Jungermannia and PO4

2398 Views 9 Replies 5 Participants Last post by Roger Miller, Jul 11, 2004

plantbrain

Discussion Starter · May 9, 2004

Here's some info

From
2002, The American Bryological and Lichenological Society, Inc.

Universidad de La Rioja, Complejo Científico-Tecnológico, Madre de Dios 51, 26006 Logroño, La Rioja, Spain E-mail: [email protected]

ABSTRACT

The effects of four increasing levels of KH2PO4 on the physiology of the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia were analyzed in the laboratory in the short term (15 d). The accumulation of P and K in the liverwort tissues was influenced (ANOVA) by the level of KH2PO4-enrichment and was significantly higher in the more enriched culture solutions. However, only the concentration of P was influenced by the effect of time (ANOVA), and the gradual P accumulation throughout the culture period contrasted with the fluctuations observed in K accumulation; these were presumably due to the higher liability of K to be leaked from the cells. Our results suggest that the analysis of P in transplants of J. cordifolia may be a useful bioindicator of short term water eutrophication both in the spatial and the temporal scales, although the highest PO43− concentration used in this study (20 mg liter−1) may induce a P saturation in J. cordifolia tissue (0.53% DM). The rates of net photosynthesis showed a significant quadratic regression with the tissue P concentration, which might resemble the action curve of mineral nutrients. Using this regression as an indicator, there was no clear deficiency zone, probably due to the relatively high tissue P concentration initially found in the liverwort. The lack of stimulation of net photosynthesis with increasing tissue P could be due either to a deficiency in other mineral elements such as N, or to an intrinsic inability to use the excess of nutrients. The decline in net photosynthesis when the tissue P concentration exceeded 0.45% DM could be interpreted as a toxicity process. Chlorophyll concentration was not affected by P enrichment, but the decline in the chlorophyll a/b ratio and in the proportions of chlorophylls to phaeopigments, together with the increase in the proportion of carotenoids to chlorophylls, suggested also P toxicity. This phenomenon needs further investigation to be confirmed in other species and conditions, but it may help to explain the disappearance of certain aquatic bryophytes in eutrophicated water courses. The physiological effects of increasing tissue K concentration (decreases in the rate of dark respiration and in the chlorophyll a/b ratio) were slighter than those of P, probably because the accumulation of K was lower than that of P (1.44 and 1.96 times the initial value, respectively). In a different experiment in which J. cordifolia was cultured in P-enriched aerated and non-aerated solutions, anoxia caused a strongly diminished P accumulation in the first three days, probably because the mitochondrial respiration was blocked. Then, a clear net loss of P from the liverwort tissues was observed, maybe caused by membrane damage.

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Jeff Kropp

· #2 · May 10, 2004

plantbrain said:
...The rates of net photosynthesis showed a significant quadratic regression with the tissue P concentration, which might resemble the action curve of mineral nutrients. ...The lack of stimulation of net photosynthesis with increasing tissue P could be due either to a deficiency in other mineral elements such as N, or to an intrinsic inability to use the excess of nutrients. The decline in net photosynthesis when the tissue P concentration exceeded 0.45% DM could be interpreted as a toxicity process.

Seems to support my observations. They speculate an N limitation but do not note any N related data. Without N data I don't think they can make a case for P "toxicity", although their paper supports a premise that too much P is detrimental to some species.

Back when I was running a P limited tank I did notice an ability to produce a lot of pearling with almost no growth. Although I don't have a diagram showing the bio-chemical process of photosynthesis at hand, my layman's observations suggest that N is used in photosynthesis, while P is involved in cellular construction and K with cellular maintainance. Could pearling be used as a subjective indicator of N availability if only pH and dKH are known?

Jeff

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Daemonfly

· #3 · May 11, 2004

Can someone put the original post into a easy to read short summary? I try to read it but it all just "blurs" and I can't concetrate enough to pull any actual information out of it. (Common problem with my brain lately..

)

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plantbrain

Discussion Starter · #4 · May 11, 2004

Jeff,
Production of O2 is considered growth from plants, algae in aquatic ecosystems, more O2=> more growth and oprimary production.
Even if your eye cannot tell where the growth is occuring, if the plants are fixing carbon, they will produce O2.
More Carbon fixed, more O2.
It's a good indicator and has been used as a determinant in measuring primary production in many research papers.

Dry weight is another method.
Both methods have their good and bad points. Typically, good research uses several methods to arrive at some conclusions.

But I did find some aspects of that paper very relevant to our discussion about the effects of P on N and supported some of your observations.

The nice thing about liverworts Riccia etc are they are great for dry weight studies and wet weight studies since they don't have roots and that whole substrate nutrient source thing is removed from the equation.

But then what role does the substrate play with all these other plants that do have roots?
So while the liverworts are good for some things, they certainly will not answer all of the question adequately, we need several nmethods to get to the bottom or at least get a better understanding.

I'm going to do a paper for an article on N cycling in aquatic ecosystems so I'll certainly touch on a few of these exchanges and also be doing a more investiagtive research into the literature.

Regards,
Tom Barr

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Jeff Kropp

· #5 · May 11, 2004

plantbrain said:
Production of O2 is considered growth from plants, algae in aquatic ecosystems, more O2=> more growth and oprimary production.
Even if your eye cannot tell where the growth is occuring, if the plants are fixing carbon, they will produce O2.
More Carbon fixed, more O2.

I did a little searching on the web for a photosynthesis flow diagram. No luck but I did run across mention of a Calvin cycle? A dark phase reaction that coverts collected C into sugars? It seemed to involve some form of P. If there was insufficient P to process all the light phase C gathered would a plant then release excess C as CO2 during the dark phase? I think I recall a large pH swing with my strong pearling, low growth, P limited observation. With P supplementation my pH swings seem minimal.

Where does N enter the biochemical process of plants?

Jeff

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plantbrain

Discussion Starter · #6 · May 11, 2004

The Calvin cycle does not involve evolution of O2.

The light reactions: they produce the reduction power for making carbohydrate sugars. Without that, the Calvin cycle will not work.

P is used a great deal in ATP-ATD the main energy source for cells.
NADPH-NADP also uses P.

The base sugars that plants use for storage are rich in PO4.

The addition of PO4 and increases in pearling seems to be more a fuction of ATP/NADPH and simpler compounds, these are quickly made.

The cell would not fix more CO2 if it's PO4 deficient, it shuts down it's CO2 fixing(reduction) and slows things down, "idles" till there's enough PO4 to resume full production. So it's not lost or wasted, it never really gets taken in. The plant cell is finely tuned to changes and environmental inputs, it'll down regulate things if there's not enough/too much etc.

N enters as NO3 or NH4. The NO3 is reduced into NH at the cholorplast cell wall and is very quickly converted from NO2=>NH4 as NO2 is toxic to plant cells internally.

NH4 is then converted into Glutamine via glutamine synthase. There are two types of GS(glutamine synthase), one in the cholorplast and an external one that plays a role in NH4 from the environment rather than from reduction of NO3.

Most of these studies are on agricultural crops but should apply in most cases to aquatic plants as well at this biochemical level.

Finding hard empirical data on aquatic plants is difficult.

Here's a few diagrams from UC Davis and some general test questions.

http://www.users.nac.net/challoran/LDrxn.htm

N cycling:
http://www.nstl.gov/research/nitrogen/ncd.html
http://www.botany.ubc.ca/biol351/351f.htm
http://www.acad.carleton.edu/curric...udy guides/nutrient uptake/12nutruptake2.html

And here's a good one for you for NH4 and NO3 assimlation and rates etc:
http://www.hort.purdue.edu/rhodcv/hort640c/nuptake/nu00001.htm

This is a good site for some of the comments on lakes and plants:
http://www.utoronto.ca/env/jah/lim/lim05f99.htm

Note Mn and NO3.

Here's something that might bother you also about high CO2 and NO3
http://www.plantphys.net/article.php?ch=e&id=158

You read all that, and you'll have a good understanding about plant biochem or a headache

Seriously, there are good info in each one of these sites.

These will help understand and argue for various observations in aquatic plants not just with N or P, but also with K, CO2 etc.

While we often want to narrow things down to one nutrient etc, it's very often several.

Enjoy, now I have to prepare fer da genetic class I have to teach, Fruitfly fun

Maybe I'll post some of these over on the APD to stir some disccusion up there also.

Regards,
Tom Barr

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Phil Edwards

· #7 · Jul 11, 2004

Interesting stuff Tom. The whole thing about increases/decreases in pigments and pigment ratios at different nutrient levels is of particular interest. Did you get the whole paper or was it just the abstract?

Best,
Phil

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Roger Miller

· #8 · Jul 11, 2004

I wasn't around for the start of this topic, but I'll put my two bits in here anyway. I suspect that I've seen the same thing that Jeff saw. In an apparently phosphate-limited tank the plants can bubble daily while there is little observable increase in plant mass. The plants are sometimes stunted.

Oxygen is evolved in step one of the photosynthetic reactions -- using Tom's UC Davis link -- but free phosphate isn't required in the reaction until ATP is produced from ADP and P in the last step of the thylkaloid membrae process.

Carbon isn't actually fixed in the photosynthetic process until you get to the dark reactions. There CO2 is combined with a simple sugar phosphate. Phosphates are not only required in the initial reactants but also required in the form of ATP later on in the process.

The page at

http://www.lions.odu.edu/~knesius/miniunits/epsilon/epsilon12.html

Provides a pretty simple diagram of the overall process, plus some details of the dark reactions.

There are a lot of steps involved between the point where O2 is evolved in the reaction to the point where free phosphate is required in large amounts. It looks to me like under pathologic conditions it should be possible to get O2 evolved without there being any actual growth.

Phosphate is essential to a lot of reactions in a plant. I read somewhere that under phosphate deficient conditions a plant can move phosphate from less essential roles to reactions where it is more necessary. I can easily imagine that a plant suffering a phosphorus shortage might shift its limited supply out of the Calvin cycle and into the Krebs cycle. The plant dies if the Krebs cycle shuts down. It can survive for a while without the products of the Calvin cycle.

Roger Miller

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Jeff Kropp

· #9 · Jul 11, 2004

Roger Miller said:
I'll put my two bits in here anyway.

Ah Ha! a plausible explanation. We are two bits richer.

But wait... in the linked diagram, CO2 is going into the "dark box"! I thought it was used during the light phase?
___
Jeff

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Roger Miller

· #10 · Jul 11, 2004

Jeff,

CO2 is used in the dark reactions only. The term "dark reaction" is unfortunate. It doesn't mean that the reaction happens in the dark. In most plants the "dark reactions" only happen while there's light to provide the NADPH and ATP. "Dark reaction" implies only that light doesn't play a direct role in the reaction.

Roger Miller

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