Insect herbivore effects on resource allocation to shoots and roots in Lespedeza capitata

Abstract

Aboveground and belowground processes in plants are intimately linked because the resources that must be divided among growth, maintenance, and development of essential structures are finite. To determine how aboveground insect herbivory affects root-system size, morphology, interactions with soil biota, and temporal patterns in the development of root systems, we grew the legume Lespedeza capitata in sunken pots in a restored prairie in south-central Kansas. The plants were manipulated in a factorial experiment that involved reduction of natural herbivory with insecticide and age of plant at harvest (2, 4, or 6 months). Herbivory reduced the aboveground sizes of plants throughout the growing season but did not affect their belowground size or root-system branching ratio. Further, the failure of aboveground insect herbivory to affect density of nitrogen-fixing nodules on L. capitata roots suggests that plants did not shift allocation of carbon to compensate for naturally occ! urring levels of folivory. We suggest that conservation of root-system structure or low rates of change in root-system structure in response to aboveground insect herbivory may be an adaptive strategy in environments with scarce soil resources, for example near species' xeric range limits.