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)