Root size and soil environments determine root lifespan: evidence from an alpine meadow on the Tibetan Plateau

Abstract

AbstractWe used a minirhizotron system to investigate the influence of three major factors—root morphology, root depth, and season of root emergence—on root survivorship and longevity in aKobresia humilismeadow on the Tibetan Plateau during the growing season of 2009. Root longevity was assessed by survival analysis, Kaplan–Meier analysis, and Cox proportional hazards regression. Root longevity was correlated positively with root diameter. A 17.5 % decrease in the risk of mortality was associated with a 0.1‐mm increase in diameter. Roots distributed in the top 10 cm of the soil had significantly shorter longevities than roots at greater depths, with a 48 % decrease of mortality risk for each 10‐cm increase in soil depth from the surface to 40 cm. Of all the factors examined, the season of root emergence had the strongest effect on root lifespan. Roots that emerged in May and June had shorter longevity than roots that emerged later in the year, and roots that emerged in September and October were more likely to survive over winter. Our findings indicated that life‐history traits of roots inK. humilismeadows are highly heterogeneous, and this heterogeneity should be considered when modeling the contribution of roots to carbon and nitrogen fluxes in this type of meadow ecosystem. Moreover, temporal, spatial, and compositional variations in root longevity must be considered.