镉对一株深色有隔内生真菌生长、矿质营养与草酸分泌的影响

【背景】深色有隔内生真菌(dark septate endophyte，DSE)广泛定殖于镉(Cd)污染生境的植物根系，具有增强植物镉耐性的重要生态功能，但人们关于DSE对镉胁迫的生理响应的了解有限。【目的】研究一株DSE嗜鱼外瓶霉(Exophiala pisciphila)对镉胁迫的矿质营养与低分子量有机酸分泌的响应。【方法】采用液体培养法，研究不同浓度(0、25、50、100、200、400 mg/L)镉胁迫对DSE菌丝生长、矿质元素(氮、磷、钾、硫、镁、铁、钙)与镉含量、草酸分泌的影响。【结果】随着镉胁迫浓度增加，菌丝生物量显著下降，降幅为22.8%−90.6%，菌丝的氮、钾和铁含量分别减少26.0%−52.8%、53.8%−92.9%和12.8%−34.3%，而磷、镁和钙含量分别增加15.4%−111.4%、20.4%−31.4%和35.1%−62.5%，硫含量在100 mg/L镉胁迫时增加25.1%。镉胁迫还导致培养液pH值下降，草酸浓度及单位菌丝草酸分泌量显著增加。相关分析发现，菌丝镉含量与硫呈显著负相关(P<0.05)，与菌丝钾含量呈极显著负相关(P<0.01)，与草酸分泌量呈极显著正相关(P<0.01)。【结论】镉胁迫显著抑制DSE的生长，改变矿质元素的吸收，促进草酸分泌。

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

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.