Seasonal dynamics of soil microbial biomass in fragmented patches of subtropical humid forest of Jaintia hills in Meghalaya, Northeast India

Aim of the study: The aim of the study was to assess the seasonal dynamics of microbial biomass and its contribution to soil system along a fragment size gradient in subtropical humid forest of Meghalaya. Area of study: The study was conducted in forest fragments located at Jarain and adjoining areas in Jaintia Hills of Meghalaya, northeast India. Material and Methods: Forest fragments of sizes ranging from 3.8 to 105 ha were selected for the study and grouped into Small (< 5 ha), Medium (> 5 and < 15 ha), Large (>15 and < 50 ha) and Very Large (105 ha) classes. Three experimental plots each of 20 x 20 m were established at the forest edge and at 50 m distance assigned as 'interior' microsite in each of the fragments for sampling of soil. Soil samples (0-10 cm depth) from each of the experimental plots were collected in replicates on seasonal interval and microbial biomass was estimated by the fumigation extraction method. Important findings: Microbial biomass- C, -N and -P varied significantly (p< 0.05) between the fragment sizes, microsites and seasons. The microbial biomass was higher in the interior as compared to the edge. It was also high during the winter season. Overall, soil microbial biomass -C, -N and -P ranged from 260 to 969; 25 to 95 and 8 to 67 µg g-1 respectively. The contribution of microbial biomass -C, -N and -P to soil organic carbon, total Kjeldahl nitrogen and phosphorus ranged from 1.48 to 1.81 %, 2.54 to 4.54 % and 3.41 to 5.22 % respectively. Fragmentation alters the microenvironmental conditions and soil properties that in turn affect the microbial biomass. Highlights: This interaction of plant, soil and microbial community would gradually degrade in the fragments due to change in vegetation composition and structure, microclimatic conditions and soil physical and chemical properties. Our results suggests that microbial mediated ecosystem processes such as nutrient cycling are more susceptible to variation at the edge which may become unstable and unpredictable in forest fragments exposed to various human disturbances.