The ameliorative effect of rice husk biochar on morpho-physiological and biochemical characteristics of African marigold (Tagetes erecta L.) under drought stress

Bedding plants are important elements in landscape construction, and their cultivation is limited by drought stress. Improving the cultivation medium of these flowers with organic materials such as biochar can be a sustainable and environmentally friendly solution to increase their tolerance to drought stress. For this purpose, a greenhouse research was conducted to mitigate the effects of drought on morpho-physiological and biochemical characteristics of African marigold by application of rice husk biochar. The factorial experiment was conducted with two factors of irrigation treatment at three levels of 100, 50 and 25% of the field capacity (FC) and biochar at three levels of 0, 3.5 and 7% (w/w) in a completely randomized design with 5 replications. The results showed that drought decreased the morphological factors of shoot height, shoot dry weight, number of leaves, number of lateral branches, number of flowers, and length and diameter of flowers, so their lowest value were obtained in 25% FC. Furthermore, the use of biochar improved the morphological traits mentioned under drought conditions. The activity of peroxidase and superoxide dismutase enzymes, hydrogen peroxide content, proline, malondialdehyde, soluble carbohydrates, chlorophyll a, chlorophyll b, total chlorophyll and carotenoid increased under drought conditions. The use of biochar reduced these biochemical traits under drought conditions. Furthermore, relative water content of leaf, cell membrane stability index and soluble proteins showed a decreasing trend under drought conditions, and the use of biochar led to the improvement of these traits. In general, 7% biochar was more effective than 3.5% in reducing the adverse effects of drought stress. Therefore, 7% rice husk biochar can be recommended as a suitable soil improver to increase tolerance to drought stress in bedding plants for landscape purposes, although more investigations are needed both under field cultivation and at other applied amounts.