Höpfner, I; Beyschlag, W; Bartelheimer, M; Werner, C; Unger, S: Role of mycorrhization and nutrient availability in competitive interactions between the grassland species Plantago lanceolata and Hieracium pilosella, Plant Ecology (2015), doi:DOI 10.1007/s11258-015-0476-6
Arbuscular mycorrhizal fungi (AMF) may serve as an effective substitute for root surface. As mycorrhizal benefits are related to nutrient availability, the trade-off between carbon investments into AMF versus roots may drive competitive interactions. We studied competitive interactions between mycorrhizal and non-mycorrhizal individuals of Hieracium pilosella L. and Plantago lanceolata L., species differing in both mycotrophic degree and carbon allocation to roots. Three fertilization treatments were used to simulate nutritional differences over the course of succession. Species-specific differences in mycotrophy were reflected in markedly larger root/shoot allocation in P. lanceolata and higher mycorrhizal growth dependency in H. pilosella. P. lanceolata dominated competition in all fertilizer treatments, enabled by its comparatively larger root biomass allocation. In contrast, under intermediate and high fertilization, H. pilosella exhibited large investments into clonal shoot growth rather than in roots. Unexpectedly, the competitive imbalance between both species was amplified by the presence of AMF. The poor competitive strength of H. pilosella indicates that AMF-dominated foraging can be less effective than root-dominated foraging in competitive interactions, particularly under high nutrient availabilities. However, the competitive imbalance was reduced in favor of H. pilosella under nutrient deficiency. Our results lend support to the idea of differing competitive success of mycorrhizal- versus root-based foraging strategy over a nutritional gradient, which may play a role in the natural distribution of species over the course of succession.
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