Phenotypic plasticity and performance of Taraxacum officinale (dandelion) in habitats of contrasting environmental heterogeneity

Ecological theory predicts a positive association between environmental heterogeneity of a given habitat and the magnitude of phenotypic plasticity exhibited by resident plant populations. Taraxacum officinale (dandelion) is a perennial herb from Europe that has spread worldwide and can be found growing in a wide variety of habitats. We tested whether T. officinale plants from a heterogeneous environment in terms of water availability show greater phenotypic plasticity and better performance in response to experimental water shortage than plants from a less variable environment. This was tested at both low and moderate temperatures in plants from two sites (Corvallis, Oregon, USA, and El Blanco, Balmaceda, Chile) that differ in their pattern of monthly variation in rainfall during the growth season. We compared chlorophyll fluorescence (photosynthetic performance), flowering time, seed output, and total biomass. Plants subjected to drought showed delayed flowering and lower photosynthetic performance. Plants from USA, where rainfall variation during the growth season was greater, exhibited greater plasticity to water shortage in photosynthetic performance and flowering time than plants from Chile. This was true at both low and moderate temperatures, which were similar to early- and late-season conditions, respectively. However, phenotypic plasticity to decreased water availability was seemingly maladaptive because under both experimental temperatures USA plants consistently performed worse than Chile plants in the low water environment, showing lower total biomass and fewer seeds per flower head. We discuss the reliability of environmental clues for plasticity to be adaptive. Further research in the study species should include other plant traits involved in functional responses to drought or potentially associated with invasiveness.