Functional traits of Epifagus virginiana (Orobanchaceae) tubers as adaptations to the Mexican beech microenvironment

Epifagus virginiana (Orobanchaceae), known as beechdrops, is a holoparasitic plant that acquires all its resources from a narrow range of host plants, restricted to North American Fagus species. To do so, beechdrops develop a vascular connection with the host via a terminal haustoria that develops as a tuber attached to the host root. We hypothesized that microenvironmental conditions can influence functional traits of the E. virginiana tuber despite this parasite's complete reliance on the host plant for its nutrition. Therefore, the aims of this study were i) to analyze the structure of the tubers of E. virginiana; ii) to assess the variation in tuber functional traits between two E. virginiana populations; and iii) to analyze how microenvironmental factors influence functional traits in the tuber. We detected that functional trait of beechdrops tuber along Mexican beech microenvironmental covaried with traits important for below-ground processes. Boosted regression trees provided a powerful analysis tool, giving substantially superior predictive performance to generalized additive models, despite the fitting of interaction terms in the latter.