Intraspecific polyploidy correlates with colonization by arbuscular mycorrhizal fungi in Heuchera cylindrica

Premise: Polyploidy is known to cause physiological changes in plants which, in turn, can affect species interactions. One major physiological change predicted in polyploid plants is a heightened demand for growth-limiting nutrients. Consequently, we expect polyploidy to cause an increased reliance on the belowground mutualists that supply these growth-limiting nutrients. An important first step in investigating how polyploidy affects nutritional mutualisms in plants, then, is to characterize differences in the rate at which diploids and polyploids interact with belowground mutualists. Methods: We used Heuchera cylindrica (Saxifragaceae) to test how polyploidy influences interactions with arbuscular mycorrhizal fungi (AMF). Here we first confirmed the presence of AMF in H. cylindrica, and then we used field-collected specimens to quantify and compare the presence of AMF structures while controlling for site-specific variation. Results: Tetraploids had higher colonization rates as measured by total, hyphal, and nutritional-exchange structures; however, we found that diploids and tetraploids did not differ in vesicle colonization rates. Conclusions: The results suggest that polyploidy may alter belowground nutritional mutualisms with plants. Because colonization by nutritional-exchange structures was higher in polyploids but vesicle colonization was not, polyploids might form stronger associations with their AMF partners. Controlled experiments are necessary to test whether this pattern is driven by the direct effect of polyploidy on AMF colonization.