Ameliorating effects of biochar on photosynthetic efficiency and antioxidant defense of Phragmites karka under drought stress.

Biochar (BC) has been reported to improve growth and drought resistance in many plants. However, adequate information on the drought resistance mechanism mediated by BC on Phragmites karka, a bioenergy plant, is not available. The impact of BC additions (0%, 0.75% and 2.5%) on plant growth and physiology of Phragmites karka under drought was examined. Growth parameters, soil water holding capacity and soil water content were significantly improved at 0.75% BC as compared with the un-amended controls. This was reflected by a system-wide increase in most measured plant parameters such as plant fresh and dry biomass, root to shoot ratio and root mass fraction with optimal water relation. Significant growth enhancement could be linked to high chlorophyll content, net photosynthetic rate and water use efficiency of plant under BC treatments. Plants treated with 0.75% BC experienced less oxidative stress due to higher photosystem II efficiency, electron transport rate and activity of antioxidant defense system. Ratio of reduced to total ascorbate, correlated positively with the drought tolerance optimum at 0.75% BC. Better water use efficiency stimulated net photosynthesis rate and efficient antioxidant defense, which helps in improving plant growth and makes P. karka a promising candidate for cultivation in arid habitats.