2.26 Nectar Secretion and Composition

Question 1

9 Factors affecting nectar secretion (with examples)

Answer 1

1 Position of flower on plant. Nectars at the bottom secrete more than those at the top e.g. Rosebay willow herb.
2 Age of the flower. Bramble flowers opening first on an inflorescence produce more nectar than those further up. The new young shoots of Ling heather that has been burnt produces more nectar than flowers on old wood plants.
3 Temperature. Blackberry is not fussy. Lime (Tilia spp) likes warm
nights and humid, humid days for best secretion.
4 Time of day. Poor secretion early in the morning then peaks as wind and sun evaporate some of the water. Nectar quality and quantity may peak at different times. Apple most visited later in the day.
5 Wind and humidity. Light wind and low humidity can concentrate nectar. Strong drying
wind and very low humidity can cause nectar to dry up.
6 Soil moisture. If this drops to the level where plants wilt, nectar production will cease. Deep rooted plants fare best. Long term issue with weather in previous months being key.
7 Nature of soil and subsoil. Acidity and alkalinity can influence nectar production. Heather (Calluna vulgaris) needs acid soil. Blackberry does well on either.
8 Topography. Heather and clover both yield better on slopes.
9 Shading. Some plants really need sunshine (Sedum spp).

Question 2

Composition of nectar

VAMOPAEO

Answer 2

30-90% water Sugars 5-70% Rest 3%:
Vitamins, principally C and B
Amino acids
Minerals
Organic acids
Pigments
Aromatic compounds
Enzymes from the plant
Occasionally lipids and alkaloids

Question 3

Mostly sucrose nectar

Answer 3

Plants with protected nectaries
Nectar derived directly from the phloem of the plant
Ribes (red and black currants) Some Rhododendron

Question 4

Equal amounts sucrose/glucose/fructose nectar

Answer 4

Clover

Question 5

Low sucrose (most common class) nectar

Answer 5

Open flowers, unprotected nectaries
Proportion of glucose generally exceeds fructose
Includes Brassica and aster families

Question 6

Sugar concentration

Answer 6

Honeybee not interested in sugar concentration < 15%
Most flowers attractive to bees in 20-40% range
Apple good example of low-yielding nectar (25%)
Higher yielding: Borage and rosebay willowherb
Large differences of sugar content can be found on same flower and flower to flower. Age of plant has dramatic effect on level of sugars.