A pot experiment with hydroponic culture was conducted to study the effect of phosphorous content in rhizosphere on colonization rate of French marigold’s (Tagetes patula L.) root system with arbuscular mycorrhizal fungi. Plants were watered with Hoagland’s nutrient solution, in four variants: with normal phosphorous content, with double P content, with half and a quarter of the normal phosphorous content described in the recipe. Inoculation was realized with three different species of arbuscular mycorrhizal fungi: Glomus intraradices, Gl.etunicatum and Gl.claroideum. Root samples were collected, washed, cleared with KOH and stained with aniline blue to distinguish the specific mycorrhizal formations. After the growing period, we measured the plant development indexes (plant height, shoot and root fresh and dry weight, total leaf area, number and weight of flowers per plant) and mycorrhization’s characteristics (rate of colonization and arbuscular richness) to find a correlation between concentration of phosphorous in medium, plant’s and mycorrhiza’s development. High phosphorous contents in nutrient solution determined a better growth and development of plants, resulting in an increased plant height, shoot and root fresh and dry weight, respectively, number and weight of flowers. A negative correlation was found between P and mycorhization, demonstrating the inhibitor effect on colonization and development of mycorrhizal fungi. Between plant development indexes and nutrient content there is a positive relation. Between plant height and total leaf area, shoot dry weight and root dry weight we found a very strong positive correlation. Also, shoot fresh weight and root fresh weight vary according to a positive correlation curve. Results show that an excessive fertilization with phosphates, even if it increases plants’ productive performances, reduces in the same time the biodiversity of symbiotic fungi from soil and the development and extent of arbuscular mycorrhizal formations in root system of the host plants.

arbuscular mycorrhiza; French marigold; phosphrous nutrition

Presentation: oral