Effects of cadmium on the growth, mineral nutrition and oxalic acid secretion of a dark septate endophyte

Abstract:

[Background] Dark septate endophyte (DSE) widely colonize plant roots in cadmium- contaminated habitats, and can enhance host plants' uptake of mineral nutrients and cadmium tolerance. [Objective] The response of DSE Exophiala pisciphila to mineral nutrient and low molecular weight organic acid secretion was studied.[Methods] Liquid culture method was used to explore the effects of different concentrations (0, 25, 50, 100, 200, 400 mg/L) of cadmium on DSE mycelial growth, mineral elements (nitrogen, phosphorus, potassium, sulfur, magnesium, iron, calcium) and cadmium content and oxalic acid secretion.[Results] With the increase of cadmium concentration, the mycelium biomass dropped by 22.8%-90.6%, and the content of nitrogen, potassium and iron in mycelia decreased by 26.0%-52.8%, 53.8%-92.9% and 12.8%-34.3%, respectively. The phosphorus, magnesium and calcium content increased by 15.4%-111.4%, 20.4%-31.4% and 35.1%-62.5%, respectively, and the sulfur content increased by 25.1% under 100 mg/L cadmium. Cadmium stress also caused a decrease in the pH value of the culture medium, and the oxalic acid concentration and the oxalic acid secretion per unit mycelium elevated remarkably. Correlation analysis showed that the cadmium content in mycelia was negatively correlated with that of sulfur and potassium (P<0.05, P<0.01), while positively correlated with oxalic acid secretion (P<0.01).[Conclusion] Cadmium stress can significantly inhibit the growth of DSE, change its absorption of mineral elements, and promote the secretion of oxalic acid.

Key words:dark septate endophytes (DSE);biomass;mineral nutrients;oxalic acid;cadmium tolerance