Grassland ecosystems occupy significant areas worldwide and represent a reservoir for biodiversity. These areas are characterized by oligotrophic conditions that stimulate mycorrhizal symbiotic partnerships to meet nutritional requirements. In this study, we selected Festuca rubra for its dominance in the studied mountain grassland, based on the fact that grasses more easily accept a symbiotic partner. Quantification of the entire symbiosis process, both the degree of colonization and the presence of a fungal structure, was performed using the root mycorrhizal pattern method. Analysis of data normality indicated colonization frequency as the best parameter for assessing the entire mycorrhizal mechanism, with five equal levels, each of 20%. Most of the root samples showed an intensity of colonization between 0 and 20% and a maximum of arbuscules of about 5%. The colonization degree had an average value of 35%, which indicated a medium permissiveness of roots for mycorrhizal partners. Based on frequency regression models, the intensity of colonization presented high fluctuations at 50% frequency, while the arbuscule development potential was set to a maximum of 5% in mycorrhized areas. Arbuscules were limited due to the unbalanced and unequal root development and their colonizing hyphal networks. The general regression model indicated that only 20% of intra-radicular hyphae have the potential to form arbuscules. The colonization patterns of dominant species in mountain grasslands represent a necessary step for improved understanding of the symbiont strategies that sustain the stability and persistence of these species.

Festuca rubra is one of the dominant species in mountain high natural values grasslands. Most herbaceous plants are involved in a symbiotic partnership with arbuscular mycorrhizas for maintaining their abundance and cover. This research was conducted to explore the changes in mycorrhizal colonization patterns and structure development due to the long-term application of treatments. A large database of microscopic images was deeply analyzed with the MycoPatt tool, for the extraction of clear mycorrhizal maps that present particular colonization strategies. The overall colonization frequency and intensity varied largely between treatments, with a maximum in organic conditions. The presence of both arbuscules and vesicles in the same root area indicate a continuous alternance of fungal strategy, from storage to enhanced transfer of nutrients. A low-mineral organic treatment permits a clear separation of colonization strategy in different parts of roots. The nutrient availability due to mineral treatment induced a restriction in mycorrhizal development, which was maintained colonization by a resistance conditions strategy. The use of mycorrhizal maps permits a deep scanning of colonized roots, identifying the real positioning of fungal structures, along with their developmental potential and the assessment of the colonization strategy.

No abstract

Long-term fertilization targets mycorrhizal fungi adapted to symbiotic exchange of nutrients, thus restricting their colonization potential and re-orienting the colonization strategies. The MycoPatt tool has a high applicability in quantifying the symbiotic process with the identification of mycorrhizal indices and projection of mycorrhizal patterns. Organic treatments increase the symbiotic process, visible in values of colonization frequency and intensity, with about 6% more than the native status of colonization. At the opposite pole, organic-mineral treatments decrease the colonization parameters by up to half of the organic treatment. All of the colonization parameters show significant correlations, except for the arbuscules/vesicle ratio (0.03). All the applied treatments, except for the organic one, record multiple root segments with a colonization degree lower than 10%. The application of treatments changes the strategy of native colonization from a transfer (40%) and storage (37%) to a predominant storage (50%) for organic treatment, and are mainly proliferative between 38–50% in mixed and mineral treatments. The high amount of mineral components increases also the presence of resistance conditions strategies. The use of mycorrhizal pattern maps, with the inclusion of colonization strategies, presents an important direction in understanding the evolution of mutual relations, and to explore in-depth the efficiency of the whole symbiotic process.

Exploring grassland microbiomes is a challenge in the current context of linking soil microorganism activity with the balance of these ecosystems. Microbiologists are constantly attempting to develop faster and lower-cost methods, and propose new and best-fitted indicators that will provide a more complex data analysis. A different concept was proposed for assessing functional microbiomes by splitting the functional ecological niche into complementary segments. The comparison with the upper and lower limits of the ecological niche provides a clearer image of community alterations due to long-term applied treatments. The method allows the extraction of the most sensitive and stable functional guilds, with the extraction of the most critical dominant–codominant functional groups in every segment of the functional niche. The resulting microbial functional–sociological model is ready to use on community-level physiological profile databases and also can be applied backward for vegetation analysis.