Effects of low nitrogen stress on photosynthetic characteristics and chlorophyll fluorescence parameters of maize cultivars tolerant to low nitrogen stress at the seedling stage

【Objectives】Chlorophyll fluorescence parameters are often used to evaluate the function of photosynthetic organs and the influence of the environment pressure. Tolerance to low nitrogen stress are largely different with different maize genotypes, which can be reflected through photosynthesis and chlorophyll fluorescence characteristics. In this paper, the response of four maize cultivars to low nitrogen stress were compared at the seedling stage for the purpose of further understanding of the mechanism of their low nitrogen tolerance.【Methods】A completely random two-factor pot experiment was conducted in greenhouse. The main factor was maize cultivars, two tolerant cultivars of Zhenghong 311 and Chengdan 30, two non-tolerant cultivars of Xianyu 508 and Beisan 2; The second factor was N levels: N 15 mmol/L(CK, Hoagland nutrition solution), 0.5 mmol/L(low N stress, LN1), N: 0.05 mmol/L(extremely low N stress, LN2). The items were measured, including individual plant dry matter and nitrogen accumulation, relative chlorophyll content(SPAD)of leaves, and the photosynthesis parameters. 【Results】The dry matter and nitrogen accumulation amounts of per plant, relative chlorophyll content(SPAD)of leaves, net photosynthetic rate(Pn), stomatal conductance(Gs), transpiration rate(Tr), variable fluorescence(Fv), maximum fluorescence(Fm), potential activity of PSⅡ(Fv/F0), the primary maximum photochemical efficiency of PSⅡ(Fv/Fm), effective light quantum yield of PSⅡ(Fv′/Fm′)and photochemical quenching coefficient(qP)of the four maize hybrids are declined sharply under the low nitrogen stress conditions. Compared with the low nitrogen sensitive maize cultivars, the reduced ranges of these parameters of the low nitrogen tolerant maize cultivars are much lower. In contrast to the above parameters, the intercellular CO2 concentrations are remarkably increased in the tested maize hybrids, and the concentration increases of the low nitrogen tolerant maize cultivars are rather less than those of the sensitive ones. The actual photochemical efficiencies of PSⅡ in the light(ΦPSⅡ)of the low nitrogen tolerant maize cultivars are decreased, while those of the low nitrogen sensitive maize cultivars are increased. In addition, the non-photochemical quenching coefficients(NPQ)of the low nitrogen tolerant maize cultivars are increased, while those of the low nitrogen sensitive maize cultivars are decreased.【Conclusions】 The negative effect of N stress on the photosynthetic system of the low nitrogen tolerant maize cultivars can be offset to some extent, so a relatively high nitrogen accumulation is kept to improve chlorophyll content and maintain high effective light quantum yield of PSⅡ(Fv′/Fm′)and photochemical quenching coefficient(qP), and keep high net photosynthetic rate(Pn)to guarantee a higher dry matter productivity.