杉木幼苗光合及叶绿素荧光特征对氮沉降的短期响应

为了探究模拟氮沉降条件下杉木幼苗光合及叶绿素荧光特征变化规律,从光合生理的角度探讨不同季节杉木幼苗对氮沉降的短期响应。选取杉木幼苗为实验对象,模拟氮沉降实验,设置4个处理水平对照(N0)、低氮（N30:30 kg/(hm²·a)、中氮（N60:60 kg/(hm²·a)、高氮(N90:90 kg/(hm²·a)。结果表明：添加氮以后,杉木幼苗的净光合速率(Pn),初始荧光产量(F₀)、最大荧光产量(F_m)、最大PSII光能转换效率(F_v/F_m)、PSII潜在活性(F_v/F₀)显著降低,水分利用率(Wue)显著增高(P<0.05)。随着氮沉降水平的增加,气孔导度(Gs)与蒸腾速率(Tr)呈现先升高后下降趋势,水分利用率呈现先下降后升高趋势。在中氮和高氮处理下,F_v/F_m、F_v/F₀值显著降低(P<0.05)。在冬季,净光合速率与气孔导度、蒸腾速率和胞间二氧化碳浓度呈极显著正相关(P<0.01),春季,净光合速率与气孔导度和蒸腾速率呈极显著正相关(P<0.01),与胞间二氧化碳浓度呈负相关。氮沉降累积达一定阈值后,增加蒸腾失水,从而降低植株的水分利用效率。在冬季,净光合速率主要受到气孔限制的影响,热耗散增加,PSII反应中心出现光抑制现象,到春季,过量的氮沉降累积破坏了幼苗的光合结构,导致胞间二氧化碳浓度上升而净光合速率下降,非气孔限制成为影响净光合速率的主要原因。中氮处理可能使叶绿体中PSII潜在活性减弱,光反应中心光合电子的传递能力降低,导致光合效率下降。

Short-term Response of Photosynthesis and Chlorophyll Fluorescence Characteristics of Fir Seedlings to Nitrogen Deposition

To explore the change law of the photosynthesis and chlorophyll fluorescence characteristics of fir seedlings under simulated nitrogen deposition condition, the short-term response of fir seedlings to nitrogen deposition in different seasons was discussed from the perspective of photosynthesis physiology. The fir seedlings were selected as experimental subjects, and the nitrogen deposition experiment was simulated with four treatment levels of the control (N0), low nitrogen (N30:30 kg/(hm².a)), medium nitrogen (N60:60 kg/(hm².a)), and high nitrogen(N90:90 kg/(hm².a)). The results showed that after adding nitrogen, the net photosynthesis rate (Pn), initial fluorescence yield (F₀), maximum fluorescence yield (F_m), maximum PSII light energy conversion efficiency (F_v/F_m) and PSII potential activity (F_v/F₀) were significantly reduced, while water utilization rate (Wue) increased significantly (P<0.05). With the increase of nitrogen deposition level, stomatal conductance (Gs) and transpiration rate (Tr) showed a tendency of increase first and then decrease, and the water use efficiency showed a trend of first decrease then increase. With the medium and high nitrogen treatment, F_v/F_m and F_v/F₀ values were significantly reduced (P<0.05). In winter, the net photosynthesis rate was significantly and positively correlated with stomatal conductance, transpiration rate and intercellular CO2 concentration (P<0.01); and in spring, the net photosynthesis rate was significantly and positively correlated with stomatal conductance and transpiration rate (P<0.01), and negatively correlated with intercellular CO2 concentration. After the accumulation of nitrogen deposition reached a certain threshold, the water loss was increased, which reduced the water utilization efficiency of the plant. In winter, the net photosynthesis rate was mainly affected by the stomatal limit, heat dissipation increased, and the PSII reaction center showed photo-suppression phenomenon; when it turned to spring, the excessive accumulation of nitrogen deposition destroyed the photosynthesis structure of seedlings, resulting in an increase in the concentration of carbon dioxide between cells and a decrease in the net photosynthesis rate. Then the non-stomatal limits became the main reason for the impact on the net photosynthesis rate. The medium nitrogen treatment could reduce the potential activity of PSII in chlorophyll, and the photosynthetic electron transfer capacity of the photoreaction center decreases, resulting in the decrease of photosynthesis efficiency.