Biogeochemical Cycling - Science topic

I believe that it has to do with the nature of the phosphates present in the sediments as Professor Tarafdar notes above. Iron and aluminum phosphates are often sequentially removed via these extractions and the mechanism, though I don't know it, is likely adding an anion that has a higher affinity for sediment binding sites, or that it brings P into solution by forming a phosphate salt.

I'm not sure what you been by "basic reasons" but an evolutionary explanation would be that as ecosystems evolved, the biogeochemical processes in those systems evolved into cyclical processes. Since the quantities of the world's elements are limited and unchanging, evolution would favor biological processes that recycled nutrient elements.

Mohammed JARULLAH Farhan

Regular/frequent  addition of undecomposed  or partially decomposed organics may enhance C:N ratio to some extent in cool climatic conditions where the decompostion rate is very slow.

Thank you for your contribution Abhishek, but I really donʻt see how that paper gets at my question.  It is a broad overview of root physiology and how it relates to plant growth, but does not get at any techniques for actually measuring uptake and recycling rates nor does it even get into the physiology specifically enough for me to think critically of how those measurements might be made.  

To be clear I think what I want to do it really quite novel and cutting edge, and as far as I can envision so far will have to be using isotopes to understand the relative and absolute amounts of nutrients in the cycle.  Most interesting to me will be how the use of arboriculture decreases (or does not decrease) the amount of nutrients lost in very young soils, and increases the nutrient capture and use at an ecosystem scale. There is an emerging technique of using isotope fractionation to quantify phosphorous that has been biologically cycled or not that I think might be useful in this context.  

The question is a good one and as a chemist I am not happy with any of the responses so far.  Most research relies on measuring molybdate reactive P before/after treatment of soil solutions/ runoff/ flow-through to discriminate between organic and inorganic forms of P in solution. Unless the species are first separated molybdate reactivity is an indiscriminate tool.  And separation itself is complex because much of the P, even if present as phosphate, may in fact be part of suspended colloids. I'm sorry to say that separation followed by measurement is the way to go, but I'm unaware of any authoritative research on the topic, i.e. selective measurement is probably a project in itself. Were I to go there I would use  chromatographic separation with  dual post column detection, e.g. using ICP on one leg and molybdate on the other.  On the ICP leg I would simultaneously measure Fe, Al and C for starters as indices of the forms in which the P may be present.  Good luck!!

Hi Maowei,

As my two prdecessors mentioned it is important to know what you have used as measurement chamber. A real static chamber is without flowthrough and is sampled at regular time intervals, by extracting a sample from the closed chamber. A flowthrough chamber system consists of a chamber flushed with outside air (or synthetic air) to be measured for CO2 or water vapour and connected with a CO2 and water vapour monitor. The half-time of the chamber turn-over is defined as the t1/2=0.69*rV where r is flow resistance (in sec/liter) and V, the Volume of your chamber in liter. Preferably the t1/2 is in the range of a few seconds.

When the chamber is not flushed, artefacts are definitely measured, since C02 when depleted due to photosynthesis on very short term, leads to a negative physiological feedback. During the night the same feedback phenomenon occurs. In that case respiration is inhibited due to a rise in CO2 concentration in the chamber thereby inhibiting respiration itself. Hence in both cases energy metabolism is inhibited. And this changes the physiology of your plant system. Maybe you used flowthrough leaf clamps?

The negative feedback does not occur when the chamber is flushed with outsde or synthetic air, with a t1/2 which is high enough (a few seconds). You see the trouble coming Maowei. When you did not flush your measuring chamber your measurements will absolutely not be representative EC measurements by upscaling from leaf to  canopy CO2 and water vapour exchange. A big problem I would say.

However when you use a flow through chamber system (leaf clamp?), upscaling to full canopy exchange is feasible on the condition that you have used flow through chambers distributed over the footprint of the EC measurement at your site. And there comes the second step for this measurement scenario. In that case you will have to use a model which simulates the footprint in function of meteorology. You can then determine weighting factors for the exchange measured in your chambers, which is maximal close and wind upward from the tower. The further from the tower in the windupward direction, the lower the scaling factor. Hence, without a footprint model, it is impossible to scale up. You will also need half hourly wind direction and wind speed (as a minimum, because atmospheric stability is also of prime importance for footprint modelling).

Here my story ends, because there are no other ways to integrate your chamber measurements in your EC measurement dataset I am afraid.

Summarizing. Your chamber measurements should be performed with a flow through (not static) system. If this is not the case, your estimates will be erroneous and not usefull due to physiological feedback. With a flow through system, you need a footprint model to scale the weighting factors of your chamber measurements positioned in the footprint of the tower.

Thats it. I have described the possibilies and impossibilities. Check out how you performed the chamber measurements and if they are genuinly static, there is no way to integrate them with eddy covariance measurements. If they are dynamic, you will need a footprint model and detailed local meteorology data to scale your chamber data.

Success mate,

Frank

Hi,

Another potential for examining this issue is to look at the maximum phosphorus sorption capacity of the sediments as well as the equilibrium phosphorus concentration. These will allow you to determine if the sediments in your system still have the capacity to bind P and at what water column P concentration your sediment acts as a sink or source of P. This will only identify the P fraction that is being released or taken up through biogeochemical interactions and will not provide information on P resuspension.

In terms of P resuspension there are a number of studies that have examined the impacts of benthivorous fish and wind driven sediment resuspension on TP in the water column.

 check out Christian Steinberg  work it is extensive in this area, including I believe a book on it. 

greetings margarete

Hi Allen,

Did you mean soil net N mineralization in the absence of plants? If that is the case, N priming results derived from plant N uptake can not be compared with soil net N mineralization, because the presence of plant roots (by their addition of extra C by rhizodeposition) can change the immobilization-mineralization turnover in soil appreciably.  Let me know if I am correct.

Another point:  Jenkinson et al (1985) used the term 'added N interaction' (ANI).  I think this is the term they used for 'N priming'.  ANI can be 'apparent' (resulted from pool substitution) or 'real' (resulting from plant roots exploring larger native soil N pool due to their larger root system in fertilized treatment compared with unfertilized treatment). Again, please let me know if I am correct.

Susantha

The respiration rate must be expressed as amount of CO2 (ug or mg or g of CO2-C or mmol of CO2) per amount of soil (g, kg) per unit time (min, hr, day or even week/month/year).

If you see the published data with the missed time units, then it is qualified as error made by authors and editors.

What is better, mg of CO2-C or mmol of CO2? In a C-balance studies mass units of carbon are better. In the studies of metabolic pathways (e.g. degradation of PCB in soil), the molar concentration is preferable.

What is better, ug, mg or g of CO2? g or kg of soil? hr or day? No strict rules, just make your numbers easy to read. There was a tendency to unify the units to international standard but it is not always justified.

Finally, per g of soil or per m^2 of soil surface? Depends on technique you use, whether you measure a flux of CO2 by chambers or incubate few g of soil in a vessel.

Methanotrophic bacteria would be the best to do that

Hello!  Perhaps one or more of the following research articles (or references therein) might be of some interest to you:

Soil Organic C and Nutrient Contents under Trees with Different Functional Characteristics in Seasonally Dry Tropical Silvopastures* (CASALS et al., 2014)

(*) = A PDF copy of this research article is available on “Google”, posted by one of the co-authors, Graciela M. RUSCH, under the aforementioned title.

 

The Influence of Strata on the Nutrient Recycling within a Tropical Certified Organic Coffee Production System (MAMANI-PATI et al., 2012)

Spatial Variability of Nutrient Stocks in the Humus and Soils of a Forest Massif (Fougères, France)

[LEGOUT et al., 2008]

The Uplift of Soil Nutrients by Plants: Biogeochemical Consequences across Scales (JOBBÁGY and JACKSON, 2004)

Plant Soil Interactions in Multistrata Agroforestry in the Humid Tropics (SCHROTH et al., 2001)

Any newer synthesis would have cited this:

Cleveland, C. C. et al. 1999. Global patterns of terrestrial biological nitrogen (N2) fixation in natural ecosystems. Global Biogeochemical Cycles 13(2): 623-645

maybe this study can help you...

Grossiord, Charlotte, et al. "Does Drought Influence the Relationship Between Biodiversity and Ecosystem Functioning in Boreal Forests?." Ecosystems: 1-11.

At the depth of 20 cm the soil temperature should be close to the mean daily temperature of the air, especially if the soil is not wet or frozen. (Based on my experience in measuring soil temperature profiles in the forest and solving equation of heat transfer.)

There are a number of software packages that you can use to design causal loop diagrams. Here are a few examples:

Vensim (free): http://vensim.com

STELLA (free 30 days trial): http://www.iseesystems.com/softwares/Education/StellaSoftware.aspx

AnyLogic (free trial): http://www.anylogic.com/

I personally prefer Vensim to design a CLD.

I see it in a paper, but i can not find it now.

I will send it to you when i find the paper.