Farmland ponds as unique ecosystems for plant diversity across diverse pondscapes

Wetlands are some of the most vulnerable habitats in the world. Permanent farmland ponds, nestled within heavily human-modified landscapes, are potential elements of naturalness but remain insufficiently studied. This is particularly true for the Mediterranean region where farmland ponds are fundamental in supporting freshwater biodiversity though strongly affected by management practices inducing changes in environmental heterogeneity and consequently of the diversity hosted by ponds. We assessed the plant diversity in response to different pondscape contexts and we defined the spatial scale hosting the higher level of plant biodiversity of farmland ponds in central Italy. We carried out vegetation surveys in 45 farmland ponds located in three areas of Tuscany, along a pondscape agriculturaldisturbance gradient. We found that species richness and composition of plant communities varied along the gradient of disturbance of pondscapes. In the most disturbed pondscape, aquatic plant communities had the lowest species richness, with the highest presence of species well adapted to disturbed environments. Conversely, more natural pondscapes tended to host a higher richness of aquatic species, with helophytes being particularly abundant in the less disturbed pondscape. Although the degree of disturbance of the pondscape significantly affected species richness and composition, the pond identity which contributes to the uniqueness of the ponds and the water-land gradient, had a stronger influence. Our findings suggest that higher plant diversity is hosted at a local scale while at the landscape scale, where greater biodiversity is preserved in ponds located in areas where agricultural activity occurs at a moderate level.