Human-induced climate change, as outlined in the IPCC’s 2023 Synthesis Report (IPCC, 2023), has begun altering weather patterns and exacerbating climate extremes worldwide. Failure to adapt to these changes poses significant risks to both human societies and ecological systems (Dodd et al., 2023). Notably, terrestrial carbon sinks play a crucial role in mitigating anthropogenic emissions, but the degradation of vegetation has increased the frequency of extreme weather events (Friedlingstein et al., 2022; Li et al., 2023). With terrestrial vegetation absorbing a substantial amount of carbon annually through photosynthesis, enhancing vegetation quality and expanding vegetated areas offer a viable means of offsetting carbon emissions (Sha et al., 2022). However, the creation of slopes through engineering excavation, particularly for large-scale hydraulic projects and road construction, has led to adverse impacts on surrounding ecosystems, including soil erosion and vegetation loss (Chen et al., 2023). While these slopes offer potential for increasing global vegetation coverage and mitigating carbon emissions, many of these slopes are characterised by rocky surfaces that are unsuitable for plant growth. Moreover, rainfall exacerbates soil erosion and nutrient loss, further hindering vegetation establishment (Xerdiman et al., 2022). To address these challenges, it is crucial to enhance the drought resistance of slope plants and mitigate soil erosion caused by rainfall. Traditional slope protection techniques usually control erosion, but they often do little to help plant growth (Yang et al., 2019). In contrast, vegetation concrete technology offers a promising solution by providing a stable substrate for vegetation growth on rocky slopes. By laying metal wire mesh and anchors to secure the substrate and incorporating cement to enhance resistance to scouring, vegetation concrete creates favour conditions for slope vegetation (Shu et al., 2022). This technology is increasingly utilised in various infrastructure projects, including water conservation initiatives, highways, and railways (Faiz et al., 2022). In conclusion, while traditional slope protection methods have limitations in facilitating vegetation growth, vegetation concrete technology represents an innovative approach for ecological restoration and vegetation improvement on slopes. By addressing the shortcomings of conventional techniques and providing conducive conditions for plant establishment, vegetation concrete offers promising prospects for enhancing slope resilience and mitigating the impacts of climate change. However, in recent years, most of the studies on vegetation concrete have focused on heavy rainfall, seismic zones and alpine areas, and relevant studies have been carried out on environmental factors such as resistance to scouring, earthquakes, and freezing and thawing, but studies on arid zones are not yet available (Qu et al., 2020; Xia et al., 2023; Yang Y S et al., 2023).

In recent years, the increasing impacts of climate change have triggered significant shifts in precipitation and temperature patterns across various regions worldwide (Cui et al., 2022; Liu K et al., 2023; Jang et al., 2022; Tang et al., 2023). The exacerbation of temperature extremes and drought occurrences contributes to heightened mortality rates in numerous plant communities globally (Hammond et al., 2022; Sadhukhan et al., 2022; Sanchez-Martinez et al., 2023). In the ecological restoration of slopes, the steep slopes lead to the formation of surface runoff for the sufficient infiltration of water on the slopes, as well as a strong evapotranspiration effect, resulting in slope plants being susceptible to drought stress. Drought represents a significant stressor to plant physiology, growth, and reproductive functions, leading to compromised photosynthetic efficiency, slowed growth rates, and observable manifestations such as decreased leaf density, shortened stems, and reduced biomass (Sanchez-Martinez et al., 2023). Moreover, drought conditions trigger an overproduction of reactive oxygen species within plants, resulting in cellular-level structural impairments. Prolonged drought periods can even culminate in cellular death and plant wilting (Sheteiwy et al., 2021a). These challenges are particularly pronounced in slope ecological restoration engineering, where vegetation faces heightened vulnerability to water stress. Despite these challenges, recent research efforts have focused on mitigating the effects of drought on ecological restoration on slopes through the development of new water-saving irrigation techniques to rationalise irrigation, the addition of water-holding agents and other means (Zhang et al., 2019; Xerdiman et al., 2022). However, these studies tend to ignore their inherent limitations. Notably the adoption of water-saving techniques and water retention agents usually requires high maintenance costs or significant resource inputs. Although these methods may reduce water use to some extent, they have yet to significantly improve the sustainability and resilience of slope ecological restoration projects. Therefore, the above methods are currently not effective in addressing the long-term viability and drought tolerance of slope ecosystems. Moving forwards, there is a critical need to reassess the predominant reliance on water-saving irrigation technologies and explore alternative strategies to bolster drought resilience in slope ecological restoration engineering. Integrating ecological principles, such as leveraging plant microbe interactions and ecosystem-based approaches, could offer promising avenues for enhancing the sustainability and resilience of slope ecosystems in the face of escalating climate challenges. By embracing a holistic and ecologically driven approach, future research endeavours can strive towards more effective and enduring solutions for mitigating the impacts of drought on slope ecological restoration engineering projects.

Arbuscular mycorrhizal (AM) fungi in the soil play a key role in addressing the challenges of drought (Huang et al., 2021). AM fungi form symbiotic relationships with approximately 80% of terrestrial plants and can significantly increase photosynthetic efficiency, biomass, and enzyme activity, among other factors (Cheng et al., 2021; Yang Y M et al., 2023). In addition, AM fungi can also enhance mineral nutrient uptake to enhance root branching and root length, promote the synthesis of plant hormones, influence gene expression, and alter secondary metabolism (antioxidants and phenolic and polyamine metabolism); at the same time, AM fungi secrete globulins that sequester heavy metals, increasing plant resistance to abiotic stressors (Sheteiwy et al., 2021b; Ahmed et al., 2023; In ‘t Zandt et al., 2023; Sheteiwy et al., 2023). Through their extraroot mycelia, AM fungi can enter soil pores and increase plants’ ability to absorb water and nutrients, thereby fostering improved plant growth (Cheng et al., 2021; Huang et al., 2021). In addition, AM fungi facilitate the effective control of the internal water balance, regulate plant stomatal behaviour, improve water utilisation efficiency, and mitigate the adverse effects of water deficit on plants (Duan et al., 2021).

AM fungi help promote plant growth to improve drought resistance, but they have been used less often in slope protection and for the first time in vegetated concrete technology. Additionally, considering the slightly alkaline nature of the specific environment of vegetation concrete and its differences from natural soils, there is a need to study in-depth the mechanisms involved in the use of AM fungi to improve the drought tolerance of plants. The aim of this study was to investigate the effect of AM fungi on plant growth physiology and drought resistance under drought stress conditions by the exogenous inoculation of AM fungi using vegetated concrete as the test soil and to investigate the effectiveness of AM fungi in improving the drought resistance of slope plants. This study aimed to provide a more scientific foundation for addressing challenges related to drought in slope greening processes.

Drought is recognised as one of the most severe abiotic stresses worldwide, and a plant’s ability to tolerate drought is crucial for its survival and growth in arid environments. Although AM fungi have been shown to improve drought tolerance in many plant species, the effectiveness of different fungal strains in targeting different plants in complex ecosystems is still unknown (Li et al., 2019; Sheteiwy et al., 2021a; Nacoon et al., 2022). Most related studies have focused primarily on applying drought stress to natural soils. However, there is still limited knowledge on the effects of inoculating plants with AM fungi in vegetation concrete, which is used as a substrate for berms and has distinct physicochemical properties that differ from those of natural soils. In this study, we simulated three drought levels in vegetation concrete and selected two pioneer plants for slope protection to investigate whether and how AM fungi inoculation could positively influence plant drought resistance within a sloped environment. Furthermore, we aimed to assess whether drought stress affects plant adaptation to drought and whether it can increase the quality of drought resistance for slope greening.

Many studies have shown that plants that form a good symbiotic structure with AM fungi tend to have greater biomass, plant height and root length (Cheng et al., 2021; Nacoon et al., 2022; Yang Y M et al., 2023). In our study, the inoculation of vegetation concrete with AM fungi improved plant growth performance and increased plant biomass. Compared with the plants that did not form symbiotic structures, the plants that formed symbiotic structures performed better to varying degrees, with increases in plant height, root length, aboveground biomass and belowground biomass; however, this phenomenon was more pronounced at 60 days, and the greatest increases were 51.59%, 42.68%, 39.71% and 115.46%, respectively. The reason for this phenomenon may be that AM fungi form symbiotic structures with plant roots; increase the expression of genes related to the root epidermis, xylem, phloem and root hairs; stimulate the growth of primary and lateral roots of mycorrhizal plants; increase the size of mycorrhizal plants; and increase the effective absorptive area of the root system, which in turn improves the water uptake capacity (Liu H et al., 2023; Xi et al., 2022). This symbiotic relationship activates the physiological regulatory mechanisms of plants and increases their resistance to environmental stresses. AM fungi can absorb nutrients and minerals that are difficult for plants to utilise directly, especially phosphate and nitrogen, through their mycelia and deliver them to plants, which can promote the synthesis of amino acids needed for protein synthesis, thus promoting the growth and development of plants (Iffis et al., 2017; Shu et al., 2022; Xi et al., 2022). The presence of AM fungi can also regulate the quality of the soil around plants, and on the other hand, AM fungi can regulate the nutrient ratios of the soil surrounding plants, improving plant nutrient status (Chareesri et al., 2020; Jia et al., 2021; Liu H et al., 2023). Moreover, the data showed that the different AM fungi had different effects on plant growth strategies. In Festuca elata, AM fungi promoted plant height slightly more obviously than did the other fungal species, and the effect of single inoculation was greater. In Cassia glauca, AM fungi tended to increase root length. However, we found an interesting phenomenon in the experiments. In Cassia glauca, although AM fungal inoculation did not significantly increase plant height, it tended to increase the number of leaves, which may be useful for obtaining more efficient photosynthesis. Moreover, the biomass of the inoculated plants increased regardless of the drought level, which further confirmed the important role of AM fungi in promoting plant growth and material accumulation.

Water is one of the most important factors limiting plant photosynthesis, Drought leads to the formation of a hydraulic gradient between the leaf and the soil, which accelerates the development of leaf water deficit by reducing leaf expansion pressure further reducing stomatal conductance, and weakening gas exchange with the atmosphere. The efficiency of photosynthesis is inhibited by this behaviour, which ultimately hinders plant growth (Huang et al., 2021; Yang Y M et al., 2023; Gui et al., 2021). In this study, the photosynthetic rate of plant leaves decreased with increasing drought, and plants inoculated with AM fungi had greater Pn and Gs values (the greatest increase was 36.7% and 210.08% respectively compared to those in the CK treatment), which provided more efficient photosynthetic and gas exchange pathways for the plants. These findings also indicated that the degree of water deficit was less harmed in plants inoculated with AM fungi (Cheng et al., 2021; Li et al., 2019; Huang et al., 2021). Therefore, plants inoculated with AM fungi have greater Ci, which corresponds to changes in Gs, more open stomata, and less restriction of CO₂ entry (Huang et al., 2020; Duan et al., 2021; Yang Y M et al., 2023). Although many studies have shown that AM fungi modulate the stomatal switching of plants in response to drought, the degree of stomatal opening also verifies the degree to which plants are subjected to drought stress, and the greater stomatal conductance after inoculation with AM fungi suggests that plants are less persecuted by drought and do not need to be upregulated to close their stomata (Abdalla et al., 2023). In terms of the transpiration rate, plants inoculated with AM fungi showed a partial decrease in transpiration rate after 30 days of drought (0.89%~37.37%), which could be attributed to the formation of the symbiotic structure of AM fungi entering the acclimatisation stage, wherein the plants still need to provide part of the photosynthesis-synthesised carbohydrates to the AM fungi in exchange for essential nutrients and minerals for growth and then need to reduce transpiration to minimise the loss of water and maintain stable growth (Bárzana et al., 2012; Sun et al., 2021). However, the increase in the transpiration rate after 60 days (0.37%~208.61%) suggested that the plants may have developed more efficient water uptake, utilisation and transport mechanisms, at which point the transpiration rate was no longer the limiting factor and did not need to be reduced to meet growth requirements (Duddridge et al., 1980; Bárzana et al., 2012). This suggests that plants inoculated with AM fungi may be more drought tolerant, and that AM fungi can regulate the water use efficiency of plants in the early stages, reducing water loss and damage caused by abiotic stresses.

As drought intensifies, plants accumulate large amounts of reactive oxygen species (ROS), such as superoxide anion radical (O^2-), hydrogen peroxide (H₂O₂) and hydroxyl radical (OH) (Huang et al., 2020; Liu H et al., 2023; Sun et al., 2021). The excessive accumulation of these ROS induced by drought stress leads to oxidative damage in plants, causing lipid peroxidation of cell membranes, leading to protein denaturation, nucleic acid damage, oxidation of carbon compounds, pigment catabolism, and induction of programmed cell death. To avoid damage caused by high concentrations of ROS, plants reduce damage under drought conditions through the antioxidant enzyme system (Huang et al., 2020; Li et al., 2022; Tsuji et al., 2022). In the present study, the SOD and CAT activities in the AM-inoculated group were significantly greater than those in the CK treatment (the greatest increases were 164.14% and 111.59%, respectively compared to those in the CK treatment), suggesting that the former has greater drought resistance and suffers less oxidative damage. The MDA content in plant tissues is often used as an important indicator of ROS homeostasis and plasma membrane damage in plant tissues (Li et al., 2022). In the present study, the MDA content in plant leaves increased significantly with worsening drought, but the accumulated MDA content in the plant leaves of the AM inoculation group was lower than that in the CK treatment (2.79~55.01%). These findings indicated that inoculation with AM fungi could reduce the oxidative damage caused by drought by increasing the activity of antioxidant enzymes, which subsequently reduced the accumulation of MDA. The data showed that the trend for the Pro content was similar to that for MDA content, and drought increased the Pro content in leaves, while inoculation with AM fungi reduced the accumulation of Pro (5.53~57.74%). It is commonly believed that plants accumulate Pro to increase drought resistance to reduce drought damage under water deficit conditions (Thangaraj et al., 2022; Wang et al., 2023). The low Pro accumulation in the inoculated group suggested that these plants were less exposed to drought and did not require excessive proline accumulation to increase drought resistance. During drought, plants also alter osmotic potential by increasing the synthesis of osmoregulatory substances to maintain normal growth and metabolism, but drought stress inhibits photosynthesis in plants, leading to a decrease in carbohydrate yield (Li et al., 2019, 2022; Yang Y M et al., 2023). In our study, AM fungal inoculation also significantly increased soluble sugars and soluble proteins in plant leaves (the greatest increases were 68.22% and 97.54%, respectively compared to those in the CK treatment). The reason for this phenomenon is that plants accumulate soluble sugars in their leaves in response to environmental stresses, a behaviour in which both maintain osmotic balance to reduce drought persecution and serve as a potential source of energy (Nacoon et al., 2022; Tsuji et al., 2022; Wang et al., 2023). During drought, plants regulate protein synthesis, inducing an increase in specific proteins with functions such as antioxidant, stress response, and signalling regulation, thereby increasing drought tolerance (Bárzana et al., 2012; Wang et al., 2023). Higher levels of soluble sugars and soluble proteins are also evidence that inoculation with AM fungi provides plants with greater drought tolerance.

We first investigated the effect of the incorporation of exogenous AM fungi into vegetation concrete on the drought tolerance of slope plants. Under drought conditions, inoculation with or without AM fungi impaired plant growth and photosynthesis. Inoculation of vegetation concrete with AM fungi increased plant height, root length and biomass. The Pn, Gs and Tr of Festuca elata were somewhat elevated after inoculation with AM fungi (the greatest increases were 36.72%, 210.08%, and 66.41%, respectively compared to those in the CK treatment), whereas the Gs and Tr of Cassia glauca increased only under MD conditions. Inoculation with AM fungi can promote drought tolerance by increasing the activity of antioxidant enzymes and the accumulation of osmoregulatory substances in plants (4.76~164.14%, 0.79~99.14%). Single inoculation is beneficial to the growth of aboveground biomass, and dual inoculation is more beneficial to the growth of belowground biomass. In the early stage of slope ecological restoration, higher aboveground biomass is more conducive to the regreening effect of slope ecological restoration projects, but the presence of plant roots in slope ecological restoration projects is one of the most important factors for reducing soil erosion and improving the stability of slopes. Therefore, in slope ecological restoration projects, the texture of slopes and sowing plants should be considered by different means. Gentle slopes or herbaceous plants are dominated by slope ecological restoration projects Slow slopes or herbaceous plant-based slope ecological restoration projects should be based on single inoculation methods, and steep slopes or shrub-based slope ecological restoration projects should be based on dual inoculation methods. The stability of slopes is a key factor in improving the sustainability of slopes; therefore, in subsequent studies, attention should be given to the effects of inoculation with AM fungi on the modulation of plant root morphology and the structure and erosion resistance of root-soil complexes to assess their contribution to the stability of ecological restoration projects on slopes.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

SG: Conceptualization, Data curation, Formal analysis, Writing – original draft. LX: Formal analysis, Resources, Writing – review & editing. DX: Funding acquisition, Writing – review & editing. ML: Resources, Writing – review & editing. WX: Funding acquisition, Project administration, Writing – review & editing. LL: Funding acquisition, Supervision, Writing – review & editing.