Aluminium (Al) is a major element of soil, and it turns into toxic forms when expose to acidic condition. Al3+ ions are released from clay minerals in acidic soils, which in turn inhibit root growth and reduce crop yields. It is reported that approximately 40–50% potentially arable lands are acidic in the world (Von Uexküll and Mutert, 1995). Root is very sensitive to Al3+ toxicity and root meristem is the primary site of Al toxicity (Ryan et al., 1993). Root growth in wheat (Triticum aestivum) is inhibited within one hour after Al3+ treatment (Ownby and Popham, 1989). Negative effects induced by Al3+ on root will further decrease grain yields and disturb nutrition balance in plant. To tolerate Al3+ toxicity, plant has evolved different tolerance and detoxify mechanisms. In general, there are two types of Al3+ defense in plant, which are Al3+ excluders and Al3+ accumulators (Watanabe and Osaki, 2002). The Al3+ exclusion process takes place mainly via organic compounds exudation, such as organic acids including citrate, malate and oxalate (Kochian et al., 2004), and phenolic compounds (Kidd et al., 2001). The Al3+ accumulators which are Al3+ resistant species, for instance rice (Oryza sativa), buckwheat (Fagopyrum esculentum) and malabar melastome (Melastoma malabathricum) (Kochian et al., 2015, Osaki et al., 2003), can detoxify or translocate Al3+ in plant. Previous studies reported that the aluminium toxicity was attenuated by fluoride in wheat (Triticum aestivum) (MacLean et al., 1992). While, high concentration of fluoride (F) is toxic to plant (Barbier et al., 2010, He et al., 2021). Aluminium has the highest binding affinity with F among metal ions (Peng et al., 2021). It is reported that Al3+ is involved in alleviating F toxicity by forming Al-F complexes in tea (Camellia sinensis) (Yang et al., 2016). However, according to Kinraide’s report, the Al-F complexes such as AlF2+ and AlF2+ are also toxic to plant (Kinraide, 1997). Aluminium ion can form some stable complexes with fluorinion which suggest a strong correlation between these two elements. Considering that fluorine is an important halogen in the environment, and the effects of Al3+ and F– on plant is not very clear, therefore, it is necessary to investigate the effects of Al3+ and F– on certain plant species.
When plants are exposed to adverse conditions, physiological changes occur in plant. The cell membrane is very sensitive to adverse conditions. As the indicators of cell membrane damage, malondialdehyde (MDA) and electrolyte leakage (EL) increase remarkably in plants under environmental stresses (Fan et al., 2015). For instance, the EL in bentgrass (Agrostis stolonifera) increased significantly after drought stress treatment (Ma et al., 2018). Photosynthesis and pigment content negatively changed in plants. The chlorophyll content and photosynthesis process in bermudagrass (Cynodon dactylon) were inhibited by salt stress (Fan et al., 2019). Besides, it is also reported that Al concentration has a negative relationship with many mineral concentrations in plants (Watanabe and Osaki, 2002). So, the ion homeostasis will change in plant when it is exposed to high Al concentration.
Tall fescue (Festuca arundinacea Schreb) is an important cool-season turfgrass which is grown in the temperate zone of the world. In the previous study, it showed phytoremediation potential of toxic elements after treated with cadmium (Huang et al., 2017). However, the effects of Aluminium fractions and its species on tall fescue are largely unknown. Therefore, the aim of this study is to illustrate the Al3+ and F– response in tall fescue which will be contributed to extend application potential of tall fescue in diverse ecological restoration.