Abstract
Remote sensing techniques in terms of monitoring plants’ responses to environmental constraints have gained much attention during recent decades. Among these constraints, climate change appears to be one of the major challenges in the Mediterranean region. In this study, the main goal was to determine how field spectrometry could improve remote sensing study of a Mediterranean shrubland submitted to climate aridification. We provided the spectral signature of three common plants of the Mediterranean garrigue: Cistus albidus, Quercus coccifera, and Rosmarinus officinalis. The pattern of these spectra changed depending on the presence of a neighboring plant species and water availability. Indeed, the normalized water absorption reflectance (R975/R900) tended to decrease for each species in trispecific associations (11–26%). This clearly indicates that multispecific plant communities will better resist climate aridification compared to monospecific stands. While Q. coccifera seemed to be more sensible to competition for water resources, C. albidus exhibited a facilitation effect on R. officinalis in trispecific assemblage. Among the 17 vegetation indices tested, we found that the pigment pheophytinization index (NPQI) was a relevant parameter to characterize plant–plant coexistence. This work also showed that some vegetation indices known as indicators of water and pigment contents could also discriminate plant associations, namely RGR (Red Green Ratio), WI (Water Index), Red Edge Model, NDWI1240 (Normalized Difference Water Index), and PRI (Photochemical Reflectance Index). The latter was shown to be linearly and negatively correlated to the ratio of R975/R900, an indicator of water status.
Highlights
Many tools allow great advancements in the understanding of plant responses to their environmental constraints
30% in precipitation, and the specific objectives of this work were: (i) to determine the spectral signature of three common species of Mediterranean shrubland (ii) to investigate how these signatures may vary depending on the diversity of plant community, (iii) and to determine how water availability may be optically characterized in terms of canopy structure and functioning
Plants 2022, 11, 505 cipitation, and the specific objectives of this work were: (i) to determine the spectral signature of three common species of Mediterranean shrubland (ii) to investigate how these signatures may vary depending on the diversity of plant community, (iii) and to determine how water availability may be optically characterized in terms of canopy structure and functioning
Summary
Many tools allow great advancements in the understanding of plant responses to their environmental constraints. Hyperspectral spectrometry, for instance, is an approach that makes it possible to understand the structure and functioning of ecosystems at different spatial scales The spectral properties of plant cover both depend on the intrinsic characteristics of plants (morpho-anatomical structure, chemical composition, physiology, etc.) and the environmental conditions. It is possible to focus on different pigments such as chlorophylls, carotenoids, and anthocyanins in the visible part of the spectrum (VIS, 400–700 nm), while in the near infrared (NIR: Near InfraRed, 700–1000 nm) or in short-wave infrared (SWIR: Short-Wave Infrared, 1000–2500 nm) regions, other information can be collected [2]. The NIR reflectance provides information on leaf tissue structure, LAI (Leaf Area Index), and leaf angular position at the canopy level, while SWIR reflectance is mediated by water and biochemical components such as cellulose, lignin and proteins
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