A copepod… or a swimming crayon? A discussion of Chap. 2 in Ecological Stoichiometry.

Posted by Jess:

Quick summary of chapter:
This chapter focuses on the chemical constituents of biochemicals, and how the relative abundances of these chemicals vary. The chemicals of interest are carbon (C), nitrogen (N), and phosphorus (P) – elements which are relatively scarce in Earth’s crust, but due to their chemical properties, are relatively abundant in living organisms. The chemical properties of C, N, and P also relate to the fact that they vary in different biomolecules – nucleic acids are relatively high in P, while lipids are C rich, and proteins have nearly no P. Two figures in this chapter, Fig. 2.2 and 2.4, show an impressive variability of the relative abundance of N and P in biochemicals, begging questions of how this variability may have evolved from or be evolving because of variability in abiotic nutrient levels.

How it relates to our work:
Cuatro Cienegas, Mexico, is famous for its numerous springs, pools, and rivers that pepper an otherwise desert landscape (as well as being the hometown Vestutiana Carranza, the man that wrote the Mexico’s Constitution). But it makes our lab perk up because of its extremely low P levels – a byproduct of its geology. The past work of the Elser lab has shown that the microbes in the region have C:P ratios as high as 5000! (Compare this to the Redfield Ratio of 106:1!) Likewise, we are discovering that the organisms here have interesting adaptations that alleviate the P scarcity – for instance, instead of using phosphorus to form membranes some of the bacteria use sulfur. I’m interested in particular how nutrient cycles may be constrained by organisms. Thus, I am spending this summer looking at C, N and P (and calcium) cycling by the microbes in Cuatro Cienegas.


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