Coastal ecosystems are exposed to extreme abiotic conditions, primarily water deficit and salt stress, as well as resource availability, which exacerbates interspecific competition. In this context, soil microbial communities may provide an advantage in coping with abiotic and biotic stresses.
This study investigates the effects of both soil microbiota and plant density on L. creticus performance under salt and water stresses. We applied two saline treatments (100 mM and 200 mM NaCl), and water deficit (complete withholding of irrigation), to plants grown either individually or in groups of three, in coastal dune soil (with the natural soil microbial community) or sterile soil. When the plants started to wilt, we measured the morphometric traits, mycorrhizal structures, and biochemical markers indicative of plant responses to abiotic stress. The latter were photosynthetic pigments (chlorophylls and carotenoids), ion content in leaves and roots, osmolytes (proline, total soluble sugars, and glycine betaine), and oxidative stress markers (malondialdehyde and hydrogen peroxide). We also analysed antioxidant mechanisms, both enzymatic (catalase, glutathione reductase, superoxide dismutase and ascorbate peroxidase activities) and non-enzymatic (total phenolic compounds and flavonoids).
Plants grown in coastal soils exhibited greater biomass compared to plants grown in sterile soils (leaf dry weights were 0.52 ± 0.07 g vs 0.28 ± 0.02 g, respectively). Plants cultivated in groups showed higher levels of osmolytes than those cultivated individually (e.g., proline concentrations were 12.70 ± 2.73 µmol/g DW vs 1.60 ± 0.41 µmol/g DW, respectively). Salt and water stresses had a negative effect on morphological development (e.g., average leaves produced in 0.2 M NaCl: 34.72 ± 9.98; in water stress: 37.71 ± 12.70; in control plants: 82.39 ± 17.45) and triggered some stress markers (e.g., total soluble sugars, control plants: 18.49 ± 3.16 mg eq. G /g DW; 0.2 M NaCl: 46.90 ± 11.72 mg eq. G /g DW; water stress: 55.35 ± 19.85 mg eq. G /g DW). These findings support the positive effects of local soil microbial communities on plant performance under abiotic stresses and population density conditions.
