Periphytic algae from rice fields: taxonomic and functional analysis in a harsh environment (NW Italy)

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Rice fields are one of the most important agricultural environments in Northern Italy. These agroecosystems are characterized by high variations in water temperature, shading by rice plants, and sporadic droughts that affect the life of aquatic organisms. In the present study, we carried out an analysis within the limits of two rice fields and their water supply canal in the Lomellina (Lombardy; NW Italy). The aims of this study were (1) to quantify the main benthic primary producers colonizing the two rice fields and their feeding canal, focusing on diatoms, green algae, and cyanobacteria; and (2) to shed light on the taxonomic and functional composition of diatom communities living in these three environments. The study was conducted during the spring and summer 2023, corresponding to the growth phases of rice plants and the peak of diatom primary productivity. A total of 54 samples were collected from these three environments, by using artificial substrates. Diatoms dominated the canal channeling water to the rice fields, while diatoms and cyanobacteria were co-present in the two rice fields. Among the diatoms, low-profile and motile guilds were dominant in the water canal while, to the contrary, we observed a higher percentage of motile tolerant species in the rice fields, such as Navicula veneta, Nitzschia amphibia and Planothidiun incuriatum, a recently described species. The analysis of the microalgae communities can be useful to define the proper management of wetland-like environments and the conservation of their biodiversity.