Wednesday, November 28, 2007

Cool Journal Articles: CO2 Enrichment and Crayfish

Blogging on Peer-Reviewed Research

I have a lot less time to read good journal articles than I used to, and KDWP has incredibly limited access to on-line journals, so I am just now getting to the latest issue of the Journal of the North American Benthological Society (JNABS; which is actually listed as December 2007). I feel like JNABS is a vastly underrated journal, but I have to admit that I’ve published two papers there, so I may not be entirely without bias.

At any rate, there are several very interesting articles in this issue, and I hope to highlight them all on this blog. The most interesting/amazing by far (in my mind) is one by John Kominoski and others (see full citation below #1). I just did a quick google-search, and apparently Kominoski has his own google-page (you can get a .pdf of this article from there).

Ok, so let’s talk about this paper a little. Oddly enough, this paper integrates subjects I find very interesting: dissolved organic matter (DOM), periphyton and crayfish. The basic premise of the paper is that as CO2 levels in the atmosphere rise, the organic chemistry of plants is going to change. This has lead to a widespread idea that herbivores feeding on these elevated CO2 plants will be less able to extract needed nutrients. My friend and collaborator Paul Frost has published one paper exploring the stoichiometry behind this, but he certainly isn’t the only one (see his citation below #2). The basic idea is that as you increase the CO2 in the atmosphere, you increase the amount of carbon in the leaves/tissues of plants. That seems great, since it means more productivity when measured in terms of energy.

Unfortunately, it also means less (by percent weight) of other essential elements (i.e., nitrogen or phosphorus). So more CO2 in the atmosphere means you have to eat more food to get the same amount of nutrients (as in a lower CO2 atmosphere). At least, that’s one theory with some support.

The kicker is that the additional C in those leaves in plants may not just be adding nutrient-poor bulk to the plant, it may be in the form of compounds that are actively toxic. That’s what Paul Frost found in the 2005 paper I mentioned earlier. His little bugs eating elevated-CO2 leaves were leaking essential nutrients.

So back to the Kominoski paper. Kominoski (or Nancy Tuchman or one of the authors) got the idea that these leaves aren’t just a direct food source to detritivores and herbivores, they are also an indirect food source to the base of the aquatic foodweb (the biofilms on rocks, often referred to as periphyton). Here’s where the DOM story comes into play. See, DOM is a fantastically important component of most aquatic ecosystems, controlling light penetration through the water column, the bioavailability of heavy metals and nutrients, has a huge effect on the pH of water, and is a ‘food’ source for bacteria and algae. DOM is just organic matter, which is a pretty broad category, and it comes from a lot of different places (animal excretion, algal release, bacterial release), but one of the biggest sources in temperate forested streams (and lakes) is leaves.

That’s right, leaves. Leaves falling into streams or lakes or wetlands leach organic compounds. You can probably imagine where this is going. Kominoski et al. found that the DOM leached out of his CO2 enriched leaves caused a different biofilm to develop than the DOM leached out of leaves raised in ambient conditions. That difference proved to be one that crayfish (a hugely important species in many aquatic ecosystems) could detect, and avoid. The implication that Kominoski et al. draw is that crayfish in a CO2 enriched world will possibly stop eating periphyton and start eating other, more nutrient-rich sources of food preferentially. Say goodbye to smaller macroinverts!

One key implication of this paper is that climate change isn’t just going to cause ecological havoc because of changes in temperature or rainfall; simply changing the CO2 content of the atmosphere will have dramatic and subtle effects on the biosphere.

Now, I don’t necessarily get everything in this paper. For example, the conclusion is somewhat tenuous. I’ve measured the grazing rate of crayfish on periphyton: For some species it is not much. Of the crayfish I’ve seen, it seems like they don’t eat periphyton unless they’re starving, but I’m no expert on that. (Hopefully some experts will email me a smarter reply about that.)

I’m also a little thrown off by a particular line in the abstract: “...cyanobacterial biovolume was higher in [elevated CO2] algal assemblages than in [ambient CO2] algal assemblages after 35 [days].” Yet in Figure 2, the differences in cyanobacterial biovolume don’t appear to be significant (visually or statistically), and leading up to the 35 day mark the different treatments appear to flip-flop in importance. So, I’m not sure I would have included that in the abstract, even though it is conceptually an appealing idea (cyanobacteria seem to be considered ‘poor quality’ food by most aquatic ecologists).

A few other notes:
- I’m curious to see on how many more posthumous papers the legendary Bob Wetzel will be a co-author. Will this be the last one? Is John Kominski (who seems pretty cool) the last first author with Wetzel as a co-author?

- I really thought this paper was Nature-worthy. That’s pretty much the holy grail of ecologists. However, after I read around a little, I realized that the implicit finding here (that CO2 enrichment will cause all kinds of weird and unexpected effects) is not that novel. Still, a great and complete story.

- I also saw a talk John Kominoski gave at NABS 2003 in Athens, GA. I talked to him at that conference, but I doubt he would remember me. I’m somewhat surprised that it has taken this long for the paper to come out. I wonder if it got rejected by a better journal, causing the delay. Formatting this thing for Nature would have been hard, and it would have been equally hard to re-format it for JNABS.

#1 Kominoski, J.S., P.A. Moore, R.G. Wetzel, and N.C. Tuchman. 2007. Elevated CO2 alters leaf-litter-derived dissolved organic carbon: effects on stream periphyton and crayfish feeding preferences. JNABS 26:663-680. DOI: 10.1899/07-002.1

#2 Frost, P.C. and N.C. Tuchman. 2005. Nutrient release rates and ratios by two stream detritivores fed leaf litter grown under elevated atmospheric CO2. Archiv für Hydrobiologie 163: 463-477

1 comment:

Beth Walker / Evan Walker said...

Both of these papers are part of my library. I'm glad to find your review!