The Effects of Light Intensity on Foraging in the Clonal Herb Glechoma Hederacea

Abstract

(1) The growth form of 12-week old clones of Glechoma hederacea grown either under neutral shading (reducing light intensity by 750%), or in full daylight, was compared. All clones were genetically identical. (2) Clones grown under shading displayed a growth form characterised by a small number of slender, unbranched stolons with long internodes, and only a few small ramets. Dry weight per unit length of stolon was low. Proportional allocation of dry weight to roots was low, whereas allocation to petioles was high. Specific leaf area was nearly three times higher in the shaded clones than in the unshaded clones. Mean ramet leaf area was the same for clones in both treatments. (3) The growth form of unshaded clones was characterised by short stolon internodes, frequent stolon branching and many large ramets. The dry weight per unit length of stolon was four times greater than in the shaded clones. Proportional allocation of dry weight to roots was high, whereas allocation to petioles was lower than in the shaded clones. (4) The results of this experiment are compared with published data analysing the response of G. hederacea to different levels of nutrient availability. G. hederacea displays qualitatively similar alterations in growth form in conditions of low light and low nutrient availability. Plasticity in growth form of G. hederacea enables clones to consolidate occupation of favourable sites, through intensive foraging, and to grow through less favourable sites, concentrating resources in extensive foraging which may result in establishment of ramets in more rewarding sites.