The effects of the canopy microenvironment on the nitrogen and carbon metabolism of tea plants

Abstract: 【Objectives】The microenvironment of tea plants affects the growth, especially the carbon and nitrogen metabolism and the tea qualities of the tea. Optimized canopy microenvironment can improve the qualities of the harvested objects. In this study, the canopy microenvironment of tea plants was changed by shading with different cover materials to explore how the carbon and nitrogen metabolism and the tea qualities of the tea plants were influenced.【Methods】Plot trials were carried out and three different kinds of shading films with different light and thermal transmittance characters were tested, with no cover as the control. The changes in the temperature and humidity of air over the canopy and tea tree leaves were measured and compared, the primary productions of the carbon and nitrogen metabolism in the tea shoots of different seasons were assayed with the amino acid components analyzer, the HPLC and so on.【Results】 After 10 days shading treatments, the differences in the microenvironment over tea shoots and the carbon and nitrogen metabolism have been observed. 1) The temperature of leaves and air above the canopy, the luminous intensity over the canopy of tea plants are decreased, and the air humidity is increased in different extents for all the three sheltering films. The air temperature of the canopy was decreased 3.1℃ by covering with the heat insulated net and 1.6℃ by the silver net, but the decrease was not significant at 12: 00 am, 14: 00 pm and 16: 00 pm. For the black net treatment, the temperature of air and leaves in the morning is higher than the other two cover treatments, and as the climate temperature increasing, the microenvironmental temperature and leaf surface temperature wavies. 2) The net photosynthetic rates of tea plants with covered treatments decrease significantly. Trough were shown with the black net and control treatments at 12: 00 am, named as a nap phenomenon. The nap phenomenon do not exist with the silver net and heat insulated net treatments at 12: 00 am. The intercellular CO2 concentrations in tea leaves of the covered treatments show an increasing trend compared with control, with the highest in the heat insulated net treatment. 3）During the high temperature and strong luminous intensity season, making moderate shading for the tea plants can promote the nitrogen metabolism and weak the carbon metabolism in some extent, and improve the qualities of the tea shoots in different seasons. Those mainly show as that he contents of chlorophyll, nitrogen, phosphorus, potassium, the contents of the total amino acid and so on are improved significantly, the contents of the components of amino acid, such as the theanine, glutamic acid, aspartic acid, are improved significantly, and the total carbon, C/N, the tea polyphenol are decreased significantly, the catechin fractions decreased but the index of catechin quality is increased, the index of bitter taste is decreased, also the canopy microenvironment under the heat insulated net has the best effects on improving the tea qualities among the three different shading nets. 4) The tea yields are decreased in some extents after the tea plants are covered by different shading materials.【Conclusions】The canopy microenvironment of tea plants can affect on the growth, especially the carbon and nitrogen metabolism and the tea qualities of the tea plants. But the tea yields are decreased in some extents after the tea plants are covered by different shading materials.