Biodiversity, ecological plasticity and conservation of charophytes in two regions along a latitudinal and aridity gradient (southern Italy and Egypt)

Charophytes are morphologically highly differentiated macroalgae, belonging to the Streptophyta. They occur in a range of freshwater and brackish (and rarely marine) habitats, mainly lakes, streams, pools and springs. Charophytes usually decline at higher nutrient loadings and are therefore used as bioindicators for habitat quality assessment. The delineation of charophyte ecological niches is a crucial prerequisite to better understand how environmental drivers shape their distribution, their present and future diversity in changing environments, and to devise suitable conservation strategies. This is specifically urgent in the Mediterranean Basin due to rapid ongoing global climate changes, increasing human pressure, and extreme hydrological fluctuations. Here, we studied the ecological niche hypervolume of charophyte populations, belonging to the genera Chara, Nitella, and Tolypella, across a latitudinal gradient encompassing southern Italy and Egypt. On the one hand, results revealed that the Italian populations, belonging to few tolerant and widely distributed species, show clear signs of environmental filtering from anthropogenic pressures. On the other hand, the Egyptian populations exhibit larger ecological plasticity than the Italian populations and a differentiation in the occupied hypervolume, suggesting that warmer climates may force charophytes to adapt to challenging environmental conditions in coping with the scarcity of freshwater environments.