## 4 Discussion
A higher reflectance means fewer internal-molecular-absorption features, as well as the involvement of structural aspects of leaf-like trichome abundance, wax thickness and texture [35]. This raises the question of the identification of the different molecules that may be characterized in such plant-plant-microorganism interactions. Indeed, we identified wavelengths that discriminated the effect of drought and coexistence with Gorse (Supplementary Table S2). Each of these values could correspond to the radiation-absorption properties of specific compounds, leaf structures and canopy architectures. Recent studies have begun to identify the molecularintersections between biotic- and abiotic-stress responses through the concept of plant immunity [36]. Considering the overall richness of the communities investigated, we showed that drought induces a reduction in reflectance with the increase in the specific richness that follows a double reciprocal profile. Our data are in accordance with those of previous studies, which concluded that neighbors increase the profiles of local adaptation, with adaptation to competition occurring in benign habitats [37]. Further studies are required to characterize the role of niche diversity versus that of chemical metabolic changes. In the specific case of the index linked to the water content of the tissues (ratio R975/R900), the effect of the Gorse varied according to the neighboring species. Gorse seems to exert a positive influence on kermes oak through its ability to conserve water in drought conditions and, therefore, has a facilitating role. This effect turns into antagonism in the case of Cistus, since it has a lower water content in the presence of Gorse in drought conditions. Because Gorse and kermes oak have different rooting systems, the observed facilitation effect is the result of niche diversity rather than the involvement of chemical mediators. However, the intense competition between Cistus and Gorse suggests that Gorse may act through the regulation of oak stomatal opening due either to volatile signal transducers or by the rhizosphere's chemical components. For instance, plants or rhizosphere microorganisms' exudation of abscisic acid is known to regulate stomatal conductance [38; 39]. Considering all the tetraspecific assemblages, a decrease in the ratio of R975/R900 was noticed, confirming the same pattern as that obtained from the trispecific plant associations [17]. In the case of the role of Gorse as a Fabaceae for nitrogen supply in the ecosystem, a clear improvement was shown for Cistus in the bispecific, trispecific and tetraspecific stands. Although it is recognized as a releaser of allebotathic compounds, these do not affect the soil-nitrogen net rates of _C. albidus_[40]. Improvements were not observed in the bispecific assemblages of _Q. coccifera_ and _R. officinalis_ (Figure 9). For the rosmary and the kermes oak, the presence of nitrogen was increased in the trispecific stands, RoQcUp and QcCaUp, respectively. Our data raise the question of the nitrogen demand of wild species. Therefore, it is likely that Cistus' nitrogen metabolism is higher than that of the two other companion species. Nitrogen, as a macronutrient, is a part not only of the composition of proteins, but also of the structure of chlorophyll, which is a major pigment in photosynthesis [41]. Our work attempted to determine the possible variations in the photosynthetic capacity of species through the NIRvP index (Figure 8). The _U. parviforus_ has a significant positive effect on the photosynthetic capacity of _C. albidus_. This is quite in accordance with the improvements in nitrogen content by the neighbor effect of Gorse, but also with other research reports [42; 43]. A similar photosynthesis improvement was also obtained with _Q. coccifera_ associated with _C. albidus_ and Gorse. The _R. officinalis_ NIRvP index increased when co-existing with the Gorse, but also in association with _C. albidus_. This result appears to have been dependent on the availability of water rather than nitrogen.