From acquisitive to conservative: The ontogenetic trajectory of root syndrome of annual and perennial co-generic species

Abstract

Perennials has been proposed as new crops because their root syndrome offers more ecosystem services and abetter use of resources than the annual one. Objective: To compare the ontogenetic trajectory of root syndromesof annual (P. gracilis and P. angustifolia) and perennial (P. pinetorum and P. mendocina) species of Physaria (Brassicaceae) and their root trait relationships.Results and Conclusion: Roots became conservative as plants grew, independently of the life cycle of the species.However, perennials invested initially more resources in increasing storage capacity (bigger and thicker roots)while annuals favored increasing the exploration capacity (higher SRL). During first anthesis we found tradeoffsbetween acquisitive and conservative traits, as expected according to the Root Economic Spectrum (RES), but after the first year, those tradeoffs disappeared and perennials were able to combine a thick and deep taproot and high investment in C reserves with some well-developed acquisitive traits such as higher SRL and total length.This suggest that root traits should be selected during the second year, when no tradeoff exist. Differences between annuals and perennials in most structural taproot traits remained constant along the ontogenetic trajectory, thus the relative position of species in the RES did not change over time. We found a gradient of root strategies supported by the RES theory: from acquisitive in the annual P. gracilis (high SRL, STD and total length) to conservative in the perennial P. mendocina (high root biomass, root diameter, tissue density and storage) with intermediate strategies in P. angustifolia and P. pinetorum.