Effect of exogenous melatonin on photosynthetic characteristics in cucumber seedlings under cadmium stress: a rapid detection method for the cadmium resistanceXinyi Wu, Henggang Li, Haotian Luo, Dian Lin and Xiaoting ZhouE3S Web Conf., 136 (2019) 07023DOI: https://doi.org/10.1051/e3sconf/201913607023