Canopy-Level Photochemical Reflectance Index from Hyperspectral Remote Sensing and Leaf-Level Non-Photochemical Quenching as Early Indicators of Water Stress in Maize

In this study, we evaluated the effectiveness of photochemical reflectance index (PRI) and non-photochemical quenching (NPQ) for assessing water stress in maize for the purpose of developing remote sensing techniques for monitoring water deficits in crops. Leaf-level chlorophyll fluorescence and canopy-level PRI were measured concurrently over a maize field with five different irrigation treatments, ranging from 20% to 90% of the field capacity (FC). Significant correlations were found between leaf-level NPQ (NPQ(leaf)) and the ratio of chlorophyll to carotenoid content (Chl/Car) (R-2 = 0.71, p < 0.01) and between NPQ(leaf) and the actual photochemical efficiency of photosystem II (Delta F/F-m') (R-2 = 0.81, p < 0.005). At the early growing stage, both canopy-level PRI and NPQ(leaf) are good indicators of water stress (R-2 = 0.65 and p < 0.05; R-2 = 0.63 and p < 0.05, respectively). For assessment of extreme water stress on plant growth, a relationship is also established between the quantum yield of photochemistry in PSII (Phi P) and the quantum yield of fluorescence (Phi F) as determined from photochemical quenching (PQ) and non-photochemical quenching (NPQ(leaf)) of excitation energy at different water stress levels. These results would be helpful in monitoring soil water stress on crops at large scales using remote sensing techniques.

在本研究中，我们评估了光化学反射指数（PRI）和非光化学猝灭（NPQ）在评估玉米水分胁迫方面的有效性，目的是开发用于监测作物水分亏缺的遥感技术。在一块设置了五种不同灌溉处理（田间持水量的20% - 90%）的玉米田上，同时测量了叶片水平的叶绿素荧光和冠层水平的PRI。发现叶片水平的NPQ（NPQ（叶片））与叶绿素和类胡萝卜素含量之比（Chl/Car）之间存在显著相关性（R² = 0.71，p < 0.01），NPQ（叶片）与光系统II的实际光化学效率（ΔF/Fm'）之间也存在显著相关性（R² = 0.81，p < 0.005）。在生长早期，冠层水平的PRI和NPQ（叶片）都是水分胁迫的良好指标（分别为R² = 0.65，p < 0.05；R² = 0.63，p < 0.05）。为了评估极端水分胁迫对植物生长的影响，还建立了光系统II的光化学量子产额（ΦP）与荧光量子产额（ΦF）之间的关系，该关系由不同水分胁迫水平下激发能的光化学猝灭（PQ）和非光化学猝灭（NPQ（叶片））确定。这些结果将有助于利用遥感技术大规模监测作物的土壤水分胁迫。