Biochar-compost addition benefits Phragmites australis growth and soil property in coastal wetlands.

Salinity stress is common for plants growing in coastal wetlands. The addition of biochar in the soil may alleviate the negative effect of salinity through its unique physicochemical properties. To test this, we conducted a greenhouse experiment where the cosmopolitan wetland plant Phragmites australis was subjected to four salinity treatments (0, 5, 10 and 15‰) and three biochar treatments (no biochar addition, with biochar addition and with biochar-compost addition, both biochar and compost were made from P. australis) in a factorial design. Both biochar addition and biochar-compost addition to the substrate enhanced belowground mass of P. australis, application of biochar-compost significantly increased total mass by 35.5% and net photosynthesis rate of P. australis by 51.4%. Both biochar addition and biochar-compost addition significantly increased soil organic carbon content by 62.9% and 31.7%, respectively, but decreased soil ammonium nitrogen content. In the saline soil, application of the mixture of biochar-compost had a strong, and positive effect on the growth of P. australis, compared to biochar alone. Therefore, incorporation of biochar and compost might be an appropriate approach to improve the productivity of P. australis growing in coastal wetlands, where soil salinity is a common environmental stress.