Nature-based solutions (NBSs), defined as actions that work with and enhance nature, providing environmental, social, and economic benefits, play a pivotal role in accomplishing multiple objectives within the Water–Ecosystem–Food Nexus domain. They contribute to facilitating the transition to more resilient agrifood systems and providing an evidence base for a broader Nexus policy dialogue. This paper describes the stepwise methodology developed in the EU-funded LENSES project to carry out a comprehensive analysis of NBSs in six pilot areas in five Mediterranean countries and presents the results of NBS implementation in four pilot areas, highlighting obstacles and opportunities. The methodology includes the development of an analytical evaluation framework and a comprehensive catalogue of Nexus-related NBSs, whose suitability needs to be assessed at the local level to achieve better use of protected/natural ecosystems, increase the sustainability and multifunctionality of managed ecosystems, and design and manage novel ecosystems. Subsequently, in a collective learning process that supported the operationalisation of the WEF Nexus, NBSs were identified that address specific contextual vulnerabilities, improve water distribution, and enhance food security while preserving ecosystems and supporting adaptation to climate change. The added value of the proposed methodology lies in the multi-stakeholder participatory approach to gain in-depth knowledge of local agri-food systems, including their main WEF-related challenges, and to facilitate overcoming barriers to NBS implementation. Finally, a final survey was conducted among a small group of purposively selected stakeholders to gain some insight into their perceptions of the impact of NBS and to gather some opinions on the main barriers and opportunities.

Recently, on the EU market, phosphonic acid residues were detected in many organic goods, although fosetyl-derivates and phosphite salts are not allowed by Reg. EC n. 889/2009. The BIOFOSF project “Solving phosphite issue in organic fruit and horticultural crops” aimed at verifying whether the phosphonic acid contamination could be due to unproper use of fertilizers/plant protection products by organic farmers, or to the plant’s ability to self-produce it spontaneously. Applying a participative approach, field case-studies on potato, rocket lettuce, and pears were carried out (organic vs. integrated systems). The ethyl-phosphonic acid and phosphonic acid were determined in soil, tubers, leaves, fruits, tree woody organs, used fertilizers, and plant protection products to correlate them to the applied farming management. Tested crops were not able to self-synthetize phosphonic acid, being its detection due to: (i) external inputs not allowed in organic farming; (ii) fertilizers/plant protection products allowed in organic farming, contaminated by fosetyl or phosphite. In addition, it was found that tree crops can stock the phosphite in their woody organs, then translocate it from branches to leaves and fruits over time. Regression models applied to field data showed that fruit trees decontamination could take more than 5 years, depending on the starting value of phosphonic acid contamination, useful to define the phosphite maximum residue limit in organic fruit crops.

The mycorrhizal fungi are symbiotic organisms able to provide many benefits to crop production by supplying a set of ecosystem functions. A recent ecological approach based on the ability of the fungi community to influence plant–plant interactions by extraradical mycelium development may be applied to diversified, herbaceous agroecosystems. Our hypothesis is that the introduction of a winter cereal cover crop (CC) as arbuscular mycorrhizal fungi (AMF)–host plant in an organic rotation can boosts the AMF colonization of the other plants, influencing crop–weed interference. In a 4‐years organic rotation, the effect of two winter cereal CC, rye and spelt, on weed density and AMF colonization was evaluated. The AMF extraradical mycelium on CC and weeds roots was observed by scanning electron microscopy analysis. By joining data of plant density and mycorrhization, we built the mycorrhizal colonization intensity of the Agroecosystem indicator (MA%). Both the CC were colonized by soil AMF, being the mycorrhizal colonization intensity (M%) affected by environmental conditions. Under CC, the weed density was reduced, due to the increase of the reciprocal competition in favor of CC, which benefited from mycorrhizal colonization and promoted the development of AMF extraradical mycelium. Even though non‐host plants, some weed species showed an increased mycorrhizal colonization in presence of CC respect to the control. Under intense rainfall, the MA% was less sensitive to the CC introduction. On the opposite, under highly competitive conditions, both the CC boosted significantly the mycorrhization of coexistent plants in the agroecosystem. The proposed indicator measured the agroecological service provided by the considered CCs in promoting or inhibiting the overall AMF colonization of the studied agroecosystems, as affected by weed selection and growth: It informs about agroecosystem resilience and may be profitably applied to indicate the extent of the linkage of specific crop traits to agroecosystem services, contributing to further develop the functional biodiversity theory.

The Water-ecosystems-food Nexus is a powerful framework developed for analyzing complex interlinkages among natural resource domains and overcoming "siloed" management practices. Multi-actor participatory approaches are increasingly recognized in Nexus research as the most effective way to identify trade-off solutions between divergent interests. Despite this acknowledged potential, the active engagement of stakeholders for the co-creation of knowledge is still limited to date, missing the opportunity for innovation processes and policy designs to be grounded in context-specific knowledge and experiences. This paper outlines the methodological framework developed to integrate stakeholder analysis and participatory tools for exploring Nexus challenges in a pilot area in Tarquinia, Italy, where a multi-stakeholder group was set up encompassing several categories at different levels, from policymakers and authorities to farmers and other end users. Systematic methodologies to target, analyze, and actively engage stakeholders were applied and multi-domain participatory tools were developed, i.e., stakeholder analysis and mapping, learning and action alliance, participatory system dynamic modelling, which broaden the agreement on potential locally-tailored solutions for sustainable farming practices and integrated management of natural resources. Mutual learning activities, tapping into actors' deep understanding of specific local dynamics, served to better frame the complexity of the Nexus and build a common understanding of local societal challenges as well as of potential innovations in farming practices, land, and water management. The methodological innovation of integrating stakeholder mapping and analysis with relevant spatial information from participatory activities, provides the fundamental baseline for spatially explicit scenario analysis in the area, ultimately increasing the relevance and transferability of the Nexus findings.