Elsayed Salah, Mistele Bodo, Schmidhalter Urs
Department of Plant Sciences, Technische Universität München, Emil-Ramann-Str. 2, D-85350 Freising-Weihenstephan, Germany.
Funct Plant Biol. 2011 Jun;38(6):523-533. doi: 10.1071/FP11021.
Leaf water potential (LWP) is an important indicator of plant water status. However, its determination via classical pressure-chamber measurements is tedious and time-consuming. Moreover, such methods cannot easily account for rapid changes in this parameter arising from changes in environmental conditions. Spectrometric measurements, by contrast, have the potential for fast and non-destructive measurements of plant water status, but are not unproblematic. Spectral characteristics of plants vary across plant development stages and are also influenced by environmental factors. Thus, it remains unclear whether changes in leaf water potential per se can reliably be detected spectrometrically or whether such measurements also reflect autocorrelated changes in the leaf water content (LWC) or the aerial plant biomass. We tested the accuracy of spectrometric measurements in this context under controlled climate chamber conditions in series of six experiments that minimised perturbing influences but allowed for significant changes in the LWP. Short-term exposure of dense stands of plants to increasing or decreasing artificial light intensities in a growth chamber more markedly decreased LWP than LWC in both wheat and maize. Significant relationships (R2-values 0.74-0.92) between LWP and new spectral indices ((R940/R960)/NDVI; R940/R960) were detected with or without significant changes in LWC of both crop species. The exact relationships found, however, were influenced strongly by the date of measurement or water stress induced. Thus, global spectral relationships measuring LWP probably cannot be established across plant development stages. Even so, spectrometric measurements supplemented by a reduced calibration dataset from pressure chamber measurements might still prove to be a fast and accurate method for screening large numbers of diverse lines.
叶片水势（LWP）是植物水分状况的重要指标。然而，通过传统压力室测量来确定叶片水势既繁琐又耗时。此外，此类方法难以轻易解释因环境条件变化而导致的该参数的快速变化。相比之下，光谱测量有潜力对植物水分状况进行快速且无损的测量，但也并非毫无问题。植物的光谱特征在不同的植物发育阶段会有所不同，并且还受环境因素影响。因此，目前尚不清楚能否通过光谱测量可靠地检测叶片水势本身的变化，或者此类测量是否也反映了叶片含水量（LWC）或地上植物生物量的自相关变化。在一系列六个实验中，我们在可控气候室条件下测试了光谱测量在此背景下的准确性，这些实验将干扰影响降至最低，但允许叶片水势有显著变化。在生长室中，将密集的植物群落短期暴露于人工光强度增加或降低的环境中，小麦和玉米的叶片水势下降比叶片含水量下降更为明显。在两种作物的叶片含水量有无显著变化的情况下，均检测到叶片水势与新的光谱指数（（R940/R960）/归一化植被指数；R940/R960）之间存在显著关系（R²值为0.74 - 0.92）。然而，所发现的确切关系受测量日期或诱导的水分胁迫的强烈影响。因此，可能无法在植物发育的各个阶段建立用于测量叶片水势的通用光谱关系。即便如此，通过压力室测量得到的简化校准数据集进行补充的光谱测量，可能仍被证明是一种快速且准确的筛选大量不同品系的方法。
