The Nano-Enriched Biochar Enhanced Photosynthetic Pigments, Growth and Essential Oil Production of Chamomile under Drought Stress

The utilization of nanoparticles-enriched biochars offers a promising approach by combining the benefits of both biochar and nanomaterials, thereby enhancing plant tolerance against water scarcity. Therefore, this research was conducted to assess the effects of solid biochar and nanohydroxyapatite-enriched biochars (1, 3, and 5 g/kg biochar) on the physiological performance and growth of German Chamomile (Matricaria chamomilla L.) under various watering levels (80–100, 55–75, and 30–50% field capacity, as normal irrigation, and moderate and severe water stresses). Water stress increased H2O2 generation, lipid peroxidation, enzymatic antioxidants, phenols, ascorbic acid contents, and essential oil, but decreased membrane stability index, nutrient and water uptakes, chlorophylls a and b, carotenoids, flavonoids, anthocyanin, and shoot and flower masses. However, application of solid, and especially nanohydroxyapatite-enriched biochars, enhanced shoot and flower masses and essential oil production under normal and limited water supply via decreasing oxidative stress, enzymatic and non-enzymatic antioxidant activities, and increasing soil pH and cation exchange capacity, nutrient contents of leaves, MSI and leaf water content and pigments. Different levels of nanohydroxyapatite similarly influenced plant performance under normal and stressful conditions. Therefore, the lowest concentration of nanohydroxyapatite (1 g/kg) was determined as an appropriate treatment for enriching biochar and improving German chamomile performance under drought stress.