest stand. It can be concluded that higher moisture content at the high altitude and the dominant bacterial species Bacillus mycoides, Pseudomonas aeruginosa, and Rhizobium sp. facilitated the rate of decomposition in decomposing leaf litter of P. longifolia.