Yale University, School of Forestry and Environmental Studies, 370 Prospect Street, New Haven, Connecticut 06511 USA.
Am J Bot. 2002 Jan;89(1):88-94. doi: 10.3732/ajb.89.1.88.
We studied relationships between spectral reflectance and photosynthesis of mountain paper birch, Betula papyrifera var. cordifolia (Regel) Fern., leaves from three different elevations on Mt. Mansfield (summit elevation 1339 m above sea level) in the Green Mountains of Vermont, USA. The different reflectance indices we used all suggested progressively increasing stress with increasing elevation. The photochemical reflectance index (PRI) indicated lower photosynthetic radiation use efficiency at higher elevations, the red edge position (λRE) indicated lower chlorophyll concentrations at higher elevations, and the structure-independent pigment index (SIPI) indicated a higher carotenoid : chlorophyll a ratio at higher elevations. The rate of change in these indices with changes in elevation was much higher than we have observed in our studies of red spruce and balsam fir reflectance along a similar elevational gradient; we take this to be an indicator of the greater susceptibility of paper birch to elevation-related stressors compared to the very stress-tolerant conifers. At all light levels, photosynthesis decreased with increasing elevation; this pattern was most noticeable in the light-saturated rate of photosynthesis (A(sat)), which was nearly twice as high in low-elevation leaves (17.0 ± 1.0 μmol·m(-2)·s(-1)) than in high-elevation leaves. The quantum yield of photosynthesis (Φ) exhibited a similar trend. Furthermore, the highest elevation leaves showed a much sharper transition from the light-limited to the light-saturated part of the light response curve than did the lowest elevation leaves. The photochemical reflectance index was highly correlated with A(sat) (r(2) = 0.99) and Φ (r(2) = 0.96). In addition to contributing to our knowledge of the ecophysiology of paper birch along a steep environmental gradient, these results are further evidence of the usefulness of reflectance measures for the rapid and noninvasive detection of plant stress, especially when used in conjunction with direct measurements of photosynthesis.
我们研究了美国佛蒙特州绿山曼斯菲尔德山（海拔 1339 米）三个不同海拔高度的山毛榉叶（Betula papyrifera var. cordifolia (Regel) Fern.）的光谱反射率与光合作用之间的关系。我们使用的不同反射率指数都表明，随着海拔的升高，压力逐渐增大。光化学反射率指数（PRI）表明，较高海拔地区的光合作用辐射利用效率较低，红边位置（λRE）表明，较高海拔地区的叶绿素浓度较低，结构独立色素指数（SIPI）表明，较高海拔地区的类胡萝卜素与叶绿素 a 的比值较高。这些指数随海拔变化的变化率比我们在红松和香脂冷杉沿类似海拔梯度的反射率研究中观察到的要高得多；我们认为这表明，与非常耐受胁迫的针叶树相比，山毛榉对与海拔相关的胁迫因素的敏感性更高。在所有光照水平下，光合作用随海拔升高而降低；这种模式在光饱和光合作用速率（A(sat)）中最为明显，低海拔叶片的 A(sat)（17.0±1.0 μmol·m(-2)·s(-1)）几乎是高海拔叶片的两倍。光合作用的量子产率（Φ）也表现出类似的趋势。此外，最高海拔的叶片在光响应曲线的光限制部分与光饱和部分之间的转变比最低海拔的叶片要陡峭得多。光化学反射率指数与 A(sat)（r(2) = 0.99）和 Φ（r(2) = 0.96）高度相关。除了有助于我们了解陡峭环境梯度下山毛榉的生态生理学之外，这些结果进一步证明了反射率测量在快速、非侵入性地检测植物胁迫方面的有用性，尤其是与光合作用的直接测量相结合时。
