Direct and indirect effects of two herbivore species on resource allocation in their shared host plant: the rhizome galler Eurosta comma, the folivore Trirhabda canadensis and Solidago missouriensis.

摘要

The effects of the rhizome-galling Eurosta comma on rhizome mass and nitrogen allocation in a clone of its host plant, Solidago missouriensis, were studied in the field in Minnesota, during 1992-93. In comparison to ungalled ramets, galled ramets initiated significantly fewer new rhizomes, and allocated less mass to leaves and stems and more to roots. Galled ramets had lower concentrations of nitrogen in roots and rhizomes but leaf and stem nitrogen concentrations were not affected. In the second year, outbreaks of the leaf-eating Trirhabda canadensis occurred in 3 of the 4 clones studied, removing～20,～50, and 100% of leaf area from clones 2-4, respectively. In the most heavily grazed clones, the influence of rhizome galls on plant resource allocation was least pronounced. Despite the overwhelming immediate impact of grazing, the presence of a gall population may be important because they decrease the ability of S. missouriensis clones to initiate new rhizomes and to recover from defoliation.