PHENOTYPIC PLASTICITY OF Euphorbia heterophylla L. AND Sida acuta Burm. F. IN RESPONSE TO SOIL FERTILITY, IRRIGATION INTERVAL AND PLANT DENSITY IN NORTHERN GUINEA SAVANNAH, NIGERIA

Background: Phenotypic plasticity is a key mechanism associated with the spread of invasive plants and previous studies have found that weeds are generally more plastic than co-occurring species. Large body of evidence for superiority in particular traits among weed species when compared to non-weeds species was reported, however, it is less clear if weeds have similar pattern of phenotypic plasticity.

Study Design: Factorial, complete randomised design.

Place and Duration of Study: Department of Biological Sciences, Ahmadu Bello University, Zaria, Kaduna State, Nigeria between May 2014 and October 2014.

Methodology: Screen-house experiment of the two weed species were carried out, each species had 486 plants and a factorial, combinations of high, medium and low levels of soil nutrient, water and density was constructed. A total of 9-10 intact plants from each treatment were randomly selected for measurement of morphological and biomass traits. ANOVA was used to test the effect of treatments and to compare differences between species.

Results: Significant differences were observed between the species, and morphological trait indicated that S. acuta with its opportunistic response recorded its highest mean values in soil rich in nutrients and low plant density (stem height 11.01 cm±2.74 and 8.52±1.43 numbers of leaves) (P<0.01), while E. heterophylla had generalist strategy with higher performance and greater plasticity in all treatment combinations (stem height 46.30 cm±7.56, and numbers of leaves 17.61±2.68) (P<0.01), hence, higher plasticity. Soil nutrient significantly influenced reproductive biomass of E. heterophylla, while no significant influence for S. acuta.

Conclusion: S. acuta exhibited a Master-of-some pattern of phenotypic plasticity, and E. heterophylla had a complex pattern exhibiting Jack-and-Master strategy.