Nature based solution to soil and vegetation recovery in Pianosa Island: Cyanobacteria as Biostimulants for Sustainable Bioaugmentation

Pianosa is a unique island in the Tuscan Archipelago (Italy), characterized by low annual rainfall, and predominantly shallow calcareous soils. Due to the presence of an agricultural colony on Pianosa land, decades of agricultural use profoundly altered soil structure and function. After agricultural activities related to the penal colony were ceased, a long-term natural recovery processes under has initiated, under the main driver of increasing climatic stress. The National Research Council (CNR) has monitored the ecosystem since the early 2000s, and in 2020 launched a new campaign to assess soil health and vegetation recovery after 40 years of abandonment. Preliminary findings indicate that vegetation resilience under climate change is strongly influenced by soil chemical, physical, and biological properties, highlighting the central role of soil microbial communities in driving ecosystem functioning. In this context, biological soil crust components, particularly cyanobacteria, are expected to play a key role in nutrient cycling, organic matter dynamics, and soil water regulation in resource-limited environments. Within this framework, we isolated and characterized native cyanobacterial strains from Pianosa soils to assess their functional traits and evaluate their potential as biostimulants for enhancing organic matter mineralization and nutrient availability in resource-limited calcareous soils. The selected strains were investigated for their ecological relevance and their capacity to influence key soil processes related to carbon and nutrient cycling. Laboratory microcosm experiments, designed to simulate early-stage soil recovery conditions, demonstrated that cyanobacterial inoculation can positively affect soil fertility indicators, including nutrient dynamics and organic matter turnover, while also improving soil water retention capacity. These findings highlight the ability of native cyanobacterial communities to modulate soil physical and biogeochemical properties. Overall, our results support the use of site-adapted cyanobacteria as a nature-based bioaugmentation strategy to restore soil functionality and enhance ecosystem resilience in Mediterranean insular systems increasingly exposed to climate change.