HYSIOLOGICAL AND SOME MORPHOLOGICAL ADJUSTMENTS IN THE ROOT SYSTEM OF LOLIUM PERENNE AS A RESPONSE TO SPATIAL NUTRIENT PATCHINESS
H.M.S.P. Madawala Weerasinghe1* and E.V.J. Tanner2
1Department of Botany, Faculty of Science, University of Peradeniya, Sri Lanka.
2Department of Plant Sciences, University of Cambridge, UK.
Accepted 07 March 2006
When roots encounter nutrient-rich zone or patch, they tend to proliferate within it and also enhance their ion uptake capacities compared to roots of the same plant outside the patch. These plastic responses in the root system seem to be a major mechanism adapted by plants to cope with the naturally occurring heterogeneous supplies of nutrients in soil (Hodge, 2004). Fast-growing species from fertile habitats seems to be more morphologically plastic in contact with nutrient patches than slow-growing species from infertile habitats (Grime, 1979; Chapin, 1980). A pot experiment was conducted to assess the morphological and physiological plasticity of Lolium perenne, a fast-growing plant from fertile habitats, when plants were exposed to heterogeneous supply of phosphorus. Each plant was exposed to P heterogeneity with a specially designed set up which included 4 plastic pots held together by clamping a small PVC tube in the middle. Each pot was filled up with P-fertilized or unfertilized soils giving 6 treatments altogether. The results indicated that even though plants were P limited, they did not show any concentration of roots into P fertilized soils compared to unfertilized soils. The biomass allocation pattern into shoots and roots also showed no significant difference among treatments. Interestingly, Lolium has shown a significantly greater physiological plasticity by increasing the specific P uptake rates when roots were exposed to unfertilized soils. It seems that L. perenne is more plastic physiologically than morphologically, and this conclusion is in contrast with the assumption that fast-growing plants are more plastic morphologically than physiologically.
Key words: Plasticity, Lolium perenne, soil heterogeneity and root proliferation.