Exploring The Impact and Influence of Rhizospheric Microbes On the Decomposition of Mangrove Leaf Litter and Biogeochemical Cycling

Abstract

Mangrove ecosystems are recognized as repositories of organic carbon. The role of rhizospheric microbes is crucial in the decomposition of leaf litter and plant debris, contributing significantly to the recycling of organic matter in soil. The disintegration of leaf litter results in release of leachates such as tannins. This study elucidated the role of rhizospheric microbes, including bacteria and fungi, in the decomposition of mangrove leaf litter and carbon cycling. Furthermore, the impact of mangrove leaf litter leachate on microbial growth and biofilm development was investigated. The leaf litter of two predominant mangrove species (Excoecaria agallocha and Heritiera fomes) from Bhitarkanika mangrove ecosystem, Odisha exhibited tannin content of 343.23±8.422342 μg/ml and 290.53 ±14.00135 μg/ml, respectively. Bacterial isolate Serratia marcescens HL2215 and a fungal isolate Trichoderma sp. CNSC-2 from the mangrove leaf litter were utilized to investigate the effect of litter leachate on microbial activity and cellulose-degrading potential. Expression of the genes (bcsG, bcsZ, GH5, and GH31) responsible for lignocellulose degradation in response to mangrove tannins was also analyzed. Microcosm experiment was conducted to investigate the efficiency of leaf litter degradation by microbes in planktonic and biofilm mode, revealing a gradual decrease in biofilm formation accompanied by a concurrent rise in CMCase activity. The planktonic mode exhibited the highest CMCase activity, with the consortium showcasing the maximum cellulose degradation (3.00950 U/ml), followed by fungus (2.684831 U/ml) and bacterium (1.855269 U/ml). The observed outcome demonstrated that bacterium and fungus sequentially play significant roles in leaf litter decomposition and carbon cycling in the mangrove ecosystem.