| 1. Arbuscular mycorrhizal (AM) associations, in which plants supply soil-borne fungi with carbon resources and fungi supply plants with mineral nutrients, are highly variable in both space and time. In this study, I investigated the seasonal variation in the AM association of the three youngest ramets of mayapple and explored the relationships between this AM association and internal (plant-based) and external factors. The AM association of mayapple is seasonally variable, but only in the small-diameter, more highly colonized secondary roots. Total AM colonization and arbuscule presence (the primary sites of nutrient exchange) within secondary roots followed the same seasonal pattern when averaged across ramets, showing a decline in May and a yearly peak in September. During the spring, the three ramets studied differed in their seasonal patterns, with the youngest ramet having the most variable seasonal pattern. For the two youngest ramets, this seasonal variation in AM association was related to soil moisture conditions in the spring, while seasonal variation in the fall was related to growth of roots, but only for the youngest ramet. None of these relationships were strong. In addition, while the capacity of the AM fungi community to establish new AM associations was both seasonally and spatially variable, variation in this external factor did not explain described patterns within the mayapple AM association. Based on these results and the known physiology of mayapple, seasonal variation in AM association of this species is probably related to internal nutrient status, most likely carbon availability, rather than external factors.;2. Students' attitudes are commonly thought to strongly influence their learning. We characterized students' attitudes toward evolution and investigated the influence of students' attitudes (pre- and post-course) toward evolution on their performance in an evolution course. Students held positive attitudes toward evolution; these attitudes were more positive following the course. We found that while attitudes prior to the course had little influence on final grades, at the end of the course, students' attitudes were positively related to final grades. However, this effect was small. We argue that pedagogical techniques directly addressing students' attitudes help reduce the influence of attitudes (especially prior attitudes) on achievement. |
