Abstract
The ecological relevance of early ontogenetic trends in root/shoot covariation in herbaceous plants is barely known. In the present study, this issue was tackled for seedlings and juvenile plants of two herbaceous species (Plantago lanceolata and Sanguisorba minor) that share several life-history traits and habitats. We measured root and shoot traits of plants growing in the same conditions. Plantago lanceolata plants develop shallow roots and increase biomass allocation to lateral roots through ontogeny. Sanguisorba minor plants form deeper root systems in which biomass allocation to the tap root increases through ontogeny. Root dry matter content was lower in the latter species. Shoot growth of P. lanceolata was linked to the biomass of lateral roots and to the biomass and morphology of the tap root whereas aboveground growth of S. minor was linked to the exploration capacity of the tap root. The number of internodes was linked to the number of first order lateral roots in the seedlings of both species, and also in juvenile plants of P. lanceolata. Specific leaf area was positively correlated with the specific length of the tap root only in S. minor; the dry matter contents of leaves and lateral roots were positively correlated in P. lanceolata. The contrasting patterns of biomass allocation of both species are linked to specific morphological and functional root-architecture traits, and could reflect different strategies of resource acquisition and soil exploration and exploitation. Plant species whose architectural features and habitats are broadly similar may differ in the way root and shoot traits relate to each other through ontogeny, thereby revealing unequal resource-use strategies.