In order to reveal the effects of low temperature on chlorophyll fluorescence parameters in Hydrocotyle vulgaris, adopting the single factor experiment design, H. vulgaris was put in the artificial climate box, and five low temperature gradients of 15 (CK), 10, 5, 0, and -- 2 ℃ were designed. The results showed that with the decreases of temperature, the values of net photosynthetic rate, Fv/Fm, qP and ETR were decreased. The rule is that lo...