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The Ecophysiology of Veronica Chamaedrys, V. Montana and V. Officinalis. III. Effects of Shading on the Phenology of Biomass Allocations--A Field Experiment
M. P. Dale and D. R. Causton
Journal of Ecology
Vol. 80, No. 3 (Sep., 1992), pp. 505-515
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2260694
Page Count: 11
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1. Veronica chamaedrys, V. montana and V. officinalis were grown in either shaded or unshaded conditions in a field experiment lasting 18 months. V. officinalis failed to grow beneath shading as a result of slug grazing. Between May and October of the first year, unshaded V. officinalis had the highest relative growth rate (RGR) and shading significantly reduced RGR in both V. chamaedrys and V. montana but to a greater extent in V. chamaedrys. 2. The proportion of biomass allocated to roots was rapidly reduced by shading, but at the end of the experiment differences between species and light environments were negligible. Root phenology was unaffected by shading. In unshaded plants, allocation to stem (SWR) was higher in both V. chamaedrys and V. montana than in V. officinalis. Shading increased SWR and allocation to petioles but only altered stem phenology. The difference in SWR between shaded and unshaded plants of V. montana became less with time. Total allocation to leaves (TLWR) in unshaded plants was ranked V. montana > V. officinalis > V. chamaedrys. The contribution of dead leaves to TWLR was greatest in unshaded plants. Shading increased TLWR in V. chamaedrys but not in V. montana. 3. In unshaded plants, biomass allocation to sexual reproduction was ranked V. officinalis > V. chamaedrys > V. montana. Whilst shading reduced allocation to sexual reproduction in V. chamaedrys, it increased allocation in V. montana. Inflorescences were subdivided into: pedicels plus peduncles; capsules plus calyces; and seeds. A second quotient (`relative allocation') was devised by expressing the biomass allocated to each of these subgroups as a proportion of the total allocated to inflorescences. Whereas shading had no influence on relative allocation in V. montana, there was an increase in the pedicel + peduncle component in V. chamaedrys. Pedicels + peduncles accounted for 50% of inflorescence biomass in unshaded V. chamaedrys, but only 30% in V. montana and V. officinalis. Relative allocation to seeds was ranked V. montana > V. officinalis > V. chamaedrys. 4. Growth form, photosynthetic characteristics and slug grazing all hindered the proliferation of V. officinalis under shading. V. officinalis had a high RGR and allocated c. 25% of plant biomass to inflorescences. 5. Shading modified allocation within and between vegetative and reproductive organs of V. chamaedrys. V. chamaedrys did not acclimatize to shading; increases in SWR in the second year, coinciding with tree canopy expansion, were supplementary to those incurred in the first year. 6. Shading had little effect on the allocation of biomass within either vegetative or reproductive organs of V. montana: changes detected in previous short-term experiments were transient. At high irradiances, V. montana was susceptible to chlorophyll photodegradation and could not sustain sexual reproductive output
Journal of Ecology © 1992 British Ecological Society