Mineralogical Changes in Clay-Sized Phlogopite and Muscovite as Affected by Endophyte-Tall Fescue Symbiosis

AbstractThe association between Neotyphodium spp. endophytes and cool-season grasses, particularly tall fescue (Festuca arundinacea, Schreb), represents a widespread type of mutualism in nature. Numerous researches were performed about positive effect of symbiosis on plant resistance to different stresses but the role of symbiosis on nutrients uptake particularly potassium uptake and K-bearing mineral transformation is not well recognized. The objective of this research was to investigate the effect of endophyte-tall fescue symbiosis on the transformation of clay-sized micaceous minerals. A pot experiment under green house conditions was carried out in a completely randomized design with factorial combinations and three replicates. The culture medium was a mixture of quartz sand (as filling material) and phlogopite or muscovite. Tall fescue 75B genotype either infected by the natural endophyte Neotyphodium or non-infected isoline was chosen for cultivation. Pots were irrigated with distilled water and complete or K-free nutrient solutions during a period of 140 days. At the end of the experiment, shoots and roots were harvested. Plant samples were prepared with dry ashing method and their K concentration was determined with flame photometer. The clay-sized particles in each pot were mineralogically studied using an X-ray diffractometer. The results showed the vermiculitization of phlogopite under both nutrient solutions conditions, but with a much higher rate in pots treated with K-free nutrient solution. In addition to vermiculite, smectite and chlorite were also detected as newly formed minerals in phlogopite amended pots. Also, a very weak vermiculitization was observed in muscovite treated media. Under the K-free nutrient solution and in phlogopite amended treatments, the 1.4/1.0 nm peak ratio for endophyte infected plants was 4 times greater than that under non-infected plants. Such a significant difference in phlogopite vermiculitization is attributed to endophyte symbiosis and its positive effects on the type and quantity of tall fescue roots secretions. A significant decrease in pH values under the rhizosphere of infected plants further confirmed this hypothesis.