We know that land cover change continues to liberate vast amounts of C from biomass to the atmosphere - about 2.2 Pg C yr-1... over 1/3 of that emitted from fossil fuel burning worldwide. However, there are reasons to suspect that C is also being stored in tropical systems - just as in the northern hermisphere. The question is just how much. While the concensus is that the sink is small, some (Townsend et al. 2002) think that tropical regions are close to C-neutral (see discussion in Houghton et al. 2004). Most of what we know about C stock changes in tropical regions comes not from direct observation but from inferences drawn from regional inversions, stable isotopes, and hemispheric gradients. Holmes et al. (2006) hve just published new estimates of soil C stocks - and changes in stocks due to forest-to-pasture conversion - in Rondonia state, Brazil. They created new soil C maps based on over 2000 soil samples. They found a slight decrease in soil C stocks for the region (-0.5% or 5.0 Tg C - 0.0005 Pg). This approach is an improvement over those that spatially extrapolate the limited number of intensive soil C studies (like mine - Conant et al. 2001). But how do these results apply to the rest of the tropics? Is their conclusion, that fertile soils with high soil C content tend to lose soil C while less fertile soils tend to gain soil C, relevant to other areas in the tropics? What is the impact of pasture management on top of all that? These are the questions that this interesting study raises.

Conant, R.T., Paustian, K., Elliott, E.T., 2001. Grassland management and conversion into grassland: Effects on soil carbon. Ecol. Appl. 11, 343-355.

Holmes, K.W., Chadwick, O.A., Kyriakidis, P.C., Sliva de Filho, E.P., Soares, J.V., Roberts, D.A., 2006. Large-area spatially explicit estimates of tropical soil carbon stocks and response to land-cover change. Global Biogeochem. Cycles. 20, 10.1029/2005GB002507.

Houghton, R.A., Joos, F., Asner, G.P., 2004. The effects of land use and management on the global carbon cycle. In: Gutman, G., Janetos, A.C., Justice, C.O., Moran, E.F., Mustard, J.F., Rindfuss, R.R., Skole, D., Turner, B.L., Cochrane, M.A. (Eds.) Land change science: Observing, monitoring and understanding trajectories of change on the Earth's surface, Dordrecht, Kluwer Academic Publishers, pp. 237-256

Townsend, A.R., Asner, G.P., White, J.W.C., Tans, P.P., 2002. Land use effects on atmospheric 13C imple a sizable terrestrial CO2 sink in tropical latitudes. Geophysical Research Letters. 29, 10.1029/2001GL013454.

A recent article by Veron et al. (2006) has a very good discussion on the history of desertification assessments and popular press reactions to scientific articles (much of that from an book chapter by Reynolds and Stafford Smith 2002). They explain that desertification is a really inclusive term, making desertification difficult to document and assess. They propose a method that could give some insight into desertification that is quite interesting: evaluating the relationship between annual precipitation and ANPP. In some cases desertification will not impact ANPP (at least in the short term), but will impact the pulse-decline response to wet or dry conditions. They go on to explain that these resposnes ought to be obervable using remotely sensed data. This approach could get to the center of desertification observation by focusing on what's important - NPP. I for one am excited to see results from such studies!

Veron, S.R., Paruelo, J.M., Oesterheld, M., 2006. Assessing desertification. J. Arid. Environ. 66, 751-763.

Take a look at the recent news feature on microbial ecology in Nature by Nick Lane (link). He uses a brief discussion of the anammox reaction as a launching point for a review of basic microbial biochemistry and a higher-level investigation of the meaning of microbial processes for studying ecosystem function. Diversity is important because of the diversity of energy releasing – redox – reactions that take place. However, diversity happens. Communities of microorganisms in ecosystems seem to be assembled to get as much energy out of the environment as possible. Thus studying the diversity of processes is interesting, but understanding how organisms function necessitates studying the behavior and efficiencies of communities, not individuals. Reducing systems to understand them has limited insofar as it decouples organisms that function in a complimentary way. What do the ideas presented here mean for understanding nitrogen and carbon cycling agricultural ecosystems?