Growth and morpho-physiological attributes of drought-tolerance in quinoa (Chenopodium quinoa Willd.) under biochar-amended soil

Chenopodium quinoa Willd. is a highly nutritious pseudocereal with the potential to address global food insecurity challenges due to current climate change scenarios. However, the water deficit significantly impacted quinoa’s growth despite its inherent tolerance to drought. This research explores quinoa’s morpho-physiological responses to water stress and investigates soil amendments, particularly biochar, as a potential agronomic strategy to mitigate the adverse effects of water scarcity. The current literature highlights that biochar, a carbon-rich material derived from pyrolyzed organic matter, can enhance soil physio-chemical properties, improve plant water status, and promote growth under water limitations. Similar to the reproductive phase, the vegetative growing cycle of quinoa is notably susceptible to the detrimental effects of drought. Agronomic strategies must be implemented to mitigate the negative effects of water stress during the vegetative growing cycle. Applying organic amendments, particularly biochar, becomes increasingly important in this context. A series of experiments were conducted to investigate the impact of organic amendments on the vegetative development of quinoa under water stress. These experiments were initiated by analyzing responses of two biochar types (derived from woodchips and vineyard pruning) and vermicompost (from cattle manure) on the Danish variety Titicaca, which is particularly susceptible to water stress during its early growth stages and widely cultivated around the globe particularly in Europe. The amendments were applied alone and in combination at a 2% (w/w) rate. The results revealed that among the organic amendments tested, woodchip biochar, alone and mixed with vermicompost, significantly improved quinoa’s growth, specifically biomass, by 22% compared to stressed control and water use efficiency. In contrast, vineyard pruning biochar negatively affected plant growth. Successively, the same variety, Titicaca, was further analysed under different woodchip biochar rates (best performing organic amendment) (0%, 2%, and 4%) and two watering regimes (100% and 50% evapotranspiration restitution). The 2% biochar rate enhanced vegetative growth, biomass by 23%, and panicle development by 66% compared to 4%, which negatively affected these parameters, highlighting the importance of choosing the right dose based on soil type. Subsequently, considering the 2% woody biochar rate, five quinoa varieties of different origins were compared and subjected to a water stress period starting from the 12 leaf stage. The results showed that biochar application consistently improved plant growth, particularly plant biomass, leaf nutrients, and enhanced C:N ratio, improving nitrogen bioavailability and translocation. Additionally, biochar addition in the soil positively affected root morphology, including elongation by 23% and development particularly fresh and dry biomass by 122% and 127%, respectively, and physiological attributes, i.e., chlorophyll content, plant water status and gas exchange than non-amended soil, although varietal differences were observed. The Pakistani variety UAFQ7 exhibited superior drought tolerance, while the Danish Titicaca was more sensitive to water stress. Moreover, the Italian variety Quipu significantly increased its yield-contributing traits and even doubled under biochar-amended soil than non-treated ones. Under water stress conditions, varieties positively influenced their stomatal morphology, stomatal regulation, and transpiration rates under biochar-amended soils by enhancing stomatal aperture dimensions and stomatal density, particularly for UAFQ7 by doubling the stomatal density than non-treated soil. Collectively, this research underscores the potential of biochar as a sustainable soil amendment to mitigate drought stress in quinoa by enhancing root development, physiological attributes, and overall plant performance. The findings highlight the need to select appropriate biochar types and rates and quinoa varieties to optimize growth under water-limited conditions, offering a promising agronomic strategy for improving quinoa cultivation in drought-prone regions.