Diurnal Variation Process And The Physiological And Biochemical Mechanisms Of Photosynthesis Of Poplar Plantation Under Continuous Cropping

For insight into poplar’s parameters of gas exchange, characteristics of physiological and ecological in the state of continuous cropping, to provide chemical ways for solving the ecological problems of poplar plantation,we choose different continous cropping of 7-year-old poplar as materials in Gaoqiao Forest of Ningyang County, Taian, Shandong Province of China. By measuring photosynthetic parameters and biochemical parameters of different algebraic poplar, we explore the influence of different generations of poplar continuous cropping on gas exchange parameters and physiological and biochemical parameters, from the aspects of stomatal limitation and the stomatal limitation to reveal the influence of continuous cropping of poplar photosynthesis process and mechanism, from the aspect of plant photosynthetic physiology to reveal the declining mechanism of productivity on continuous cropping poplar plantation and reveal the response process and mechanism of the index of photosynthesis efficiency under poplar continuous cropping’s condition. Come to the conclusions:(1) The effects of continuous cropping on photosynthesis parametersBefore 13:00, the second-generation forest light use efficiency(LUE) is higher than the first-generation; 13:00 after, the first-generation`s LUE overtake the second-generation, and the first-generation`s net photosynthetic rate(Pn) is significantly lower than the first-generation,and water use efficiency(WUE) is higher than the first-generation. Before 13:00, the second-generation stomatal limitation value(Ls) is greater than the first-generation and intercellular CO2 concentration(Ci) is less than the first generation, indicating continuous cropping enhanced stomatal limitation of the morning period.(2) The effects of continuous cropping on biochemical parametersThe content of soluble sugar(Ss) and proline(Pro) of second-generation forest is higher than first-generation all day. The diurnal variation curves of superoxide dismutase, peroxidase and catalase have similar trends. The peak is at about 13:00, and it is manifested that first-generation is higher than the second-generation. The content of MDA of second-generation is higher the first-generation. That means continuous croping has increased the membrane lipid peroxidation. Meantime, the second-generation chlorophyll content is higher than second-generation, that means continuous croping causes barriers to the synthesis of chlorophyll.(3) Limiting factors of photosynthesisIntercellular CO2 concentration(Ci) and the change trend of stomatal limitation(Ls) on the contrary, and the change has the synchronicity of the two factors.( 11:00 in the morning time before) with time in the afternoon(after 13:00) limit of two generations of plantation Pn for different reasons, mainly to stomatal limitation in the morning,(This is due to the stomatal factors of CO2 are in short supply),while in the afternoon to the stomatal limitation(This is due to environmental factors of stress has led to the decrease of the mesophyll cells photosynthetic mechanism of photosynthetic capacity).