Title : Population status, soil properties and microbial colonization in Himalayan Silver Birch (Betula utilis D. Don)
The Himalayan silver birch (Betula utilis D. Don), commonly known as bhojpatra, is a multipurpose and broadleaved deciduous tree. It grows up to 4500 m asl and represents one of the dominant species of the tree line in Indian Himalayan region (IHR). It often grows in association with Abies pindrow, A. spectabilis, Prunus cornuta, Acer accuminatum, Sorbus foliolosa, Pinus wallichiana, and Rhododendron campanulatum. Its bark is a striking feature which is smooth, shining and reddish white bearing numerous paper-like layers with broad horizontal rolling nature. B. utilis grows efficiently in acidic, neutral and alkaline soils and shady moist habitat. The tree is a source of many biochemical compounds which possesses anti-cancerous, anti-HIV, antimicrobial, antioxidant, and antifertility properties. Factors such as over-exploitation, deforestation, overgrazing, natural calamities, snowdrift, forest fire, landslides, etc., influence the regeneration of B. utilis. The species has also been reported for a suppressive effect on the microbial population in its rhizosphere.
The aim of the present study is (1) to assess its population status in IHR, and (2) to evaluate soil and plant growth related properties including physicochemical and enzyme activities in rhizosphere soil along with the root associated microbial communities. The study sites were located at Rohtang Pass, Solang Valley and Hamta Pass in Himachal Pradesh, North Western Himalaya, India. Ten quadrates (10x10) were laid for the assessment of birch population. The physicochemical properties and activities of six soil enzymes (arylsulfatase, acid and alkaline phosphatase, β -glucosidase, dehydrogenase, and urease) were estimated following standard procedures in two, active (summer) and dormant (winter), seasons. Root-associated microbial communities were studied following microscopy using trypan blue staining method.
The highest total tree and B. utilis density recorded was 1430 Ind ha-1 and 700 Ind ha-1, respectively. The soil moisture content, pH, organic carbon, available phosphorus, nitrogen and potassium were recorded ranging from 15.17- 43.92%, 5.17 - 6.03, 1.64 ± 0.06 - 3.36 ± 0.01 %, 0.005 ± 0.001 – 0.0375 ± 0.002 ppm, 11 ± 3 - 57 ± 3 ppm and 140 ± 1 - 477 ± 7 ppm, respectively. Higher alkaline phosphate (411.21 ± 7.49 µg pNP/g), β –glucosidase (48.77±1.69 µg pNP/g) and dehydrogenase (0.84 ± 0.03 µg TPF/g) activities were recorded in dormant season, while higher urease (28.40 ± 0.33 µg N/g dry soil/h), arylsulfatase (24.16 ± 0.88 µg pNP/g and phosphatase (331.63 ± 5.41µg pNP/g) activities were recorded in active season. Microscopy revealed colonization of a variety of microbial endophytes (both bacterial and fungal) in birch roots, being higher in active season. Fungal endophytes have majorly consisted of fungal mycelium and dark septate endophytes. Some nematode-like structures were also observed in the cortical root cells of birch.
Frequent monitoring of the populations might form the baseline for conservation and management of birch forest. Soil microbial communities are responsible for the variation in various ecological processes through biogeochemical cycling under llow-temperatureenvironment. Further, the association of specific groups of microorganisms and activity of soil enzymes my be considered as the health indicators of soil, plant and the environment.
Take Away Notes:
• Ecological importance of a timber line tree species (Himalayan birch) of IHR along with its population status.
• The economic importance of Himalayan birch for its bioprospection.
• The role of soil microbial and enzyme activities as indicators of a specific climate.