Carl Ramirez:

Can we encourage atmospheric Nitrogen deposition to reduce N2O greenhouse gases in the atmosphere?

I’m afraid I don’t know enough about atmospheric chemistry to know if there is a process by atmospheric N2O can be converted to NOx (and then come down in rain). I’m not sure that we would want to do that deliberately given the impacts of NOx deposition on ecosystems (acidification, fertilization)

Anonymous Attendee:

What surprised you the most when conducting your research?

Nice question! Very early on we discovered that the identify of the nutrient (N vs P) limiting phytoplankton growth could be determined by zooplankton community structure (Daphnia vs copepods). This was completely unknown at the time and very surprising! I will never forget the first time I made the graphs that showed it. This led me down the path to ecological stoichiometry.

See:

  Elser, J.J., M.M. Elser, N.A. MacKay, and S.R. Carpenter. 1988. Zooplankton-mediated transitions between N and P limited algal growth. Limnol. Oceanogr. 33: 1-14.

And

  Sterner, R.W., J.J. Elser, and D.O. Hessen. 1992. Stoichiometric relationships among producers, consumers, and nutrient cycling in pelagic ecosystems. Biogeochemistry 17: 49-67.

k Hoshizaki:

>20 years have passed since I took your special lecture of stoichiometry in Kyoto, Japan, during your sabbatical. Tow questions: 1) Do you know any example for stoichiomery study in soil ecosystems? 2) How oranism C:N:P ratio respond to pulsed resources (e.g. seasonal food pulse) ?

(wonderful to be back in touch with you. I wrote my chapters for the stoichiometry book during that trip to Japan)

Yes, ES is getting established in soil studies. Examples:

  Cleveland, C.C., Liptzin, D. C:N:P stoichiometry in soil: is there a “Redfield ratio” for the microbial biomass?. Biogeochemistry 85, 235–252 (2007).
  Mulder, C., and J.J. Elser. Soil acidity, ecological stoichiometry and allometric scaling in grassland food webs. Global Change Biology 11: 2730-2738.
  Butler, O., T. Lewis, M. Rezaei Rashti, S. Maunsell, J.J. Elser, and C. Chen. 2019. The stoichiometric legacy of fire regime regulates the roles of micro-organisms and invertebrates in decomposition. Ecology 100: e02732.

My answer on the Zoom had to do with storage of elements and how this might affect C:N:P ratios and decouple growth from C:N:P (i.e. “break” the Growth Rate “Rule”

Junfeng Wang:

Hi, Professor Elser, is the N:P ratio in RNA the best food nutrient for a species or an organism? , and according to the N:P ratio in RNA, could we improve the bioasss by optimzing the N:P ratio in food or fertilizer? Thank you.

I am not sure about the first part of your question but, yes, biomass production can be optimized (and use efficiency maximized) by matching N:P ratio to the demands of the consumer or crop. In agriculture fertilizers are formulated differently according to the particular crop.

Frieda B. Taub:

Will lake sediments become fertilizers of the future?

Hi Frieda! There is already some discussion of this. It would be a disaster on top of a disaster, as extracting sediments from the bottom of a lake or bay or estuary would be environmentally destructive, adding insult to an already insulted (eutrophied) ecosystem.

Carl Ramirez:

Is it feasible to extract Phosphorus from watercourses since that's where Phosphorus from fertilisers goes?

Yes, see answer to preceding question.

It would be much better to keep the phosphorus in the food system where it belongs and OUT OF the water system!

Kaydee Barker:

Amazing talk, thank you Dr. Elser. You led me to questions and then answered those questions throughout the talk. I do have a couple questions remaining.

First, given the wide variation in stoichiometry of primary producers depending on the environmental conditions, are broad-level assumptions about producer stoichiometry (species means, for instance) still useful in understanding ecosystems dynamics, or do you think it’s really necessary to always measure stoichiometry in the specific ecosystem you are studying?

I hope my answer was OK. In many situations we need to make assumptions about things we haven’t or can’t measure. Now that we have more and more studies of C:N:P ratios in different organisms and pools (e.g. foliage, soil, sediments, lake water, seston, zoop biomass, etc etc) we have a much better basis for making those assumptions / assignments than we did previously, when people tended to assign some semi-arbitrary value (e.g 106C :16N: 1 P) to everything!

But, as I said, it’s better to do the actual measurements.

Kaydee Barker:

Additionally, did you measure any sort of respiration in the various lakes? For example, respiration of nitrous oxide in the lakes that are high in N?

My talented PhD student Michelle McCrackin studied denitrification in the lakes in our N deposition study. You can see her findings here:

  McCrackin, M., and J.J. Elser. 2012. Denitrification kinetics and denitrifier abundances in sediments of lakes receiving atmospheric nitrogen deposition (Colorado, USA). Biogeochemistry 108: 39-54.
  McCrackin, M., and J.J. Elser. 2011. Greenhouse gas dynamics in lakes receiving atmospheric nitrogen deposition. Global Biogeochemical Cycles 25: GB4005 doi: 10.1029/2010GB003897.
  McCrackin, M., and J.J. Elser. 2010. Atmospheric nitrogen deposition influences denitrification and nitrous oxide production in lakes. Ecology 91: 528-539.

Kaydee Barker:

And one more. What have you found so far might be a solution for increasing cycling rather than loss of P in agriculture?

There is a lot of work going on the generate recycled fertilizers from various wastes. The most developed commercially now is struvite-based fertilizers generated in wastewater treatment plants. See https://ostara.com/. You can follow these developments and find out more via https://phosphorusalliance.org/ and https://www.phosphorusplatform.eu/

Mark Daniels:

How much phosphorous can the Haber-Bosch process replace from mineral mining reliance?

? The Haber-Bosch reaction produces ammonia for fertilizer from N2 gas in the atmosphere. It does not produce any phosphorus for fertilizer. And phosphorus cannot substitute for nitrogen in fertilizer (or vice versa)

Enzai DU:

Hi, Jim, thanks for your great talk. Would you please share your thoughts about the biogeochemical niche that has been recently proposed? Enzai Du from Beijing Normal University.

This is an intriguing idea that seems related to the concept of “stoichiometric niche” proposed by Angelica Gonzalez and colleagues

https://www.frontiersin.org/articles/10.3389/fevo.2017.00110/full

Todd Royer:

Thanks Jim, great talk. Regarding the N deposition work, and N:P ratios more generally, how do we handle the strong preference for ammonium over nitrate shown by many microorganisms? Is there reason to partition N:P into ammonium:P or nitrate:P?

Yes it is true to not all microbes treat NH4 and NO3 the same; the latter being more energetically expensive to process. For sake of “simplicity”, in ES theory we tend to squint our eyes and pretend that such things don’t matter. But they sometimes or often will and then inferences from simplified ES won’t work so well. As you know, often such tradeoffs get made in trying to find an approach that can work without getting too buried in details.

xiaoming wan:

Thanks for the wonderful talk. I have one question. Do the predators show preferences to prey with high P content? I am always wondering why kids hate vegetables so much.

The behavioral dimensions of stoichiometry are quite interesting. More work on this has been done with nitrogen and with insects. Many herbivorous insects prefer more N-rich food items; you can read about his in the book The Inadequate Environment. My talented PhD student found the opposite however for locusts – they prefer to eat (and perform better) on N-poor food. See

  Cease, A.J., J.J. Elser, C.F. Ford, S. Hao, L. Kang, and J.F. Harrison. 2012. Livestock overgrazing promotes locust outbreaks by lowering plant nitrogen content. Science 335: 467-469.

Much less has been done with effects of food P content (C:P ratio) on feeding choices. It is a very open field!

Naijia Xiao:

How much is variance of element compositions within a species responding to environmental changes (like seasonal), compared with the variance of element compositions between different species?

This is the question of stoichiometric homeostasis. As I discussed early in the talk, the generalization is that photoautotrophs (algae, plants) are more plastic / less homeostatic than heterotrophs (animals, bacteria). But there is much discussion! Here’s a review from 10+ years ago.

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0706.2009.18545.x

Mark Daniels:

In your opinion, how can phosphorous be more responsibly used when we are facing an unprecedented global growth in human population? How can we mitigate our biogeochemical footprint given our growing reliance on phosphorous?

We need do a lot of things:
  1. Develop crops that use P more efficiently
  2. Use fertilizer more efficiently so that less is lost.
  3. Reduce food waste.
  4. Reduce the amount of meat in our diets (or switch to synthetic meat!)
  5. Start to recycle P from various sources: food waste, manure, human waste

We can also try to limit population growth by humane means, such as empowering women with education and business opportunities.

Zhanfei Liu:

Thanks Prof Elser! Appreciate your foundational work about GRH, but it seems that your data collection has been focused on zooplankton. I am wondering how about the prokaryotes or organisms of higher trophic levels, such as fish larvae, in terms of GRH?

Yes there is a lot of work on GRH in bacteria. See work of Jim Cotner and others.

Example

  Phillips KN, Godwin CM, Cotner JB. The Effects of Nutrient Imbalances and Temperature on the Biomass Stoichiometry of Freshwater Bacteria. Front Microbiol. 2017;8:1692. Published 2017 Sep 8. doi:10.3389/fmicb.2017.01692
  Godwin, C., Cotner, J. What intrinsic and extrinsic factors explain the stoichiometric diversity of aquatic heterotrophic bacteria?. ISME J 12, 598–609 (2018).

Less has been done with fish and fish larvae from perspective of GRH. Fish larvae are an interesting case as there is a transiton of P use from RNA production in early stages towards ossification (bone production) later.

Esteban Balseiro:

Thank Jim for a very nice talk, best regards from Patagonia. Esteban

Hola amigo!

Mark Daniels:

How much phosphorous can the Haber-Bosch process replace from mineral mining reliance?

See above: ? The Haber-Bosch reaction produces ammonia for fertilizer from N2 gas in the atmosphere. It does not produce any phosphorus for fertilizer. And phosphorus cannot substitute for nitrogen in fertilizer (or vice versa)

Timothy Burnette:

Great talk, Jim! Thanks!

Thanks!

Kaydee Barker:

Thank you Dr. Elser!

You’re welcome!

John Jacobs:

Thank you for the wonderful talk and your time this evening Jim. I have enjoyed listening to "the man himself" regarding your studies and ecological stoichiometry. Sending many thanks from an undergraduate student at Colorado State University. Best, John Jacobs

You’re welcome!