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• Study was conducted to determine the best medium for in vitro pollen germination of B. utilis. • An effect of sucrose, boric acid, calcium nitrate, magnesium sulfate, potassium nitrate and time of incubation on pollen germination and tube growth was investigated. • The germination rate and pollen tube length varied significantly with different concentrations and incubation time. • Pollen grains collected immediately after anther dehiscence showed the best germination ability however steadily decreased with time. The study was conducted to determine the optimum medium for in vitro pollen germination for B. utilis based on germination percentages and length of the pollen tube. Studies about pollen germination and tube growth of B. utilis are limited. Therefore, this study aimed to investigate the effects of sucrose (1, 3, 5, 10 and 15%), boric acid (25, 50, 100 and 200 ppm), calcium nitrate (50, 100, 200, 300 and 400 ppm), magnesium sulfate (50, 100, 200 and 300 ppm) and potassium nitrate (50, 100 and 200 ppm) and time of incubation on pollen germination and tube growth. Pollen germination rates and tube growth were recorded periodically at 2, 4, 6, and 10 h. The length varied significantly with different concentrations and incubation time. The germination rate and pollen tube length varied significantly with different concentrations and incubation time. Pollen germination was maximal (98 ± 6.1%) when the germination medium contained 10% sucrose solution supplemented with 100 ppm H 3 BO 3 , 300 ppm Ca(NO 3) 2 , 200 ppm MgSO 4 and 100 ppm KNO 3, after 6 h of incubation. In addition, results revealed that pollen grains collected immediately after anther dehiscence showed the best germination ability but gradually decreased with time. [ABSTRACT FROM AUTHOR]

The Himalayas is one of the most ecologically sensitive and fragile areas in the world. The climate of the region is dominated by the monsoon seasonality, with typical dry winters and abundant summer precipitations. Here, forest vegetation spreads up to the world’s highest elevations, where cold temperatures and early spring droughts represent the main limiting factors for growth. In this study, we applied a dendro-anatomical approach to assess xylem trait chronologies and their association to local climate variability in the diffused broadleaved Betula utilis D Don close to the treeline (above 3900 m a.s.l.). We measured tree-ring width on increment cores from 73 trees. On seven cores, we prepared 12 μm thick sections, which were analysed with ROXAS for the assessment of ring-based xylem parameters. We then built up the corresponding trait chronologies and analyzed them against the time series of monthly temperatures and precipitations. Mean ring width (MRW), mean vessel area (MCA_V) and ring-specific hydraulic conductivity (Kr) positively correlated with summer temperatures in the previous and current year. In addition, MCA_V was significantly associated with March precipitations. Instead, fibres’ area showed a widely negative correlation only with temperatures during the previous and current season suggesting that fibres get narrower when vessels are wider. These results revealed that Himalayan birch is well adapted to the monsoon seasonality and is responding positively to atmospheric warming, thus suggesting the potential for this species to further expand in altitude under the forecasted climate change scenarios. [ABSTRACT FROM AUTHOR]

Betula utilis is a major constituent of alpine treeline ecotones in the western and central Himalayan region. The objective of this study is to analyse for the first time the performance of different climatic predictors in modelling the potential distribution of B. utilis in the subalpine and alpine belts of the Himalayan region. Using Generalized Linear Models (GLM) we aim at examining climatic factors controlling the species distribution under current climate conditions. We evaluate the predictive ability of climate data derived from different statistical methods GLMs were created using least correlated bioclimatic variables derived from two different climate data sets: 1) interpolated climate data (i.e. WORLDCLIM; Hijmans et al., 2005), and 2) quasi-mechanistical statistical downscaling (i.e. CHELSA; Karger et al., 2016). Model accuracy was evaluated using threshold-independent (Area Under the Curve) and threshold-dependent (True Skill Statistics) measures. Although there were no significant differences between the models in AUC, we found highly significant differences (p ≤ 0.01) in TSS. We conclude that models based on variables of CHELSA climate data had higher predictive power, whereas models using WORLDCLIM climate data consistently overpredicted the potential suitable habitat for B. utilis . Although climatic variables of WORLDCLIM are widely used in modelling species distribution, our results suggest to treat them with caution when topographically complex regions like the Himalaya are in focus. Unmindful usage of climatic variables for environmental niche models potentially causes misleading projections. [ABSTRACT FROM AUTHOR]

The unavailability of weather records from the orography dominated high Himalayas restricts our understanding in long term perspective. However, remote high-altitude regions of Himalaya silently testify the regional climate and can provide valuable insights of real climatic challenges in the absence of instrumental observatories. The tree-species over such high-altitude regions with negligible anthropogenic pressure have the potential to reveal the clear climate upheavals in long-term perspective. In the present study tree-ring samples of Himalayan birch from a high-altitude cold-arid region of Lahaul-Spiti, Himachal Pradesh were analysed and two ring-width chronologies were developed. The response function analyses showed direct relationship between the summer temperature and ring-width chronologies of Himalayan birch. Using the relationship we have reconstructed mean summer temperature (June-July) back to AD 1752 for the Lahaul-Spiti region of Himachal Pradesh. We have developed the first record of summer temperature from the Indian western Himalaya using tree-ring-width chronologies that have direct relationship with summer temperature. Further, our study in accordance with instrumental as well as other tree-ring based summer temperature records suggested that the high-altitude western Himalaya is not warming unprecedently during summers. However, slight warming pattern have been observed in the summer temperature in the later part of the reconstruction. The temperature reconstruction also reflects strong spatial correlation with gridded temperature for the western Himalaya. [ABSTRACT FROM AUTHOR]

Litter decomposition plays a vital role in carbon and nutrient budget of forest ecosystems, but our understanding of this process for high altitude ecosystems, especially the timberline zone, is not very clear. We studied leaf litter decomposition of Betula utilis , which is the main timberline species of Western Himalaya. We placed 144 litterbags (each containing 10 g of oven dried litter) at three 'spatially well separated sites' in Oct 2014, to study the direction and magnitude of change in key variables associated with leaf litter decomposition and to test for generality of decomposition process across these spatially distant sites. The results revealed that initial nutrient concentration and lignin content of litter was significantly different for the sites. Further, magnitude of mass loss and decay rate was found to be greater for up to 34 weeks (19.03 ± 4.55% and 0.35 ± 0.06 yr−1 respectively), which reached 47.01 ± 1.98% and 0.17 ± 0.01 yr−1 respectively, after 4 years. N, P and K concentrations showed sharp decease for up to 34 weeks, after which N consistently increased with incubation time, whereas P and K concentrations were relatively stable. The lignin and cellulose contents decreased consistently with incubation time (from 12.29 ± 1.21% to 5.21 ± 0.50% and from 16.87 ± 1.01% to 8.25 ± 0.50% respectively). There were significant increases in C:N and lignin:N ratios for up to 34 weeks, followed by a continuous decrease thereafter. The change in various variables associated with litter decomposition was not consistent among the sites and the magnitude of change was greater during initial stages due to leaching of labile components. The increase in N and decreases in C:N and lignin:N ratios with incubation time might be due to microbial immobilization of N and are important for nutrient conservation in timberline ecosystems, as such changes are related to faster decomposition of recalcitrant fraction of litter, N mineralization and building of soil nutrient pool. • We assessed leaf litter decomposition at three distantly located sites in timberline zone of western Himalaya. • Betula utilis leaf litterbags were placed on forest floor and consequently sampled for up to 206 weeks (4 years). • Leaf litter decomposition rate in timberline forest was considerably slow and differed among sites. • Nitrogen content increased, whereas C:N and lignin:N ratios gradually decreased in later stages of decomposition. • Slow litter decomposition could be a key process in nutrient release and efficient nutrient recycling in timberline forests. [ABSTRACT FROM AUTHOR]

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. Microbial endophytes and soil enzymes with respect to B. utilis rhizosphere. Unlabelled Image • Assessment of physico-chemical properties and enzyme activity in B. utilis rhizosphere soil • Assessment of microbial colonization with respect to mycorrhizae and dark septate endophytes • Presence of B. utilis roots – nematode association under sub-alpine location • Occurrence of negative rhizosphere effect by B. utilis roots [ABSTRACT FROM AUTHOR]

Betula utilis (BU), an important medicinal plant that grows in high altitudes of the Himalayan region, has been utilized traditionally due to it's antibacterial, hepatoprotective, and anti-tumor properties. Here, we demonstrated the longevity and amyloid-β toxicity attenuating activity of B. utilis ethanolic extract (BUE) in Caenorhabditis elegans. Lifespan of the worms was observed under both the standard laboratory and stress (oxidative and thermal) conditions. Effect of BUE was also observed on the attenuation of age-dependent physiological parameters. Further, gene-specific mutants and green fluorescent protein (GFP)-tagged strains were used to investigate the molecular mechanism underlying the beneficial effects mediated by BUE supplementation. Our results showed that BUE (50 μg/ml) extended the mean lifespan of C. elegans by 35.99% and increased its survival under stress conditions. The BUE also reduced the levels of intracellular reactive oxygen species (ROS) by 22.47%. A delayed amyloid-β induced paralyses was observed in CL4176 transgenic worms. Interestingly, the BUE supplementation was also able to reduce the α-synuclein aggregation in NL5901 transgenic strain. Gene-specific mutant studies suggested that the BUE-mediated lifespan extension was dependent on daf-16 , hsf-1 , and skn-1 but not on sir-2.1 gene. Furthermore, transgenic reporter gene expression assay showed that BUE treatment enhanced the expression of stress-protective genes such as sod-3 and gst-4. Present findings suggested that ROS scavenging activity, together with multiple longevity mechanisms, were involved in BUE-mediated lifespan extension. Thus, BUE might have potential to increase the lifespan and to attenuate neuro-related disease progression. Unlabelled Image • Betula utilis ethanolic extract (BUE) extends the lifespan of Caenorhabditis elegans under normal and stress conditions. • BUE enhances stress resistance (oxidative, thermal): reduces lipofuscin in C. elegans. • BUE enhances the expression of both SOD-3 and GST-4 transgenic strains of C. elegans. • BUE enhances the neuroprotection in transgenic C. elegans. [ABSTRACT FROM AUTHOR]