I know the answer is "depends on the plant", but I was wondering how
long it would take for the energy investment a plant makes in growing eg
a new leaf or stalk to be recouped.

I thought here might be a good place to ask - any ideas?

On 10/06/17 14:23, Clive George wrote:
I know the answer is "depends on the plant", but I was wondering how
long it would take for the energy investment a plant makes in growing eg
a new leaf or stalk to be recouped.

I thought here might be a good place to ask - any ideas?

What do you mean by 'recouped'. They energy the plant gathers is used to
create some seeds. Once that is done then it's 'purpose' has been
fulfilled. When it dies that energy is returned to the soil, moulds,
bacteria...

On 10/06/2017 16:04, RedAcer wrote:
On 10/06/17 14:23, Clive George wrote:
I know the answer is "depends on the plant", but I was wondering how
long it would take for the energy investment a plant makes in growing eg
a new leaf or stalk to be recouped.

I thought here might be a good place to ask - any ideas?

What do you mean by 'recouped'. They energy the plant gathers is used to
create some seeds. Once that is done then it's 'purpose' has been
fulfilled. When it dies that energy is returned to the soil, moulds,
bacteria...

(answering both you and Chris)

It's not just seeds though is it? Every year trees poke out new leaves,
and the energy/material to create those comes from somewhere.
Photosynthesis will at some point create enough new stuff
(energy/material) to make that worthwhile, but eg a leaf weighing 1g
will need to photosynthesise that much to do so.

Think about a potato - the tuber is basically an energy store, and one
day it sprouts and starts using that energy to create those sprouts and
leaves. It is investing that, in the hope that the sprouts and hence
leaves etc will return that energy and then some. My question could be
phrased as how long does the potato take to break even.

So I suppose another question is how much stuff does a leaf generate in
a day?
Do leaves only grow as fast as they photosynthesise, ie only during the
day, or can they used stored food from the parent plant to grow? I'd
expect the latter.

(and yes, I know about photosynthesis, that's kind of the background to
the question)

On 10/06/2017 18:58, Chris Hogg wrote:
On Sat, 10 Jun 2017 18:28:29 +0100, Clive George
wrote:

It's not just seeds though is it? Every year trees poke out new leaves,
and the energy/material to create those comes from somewhere.
Photosynthesis will at some point create enough new stuff
(energy/material) to make that worthwhile, but eg a leaf weighing 1g
will need to photosynthesise that much to do so.

Think about a potato - the tuber is basically an energy store, and one
day it sprouts and starts using that energy to create those sprouts and
leaves. It is investing that, in the hope that the sprouts and hence
leaves etc will return that energy and then some. My question could be
phrased as how long does the potato take to break even.

So I suppose another question is how much stuff does a leaf generate in
a day?
Do leaves only grow as fast as they photosynthesise, ie only during the
day, or can they used stored food from the parent plant to grow? I'd
expect the latter.

(and yes, I know about photosynthesis, that's kind of the background to
the question)

Hmm...OK. But the energy to produce new leaves in Spring comes from
sugars and other carbohydrates stored in the twigs, branches etc from
the previous year's leaves. The same with potatoes: they store energy
from the previous year as carbohydrate; it's what a potato is. In
round figures, a potato contains about 80 Calories of carbohydrate per
100g, i.e. about 20g of carbohydrate per 100g, the rest being water*.
Those 20g fuel the early growth until the stalk and leaves get above
the surface and start the photosynthesising process all over again.
While it probably isn't 100% efficient (few chemical reactions are,
and I don't know how inefficient it is, which is probably the nub of
your question), it's basically just one form of carbohydrate (the
potato) being converted to another form (the stem and leaves). Its
much the same with leaves of trees, I imagine.

Yes, exactly. So my question is, how long does the leaf have to be
around before it has generated enough energy to replace that stored
energy which was used to make it?

In article ,
Clive George wrote:

Yes, exactly. So my question is, how long does the leaf have to be
around before it has generated enough energy to replace that stored
energy which was used to make it?


I have thought of that question in the past, and occasionally tried
looking up, but have found nothing useful.


Regards,
Nick Maclaren.

In article , says...

In article ,
Clive George wrote:

Yes, exactly. So my question is, how long does the leaf have to be
around before it has generated enough energy to replace that stored
energy which was used to make it?


I have thought of that question in the past, and occasionally tried
looking up, but have found nothing useful.

Hydroponic growers might know

Janet

On 11/06/2017 00:13, Clive George wrote:
On 10/06/2017 18:58, Chris Hogg wrote:
On Sat, 10 Jun 2017 18:28:29 +0100, Clive George
wrote:

It's not just seeds though is it? Every year trees poke out new leaves,
and the energy/material to create those comes from somewhere.
Photosynthesis will at some point create enough new stuff
(energy/material) to make that worthwhile, but eg a leaf weighing 1g
will need to photosynthesise that much to do so.

Think about a potato - the tuber is basically an energy store, and one
day it sprouts and starts using that energy to create those sprouts and
leaves. It is investing that, in the hope that the sprouts and hence
leaves etc will return that energy and then some. My question could be
phrased as how long does the potato take to break even.

So I suppose another question is how much stuff does a leaf generate in
a day?
Do leaves only grow as fast as they photosynthesise, ie only during the
day, or can they used stored food from the parent plant to grow? I'd
expect the latter.

(and yes, I know about photosynthesis, that's kind of the background to
the question)

Hmm...OK. But the energy to produce new leaves in Spring comes from
sugars and other carbohydrates stored in the twigs, branches etc from
the previous year's leaves. The same with potatoes: they store energy
from the previous year as carbohydrate; it's what a potato is. In
round figures, a potato contains about 80 Calories of carbohydrate per
100g, i.e. about 20g of carbohydrate per 100g, the rest being water*.
Those 20g fuel the early growth until the stalk and leaves get above
the surface and start the photosynthesising process all over again.
While it probably isn't 100% efficient (few chemical reactions are,
and I don't know how inefficient it is, which is probably the nub of
your question), it's basically just one form of carbohydrate (the
potato) being converted to another form (the stem and leaves). Its
much the same with leaves of trees, I imagine.

Yes, exactly. So my question is, how long does the leaf have to be
around before it has generated enough energy to replace that stored
energy which was used to make it?

I seem to remember doing something at school ( a very long time ago) and
the leaf doesnt grow then start producing, but rather each cell starts
production immediately so the pay back time is pretty much straight away
and increases as more cells are added

--
Charlie Pridham
Gardening in Cornwall
www.roselandhouse.co.uk

On 10/06/2017 14:23, Clive George wrote:

I know the answer is "depends on the plant", but I was wondering how
long it would take for the energy investment a plant makes in growing eg
a new leaf or stalk to be recouped.

Depends on the plant *and* the climate.

I thought here might be a good place to ask - any ideas?

Slowest growing desert plants like lithops manage to save enough energy
in a very good year to add another leaf pair and/or flower. But they are
restricted to only growing in a brief period by the very arid climate.

Common or garden plants the true leaves are pretty much self sustaining
from the moment they first appear. That is why you have to persecute
couch grass or ground elder so aggressively to get rid of it. Any leaves
that can see sunlight will be storing energy back into the roots.

Orchids and ferns are probably amongst the most tenuous plants where
payback has to be almost instant since their seed is basically dust with
no reserves for the young plant to fall back on.

If the ambient temperature is about 30C and humid then C4 photosynthesis
allows even faster payback for less water use eg maize and sugar cane.

https://en.wikipedia.org/wiki/C4_car...the_C4_pathway

--
Regards,
Martin Brown

On 11/06/2017 10:04, Nick Maclaren wrote:
In article ,
Clive George wrote:

Yes, exactly. So my question is, how long does the leaf have to be
around before it has generated enough energy to replace that stored
energy which was used to make it?

I have thought of that question in the past, and occasionally tried
looking up, but have found nothing useful.
I'd hazard a guess at less than a few days at least for those plants
like orchids and lithops whose seeds are little more than dust. The
plant has few reserves to fall back on after growing a root so the first
true leaves have to more than break even if the seedling is to survive.

They also add to the mass of the plant. I'd suggest as a ballpark number
the plant has broken even when the dry mass of the plant exceeds that of
the seed. Or for a ballpark with a live plant 5x the mass of a dry seed.

--
Regards,
Martin Brown