遮荫对水稻冠层叶片SPAD值及光合、 形态特性参数的影响

SPAD（soil-plant analysis and development）计是一种快速、 方便、 非破坏性的诊断植物叶片相对叶绿素或氮含量的仪器，与传统的氮营养诊断方法相比，此仪器节省时间、 劳力和资源。本试验通过未遮荫和遮荫的方法观察水稻冠层叶片SPAD值、 叶绿素含量、 叶绿素荧光、 光合参数、 叶片厚度和比叶重（叶片干重除以叶片的面积）等生理形态指标的变化，建立SPAD值与光系统II（PSII）最大量子产量（Fv/Fm）之间的回归关系。结果表明，遮荫条件下，甬优9号(YY9)和丙9363(B9363)冠层叶片变薄、 SPAD值、 叶绿素a/b、 比叶重、 电子传递速率（ETR）降低,但快速光曲线的初始斜率无明显变化; 同时， 遮荫导致了叶片的呼吸速率、 最大净光合(Pmax)、 量子效率、 光补偿点和饱和点降低，表明水稻叶片为适应弱光环境， 降低光合能力、 减少呼吸消耗， 以增加对有限光能的利用。不同光照条件下，水稻冠层叶片SPAD值与PSII的Fv/Fm的回归方程呈指数式关系（YY9 R2=0.896; B9363 R2=0.833）, 表明SPAD计可以快速、 无损、 有效地评估水稻冠层叶片的光合作用进程，当SPAD值小于35时，其光合过程可能处于受损状态。

Effect of shading on leaf SPAD values and the characteristics of photosynthesis and morphology of rice canopy

 Soil-plant analysis and development （SPAD） meter is a quick, portable，non-destructive diagnostic tool for the measurement of relative chlorophyll or nitrogen（N）content in leaves. SPAD meter is time, labor and resources saving compared to traditional N nutrition diagnosis methods. The experiment with and without shading treatments was conducted in paddy field with rice cultivars YY9 and B9363. The physiomorphology indices including leaf SPAD values, chlorophyll contents, chlorophyll fluorescence and photosynthetic parameters, specific leaf weight and blade thickness in rice canopy were measured to establish the regression relationship between SPAD values and the maximum quantum output in photosystem II (Fv/Fm of PSII) at rice growth stages. The results show that under the shading treatment, there is decline in the leaf SPAD values, chlorophyll a/b ratios, specific leaf weights and electron transport rate.   The thickness of leaves becomes thin in rice canopy;   the initial slopes of rapid light curves do not change obviously.   The respiration rate, the maximum net photosynthetic efficiency (Pmax), the quantum efficiency, light compensation point and saturation point of leaves are decreased to reduce photosynthetic capacity and consume through breath, and increase the utilization of limited light energy under weak light environment. Under both the shading and without shading treatments, exponential relationships exist between the leaf SPAD values and the Fv/Fm of PSII in rice canopy. For cultivar YY9, the  coefficient  of determination R² is 0.896 and for B9363 is 0.833. Therefore, the leaf photosynthetic process in rice canopy can be evaluated quickly, non\|destructively and efficiently using SPAD meter, and the SPAD reading of lower than 35 may be used to indicate the impairment in photosynthetic process of rice.