GROWTH OF ARBUSCULAR MYCORRHIZAL MYCELIUM IN CALCAREOUS DUNE SAND ANDITS INTERACTION WITH OTHER SOIL-MICROORGANISMS AS ESTIMATED BY MEASUREMENT OF SPECIFIC FATTY-ACIDS

Fatty acid analysis was used for determining the extent of the develop ment of the external mycelium of AM fungi (mixed inoculum from a sand dune) growing from roots of Festuca rubra and Plantago lanceolata in c alcareous dune sand. The plants were raised in chambers specially desi gned to permit the growth of AM mycelium in root-free compartments. In two separate experiments, growth of external mycelium in the root-fre e compartments was detected and the amount of mycelium was estimated u sing the indicator of AM fungal biomass, phospholipid fatty acid (PLFA ) 16:1 omega 5. The results showed that the PLFA 16:1 omega 5 was suit able for estimating the mycelium emerging from the mixed inoculum obta ined from the field roots of F: rubra and P lanceolata. The PLFA 16:1 omega 5 showed external mycelium to become established in the root-fre e compartments within a period of 3 weeks and the amount of mycelium t o continue to increase at 6 and 9 weeks. Increases in neutral lipid fa tty acid (NLFA) 16:1 omega 5 (indicator of storage lipids) over time w ere inconsistent between the two experiments, but appeared to follow p atterns of sporulation in each experiment. In both experiments, the ro ot-free compartment was colonised by saprophytic fungi to a greater ex tent in the case of non-mycorrhizal than of AM treatment, as indicated by an increase in PLFA 18:2 omega 6,9 (indicator of saprophytic fungi ). The absence of an increase in the case of AM treatment indicates th at AM fungal mycelium can negatively affect the growth of saprophytic fungi in this soil type. This result was, however, only weakly support ed by measurements of ergosterol content. The analysis of bacteria spe cific PLFAs showed that bacterial biomass was not affected by the AM m ycelium.