[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
A table of Photosynthetic adaptations to variations inirradiance(light)
- To: <Aquatic-Plants at actwin_com>
- Subject: A table of Photosynthetic adaptations to variations inirradiance(light)
- From: Thomas Barr <tcbiii at earthlink_net>
- Date: Sun, 14 Jul 2002 14:48:15 -0700
- In-reply-to: <200204012048.g31Km1Q25125 at acme_actwin.com>
- User-agent: Microsoft-Outlook-Express-Macintosh-Edition/5.02.2022
> Now I'm reading 4-5 w/g, overdriving bulbs to get the last lumen possible,
> etc. What happened - have modern plants developed light resistance somehow?
> Ah, progress. Always "more is better". I long for the good old days.
> George Booth in Ft. Collins, CO (gbooth at frii dot com)
Well more light does not equate better growth in some/numerous cases.
Most folks will find that 2 watts a gallon will do the trick for about any
tank set up unless the tank is real deep etc. I like the growth of many
plants better at lower light values. Things tend to be a bit more flexible
concerning dosing (and mental forgetfulness--"did I add the PO4 yesterday or
was it the day before?"_).
I have some very high light tanks and wanted to see how lighting affects
uptake rates. From these high light tanks I can then come back to a lower
lighting tank and optimize nutrient levels better now knowing what goes on
if things are sped up at a higher rate. It was harder to see the pattern at
lower light and the uptake. But equating the higher light as the same except
higher uptake is not a complete argument but I think it's telling enough to
make the assumption here for our purposes.
From that higher light dosing, I've found that at lower lighting(say 2
watt/gal), I can maintain these same high light nutrient levels(CO2, traces,
NPK etc) but at low lighting and get excellent growth across the board.
Uptake is slower, I'll dose 1x a week instead of 2-3 times a week for
But the maintained levels are the same.
NO3 still 5-10ppm
Lots of traces(I do add this one 2x a week still)
This yields very very little algae(less than the high light) but very lush
If you consider lower light shade leaves/plants versus sun leaves/plants,
some interesting comparisons appear. (Sun and shade leaves can occur on the
same plant- we commonly refer to sun as a high light plant and the shade as
a low light plant- sometimes a plants starts off a sun plants and slowly
over the course of the season gets shaded and becomes a shade plant etc)
Some terms can be looked up if folks are unfamiliar with these
units/measures etc. It should be noted that this is for general plant
physiology, note specifically aquatic plants. (From Mahall 2002)
Characteristic: Low light: High light:
light compensation* low(.5-2) high(50-100)
light saturation low(10) high(1500-2000)
Rates of dark
respiration low high
Quantum yield same or high same or low
Leaf thickness thin thick
Number of stomata low high
Stomatal conductance low high
Thylakoids/granum many(100-200) few (5-10)
Orientation of grana random horizontal
components per unit small high
Chl a/b low(2.5) high (4)
unit area low high
unit leaf weight high low
Chl/photosynthetic higher lower
(Rubisco) per unit
leaf weight or area low high(10X)
per area, weight or low high(4X)
Photosynthate leaked low high
Basically at lower light, plants are more efficient. Photoxidation is less a
problem, the plant has more time to relocate nutrients from old tissue to
new tissue or from root to shoot. Leaf area generally increases, less
nutrients are required to run photosynthesis, less proteins, enzymes etc to
grow. The plant afford to wasteful at higher light, but if things fall below
the light compensation point, the plants will die. PCP is where the quatum
yield is less than respiration. Intake of the "plant's food" is less than
the energy/maintenance requirements of the plant.
It makes sense not to have all this extra photosynthetic machinery hanging
around if there's not the light to run it. It takes a lot more energy to
maintain all that machinery. If the plant has only a small efficient
photosynthetic machine, it won't need to allocate the respiration /
photosynthate to maintenance. Growth is slower but less wasteful.
Considering electrical cost(some of us are sensitive to this issue),
efficient use of lighting, since it's often the biggest source of electrical
usage, is not a bad goal to consider.
Better nicer growth, less algae problems, lazy dosing, less pruning etc may
be something many are looking for. Lower electrical cost certainly are for