Physiological Response On Photosynthesis With Seedlings Of Two Ammopiptanthus (Leguminosae) Species To Low Temperature

Both Ammopiptanthus nanus (M.Pop.)Cheng f. and A.mongolicus are peculiar cold tolerant evergreen broad-leaved shrub in the northwest desert area of China, and have been listed as the national-level rare and endangered species, they can overwinter normally and maintain evergreen at -20°C~-30°C or even lower temperature. Their's unique biological characteristics and adaptability have important scientific research value for study the adaptation mechanisms of plants under extreme environmental conditions and plant ecosystem diversity. However, the mechanism of both species being able to overwinter normally and maintain evergreen under low temperature is not clear, and it has not been seen any interrelated research report at home and abroad. In the present study, seedlings of A.nanus and A.mongolicus were used as materials to investigate the effects of low temperature on leaf chlorophyll fluorescence parameters, chloroplast pigment contents and anti-oxidative system in chloroplast, and the capability and physiological response on photosynthesis to low temperature of both species were preliminarily studied. The results might provide some information on basic theory for the research of physiological response on photosynthesis to low temperature of the Ammopiptanthus, and might lay a foundation for further revealing and understanding the mechanism of resistance to low temperature of both species. These are not only have important significance for use and protection the endangered species, but also can provide evidences for plant photosynthesis research under special conditions. The main results are as follows:1.Low temperature above zero caused reversible inactivation of PSⅡreaction center of both species, and did not cause photoinhibition. Photosynthetic membrane systems were not damaged, the increased activity of antioxidant enzymes protected the thermal energy dissipation system of excess photon energy, and enhanced the self-protection ability of photosynthesis.2.Low temperature above zero had a certain impact on the absorption and transmission of light energy of both species, the antenna peripheral components of PSⅠand PSⅡwere more sensitive to low temperature above zero. Under low temperature above zero the capacities of dissipate excess light energy in the form of thermal were enhanced, which were self-protection mechanisms of both species'photosynthetic system. Both species'photosystem had strong adaptability and resistance to chilling temperature.3.Low temperature below zero caused irreversible inactivation of PSⅡreaction center of both species, thylakoid membrane were damaged, photochemical efficiency declined, caused serious photoinhibition. Under freezing temperature the capacity of dissipate excess photon energy in the form of thermal were enhanced, which could protect photosynthetic system from being damaged by freezing temperature.4.Under low temperature below zero, the antioxidant enzymes in both species of Ammopiptanthus still had high activity. To some extent it could protect the excitation channels of excess energy, and enhance the capacity of dissipate excess photon energy in the form of thermal. Both species'photosystem had strong adaptability and resistance to freezing temperature.5.Under low temperature, both species of Ammopiptanthus had a certain capacity of photosynthesis, and they could maintain photosynthetic efficiency at low level under low temperature below zero. Compared with the cold-sensitive plants, both species of Ammopiptanthus had stronger adaptability and tolerance to low temperature. The photosynthesis of both species of Ammopiptanthus have certain degree of difference under low temperature. Photochemical reaction of A.mongolicus was easily affected by low temperature above zero, while that of A.nanus had relatively poor tolerance to low temperature below zero.