Influence of root herbivory on growth response and carbon assimilation by white clover plants

One of the most significant pests of white clover (Trifolium repens L.) is the clover root weevil (Sitona lepidus L. Coleoptera; Curculionidae). The adult of this species feeds on the leaves of the plant. However, root feeding by the larvae is more insidious. An experiment is described that was designed to test the hypothesis that root nodule herbivory by early instar larvae of S. lepidus reduces the assimilation of C by plants of white clover. White clover plants were grown ( larvae) in individual growth chambers and the net carbon (C) assimilation by each plant was estimated by monitoring CO2 flux in the chambers. White clover plants which had been infested with larvae had a significantly (P < 0.01) reduced biomass when compared with the control plants and tended to have a smaller root:shoot ratio (0.68 versus 0.78). The number of nodules on the clover roots were significantly (P < 0.05) reduced by the weevil infestation. The diurnal pattern of the mean C flux during the experiment shows that 44 +/- 2.5% less C was assimilated during the light period, and 39 +/- 3.3% less C was lost in respiration during the dark phase, by the infested plants. Significant treatment differences in net C accumulation were evident only towards the end of the study period with the control plants showing a significant (P < 0.05) net gain of C from day 19 onwards. This study demonstrates the initial impact of specialised nodule herbivory on the clover plants. (C) 2002 Elsevier Science B.V. All rights reserved.