A domestic plant differs from its wild relative along multiple axes of within-plant trait variability and diversity

Abstract

AbstractFor 10,000 years humans have altered plant traits through domestication and ongoing crop improvement, shaping plant form and function in agroecosystems. To date, studies have focused on how these processes have shaped whole-plant or average traits; however, plants also have characteristic levels of trait variability among their repeated parts, which can be heritable and mediate critical ecological interactions. As concerns about sustainable pest management increase, there is growing interest in approaches that increase trait diversity in crop agroecosystems. Here, we examine an under-appreciated scale of trait variation – among leaves, within plants – that may have changed through the process of domestication and improvement in a key crop.We explore how levels of within-plant, among-leaf trait variability differ between cultivars and wild relatives of alfalfa (Medicago sativa), a key forage crop with an 8,000 year cultivation history. We grew individual plants from 30 wild populations and 30 cultivars, encompassing a range of domestication and improvement histories. For each plant, we quantify variability in a broad suite of physical, nutritive, and chemical leaf traits, including measures of chemical dissimilarity (beta diversity) among leaves.We find that intra-individual trait variability has changed over the course of domestication and crop improvement, with effects often larger than changes in trait means. Cultivated alfalfa had elevated variability in SLA, trichomes, and C:N; increased diversity in defensive compounds; and reduced variability in phytochemical composition. We also elucidate fundamental associations between trait means and overall investment in secondary metabolites with patterns of among-leaf variability and chemical diversity.We conclude that within-plant variability is an overlooked dimension of trait diversity in this globally critical agricultural crop. We find that trait variability is actually higher in cultivated plants compared to wild progenitors for multiple nutritive, physical, and chemical traits, highlighting a scale of variation that may mitigate loss of trait diversity at other scales in alfalfa agroecosystems and in other crops with similar domestication and improvement histories.