Goldenrod Ball Gall Effects on Solidago altissima: 14C Translocation and Growth

Abstract

The purpose of this investigation was to determine whether the effects of the goldenrod ball gall on carbon translocation and growth in ramets of Solidago altissima can account for changes in biomass allocation and total biomass observed in galled ramets. To do this, individual leaves of S. altissima were labeled with carbon—14 introduced as CO2. The 14C was introduced into ramets that had ball galls caused by the fly Eurosta solidaginis and into ungalled control ramets; gall size (large vs. small) and point of introduction of the label (above vs. below the gall) were experimental factors. After 5 d the ramets were harvested and their component organs were assayed for 14C using liquid scintillation. In addition, a field cohort of 359 galled and ungalled was followed during the period of gall growth to determine the effect of the gal on stem height growth. Gall size and labeling position had no effect on the percent of 14C translocated out of the labeled leaf but did affect the distribution of translocated 14C. Translocation to underground organs was reduced when the label was introduced above the gall, the reduction being related to gall size. Large galls reduced translocation to the apical bud when the label was introduced below the gall, but small galls did not. Translocation to underground organs was not affected by the gall when the label was introduced below the gall and translocation to the apical bud was not affected by the gall when the label was introduced above the gall; these results indicate that the goldenrod ball gall is a nonmobilizing gall. The presence of a gall did not significantly affect final stem height but did slow the growth of ramets during the period of most rapid gall growth. The observed effects of the gall probably explain changes in resource allocation shown by other studies but do not account for the overall decrease in biomass of galled ramets.