Institute of Agroenvironmental and Forest Biology, National Research Council of Italy (CNR), Via Marconi 2, 05010 Porano, TR, Italy; Department for Innovation in Biological, Agro-Food and Forest Systems (DIBAF), University of Tuscia, Via S. Camillo de Lellis snc, 01100 Viterbo, Italy.
Institute of Agroenvironmental and Forest Biology, National Research Council of Italy (CNR), Via Marconi 2, 05010 Porano, TR, Italy; Institute of Agroenvironmental and Forest Biology, National Research Council of Italy (CNR), Via Salaria km 29,300, 00016, Monterotondo Scalo, Roma, RM, Italy.
Sci Total Environ. 2018 Jan 15;612:1030-1041. doi: 10.1016/j.scitotenv.2017.08.167. Epub 2017 Sep 7.
This study investigates the functionality of a Mediterranean-mountain beech forest in Central Italy using simultaneous determinations of optical measurements, carbon (C) fluxes, leaf eco-physiological and biochemical traits during two growing seasons (2014-2015). Meteorological variables showed significant differences between the two growing seasons, highlighting a heat stress coupled with a reduced water availability in mid-summer 2015. As a result, a different C sink capacity of the forest was observed between the two years of study, due to the differences in stressful conditions and the related plant physiological status. Spectral indices related to vegetation (VIs, classified in structural, chlorophyll and carotenoid indices) were computed at top canopy level and used to track CO fluxes and physiological changes. Optical indices related to structure (EVI 2, RDVI, DVI and MCARI 1) were found to better track Net Ecosystem Exchange (NEE) variations for 2014, while indices related to chlorophylls (SR red edge, CL red edge, MTCI and DR) provided better results for 2015. This suggests that when environmental conditions are not limiting for forest sink capacity, structural parameters are more strictly connected to C uptake, while under stress conditions indices related to functional features (e.g., chlorophyll content) become more relevant. Chlorophyll indices calculated with red edge bands (SR red edge, NDVI red edge, DR, CL red edge) resulted to be highly correlated with leaf nitrogen content (R>0.70), while weaker, although significant, correlations were found with chlorophyll content. Carotenoid indices (PRI and PSRI) were strongly correlated with both chlorophylls and carotenoids content, suggesting that these indices are good proxies of the shifting pigment composition related to changes in soil moisture, heat stress and senescence. Our work suggests the importance of integrating different methods as a successful approach to understand how changing climatic conditions in the Mediterranean mountain region will impact on forest conditions and functionality.
本研究利用光学测量、碳（C）通量、叶片生态生理和生化特征的同步测定，研究了意大利中部地中海山区山毛榉林的功能。在两个生长季节（2014-2015 年）中，气象变量存在显著差异，突出了 2015 年仲夏热应激与水分减少相结合的情况。结果，由于两年间胁迫条件和相关植物生理状况的差异，观察到森林的 C 汇能力不同。在冠层顶部计算了与植被有关的光谱指数（VIs，分为结构、叶绿素和类胡萝卜素指数），并用于跟踪 CO 通量和生理变化。与结构有关的光学指数（EVI 2、RDVI、DVI 和 MCARI 1）被发现更能跟踪 2014 年净生态系统交换（NEE）的变化，而与叶绿素有关的指数（SR 红边、CL 红边、MTCI 和 DR）在 2015 年提供了更好的结果。这表明，当环境条件不对森林汇能力构成限制时，结构参数与 C 吸收更紧密相关，而在胁迫条件下，与功能特征（如叶绿素含量）有关的指数变得更加相关。利用红边波段计算的叶绿素指数（SR 红边、NDVI 红边、DR、CL 红边）与叶片氮含量高度相关（R>0.70），而与叶绿素含量的相关性较弱，但仍然显著。类胡萝卜素指数（PRI 和 PSRI）与叶绿素和类胡萝卜素含量都有很强的相关性，这表明这些指数是与土壤水分变化、热应激和衰老相关的色素组成变化的良好替代指标。我们的工作表明，将不同方法相结合是了解地中海山区气候条件变化将如何影响森林条件和功能的重要方法。
