Mangrove forests stabilize shorelines, support biodiversity, and store carbon (Reef et al., 2010; Reef et al., 2019; Macreadie et al., 2021). Avicennia marina (grey mangrove) dominates many Indo-Pacific and Arabian coasts and tolerates harsh conditions, high salinity, hypoxia, and nutrient-poor soils, through salt-secreting glands and pneumatophores (Thatoi et al., 2016). In the Arabian Gulf, however, restoration is challenged by hypersalinity (>40 ppt), very low rainfall (<100 mm yr^-1), high evapotranspiration, and rapid coastal degradation from industrial and urban development (Friess et al., 2019; Chang et al., 2020). As a result, natural regeneration is often weak, highlighting the need for improved restoration strategies (Chang et al., 2020).

A. marina establishment in hypersaline soils is mainly limited by osmotic stress during germination and early seedling growth. Although the species can mitigate salinity via salt compartmentalization, osmolyte production, and stomatal regulation (Duke, 2017; Friess et al., 2019; Nizam et al., 2022), restoration success is still constrained by extreme salinity and nutrient limitation. Trials from other arid coasts show that seawater dilution/controlled irrigation and propagule or substrate pre-treatments reduce osmotic shock and improve vigor, while targeted nutrient additions help sustain early growth under low rainfall (Naidoo, 1987; Naidoo, 2009; Kimera et al., 2024; Dhawi, 2025).

Substrate amendments are especially important in degraded sabkha soils. Organic materials (e.g., compost, peat moss, treated sewage sludge) can improve water retention, moderate temperature, stimulate microbial activity, and supply labile nutrients; in the Gulf, treated sewage sludge has increased survival and growth by improving moisture and nutrient availability across tidal cycles (Erftemeijer et al., 2021; Dhawi, 2025). Mineral fertilizers (balanced NPK) can also enhance growth, but excessive inputs in hypersaline soils can induce osmotic shock or toxicity, requiring careful dosing (Feller et al., 2003; Miah and Moula, 2019; Erftemeijer et al., 2021; Hsiao et al., 2024). Red soils/clays may further help by increasing water-holding capacity and nutrient retention, especially when blended with amendments such as perlite and fertilizers (Cao and Zhu, 1999; Lu et al., 2005; Ghasemi et al., 2010; Ghasemi et al., 2012). Biological amendments (Multi-microbial consortium) can improve nutrient uptake and stress tolerance, and actinobacteria-based approaches have shown promise in the Gulf, but field-scale tests, particularly for mycorrhiza, remain limited (El-Tarabily et al., 2021; Alkaabi et al., 2022; Sulistiono et al., 2024; Zeng et al., 2025).

Despite growing interest in substrate-based restoration, key knowledge gaps remain in the Arabian Gulf. Multi-site field trials that directly compare organic, mineral, and microbial amendments—alone and in combination—across contrasting hydrological settings are rare, and amendment effects are seldom evaluated in relation to site-specific tidal/hydrological context (Chang et al., 2020; Friis and Burt, 2020; Dhawi, 2025).

Gap: The relative performance of commonly used amendments under inland seawater-irrigated sabkha versus coastal tidally inundated sabkha is not well quantified.

Aim: We tested whether fertilizer, red soil, peat moss, and mycorrhizal inoculation improve A. marina seedling establishment in eastern Saudi Arabia by conducting replicated field trials at Qurayyah (inland, high-salinity, seawater-irrigated) and Rhaimah (coastal, tidally inundated) from April–July2025.

Hypotheses: (H1) organic amendments (peat moss; red soil mix) increase survival and improve growth/physiological status (height, chlorophyll, SPAD) relative to controls; (H2) mycorrhizal inoculation enhances foliar nitrogen and photosynthetic proxies under saline stress; and (H3) treatment benefits are stronger at the tidally inundated coastal site than at the inland seawater-irrigated site.

Mangrove ecosystems, particularly Avicennia marina, along Saudi Arabia’s eastern coast provide critical ecological functions, including shoreline stabilization, carbon sequestration, and biodiversity support. They serve as nature-based solutions for climate mitigation and coastal resilience (Shaltout et al., 2021; Macreadie et al., 2021; Alsumaiti and Shahid, 2019; Chang et al., 2020; Al-Nafisi et al., 2009). However, restoration in arid and hypersaline environments remains challenging due to extreme abiotic stressors such as high salinity, nutrient-poor soils, freshwater scarcity, and intense solar radiation (Shaltout et al., 2021; Macreadie et al., 2021; Alsumaiti and Shahid, 2019). Soil organic matter is central to improving nutrient availability and soil stability, as demonstrated by earlier studies (Pribyl, 2010; Post and Kwon, 2000; Ali et al., 2009). Physiological responses of mangroves to salinity stress were first systematically characterized by Ball (2002), providing foundational knowledge for restoration research. High salinity reduces photosynthesis and water-use efficiency, although genetic variation within A. marina provides some resilience (Ball et al., 1988; Mohammadizadeh et al., 2009). Stressors such as high irradiance and temperature further exacerbate these challenges by inducing photoinhibition and reducing seedling survival (Martin et al., 2010; Lovelock et al., 2009; Mohammadizadeh et al., 2009). The July mortality pulse at QR is consistent with a seasonal stress window in hyper-arid sabkha systems, where extreme heat and evaporative demand can rapidly increase near-surface salinity and exacerbate physiological stress in recently established seedlings under managed (pumped) hydrology. In contrast, RH benefits from regular tidal exchange that moderates salt accumulation and maintains intertidal hydroperiod conditions, which likely reduces the magnitude of abrupt mortality events. These observations reinforce that hydrology (natural tidal exchange versus engineered inundation) is a primary determinant of survival stability and project permanence.

Field experiments highlight the potential of soil amendments in mitigating these stressors. In Iran, red clay improved water retention and seedling growth (Ghasemi et al., 2010; Ghasemi et al., 2012), while in China, red soil mixed with perlite enhanced water-holding capacity for halophytes (Lu et al., 2005). Outcomes were strongly site-specific: tidal flushing at Rahimah favored peat moss, while Qurayyah’s inland soils responded moderately to red soil (Ball, 2002; Ghasemi et al., 2010; Lu et al., 2005). These findings corroborate regional studies stressing the importance of tailored soil management in arid mangrove restoration (Bhat and Suleiman, 2004; Bhat et al., 2004; Almahasheer et al., 2013; Almahasheer, 2021). Nutrient constraints, especially nitrogen and phosphorus, further limit A. marina productivity in the Red Sea and Arabian Gulf (Almahasheer, et al., 2016). Fertilization trials in Saudi Arabia and India show that balanced NPK additions improve growth, but overuse risks osmotic stress and microbial imbalance (Saintilan, 2003; Osman and Abohassan, 2010; Kumar et al., 2011; Romero et al., 2012; Hsiao et al., 2024). Microbial inoculants, particularly mycorrhiza, enhance nutrient cycling and mitigate salinity stress, with Gulf nursery studies demonstrating improved root–soil nutrient exchange (Al-Guwaiz et al., 2021; Alkaabi et al., 2022; Zeng et al., 2025).

Organic amendments, including peat moss, mycorrhiza, and red soil, consistently enhanced seedling survival and physiological performance by improving water retention, nutrient availability, and salinity buffering (Dharmayasa et al., 2025; Dhawi, 2025; El-Tarabily et al., 2021; Sulistiono et al., 2024; Chang et al., 2020; Abou Seedo et al., 2017). Nevertheless, variability in field conditions, such as algal blooms, stagnant water, and irregular irrigation, created inconsistencies, as observed in global and regional studies (Erftemeijer et al., 2017; Abou Seedo et al., 2017; Abrogueña et al., 2022; Erftemeijer et al., 2020; Xiao et al., 2022; Mousavi et al., 2024). Meteorological extremes also shaped restoration outcomes. At Qurayyah, seedling survival declined sharply after June, correlating negatively with rising air temperatures, declining humidity, wind stress, and solar radiation, while positively linked to soil moisture and reduced salinity, confirming the buffering role of amendments (Ball, 2002; Ball et al., 1988; Guo et al., 2018; Basyuni et al., 2014; Abrogueña et al., 2022). In contrast, Rahimah’s tidal influence supported higher survival under peat moss. Red soil outcomes varied with site hydrology and structure, aligning with evidence from China and Iran (Lu et al., 2005; Ghasemi et al., 2010; Ghasemi et al., 2012). Organic amendments broadly mitigated heat and desiccation stress, which are critical constraints in sabkha and coastal flat environments (Martin et al., 2010; Lovelock et al., 2009).

Sustainable alternatives to peat moss are increasingly important due to concerns over unsustainable extraction. Compost and biochar derived from date palm residues improve soil fertility and water retention in arid regions (El Janati et al., 2023; Kavvadias et al., 2024). These align with circular-economy principles and offer viable substitutes. Locally sourced materials, including composted date palm residues, coconut coir, and Al-Ahssa red clay, further enhance feasibility (El Janati et al., 2023; Kavvadias et al., 2024). Recent evidence confirms that organic amendments and artificial soil elevation not only improve restoration outcomes but also enhance blue carbon storage, integrating mangrove rehabilitation into global carbon accounting frameworks (Corona-Salto et al., 2024; Gijsman et al., 2024; Kimera et al., 2024). Moreover, hydrological classification tools and tidal management strategies are critical to maximize restoration performance (Van Loon et al., 2016; Jiang et al., 2019; Alrubaye et al., 2023; Al-Zewar et al., 2023). Soil carbon evaluation using the loss-on-ignition method remains central to restoration assessments (Ball, 2002). Kuwaiti studies highlight that soil classification and tailored management are key for successful establishment (Bhat and Suleiman, 2004; Bhat et al., 2004). Despite the demonstrated benefits of peat moss and mycorrhiza, sharp summer declines confirm that no single amendment fully counters combined stressors of heat, salinity, irradiance, and hydrological extremes. A holistic restoration framework for Gulf mangroves should therefore integrate sustainable organic amendments (e.g., agricultural waste), nursery-based acclimation with salt-gradient irrigation and staged light exposure, coupled with hydrological management and continuous environmental monitoring. Together, these measures strengthen seedling establishment, build soil carbon stocks, and support long-term ecosystem resilience under accelerating climate pressures (Motamedi et al., 2014; Jiang et al., 2019; Alrubaye et al., 2023; Al-Zewar et al., 2023; Mousavi et al., 2024).

While our study relied on integrative physiological indicators such as chlorophyll content and foliar nitrogen to assess salinity impacts on plant performance and survival, we acknowledge that more specific biomarkers of salinity stress such as proline accumulation as an osmoprotectant, enhanced activities of antioxidant enzymes (e.g., superoxide dismutase, catalase, and ascorbate peroxidase) to mitigate oxidative damage, maintenance of favorable Na⁺/K⁺ ratios through ion compartmentation, and upregulation of molecular markers (e.g., SOS1 and NHX1 genes), have been reported in A. marina and could provide additional mechanistic insights (Jithesh et al., 2006; Kavitha et al., 2008; Patel et al., 2010; Natarajan et al., 2021). A key limitation of this study is that we did not directly quantify salinity-stress physiology (ionic, osmotic, and oxidative responses). In the pilot phase, we intentionally relied on non-invasive measurements (survival, height, SPAD/chlorophyll, visual health) to minimize disturbance and avoid harming the limited number of living plants. For future work, we recommend incorporating a targeted biomarker panel to confirm salinity stress: Na⁺/K⁺ ratios, proline (for osmotic adjustment), MDA (for lipid peroxidation), antioxidant enzymes (SOD, CAT, POD/APX), chlorophyll fluorescence (e.g., Fv/Fm), and water potential. These metrics would directly link hydrological/salinity conditions to physiological stress pathways and strengthen causal attribution. Furthermore, treatments were not fully factorial, and co-application (combination) effects were not directly tested; therefore, interaction effects (synergy or redundancy) among organic inputs, (MMC), and nutrient additions remain unresolved and should be quantified in a targeted factorial experiment. This study was conducted as a replicated pilot across strongly contrasting hydrological settings, so the field layout prioritized operational feasibility. Another key limitation is potential spatial confounding (pseudoreplication), because treatments were not fully randomized (QR used repeating row blocks; RH used alternating rows), meaning treatment effects may be partly confounded with row position and underlying spatial gradients (e.g., micro-topography, salinity/moisture, irrigation distribution). We therefore interpret treatment differences as field-evidence signals and focus on consistency across replicated rows and months. Future work should employ randomized/blocked designs aligned to dominant gradients, while retaining row/block identifiers (plus elevation and porewater salinity where feasible) to support mixed-effects models (e.g., logistic mixed models for survival and linear mixed models for continuous traits), thereby improving inference while remaining practical in sabkha/intertidal conditions.

In summary, this study demonstrates that while A. marina possesses remarkable adaptations to withstand the harsh conditions of the Arabian Gulf, restoration success is highly dependent on targeted soil management and site-specific strategies. Peat moss consistently enhanced soil carbon accumulation and seedling survival across both coastal and inland sites, while red soil and microbial amendments offered complementary benefits under certain conditions. Nevertheless, seasonal extremes and field variability underscore the need for integrated approaches that combine sustainable organic amendments, hydrological management, and adaptive nursery practices. Looking forward, adopting locally sourced and circular-economy amendments such as date palm compost and biochar can reduce reliance on unsustainable materials, while simultaneously enhancing carbon sequestration and ecosystem resilience. These findings contribute to advancing nature-based solutions for coastal restoration in arid, hypersaline regions, aligning directly with Saudi Vision 2030 and global climate mitigation efforts.

This study demonstrates the efficacy of organic soil amendments particularly peat moss, mycorrhiza, and red soil in enhancing the survival, growth, and physiological performance of A. marina seedlings under the arid, hypersaline conditions of Saudi Arabia’s eastern coast. At Qurayyah, peat moss and red soil not only improved foliar nitrogen uptake and photosynthetic efficiency but also significantly enriched soil organic matter. At Rahimah, peat moss increased survival more than four-fold compared to the Control, highlighting its effectiveness in buffering seedlings against climatic and edaphic stressors through improved soil moisture retention and salinity mitigation.

These findings emphasize that successful mangrove restoration in Gulf sabkhas requires more than soil amendments alone. Micro-site factors such as tidal proximity, elevation, and soil moisture proved critical to establishment, while extreme summer stressors underscored the need for complementary measures. Nursery-based acclimation to sunlight, salt-gradient conditioning, elevation-specific planting, temporary shading, and supplemental freshwater emerge as essential strategies to enhance long-term resilience.

A forward-looking framework for mangrove restoration in the Gulf region should integrate organic amendments, precise hydrological and spatial planning, nursery acclimation strategies, and long-term monitoring to maximize success in these challenging arid environments. Future research priorities include exploring synergies among amendments and microbial inoculants, characterizing microbial community dynamics (particularly in response to multi-microbial consortia), and evaluating long-term carbon sequestration and ecosystem resilience. In particular, subsequent studies would benefit from comprehensive microbiological assessments, such as quantification and functional profiling of bacterial (Bacillus spp.), non-mycorrhizal fungal (Trichoderma spp.), and other components to elucidate the individual and interactive contributions of microbes within commercial consortia like Mikro-Myco®. Collectively, these integrated approaches can establish mangrove restoration as a pivotal element of sustainable coastal management, blue carbon initiatives, and climate adaptation in Saudi Arabia and analogous arid coastal regions globally.