Prolonged increases in droughts and heatwaves globally affect evapotranspiration rates, reducing soil water availability, thereby altering ecosystem functioning, biogeochemical cycles, and plant-soil interactions. This study examined the potential of marine-derived additives as a sustainable strategy for improving soil water dynamics. Novel biopolymers from thermophilic bacteria, including six exopolysaccharides (EPS1-EPS6) and four biosurfactants (BS1-BS4), and biomasses from seaweeds (BM1-BM4) and marine cyanobacteria (BC1-BC2), were investigated for their wetting properties and effects on water retention at a laboratory-scale soil model. Wetting properties, including reduction of contact angle (RCA) and atmospheric-air moisture uptake (AMU), were monitored for 36 hours at 30 ^°C. The effect on soil water retention was evaluated by measuring water loss in soil microcosms (10 g of soil and 10 ml of water) treated with each biopolymer/biomass (at 0.5 or 1% w/w) and kept at 22 ^°C until complete evaporation occurred (about 200 hours).

BC2 derived from Leptolyngbya sp. 43.3 s was the best wetting agent (RCA =39%), while the EPS4 produced by Bacillus horneckiae SBP3 was the best humectant (AMU =180%). Furthermore, soils amended with bacterial biopolymers (EPS4, EPS5, EPS6, BS1 and BS3), as well as biomasses derived from cyanobacteria (BC2) and seaweed (BM1–BM4), produced better improvement in soil water retention, with marked effects at the concentration of 1% w/w.  The lipopeptide BS1 was the most effective at reducing water loss during a specific time of 96-125 hours at both concentrations.

These findings emphasized the ecological potential of these materials as nature-based solutions to improve soil-mediated ecosystem resilience to drought under climate change. However, future studies need to verify if these long-term positive effects persist.

PRIN 2022 PNRR “SeaForSoil: Marine biopolymers to develop novel strategies to increase the water retention in soil for sustainable farming systems under water constraints” (P2022M7S2J), funded by Italian Ministry of University and Research.