Soil Organic Carbon Pools under <i>Terminalia chebula</i> Retz. based Agroforestry Systemin Himalayan Foothills, Indiax

Physiological and molecular insights into the allelopathic effects on agroecosystems under changing environmental conditions

Allelopathy is a natural phenomenon of competing and interfering with other plants or microbial growth by synthesizing and releasing the bioactive compounds of plant or microbial origin known as allelochemicals. This is a sub-discipline of chemical ecology concerned with the effects of bioactive compounds produced by plants or microorganisms on the growth, development and distribution of other plants and microorganisms in natural communities or agricultural systems. Allelochemicals have a direct or indirect harmful effect on one plant by others, especially on the development, survivability, growth, and reproduction of species through the production of chemical inhibitors released into the environment. Cultivation systems that take advantage of allelopathic plants' stimulatory/inhibitory effects on plant growth and development while avoiding allelopathic autotoxicity is critical for long-term agricultural development. Allelopathy is one element that defines plant relationships and is involved in weed management, crop protection, and microbial contact. Besides, the allelopathic phenomenon has also been reported in the forest ecosystem; however, its presence depends on the forest type and the surrounding environment. In the present article, major aspects addressed are (1) literature review on the impacts of allelopathy in agroecosystems and underpinning the research gaps, (2) chemical, physiological, and ecological mechanisms of allelopathy, (3) genetic manipulations, plant defense, economic benefits, fate, prospects and challenges of allelopathy. The literature search and consolidation efforts in this article shall pave the way for future research on the potential application of allelopathic interactions across various ecosystems.

Impact of progressive and retrogressive land use changes on ecosystem multifunctionality: Implications for land restoration in the Indian Eastern Himalayan region

Land use change, anthropogenic exploitation and climate change have impacted the flow of services in the Himalayan region. The dominant land uses in the region including natural forest, degraded forest, rubber (Hevea brasiliensis) plantations, Areca catechu plantations, Areca agroforestry and Piper agroforestry were considered for the study. A progressive shift in land use was defined as the conversion and restoration of a less productive system like degraded land to plantations or agroforestry systems. A land use shift was considered retrogressive when it entails the establishment of plantations after clearing natural forests or anthropogenic disturbance of natural forests resulting in forest degradation. The objectives of the current study were to estimate changes in soil properties, stand structure, tree biomass, fine root production and carbon storage following a progressive and retrogressive shift in land usage. The aboveground biomass (105.9 Mg ha-1) was highest in the natural forest, followed by Areca agroforestry (100.2 Mg ha-1) and least in the degraded forest (55.3 Mg ha-1). The aboveground biomass carbon (47.1 Mg ha-1) of Areca agroforestry was comparable with that of natural forest (51.3 Mg ha-1). The highest proportion of passive carbon concentrations was observed under Areca agroforestry, whereas the lowest (4.13 g kg-1) was found under Areca plantations in the 0-25 cm soil depth. With the progressive shift in land use from degraded forest to agroforestry, SOC stocks increased by 27.6 % and 3 % under Piper and Areca agroforests, respectively. SOC stocks decreased by 8.5 % with a shift in land use from natural forests to Areca plantations. The production of fine roots was maximum in the Areca agroforest (13.2 Mg ha-1) and lowest under rubber plantations (4.2 Mg ha-1). The results show that progressive shifts from degraded forest to agroforestry can considerably increase carbon stocks, plant species diversity and multifunctionality than shifts to monoculture plantations thereby supporting improved biodiversity and mitigation of climate change.

Build-up of labile, non-labile carbon fractions under fourteen-year-old bamboo plantations in the Himalayan foothills

Carbon fractions under different bamboo species viz., Bambusa balcooa, Bambusa bambos, Bambusa nutans, Dendrocalamus hamiltonii, Dendrocalamus asper and Dendrocalamus strictus were evaluated to understand the potential of these different bamboo species in soil rehabilitation in Himalayan foothills. The highest accumulation of the different carbon fractions likes very labile (6.12 mg g⁻¹), less labile (2.55 mg g⁻¹) and non-labile (11.40 mg g⁻¹) was observed under D. hamiltonii, while highest labile fraction (3.17 mg g⁻¹) was recorded under D. strictus. The highest active (8.85 mg g⁻¹) and passive pool (13.95 mg g⁻¹) were recorded under D. hamiltonii. Higher carbon management index (CMI) was obtained under D. hamiltonii (186.04) which was comparable with D. strictus (182.66) and B. nutans (179.24). Among all the six species, D. hamiltonii had the highest buildup of active and passive pool in both the soil depths. Bamboo plantations irrespective of the different species helped in enhancing the SOC fraction and enhanced C buildup in the soil in comparison to the open fallow land and holds potential in combating the problems of land degradation and soil rehabilitation.