The Vegetative Growth of Helianthus annuus and Phaseolus vulgaris as Affected by Seasonal Factors in Freetown, Sierra Leone

Abstract

Sand-culture experiments were carried out in full daylight at successive weekly intervals between March and December 1969, to investigate the effects of seasonal changes in climatic factors on the growth of Helianthus annuus and Phaseolus vulgaris in Freetown. Values for a number of growth parameters were calculated from the dry weights of the leaves, stems, and roots, and from the leaf areas. Simultaneously the diurnal changes in climatic factors were recorded. Multiple regressions linking light, temperature, and relative humidity with some of the growth parameters were calculated. The total variance accounted for in the regressions of relative growth-rate, net assimilation rate, and leaf weight ratio on light, temperature, and relative humidity ranged from 51 to 60 per cent in P. vulgaris. In H. annuus relative humidity was less important; the percentage proportion of total variance accounted for in the regression of leaf weight ratio (and leaf area ratio in both species) on light and temperature was not significant. The results showed that H. annuus grew faster than P. vulgaris , but the latter's growth was depressed less by the dull weather of the rainy season. The relative growth-rates of both species were positively dependent on light and temperature while their net assimilation rates were negatively dependent on relative humidity, and their leaf area ratios negatively dependent on light. All parameters used except leaf area ratio and leaf area to leaf weight ratio showed seasonal variations corresponding to dry and rainy seasons. The initial and final values of leaf area ratio and weight ratios were always different but did not vary in the same direction in both species. The results are discussed in relation to similar work done elsewhere.