Age-related changes in root traits are linked to internal nitrogen cycling in the perennial forb Physaria (Brassicaceae)

Abstract

Age-related changes in root morphology and physiology, and the relationship with N dynamics between species that differ in resource use (i.e., conservative or acquisitive) and lifespan strategies are largely unexplored and experimental evidence very scarce. Objective: to compare age-related changes in root traits and their relationship with internal N recycling in two co-generic perennial species differing in their resource-use strategy and plant lifespan. We hypothesized that the root system of both species will become more conservative with age, but the root system of the acquisitive short-lived Physaria pinetorum (Brassicaceae) will decrease its acquisition capacity while the conservative long-lived P. mendocina will increase its storage capacity. Results and conclusion: we confirmed that the root system of both species shifts from acquisitive to conservative with age, reducing N acquisition and relying either on N translocation from leaves or root stores to sustain growth and grain filling. As hypothesized, the species responded differentially according to their longevity and resource-use strategy: P. pinetorum showed a great loss of acquisition and storage capacities with absolute age, and turned to N stores when acquisition was deficient while P. mendocina increased storage capacity with age and obtained N from resorption to sustain allocation to grain, decreasing the quality of its litter. Species differing in their plant lifespan and resource use strategies have different patterns of N dynamics with age, that could affect yield stability and the provision of ecosystem services.