Endophytes associated with Himalayan silver birch (Betula utilis D. Don) roots in relation to season and soil parameters

Abstract

Biological processes in soil are driven and mediated by root and soil microbiome (microbial communities) and are sensitive to many environmental variations. Soil microbial communities compete for nutrient and space and form mutualistic associations with host plants. Rhizosphere, the connecting site of plant roots with soil, influences the soil health and plant-microbe interactions. Soil enzyme activity, which is considered to be the biological indicator of soil health, is significantly influenced by microbial functioning. Betula utilis D. Don is a dominant treeline forming species that has been extensively studied for the impact of climate-mediated variations in sub-alpine Himalayan region. However, the microbial ecology of this species remains almost unexplored. Therefore, the present study aims to assess the endophytic communities associated with B. utilis roots along with the status of enzymes, nutrients, and microbial communities in rhizosphere soil in two seasons from three sites in North-Western Himalaya. Activity of soil enzymes (acid and alkaline phosphatase, aryl sulfatase, β-glucosidase, urease and dehydrogenase) varied statistically with respect to seasons. Except dehydrogenase, the soil enzymes activity correlated with pH, organic carbon, and phosphorus content in soil. High dehydrogenase activity is attributed to high microbial activity in dormant season. B. utilis roots were found to be colonized with a range of microbial communities namely, mycorrhizae, dark septate endophytes (DSE), bacterial endophytes and unidentified nematode like structures (NLS). While, in general, DSE colonization was higher during growing season, mycorrhizae dominated the roots during dormant season. Significant differences were obtained only in mycorrhizal colonization with respect to seasons and sites. Further, significant correlations were obtained among soil nutrients, enzyme activity, and microbial counts during growing season. B. utilis roots exerted negative rhizosphere effect on microbial communities. The study will have implications in understanding plant-microbe interactions under sub-alpine Himalayan region.