In article ,
"David E. Ross" wrote:

On 1/3/2010 9:29 PM, Wildbilly wrote:
In article ,
"David E. Ross" wrote:

On 1/3/2010 5:13 PM, Wildbilly wrote:
In article
,
Frank wrote:

On Dec 29 2009, 11:56 am, "David E. Ross"
wrote:
On 12/22/2009 11:03 AM, Frank wrote:

Sunleaves are the large leaves at the base of and associated
with secondary branches.

I assume their role is to feed the secondaries with products
of photosynthesis and release of stored mobile nutrients such
as N, P, K.

That being understood, what is the effect of pruning out
one or the other, as when making a plant into a bonsai?
If we're trying to arrest stem elongation by pinching back,
does it leave the plant stronger to remove just the tip in
question without removing the sunleaves?

I don't think "sunleaves" are any different from other leaves. They are
larger primarily because they are on branches that are sufficiently
mature to sprout side branches. When the side branches mature, they too
will have larger leaves. All leaves participate in photosynthesis once
they have opened up from their buds.

Leaves -- even the larger leaves on mature stems -- do not usually store
or release N, P, and K. Leaves use those nutrients to produce sugars.
Only fleshy leaves (e.g., on succulents) might store any nutrients other
than sugar.

What accounts for the various spots and blanching on older
leaves specific to a given deficiency? I would have thought
nutrient translocation to be the cause.

Plants will, of necessity, use what energy and nutrients they have for
their meristems (growing tips). As the plants get larger, and they have
more meristems, more resources are diverted from the earlier leaves, to
their detriment, to the benefit of the new growth.

Quite correct. Nutrients are diverted to the meristems, but they are
not depleted from the older leaves. It's just that the older leaves
fail to receive as much nutrients as they received while still growing.

In the meantime, the older leaves still receive enough nutrients to
engage in photosynthesis, producing sugars that are transported by sap
to the meristems and elsewhere within the plant. Other plant tissues
convert the sugars into starches, cellulose, and other carbohydrates.
And still other plant tissues combine the sugars with other nutrients to
produce proteins and oils. It does not take large basal leaves to
produce sugars; any leaf containing chlorophyll can do this. Even stems
containing chlorophyll can do this.

Still, new growth up above, means shadows below, at least for plants
that I have grown.

Which is why I prune my roses and peach tree to an "open vase" pattern,
with the new growth directed outward to allow the sunlight to penetrate
to the center.

Hmmm, an "open vase" pattern would seem to be an esthetically radical
step for a bonsai. (See Common Styles:
http://en.wikipedia.org/wiki/Bonsai#Common_styles ), but of course
opening up a plant to more sunlight and air flow, as in cane or cordon
pruning, which is used in commercial crops, such as grapes or espalier
fruit trees, is a judgement call.

There is a trade-off in opening up plants to sunlight. It increases the
surface area exposed to sunlight, which would increase photosynthesis
and decreases the chance of mold and mildew. Conversely, it increases
the chance of sunburn on fruit and its' attendant loss of production.
Pays yo' money, and takes yo' chances.

Most of my experience is with annuals (tomatoes, peppers, cucumbers,
squash) where an arbor (cage) or trellis seem to offer the advantages of
more sunlight, without the pruning.

On the matter of nutrients, plants, especially leafy plants such as
lettuce and spinach, will store nitrogen in their leaves when abundantly
supplied with nitrogen, as with rapidly absorbed chemical fertilizers,
which will make their leaves targets for insects.

The leaves do produce and other compounds besides glucose, such as
anthocyanins, which are translocated, and responsible for the colors of
the flowers and the fruit.

In grapevines, when the adhesion forms between the petiole and the
branch, these anthocyanins are trapped in the leaf, causing it to change
color, and gives the wine country its' Fall colors.
--
³When you give food to the poor, they call you a saint. When you ask why the poor have no food, they call you a communist.²
-Archbishop Helder Camara
http://tinyurl.com/o63ruj
http://countercurrents.org/roberts020709.htm