Toxicological assessment of invasive Ageratina adenophora on germination and growth efficiency of native tree and crop species of Kumaun Himalaya.

The present study was designed to assess the allelopathic potential of invasive weed Ageratina adenophora leaf extracts on seed germination and seedling development efficiency of native tree [viz. Quercus leucotrichophora A. Camus (Oak) and Pinus roxburghii Sarg. (Pine)] and crop [(Triticum aestivum L. (Wheat) and Lens culinaris Medik. (Lentil)] species of Kumaun Himalaya. Pot experiments were conducted in the glasshouse of the Botany Department, D.S.B. Campus, Kumaun University Nainital, following a Completely Randomized Block Design (CRBD) with three treatments (C1-25%, C2-50%, and C3-100% of aqueous leaf extract) and one control, each with five replicates. The experiment lasted one year for tree species and continued until the seed maturation phase for crop species. Parameters such as seed germination proportion, root and shoot measurements, biomass, and crop productivity traits were recorded accordingly. Our bioassay results indicated that the inhibitory effect of leaf extracts on the measured traits of the selected native species was proportional to the applied extract concentrations of A. adenophora. Overall, lentil among crops and oak among tree species exhibited more inhibition compared to wheat and pine, respectively. At the highest concentration, reductions of 44%, 34%, 36%, and 24% in biomass production capacity were recorded for wheat, lentil, pine, and oak, respectively, while wheat and lentil productivity decreased by up to 33% and 45%, respectively. These results suggest that water-soluble allelochemicals produced by A. adenophora may impede the establishment of selected crop and tree species in agroecosystems and forest ecosystems invaded by this weed species. However, further studies on the characterization of phytochemicals and their specific role in seed germination and growth are warranted. Furthermore, the allelopathic potential of A. adenophora can be explored for the preparation of biopesticides and nature-friendly option to improve soil health, crop productivity, and reduce environmental pollution and management of this invasive weed.

Dynamics of nitrogen mineralization and fine root decomposition in sub-tropical Shorea robusta Gaertner f. forests of Central Himalaya, India.

This study aimed to examine the effects of spatial and temporal variability in edaphic, and climatic attributeson soil net nitrogen mineralization rate, and to understand the pattern of fine root decomposition of dominant and co-dominant tree species, and its influence on the nutrient cycling in forest ecosystems. Study was carried out at four different sites in sub-tropical forest ecosystems of Shorea robusta, in foothills of Central Himalayan region, India. Co-dominant tree species at four sites were Mallotus philippensis (site A), Glochidion velutinum (site B), Holarrhena pubescens (site C), and Tectona grandis (site D). Buried bag technique was used for nitrogen mineralization, while fine root decomposition was determined using fine root mesh bags. Seasonal variation, soil depth, soil characteristics, and site variability, all significantly (p < 0.05) affected nitrogen mineralization rates. Fine root decomposition was significantly affected by nutrient concentration of fine roots. Total mineral nitrogen was maximum at site D (16.24 ± 0.96 µg g-1 soil), while minimum at site C (10.10 ± 0.84 µg g-1 soil). Maximum nitrogen mineralization (13.18 ± 0.18 µg g-1 month-1) was recorded during summer season at site D, while the minimum nitrogen mineralization (3.20 ± 0.46 µg g-1 month-1) was recorded during rainy season at site C. Inorganic-N and net nitrogen mineralization was relatively higher in 0-20 cm soil layer than 20-40 cm and 40-60 cm soil layer. The fine roots showed 70.61-74.82 % weight loss on completion of 365 days of decomposition process. Maximum fine root decomposition was observed in the G. velutinum, and minimum in T. grandis. A significant positive correlation (p < 0.05) was observed between root nitrogen and carbon content, and decomposition rates per month. This study concluded that the spatial and temporal variability in soil nitrogen mineralization rates and fine root decomposition optimises nutrient cycling in forest ecosystems, which can contribute to the development of sustainable forest management practices.

Monitoring the distribution pattern and invasion status of Ageratina adenophora across elevational gradients in Sikkim Himalaya, India.

Understanding the spread intensity and population dynamics of invasive plant species is a prerequisite for developing management strategies in the Himalayan Forest ecosystems that are experiencing an accelerated rate of climate change. Although there are studies on the occurrence of few invasive species in the Himalayan ecosystems, systematic information on their intensity of spread and species association is still missing. Considering existing data gaps, we aimed to assess the intensity of spread and distribution pattern of A. adenophora, one of the high-concern invasive species (HiCIS) of India that is causing havoc in the Himalayas, across an elevational gradient. Field data were collected in 2018 and 2021 in the Indian federal state of Sikkim, located in the Eastern Himalayas. We analyzed the population status and species association of A. adenophora along an elevational gradient ranging from > 600 m to 2700 m above sea level, which was divided into seven gradients of 300 m width, and each gradient was further randomly sampled. Overall, 81 species were present in association with A. adenophora, including 58 herbs, 19 shrubs, and 4 climbers, belonging to 30 families and 67 genera in the region. No other species continuously co-occurred along with A. adenophora throughout the elevation ranging from > 600 m to 2700 m. The species observed increased frequency (100%), density (40.51 ind./100 m2), and basal cover (11.25 cm2/m2) in the elevational gradient 1500-1800 m in 2018. In 2021, A. adenophora dominated the highest elevational gradient (< 2400-2700 m) with increased frequency (99.96%), density (58.41 ind./100m2), and basal cover (42.54 cm2/100m2), which demonstrated rapid invasion and improved plant health and reproductive vigor in comparison to the lower elevational gradient in Sikkim Himalaya. Despite being completely absent at the highest elevation (< 2400-2700 m), in 2018, it observed gregarious spread at the highest elevation in 2021, which is of serious concern to ecologists. The presence of the targeted species in all seven studied altitudinal gradients reflects stage III of the species invasion. An enormous shift in the distribution pattern along elevational gradients within a short time span is alarming for the Himalayan ecosystem since it is becoming a thriving habitat for invasive species owing to anthropogenic activity. We mapped the potential geographical extent using the species distribution model (SDM) and predicted the suitable habitat of distribution in Sikkim Himalaya. In order to curtail the spread and counteract the negative impact of this species on native vegetation in Sikkim Himalaya and ultimately reverse the process, local and regional initiatives for its biological control and management must be taken.

Energy and monetary efficiencies at the different altitudinal agroecosystems in central Himalaya, India.

Himalayas with diverse topographical and ecological zones sustain diverse agroecosystems. Differences in precipitation regimes, cropping systems, land-use systems and availability of resources significantly affect energy flow within agroecosystems (AGEs) of the region. Thus, the present study was aimed to evaluate the energy use pattern and economic profitability of different sized agroecosystems (small, medium and large) along the altitudinal gradient [very low altitude (VLA), low altitude (LA), mid altitude (MA) and high altitude (HA)] of Central Himalaya, India. The sampling was carried out following random stratified design and total 108 agroecosystems (4 altitudes× 3 sizes × 3 replicates × 3 seasons) were assessed. Data collected on quantities of agricultural inputs and outputs were converted to energy values using standard energetic constants and monetary values on the basis of local market price. Low altitude agroecosystems predominantly support cereal + pulse based cropping systems while, high altitudes favour cash crop cultivation (vegetables). Significant variation (P < 0.05) in total input and output energy was observed seasonally, while differences were insignificant across sizes and altitudes. Irrespective of the sizes and seasons, farmyard manure (organic fertilizer) contributed major share of total energy inputs across all altitudes in the order: HA AGEs (66.7 %) > MA AGEs (66.1 %) > VLA AGEs (62.6 %) > LA AGEs (52.1 %). The share of non-renewable energy inputs (inorganic fertilizers and fuel) declined along altitudinal gradient as: LA (31.1 %) > VLA (26.9 %) > MA (12.5 %) > HA (11.8 %). Seasonally, highest net energy was recorded during rainy season (92286 M J ha-1 yr-1) followed by summer (68906 M J ha-1 yr-1) and winter (18686 M J ha-1 yr-1). The economic yield significantly increased with increasing altitude and was recorded maximum for large sized agroecosystems. Energy use efficiency (EUE) differed distinctly (P < 0.05) across seasons and was recorded maximum during rainy season (8) while, across sizes and altitudes it did not vary significantly. EUE did not reflect any definite pattern along altitudinal gradient [HA AGEs (3.84) > VLA AGEs (3.81) > LA AGEs (3.56) > MA AGEs (3.01)]. Benefit-cost ratios (BCR) differed significantly (P < 0.05) along altitudes and was maximum at VLA AGEs (5.27) however, differences were insignificant across sizes and seasons. From present study, it can be concluded that season and altitude had significant impact on the energetics and economic flow of the agroecosystems while, no marked differences were observed for size classes. High altitude agroecosystems were energetically efficient while, monetary wise very low altitude systems.