Watering regime affects aboveground and belowground trait covariation in a hybrid Silphium population

Premise of the studyPerennial, herbaceous members of the sunflower family (Asteraceae) can provide valuable agronomic products from aboveground biomass, as well as ecosystem services belowground. Aboveground and belowground trait covariation can be affected by environmental conditions such as the location of available water. Here, we investigated the effects of watering regime on trait covariation in Silphium (Asteraceae), an emerging perennial oilseed crop. MethodsSilphium integrifolium Michx. and S. perfoliatum L. are native North American species adapted to well-drained and moist soils, respectively. Using a backcrossed F1 hybrid S. integrifolium x S. perfoliatum population, we conducted a greenhouse experiment where plants were either watered at the soil line ("top-watered") or from below using watering trays ("bottom-watered"). Aboveground biomass, root distribution, and root morphology (e.g., specific root length) were measured destructively. Key resultsCompared to top-watered plants, bottom-watered plants were smaller aboveground and belowground, with a higher proportion of roots in the upper portions of the pots and higher specific root length. Negative relationships between aboveground biomass and specific root length were steeper for bottom-watered than top-watered plants. ConclusionsThe location of available water impacts aboveground biomass, the distribution and morphology of the root system, and relationships between aboveground and belowground plant structures. This work suggests that resource allocation depends in part on the location of available water, and has relevance for ongoing efforts aimed at developing perennial, herbaceous species that offer both economically viable products as well as ecosystem services.