## 1 Introduction  
Soil constitutes a complex ecosystem whose functionality is largely dependent on its own microbiota. This microbial community can be influenced by environmental factors such as climate, moisture levels and soil physicochemical properties. In the Mediterranean region, climate change is exacerbating drought conditions, reducing annual precipitation and raising temperatures, thereby intensifying water scarcity. This climatic situation not only threatens agricultural productivity but also accelerates some processes involving desertification, soil salinisation and prolonged drought periods. In this context, sustainable agricultural practices, enhanced irrigation efficiency and technological innovation are essential tools [1]. Under the current climate scenario, there is a pressing need to develop sustainable strategies to increase crop productivity and restore degraded soils, which are environmentally friendly strategies. To achieve this goal, one feasible strategy might be the installation of hydroinfiltrators in agricultural soils, a cutting-edge and nature-based device composed of biochar [2]. Biochar is a carbon-rich material produced by heating biomass at temperatures above 250 \({}^{\circ}\)C under limited or no oxygen supply through a thermochemical process known as pyrolysis or charring, which is also used in the production of charcoal [3]. However, unlike charcoal, it is specifically produced for use as soil amendment or in broader environmental management. A key feature of biochar is its high content of stable organic carbon, largely in the form of fused aromatic ring structures, formed during pyrolysis and crucial in the mineralisation and adsorption properties. Consequently, biochar typically contains high levels of carbon, and it is often enriched in phosphorus (P), as well as metals like calcium (Ca), magnesium (Mg), and occasionally nitrogen (N). Biochar may offer several benefits improving soil structure, enhancing microbial activity and contributing to the reduction in greenhouse gas emissions [4]. The influence of biochar on soil microorganisms is diverse and complex. According to several studies [5; 6], biochar can affect microorganisms both directly through potential toxicity and the release of volatile organic compounds (VOCs), as well as indirectly, by modifying soil physicochemical properties, altering nutrient availability and influencing enzymatic activity [4; 7]. Plant-growth-promoting bacteria (PGPB) comprise a wide variety of microorganisms with the ability to colonise plants, promoting their growth through both direct and indirect mechanisms. Direct mechanisms include the supply of essential nutrients (N, P, Fe...) and the synthesis of phytohormones (auxins, cytokins, gibberellins, ethylene...) [8]. On the other hand, indirect mechanisms may enhance plant protection against pathogens through the secretion of diverse substances (hydrolytic enzymes, siderophores, antibiotics, volatile compounds...) and the induction of systemic resistance, among other processes [9; 10]. Under saline conditions, halotolerant PGP bacteria exhibit a selective advantage: they can maintain their active metabolism, produce beneficial compounds, and promote plant adaptation by accumulating osmoprotectants, antioxidants, and protective enzymes [1; 11]. Studies involving _Bacillus_, _Pseudomonas_, _Azospirillum_, and _Halomonas_ strains have reported salt tolerance enhancement in crops such as wheat, rice, and tomato [8]. Additionally, these studies have also shown other advantages such as improved root development, water retention, higher chlorophyll content, and larger biomass production [1; 12]. Another approach involves the use of biochar as an organic amendment in combination with the application of plant-growth-promoting bacteria, representing an innovative and effective alternative. Both strategies, when combined, can act synergistically to mitigate the effects of salt stress, improve soil physicochemical properties and reactivate its microbiota [13].