Water temperature - affect on plants

[scottward]

Hi guys,

I now have a reasonably good understanding of how light, CO2 and nutrients are related with regards to growing aquarium plants.

I understand that light drives CO2 uptake and in turn CO2 uptake drives nutrient uptake.

In an ideal situation, the only limiting factor to plant growth would be the plants themselves; i.e. the plants would receive the maximum amount of light energy that they can use in conjunction with non-limiting levels of CO2 and non-limiting micro/macro nutrients (EI).

I also understand that this ideal situation would involve a great deal of work on the part of the hobbyist!

So, as hobbyists, we reduce the lighting to something that is comfortable and suits us. This in turn reduces CO2 demand and nutrient demand. Meeting the nutrient demand using the EI approach is easy, meeting the CO2 demand is more challenging but with patience it is doable, and eventually we get there.

Ok - so now I want to talk about how water temperature 'rocks the boat' in the context of what I have said above...

Easiest way for a hobbyist (i.e. not a biologist or chemist) to understand this is probably by way of example.

Let's say I have a tank set up, and it's doing nicely -
- the photoperiod is regular (10 hours) and intensity is adequate for the plant species
- CO2 injection is regular, circulation is good etc (let's say CO2 is non-limiting)
- EI fertilisation (non-limiting).
- water temperature is 25 degrees celcius

Ok, so my above example tank is ticking along very nicely. I already understand what will happen if I start to increase the lighting...no need to go there.

But what happens if the *temperature* were to increase from 25 to 35 degrees (gradually over 24 hours)? This is what I think would happen, but need clarification from the guru team:
- my understanding is that for a 10 degree change in temperature a plants metabolic rate would approximately double (i.e. hungrier plants!)
- firstly - lighting - is it possible that the lighting level will no longer provide enough energy for the plants?
- secondly - co2 - if the lighting level can stay as it is, can temperature drive CO2 uptake in the same way that lighting can? My understanding here is yes (spoke to Tom about this already)- CO2 requirements will also be approximately doubled.
- thirdly - micros/macros - can safely ignore this as dosing EI (non limiting at all light levels) - and temperatures???

I guess most of my uncertainty at the moment is around the lighting. I understand that if I increase the water temperature, the plants are going to need more CO2 (and would need more nutrients if EI was not being used). But would the lighting have to increase as well?? If the plants want to metabolise faster due to the increase in temperature - they can only get this energy from more light can't they??

If the answer to this question is yes - that the plants would need more light - how would I know how much to add?

Scott.

 

[Philosophos]

Tom mentioned something a while back about designing EI dose levels for a certain temperature.

Most of us attempt keep tanks in the 24-27C range IME. This means, if your estimations for metablolism are correct, only a +/- 20% variance from intended dosing levels. That would mean say 24ppm NO3 vs 20ppm NO3 uptake; I'd probably just dump in an extra few ml of ferts if this were the issue.

I run a hot tank; 27c. So far, I've increased dosing a little here and there just to make sure nothing is lacking, and I almost always try to push CO2 as high as it can go.

-Philosophos

 

[Tom Barr]

Tom mentioned something a while back about designing EI dose levels for a certain temperature.

Most of us attempt keep tanks in the 24-27C range IME. This means, if your estimations for metablolism are correct, only a +/- 20% variance from intended dosing levels. That would mean say 24ppm NO3 vs 20ppm NO3 uptake; I'd probably just dump in an extra few ml of ferts if this were the issue.

I run a hot tank; 27c. So far, I've increased dosing a little here and there just to make sure nothing is lacking, and I almost always try to push CO2 as high as it can go.

-Philosophos

I chose 82-84F since this is the min upper ranges for Altums, discus, Cardinals etc.
They will breed and live long in such conditions(well, Altums ain't breeding).

Plants are fine there as well.

But in general, 75-77F is a nice temp.
Mosses, Bryophytes, ferns etc, some shrimp are better optimalized at say 72F.
Some Bryptophytes do not do well unless they are in the 50-60F ranges.

But 72 , 78 and 84F are good hobbyist ranges to chose, low, med and high temp ranges.

Regards,
Tom Barr

 

[scottward]

Hmmm. So in the absence of any cooling over summer, when my tank gets up to as warm as 35C (95F), it would seem that I might as well give up on the plants at this time of year? I would need to inject huge quantities of CO2??

I can't afford a chiller.

Tom - you missed my question about light. Can you clarify for me how light works in relation to temperature changes? Does higher temps mean more light energy needed? Sorry if you have already answered this, I mustn't have cottoned on.

Scott.

 

[Gerryd]

Hi Scot,

Can you use native plants that are already adapted to the enivronment???

I would think that a combination of high temperatures (less 02) and HIGHER C02 may bear watching.... It may be easy to tip too far off the edge of too much c02 or not enough 02. A powerhead for surface ripple may help here.

I would not give up but absent a cooling fan on the surface not much you can do.....

I think we might be surprised at the plants that survive.. At least you will know for the future.

Hope this helps.

 

[ceg4048]

Hmmm. So in the absence of any cooling over summer, when my tank gets up to as warm as 35C (95F), it would seem that I might as well give up on the plants at this time of year? I would need to inject huge quantities of CO2??

I can't afford a chiller.

Tom - you missed my question about light. Can you clarify for me how light works in relation to temperature changes? Does higher temps mean more light energy needed? Sorry if you have already answered this, I mustn't have cottoned on.

Scott.

Hi,
Here is an example of an unlimited EI tank, sitting in a glass conservatory which generated peak daytime summer temperatures of 37C or higher (depending on cloud cover). I see no reason whatsoever to give up. Warm temperatures simply increase the metabolic rate so that nutrient consumption is possibly higher. If nutrients and CO2 are unlimited then I would assume that this simply produces higher growth rates. Higher temperatures also increase the risk of algae however. The problem with high temperatures is with fish not with plants.

Cheers,

 

[Biollante]

No

I think the specific answer to your question is no; there is no need to increase the lighting to account for the increased uptake of nutrients (and CO2).

As I understand (see disclaimer below) the Q10 temperature assumes a constant light energy input. Q10 (temperature coefficient) - Wikipedia, the free encyclopedia

The Arrhenius equation gives a similar outcome for the temperature dependence of the rate constant, and therefore, rate of a chemical reaction. Arrhenius equation - Wikipedia, the free encyclopedia

Temperature effects on the photosynthetic response of C3 plants to long-term CO2 enrichment relates only temperature and partial pressures of CO2. SpringerLink - Journal Article

Temperature and rooted aquatic plants SpringerLink - Journal Article showed that P. perfoliatus is capable of physiological adjustment to higher temperatures, generally I think that the plants that are able adjust; and that there is a physiological adjustment.

I have a similar situation here in the Salt River Valley (Chamber of Commerce prefers ‘Valley of the Sun’) of Arizona, routine daytime temperatures exceed 43 C (110 F) the highest so far being 47 C (117 F), this year we seem to be averaging 42 C (106 F).

I have four aquariums in a screen-enclosed porch; I also have a number of other larger water systems of a semi agricultural nature outside.

I have maintained a number of aquariums on the porch for the last ten years.

I use fans; in dry weather (“It’s a dry heat”), the water temperature rarely exceeds 29 C (85 F). We do catch the northern tip of the Mexican Monsoon and it can get wet, even though this lowers the ambient temperature, it reduces the evaporative cooling dramatically. On occasion, I have seen the temperature exceed 33 C (92 F). It does seem to drive the angels and tetras into a breeding frenzy.

At night in humid conditions, I do aerate.

Mainly it is the increased nutrient demand I have noticed and I use at least half again as much CO2. I increase dosing by about a fifth, maybe even a bit more on the NO3. The plants just shoot out, I let a number grow emergent, It seems to reduce the CO2 demand, since; well they get CO2 from the air.

One tank has lights, a 55-gallon tank has 160 watts; four T-12 shop lights suspended 10 inches above the water.

Enough ramblings.

Biollante

 

[Biollante]

More Ramblings

Sorry to ramble on so…

I think part of the confusion stems from the language we use in the aquatic plant community.

We say “light drives the process” and that is true everything else being equal. Also in our day-to-day lives, we think of temperature in terms of what it “feels like.”

Temperature is actually a measure of average kinetic energy Temperature - Wikipedia, the free encyclopedia.

We speak of light driving the photosynthetic process and this is true as long as there is sufficient kinetic energy Temperature - Aquatic Plant Management in Florida Waters. At temperatures below a certain point, there is simply not enough kinetic energy to sustain photosynthesis, at temperatures above a certain point the plants are, well, cooked, and again no amount of light will drive photosynthesis.

Of course different plants are better adapted to different temperatures, I’ll let someone else get into the ‘hows and whyfores’ I have observed that some plants simply adapt to the higher temperature. Some would not survive direct transplantation to high temperatures, but seem gradually to adjust to the changing conditions of the aquarium. Some plants become ‘fluffier, more buoyant, some a bit stringy, some really robust, mainly they just grow. I do keep two of the tanks at 25.5 C (78 F) minimum year around.

Biollante

 

[Tom Barr]

I think with small fans, they make them specifically for aquariums..............your aquarium should not get that warm, maybe a few days, but the average will be more like 30C, it cools off at night and so does the aquarium, smaller tanks will go up/down with the day, larger tanks will move more to the average temp over the entire day/night.

A fan will help cool things pretty well where it is drier also.
Place on a timer. Some also reverse the light to come on early and shut off before the warm part of the day.

Plants are fine..........as long as you have enough CO2 and nutrients.
At 40C and above, not much is going to make it if that temp is sustained........but it's typically just a daytime peak.

Chillers are expensive to buy and run, I'd not suggest it, try the fans.

Regards,
Tom Barr

 

[VaughnH]

Isn't it true that plants don't require a specific amount of light to grow in good health? Depending on the specific plants, they do require that the light be above some lower level, or the plants just won't grow. So, if that tank at 25C is growing well, and the temperature goes up to 35C (assuming the plants will tolerate such a temperature), the growth will accelerate, but only up to what the light intensity will support. So, you would need to provide more fertilizers if you were not fertilizing at a non-limiting amount for that entire temperature range, but wouldn't need to change the lighting at all.

 

[ceg4048]

Hoppy, as I understand it, each species has something called a Light Compensation Point (LCP). This is the amount of light energy that produces a carbohydrate level equal to the carbohydrates consumed on a daily basis. So at LCP the plant produces the same amount of energy that it consumes. At PAR levels below LCP the balance is negative and food production cannot support required food consumption, so the plant dies. At LCP no growth occurs, and above LCP the plant can "put on weight" so to speak, and grow. I assume that the magnitude of the difference between carbohydrate production and consumption should be a factor in growth rate (assuming that nutrient/CO2 uptake support this rate).

As far as I can see, I agree with you that there should not be a requirement to increase light, only possibly nutrient/CO2 if the levels are marginal to begin with - perhaps if PAR is at or very near LCP there might be an issue, but adding more light, in practical terms would probably only have a detectable effect of increasing the temperatures further, while actually raising the nutrient/CO2 demand, so this is to be avoided, otherwise you actually create the very same problem that you feared.

As I noted previously, I saw no deleterious effect of elevated peak temperatures. At the time there were probably at least 40 different species in the tank including moss. I'd have to admit that two fern types, Java and needle leaf, did the poorest in terms of "appearance" but certainly not in terms of mass accretion.

As Tom indicated, cooling fans should help if there is a concern, but high flow + unlimited nutrients/CO2 turn a lot of potential problems into absolute non-issues.

Cheers,

 

[Tom Barr]

Hmmm. So in the absence of any cooling over summer, when my tank gets up to as warm as 35C (95F), it would seem that I might as well give up on the plants at this time of year? I would need to inject huge quantities of CO2??

I can't afford a chiller.

Tom - you missed my question about light. Can you clarify for me how light works in relation to temperature changes? Does higher temps mean more light energy needed? Sorry if you have already answered this, I mustn't have cottoned on.

Scott.

No,m not giving up is hardly what the rest of us are doing if we do not use AC to cool the house down..............we might add a bit more CO2 mostly, do more water changes etc.

You might need to add say 10ppm more CO2 etc.
Most of the change will be with respect to CO2, the ratio of C to N is 40:1, so the increase in NO3 dosing would only be 0.25ppm N-NO3, so about 1ppm....not much.

So the effects are mostly with CO2.

No, higher temps do not imply more light is needed.
I'd say more the reverse, higher temps => should add less light to compensate for increasing temps(lights add heat), and the increase in CO2 demand.

Reducing light will balance the increase in CO2 demand from increased temp in other words.

The CO2 is proportional to the increase in temps.
The CO2 is also proportional to the light intensity.

As you reduce temps, it's easier to dial in a CO2 ppm level, manage CO2 etc, much like less light also affects CO2 demand.

Same general thing really.

Regards,
Tom Barr

 

[scottward]

Hi Guys,

Thanks for all the info and advice. I will continue to focus on my CO2 as the weather warms up.

Scott.