Effect of inoculation with Suillus luteus on aluminum resistance of Pinus massoniana seedlings

To explore the mechanism of Ectomycorrhiza fungi enhancing aluminum tolerance of Pinus massoniana, and provide theoretical basis for the study of aluminum resistance mechanism of P. massoniana.

Using the hydroponic method, different concentrations of Al³⁺ were treated (0, 0.2, 0.4, 0.8, 1.2 mmol·L^-1) to determine the growth, osmoregulation substances, malondialdehyde, chlorophyll content, and antioxidant enzyme activity of two types of P. massoniana seedlings.

1) Aluminum stress inhibited the growth of P. massoniana seedlings, and inoculation with Sl significantly promoted the high growth and biomass accumulation of P. massoniana seedlings. 2) Compared with non inoculation, inoculation with Sl reduced the content of malondialdehyde (MDA), and showed a trend of first decreasing, then increasing, and then decreasing with the increase of Al³⁺ concentration. However, it increased the activity of peroxidase (POD) and superoxide dismutase (SOD), which increased the most when the concentration of Al³⁺ was 0.2 mmol·L^-1 and 0.4 mmol·L^-1, respectively. 3) Compared with non inoculation, inoculation with Sl significantly increased the chlorophyll content of P. massoniana seedlings, with a maximum increase of 50.88% at 0.2 mmol·L^-1. Afterwards, with the increase of Al³⁺ concentration, there is a trend of first increasing and then decreasing. When the concentration of Al³⁺ was 0.2 mmol·L^-1, the chlorophyll content of P. massoniana seedlings inoculated with Sl increased by 108.06% compared to the aluminum free treatment. 4) Compared with non inoculation, inoculation with Sl significantly reduced the soluble sugar content and proline content in the leaves of P. massoniana seedlings (except for 0.4 mmol·L^-1), with the largest decrease at 0.2 mmol·L^-1. Afterwards, with the increase of Al³⁺ concentration, the overall trend showed a first decrease and then an increase. However, it increased the accumulation of soluble proteins and had the greatest promoting effect at 1.2 mmol·L^-1, an increase of 30.13% compared to the aluminum free treatment. In addition, MDA showed a highly significant positive correlation with POD activity, proline, and soluble sugar (P < 0.01), with the highest correlation with soluble sugar being 0.775; SOD was highly significantly positively correlated with chlorophyll (P < 0.01), and negatively correlated with proline and soluble sugar (P < 0.01).

Within a certain concentration range, inoculation with Sl significantly enhances host plant enzyme activity, improves leaf light energy utilization efficiency and osmotic substance content, enhances its aluminum resistance, and thereby promotes the growth of mycorrhizal P. massoniana seedlings. The promotion effect is greatest when the concentration of Al³⁺ is 0.2 mmol·L^-1.