Abstract
Two common ecological assumptions are that host generalist and rare species are poorer competitors relative to host specialist and more abundant counterparts. While these assumptions have received considerable study in both plant and animals, how they apply to ectomycorrhizal fungi remains largely unknown. To investigate how interspecific competition may influence the anomalous host associations of the rare ectomycorrhizal generalist fungus, Suillus subaureus, we conducted a seedling bioassay. Pinus strobus seedlings were inoculated in single- or two-species treatments of three Suillus species: S. subaureus, S. americanus, and S. spraguei. After 4 and 8 months of growth, seedlings were harvested and scored for mycorrhizal colonization as well as dry biomass. At both time points, we found a clear competitive hierarchy among the three ectomycorrhizal fungal species: S. americanus > S. subaureus > S. spraguei, with the competitive inferior, S. spraguei, having significantly delayed colonization relative to S. americanus and S. subaureus. In the single-species treatments, we found no significant differences in the dry biomasses of P. strobus seedlings colonized by each Suillus species, suggesting none was a more effective plant symbiont. Taken together, these results indicate that the rarity and anomalous host associations exhibited by S. subaureus in natural settings are not driven by inherently poor competitive ability or host growth promotion, but that the timing of colonization is a key factor determining the outcome of ectomycorrhizal fungal competitive interactions.
Highlights
A fundamental axiom in biology is the existence of tradeoffs, which are commonly defined as an increase in performance in one area being correlated with a decrease in performance in another area [1]
In the single-species treatments, 100% of the seedlings inoculated with S. americanus were colonized, 85% of the seedlings inoculated with S. subaureus were colonized, and none of the seedlings inoculated with S. spraguei were colonized
In terms of mycorrhizal colonization, all three species showed no significant differences among the single- and two-species treatments (Fig 1A–1C), despite trends indicating that S. subaureus was the competitive inferior to S. americanus and that S. spraguei was competitively inferior to both other Suillus species due to its lack of colonization in all treatments
Summary
A fundamental axiom in biology is the existence of tradeoffs, which are commonly defined as an increase in performance in one area being correlated with a decrease in performance in another area [1]. Tradeoffs generally focus on specific traits that shape the life history strategy of a given species [2]. Many organisms exhibit tradeoffs among growth, storage, and reproduction based on energetic constraints [3]. These tradeoffs are frequently conceptualized as bifurcations in allocation, commonly referred to as Y.
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