Some Factors Affecting Nectar Secretion in Red Clover

Abstract

The influence on nectar secretion in Trifolium pratense L. of temp., light, humidity, and genotype was studied. A modified Gubin centrifuge method was used to measure vol. yields; sugar concns. were derived from refractive indices read with an Abbe refractometer. The effect of night temp. in the range 50[degree] to 78[degree] F was studied under conditions of both natural and artificial illumination. No significant differences could be detected in the amt. of nectar secreted over this range. Over a period of 2 mos. a quantitative relationship between wt. of sugar secreted in nectar and the amt. of solar radiation incident upon the plant was observed. A highly significant inverse correlation of _0. 83 was found between atmospheric vapor pressure and sugar concn. of nectar over a 4-wk. period. Post_secretion hygroscopic changes appeared to be rapid enough to account for the approach to equilibrium between nectar and atmosphere. The relation of genotype to secretion was studied in 3 clonal populations. The apparent superiority in yield of one clone suggests the possibility of selecting for high nectar_yielding strains. The sugar concn. of the nectar within each clone was relatively constant, the major part of the variability being attributable to day-to-day variation in environment. On the basis of the observed effects of the factors studied the hypothesis is advanced that nectar is secreted as a soln., the concn. of which is comparatively constant within a sp., and that the vol. secreted is dependent on the amt. of sugar or sugar precursor available.