Good evening Christine. I finally have something to contribute but it might
not be related. Several conifer species, I believe Douglas fir is one of
them, will put out cones under two conditions - when the tree is very
healthy and can "afford" such investments, but also when the tree is under
extreme stress at which point it's a last-ditch effort to pass on those
genes prior to death. Think "selfish gene theory" for how and why that
mechanism would endure, from an evolutionary perspective. I don't know if
that answers why the Dutch clover nectar would sometimes be appealing to
bees and other times not. But not all reproductive events occur when the
plant is healthy. Sometimes, just the opposite. Under those circumstances,
I can see how the plant would put out just enough to spread genes around,
but not sacrifice any sugar it didn't have to, on the long shot that
survival might yet be possible. I don't know if flowering plants have any
mechanism like I just described for conifers, but it seemed at least
plausible.
Kathryn Kerby
Frogchorusfarm.com
Snohomish, WA
-----Original Message-----
From: Informed Discussion of Beekeeping Issues and Bee Biology
[mailto:[log in to unmask]] On Behalf Of Christina Wahl
Sent: Wednesday, June 18, 2014 12:20 PM
To: [log in to unmask]
Subject: [BEE-L] Nectar secretion
I've often wondered why blooms of specific plant species are visited some
years, but not every year. Dutch clover was a major honey plant in northern
NY when I was young, but not now. For the last several years, I've watched
it....no bees. However, this year I see bees working the Dutch clover.
What is different?
There is a paper I found from the Journal of Plant Physiology, vol. 27, no.
1, Jan 1952, pp 95-110, called "Some factors affecting nectar secretion in
red clover" by R. W. Shuel. Here is a quote:
"Little is known about the basic mechanism of nectar secretion. Two general
theories are extant: 1. That sugar secretion and water secretion are
distinct phases, water secretion being analogous to guttation and dependent
on root pressure (cited) 2.That secretion occurs as one phase, nectar being
secreted in its final form as the result of a specific cellular activity
(cited). Bonnier (cite) has presented evidence for a positive relationship
between secretion and root pressure. (NOTE: This is basic plant
physiology; I was trained in this, and can confirm it to be true...it is
similar to guttation) Radtke (cited) on the other hand, has shown that
secretion can occur in the absence of root pressure in isolated flowers
floated on sucrose solutions (cited, but NOTE: from a physiologist's point
of view...big deal. Ask me why if interested.)
Recently Arens (cite) has advanced an hypothesis in which secretion,
absorption, and transport of solutes are treated as closely related
phenomena dependent on electro-osmotic currents at the surface of the
tonoplast. The energy necessary for the maintenance of the
oxidation-reduction potentials across the membrane is assumed to be supplied
by respiration."
From this I gather that the quality of nectar is a product of two processes:
one that is essentially the same as guttation, but the second is more
nebulous...sugar production is driven by respiration, and may or may not
occur depending on the level of plant stress. If the point of nectar
production is to attract pollinators, then it seems to me that the process
which supplies sugar is essential, else why bother with nectar production at
all? Yet we have years where certain plants flower but do not make a nectar
that is attractive to honeybees. Is that nectar attractive to other
pollinators? If not...well, Occam's razor would suggest that there is no
reason to produce flowers, at all, if they cannot be pollinated. This year
my peach trees did not bloom. I assume that the reason is it was too cold
during the winter. That makes sense to me...the plant was too severely
stressed, so it didn't make an effort to reproduce in favor of simply
replenishing itself and surviving. However, if the peaches had bloomed and
produced a nectar that was low in sugar and unattractive to
pollinators...that just does not make sense. Yet that seems to happen among
some plants, such as the Dutch clover.
Do any of you know more about this? Why do some plants bother to produce
flowers that haven't got enough sugar to attract pollinators like honey
bees? Or, are they attracting DIFFERENT pollinators...and if so, what ones?
Christina
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