Boron (B) deficiency and H⁺toxicity are two prominent factors that severly restrict trifoliate seedlings growth in acid soil. Exogenous B can support to mitigate the harm of H⁺toxicity, however, research on the protective mechanism and the impact of physiological processes in citrus is limited. To fill the above gaps, the current study was performed on trifoliate rootstock using two pH levels (pH 4 and pH 6) and various B treatments (B0, B1, B2, B3, B4) to identify how B confers tolerance to H⁺ toxicity in trifoliate rootstock. Our results illustrate that H⁺toxicity suppressed plant growth, specifically the root elongation (27.22%). Boron capitalized the positive effect on plant growth as soon as it is applied to culture medium. The supply of B increased the activity of antioxidant enzymes and the content of antioxidant substances in root of trifoliate seedlings under H⁺ toxicity to scavenging the massively accumulated reactive oxygen species (ROS), reducing the malondialdehyde (MDA) content (12.07%-53.45%) and promoting root development. Meanwhile, the higher levels of osmolytes after B supply in root were better for maintaining water in cell and resisting H⁺ toxicity. Furthermore, B supplementation improved nutrients content including macro and microelements in root, especially the elements constituting superoxide dismutase (SOD), which in turn activated the antioxidant enzymes system. In conclusion, the ameliorative effects of B to H⁺toxicity in trifoliate seedlings was based on B homeostasis, improved antioxidant defense system, and then nutrient content. These findings provide a new insight into the regulation of H⁺toxicity tolerance of citrus by B fertilizer application in acid soils.

硼 (B) 缺乏和H ⁺毒性是严重限制酸性土壤中三叶幼苗生长的两个突出因素。外源B有助于减轻H ⁺毒性的危害，但对其保护机制和对柑橘生理过程影响的研究有限。为了填补上述空白，目前的研究是使用两个 pH 水平（pH 4 和 pH 6）和各种 B 处理（B0、B1、B2、B3、B4）对三叶砧木进行的，以确定 B 如何赋予对 H + 毒性的^耐受性在三叶砧木中。我们的结果表明H ⁺毒性抑制植物生长，特别是根伸长 (27.22%)。硼一经应用于培养基就发挥了对植物生长的积极作用。B的供给提高了H ⁺毒害的芪苗根系抗氧化酶活性和抗氧化物质含量，清除大量积累的活性氧（ROS），降低丙二醛（MDA）含量（12.07%-53.45%） ) 并促进根系发育。同时，根部补B后较高水平的渗透剂有利于维持细胞水分和抵抗H ⁺毒性。此外，B 的补充提高了根中包括常量元素和微量元素在内的养分含量，尤其是构成超氧化物歧化酶 (SOD) 的元素，进而激活了抗氧化酶系统。综上所述，B 对蒺藜幼苗H ⁺毒性的改善作用基于 B 稳态、抗氧化防御系统的改善以及养分含量。这些发现为在酸性土壤中施用硼肥对柑橘的H ⁺毒性耐受性的调节提供了新的见解。