Soil eutrophication reduces fungal colonization in Berberis microphylla roots in Patagonia (Argentina)

Soil eutrophication can trigger drastic changes in biological interactions. However, it is not clear, particularly in forest ecosystems, how different symbiotic microorganisms respond to eutrophication or how responses might differ according to the nutrients involved (e.g., additive vs. interactive effects). In this study we evaluated how arbuscular mycorrhiza (AM) and dark septate endophyte (DSE) colonization of Berberis microphylla, a native shrub, was affected by the addition of inorganic nitrogen, phosphorus and potassium. We used a factorial experimental design (8 fertilization treatments applied to 31.5 × 45 m plots) in Río Negro (Argentina). We found that N and P fertilization reduced mycorrhizal colonization, while N, P and K fertilization reduced DSE colonization; however, we found no additive effect on either mycorrhizal or DSE colonization. Mycorrhization percentages were close to 20% in the control and potassium-only plots, and between 3 and 5% in the remaining treatments. DSE colonized over 50% of plants in the control plots, whereas this value fell below 20% with fertilization. Our results show that changes in even a single soil nutrient can severely affect these fungal-plant associations, evidencing the high impact of eutrophication on forest soils. Considering the crucial role of these symbiotic interactions, it is essential to control anthropogenic eutrophication.