the light! the heat! the feedback! Sometimes, the devil IS in the details. I’ve been thinking about feedbacks between community community structure and function lately, and run into a few curious roadblocks, as well as one very very interesting story.

First, the roadblocks. Just what do we mean by structure and function, particularly in reference to a biological community? Structure seems obvious – the static properties of a biological system that we can go out, stare at, and say,”Oh, yes, hello structure!” I of course often think of things like biodiversity or biomass, but one could also reference Carbon to Nitrogen ratios, physical structure, or others.

But function – that’s more nebulous. The first thing that springs to mind is, what is the opposite of a static property. Why, a rate, of course. So, a rate process…but that’s awfully nebulous. I mean, what can’t be measured by a rate? Which leads to thinking more about the flux of matter and energy within a system. Far more tractable, but then, what gets cut out?

I am struck by the example of potential feedbacks between climate change and the nutrient content of plants. This is a lovely example drawn from a 2008 PNAS paper by Ollinger and colleagues. In it, they basically show that plants with higher nitrogen content tend to have shinier leaves. The more nitrogen in the canopy, then, the higher the albedo. Higher albedos then cool an area, or at least decrease warming as light is reflected back.

This is curious – as climate change work in the Harvard forest (or, sorry, the Hahvad Forest) have shown that warming soils can lead to faster nutrient cycling and more N availability. More N availability can change the albedo of leave in local plants, or can even cause a shift in the plant species composition to shift towards plants with more nitrogen per unit carbon.

It’s a really interesting feedback.

At the same time, even if this does something with respect to warming, CO2 is on the rise, also possibly changing C:N ratios. So, caution is warranted to thinking that Nitrogen is the solution. Indeed, considering the myriad of other changes in nutrient cycling and plant stoichiometry, the devil really IS in the details here as well, and hence caution is warranted before someone goes off, all IronEx style, and proposes fertilizing the planet to slow climate change. After all, we’re doing that already!

But it all raises an interesting question in my mind – is slowing temperature change a “function”. I would say yes – that it is the service provided by the ecosystem. It is not a flux of matter or energy, but it is still something that the system does, and hence, a function.

And functions like these are becoming more important as time goes by!

S. V. Ollinger, A. D. Richardson, M. E. Martin, D. Y. Hollinger, S. E. Frolking, P. B. Reich, L. C. Plourde, G. G. Katul, J. W. Munger, R. Oren, M.-L. Smith, K. T. Paw U, P. V. Bolstad, B. D. Cook, M. C. Day, T. A. Martin, R. K. Monson, H. P. Schmid (2008). Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks Proceedings of the National Academy of Sciences, 105 (49), 19336-19341 DOI: 10.1073/pnas.0810021105

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