36 Print ISSN 1843-5246; Electronic ISSN 1843-5386 The Variation of Mycorrhizal Colonization Parameters in Festuca Rubra under the Influence of Climatic Factors and Differentiated Fertilization Roxana VIDICAN*, Vlad STOIAN, Ioan ROTAR, Florin PĂCURAR Faculty of Agriculture, University of Agricultural Sciences and Veterinary Medicine Cluj- Napoca, 3-5 Manastur St., 400372 Cluj-Napoca, Romania; roxana.vidican@usamvcluj.ro Abstract: Intensification of natural ecosystems may be beneficial for a series of plants, which are favored to become the dominant at the level of grass cover. However, no matter how low would be the inputs applied, the first effects are observed in the symbiotic organisms of existing plants in the ecosystem. Adaptation of plants and soil microorganisms to environmental conditions have made the type and dosage of fertilizer applied to become factors with limiting effect on the balanced evolution of mycorrhizal fungi. For mycorrhizal colonization of Festuca rubra plant, climatic factors play a small role, from this consideration is necessary to identify the dose and type of fertilizer to ensure the stability in time of colonization parameters. To study the effect of increasing soil nutrient resources on the mycorrhizal colonization parameters in Festuca rubra, we set up an experiment with six degrees of fertilization, in addition to unfertilized control were applied to two types of organic fertilization and three types of mineral fertilization. Balancing the colonization and reducing fluctuations in time of colonization parameters is influenced in a high degree by nitrogen, whether it comes from manure or synthetic fertilizers. At the end of growing season it is observed the superiority of combined fertilizers (manure + NPK or Eurofertil mezocalc supplemented with nitrogen), which ensure the highest values of the colonization degree. Keywords: mycorrhizal colonization, colonization degree, organic fertilization, mineral fertilization, fertilization doses, vegetation sequences. INTRODUCTION The roots of vascular plants are in private contact with a substrate and even in the case that this is represented by soil, water or bark, the functionality and development are all influenced by various biotic and abiotic factors. A complex of microorganisms resides in a diversity of niches within the substrate, affecting the roots hence the plants performance through multiple means. The most frequent organisms associated with plants are the environmentally adapted fungi from soil, which form root-fungus partnerships called “mycorrhiza” (Peterson, 2004). These symbioses are present in the roots of the large majority of plants (Varma, 2008). The main benefit for the host plant in a mycorrhiza symbiosis is the enhancement of immobile nutrient assimilation, especially of phosphorus (Jakobsen, 2011). Matured ecosystems are characterized by a continuous and cyclic movement of the elements between the biotic and abiotic components. The mycorrhiza has the purpose to adjust the composition and functionality of a community, by correctly allocating food resources and influencing the growth of interfering plants. The increase of fertilization levels (20 or 40 t/ha manure) or the usage of unconventional fertilizers (20 or 60 t/ha waste water sludge) at a lucerne culture, can benefit directly on the intensity of symbiotic microorganisms activities, thus enhancing the ability to biologically bond nitrogen (Vidican et al., 2012). A highly important role, besides Bulletin UASMV serie Agriculture 70(1)/2013, 36-43