Effects of low temperature and poor light stress on the chlorophyll fluorescence parameters in the seedling of pepper

The effects of the combination of poor light with two lower temperatures and critical temperatures stress on the chlorophyll fluorescence parameters in the seedling of pepper were studied by using modulated chlorophyll fluorometer. The results indicated that under two lower temperatures (19 ℃/12 ℃) and critical temperature (15 ℃/8 ℃), Fv/Fm, Fv/Fo and qP decreased, but qN increased. The change of the four parameters were less under the light density of 30 μmol?m-2?s-1 than the light density of 90 μmol?m-2?s-1, which meant that poorer light reduced the sensitivity of pepper to low temperature and increased the photochemical activity of PS , but the photochemical quenching (qP) decreased and the non-photochemical quenching(qN) increased at the same time.