Effects Nitrogen Fertilization On Photosynthetic Capacity And Spectral Properties Of Phyllostachys Pubescens

Phyllostachys pubescens, is the most widely planted bamboo species with the highest economic and ecological benefit, which plays a very important role in the development of bamboo industry in our country. In this study, we used the modern plant physiology, biophysics and bamboo forestry cultivation as the theoretical basis, and used1year-,3year-and5year-old P. pubescens as the experimental materials which were treated by nitrogen fertilization. In order to provide theoretical basis for the rational fertilization in the ecological and efficient cultivation of P.pubescens, as well as building a fast, accurate and non-destruction measurement technique for fertilization, we investigated the growth of diameter at breast height and the production of bamboo shoots and woods, and determined the pigment content, photosynthetic rate, chlorophyll fluorescence kinetics, reflectance spectra and fluorescence spectra of the leaves. The main research results as follows:(1) The production of winter bamboo shoots, spring bamboo shoots and bamboo woods was raised according to the increase of nitrogen fertilization level, and it was raised by15.3%(P<0.01),27.1%(P<0.01) and41.0%(P<0.01), respectively, at the fertilization level of250kg·hm-2. However, the production was not markedly increased following the increase of fertilization level. Comparing to the fertilization in July, the production of winter bamboo shoots, spring bamboo shoots and bamboo woods was significantly increased by fertilization in May, with the increase of57.3%(P<0.01),13.3%(P<0.01) and21.2%(P<0.01), respectively.(2) The pigment content and photosynthetic rate in P. pubescens leaves were markedly increased by nitrogen fertilization. At the level of250kg·hm-2, the content of chlorophyll a, chlorophyll b and carotenoids was raised by19.9%(P<0.01),31.7%(P<0.01) and14.0%(P<0.01), respectively, and the Amax was raised by16.5%(P<0.01). Beside that, Cond reached to the maximum level while Ci with the minimum level. There were no significant difference in the pigment content and photosynthetic rate between the levels of400kg·hm-2and250kg·hm-2. The effects of nitrogen fertilization on3year-old and5year-old P. pubescens were similar to that on1year-old plants. Comparing to the fertilization in July, the content of chlorophyll a, chlorophyll b and carotenoids was increased by12.2%(P<0.05),15.3%(P<0.05) and10.4%(P<0.05), respectively, and the Amax and Cond were also raised remarkablely.(3) The fluorescence intensity at J, I and P point was markedly increased following the increase of nitrogen fertilization level, and the fluorescence reached to the highest intensity at the level of250kg·hm-2. The absorption flux per RC (ABS/RC), electron transport flux per RC (ETo/RC), trapped energy flux per RC (TRo/RC) and dissipated energy flux per RC (DIo/RC) were reduced by fertilization, and they were reduced by29.2%,33.7%and27.3%, respectively, at the level of250kg·hm-2. There were no remarkable change in maximum quantum yield of primary photochemistry (cpPo), quantum yield of electron transport (φpEo), and probability that a trapped exciton moves an electron into the electron transport chain beyond QA (Ψo). In the treatment of250kg·-hm-2nitrogen fertilization, phenomenological energy fluxes such as RC/CSo and RC/CSM were increased by55.8%(P<0.01) and73.2%(P<0.01), respectively, and performance indexes such as PIABS and PICS were increased by24.5%(P<0.01) and37.5%(P<0.01), respectively. Those results indicated that nitrogen fertilization affected the photosynthesis of P. pubescens leaves by increasing the reaction center activities of PSⅡ.(4) According to the increase of nitrogen fertilization level, the reflectance in leaves of P. pubescens was reduced gradually. In the treatment of250kg·hm-2nitrogen fertilization, the red edge position moved to long wavelength, and the reflectance was decreased by12.6%at wavelength of550nm, whose average rangeability reached to26.4%. The reflectance spectrum parameters such as SR705, mSR, rNDV1, mND and gNDV were markedly affected by nitrogen fertilization, and their change kept the same trends with the fertilization level. The spectrum parameters in the treatment of fertilization in May were higher than that in July.(5) In the fluorescence excitation spectra, the peak at wavelength of685nm (FH685) and735nm (FH730) showed the energy distribution of PSⅡ and PSⅠ, respectively. The ratio of peak value (FH685/FH735), peak area (FA685/FA735) and peak half-width (FW685/FW735) was significantly affected by nitrogen fertilization. With the increase of nitrogen fertilization level, FH685/FH735was decreased gradually, and FA685/FA735and FW685/FW735were increased gradually. Comparing with the control, a significant difference was found in FA685/FA735and FW685/FW735at the fertilization level of250kg·hm-2.The above results demonstrated that rational fertilization can promote the growth and development of P. pubescens, and increase the production of bamboo shoots and woods, that the chlorophyll fluorescence kinetics, reflectance spectra and fluorescence spectra from the leaves well related with the growth of P. pubescens. Therefore, the chlorophyll fluorescence kinetics and reflectance spectra can be used as the fast, accurate and non-destruction measurement technique for fertilization, and the response curve of fluorescence spectra to nitrogen fertilization might be used as a new method to identify and evaluate the fertilization effects in the future.