The valorization of invasive biomasses (BMs), periodically removed and treated as special waste, could contribute to the development of new strategies to increase soil water retention, especially in scarcely hydrated conditions. In the framework of PRIN PNRR 2022M7S2J SeaforSoil project, biomasses of Agardhiella subulata (Rhodophyta) (BMAs), Ulva ohnoi (Chlorophyta) (BMUo) and Chaetomorpha aerea (Chlorophyta) (BMCa), from the brackish lake Ganzirri (Lagoon of Capo Peloro, Messina, Italy) and their phycocolloids (PCs) were explored as novel wetting and humectant agents. To these purposes, we evaluated the BMs ability to improve soil water retention and overall soil quality, as well as their potential ecotoxicological impacts, in order to evaluate their use in agriculture.

The BMs, possessing different sulphated PCs, exhibited different hydrating performances, with BMUo (ulvan rich) being the most efficient wetting agent (reduction in water contact angle from 72° to 56°), which is proposed for the recovery of high degraded soils. BMAs (κ-carrageenan rich) was the best humectant agent (moisture uptake 25.7%) and it was able to increase soil water retention under simulated high solar irradiance (2.2%). The addition of the BMs did not cause toxic effects on i) the Vibrio harveyi luminescence, toxicological ii) Lepidium sativum L. and iii) Sorgum saccharatum L., and did not reduce the growth of Lactuca sativa L. Moreover, they efficiently increased the plant-available water content in soil of approximately 2-fold as compared to the unamended ones. According to the soil quality index, the addition of BMUo improved both the properties and functions of the degraded soil and did not affect them during lettuce cultivation. As not toxic and eco-friendly hydrating agents, the macroalgae biomass can be proposed as a dual-purpose strategy: in reducing the ecological pressure of allochthonous species and in improving soil quality for sustainable agriculture, especially in degraded soils.