Abstract: Taking squash (Cucurbita pepo L.) variety Alan as test object, this paper studied the effects of exogenous Ca²⁺ on the morphological and photosynthetic characteristics and chlorophyll fluorescent parameters of squash seedlings under the cross-stress of high temperature and strong light. Under the stress, applying 5-20 mmol·L^-1 of Ca²⁺ increased the plant height, leaf area, chlorophyll and carotenoid contents, photosynthetic rate (P_n), stoma conductance (G_s), transpiration rate(T_r), maximal PSⅡ efficiency (F_v/F_m), actual PSⅡ efficiency (Φ_PSⅡ), and photochemical queching coefficient (q_P), and decreased the intercellular CO₂ concentration (C_i) and non-photochemical fluorescence quenching coefficient (NPQ), suggesting that this application of exogenous Ca²⁺could effectively mitigate the damage of high temperature and strong light stress on the squash seedlings leaf, and make it keep more rapid photosynthetic electron transfer rate and higher PSⅡ electron transfer activity. Among the treatments of applying Ca²⁺, 10 mmol Ca²⁺·L^-1had the best effect. When the Ca²⁺application rate exceeded 40 mmol·L^-1, no mitigation effect was observed on the high temperature and strong light stress.

Key words: squash (Cucurbita pepo), high temperature and strong light stress, Ca²⁺ treatment, photosynthesis, chlorophyll fluorescence