NIR hyperspectral imaging for monitoring water patterns during dehydration of nonvascular epiphytic communities: the power of water absorption bands.

Description

The work aims at developing water maps for understanding water management of microclimates composed by nonvascular epiphytic communities (lichens and bryophytes) and how they prolong water availability depending on the composition of the community. An aquaphotomic approach, focusing on water absorption bands, is used to understand water behaviour among the different communities. To achieve this aim, water status of bark, lichens (crustose and foliose) and bryophytes was monitored by means of near-infrared (NIR) hyperspectral imaging (HSI) in the spectral range 1000-2500nm. Communities naturally supported by chestnut bark and composed by a single organism, or binary andternary samples were analysed, for a total of 32 samples. Non-colonised bark was also analysed. The organisms were submitted to a hydration protocol, then let dry at room temperature and humidity with NIR-HSI acquisition every 45 minutes for 15 sampling points. Three points were added for reaching dry condition, obtaining 576 images. At each sampling time the samples were weighed to build their dehydration curve. The system can be considered stable since the variability of weight and NIR spectra is ascribable mainly to water content variation. Exploratory data analysis was performed by means of PCA, comparing the drying trajectory in the orthogonal space defined by the lowest-order components with the dehydration curve. Then, PLS regression is proposed with the aim of extracting not only the water pattern inside the organisms but also a water content estimation. Significative wavelengths, according to the WAMACS list of absorption bands in the first OH overtone, were individuated and used to build aquagrams, together with important wavelengths highlighted in PCA and PLS. Moreover, water pattern maps were developed for understanding spatial distributions. The study of the communities in water-stress condition plays a crucial role in understanding how these organisms are facing the climate change and water scarcity / overabundance.

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