There is a news item in Nature (click here; subscription required; see also Agecoblog 7/25 entry) today reporting on the potential for C sequestration while building new terra preta soils. The potential is huge - if you look at how much C terra preta soils contain relative to other soils (250 versus 100 t C ha-1). The added char could come from any kind of organic waste or as a by product of biofuels. At one point the article states that all of the C emitted could be stored in terra preta nova soils (practical questions about how to get all of that stuff into the soil notwithstanding). Isn't it interesting to think of creating waste-deep repositories for char as an environmental solution!

The standard model is that leaf litter falls to the soil surface and their breaks down. During breakdown, some of it moves into the soil either as dissolved organic matter or as particulate organic matter. But there are a few lines of evidence suggesting that this isn't really the way things work. Stable isotopic labelling coupled with litter addition, removal, and switching experiments suggest that litter contributes only a small amount to belowground C (see some of Margaret Torn's recent work). A new paper in this week's Nature (Austin and Vivanco 2006) suggests that in some ecosystems almost all of the decomposition is done via photo-oxidation and that very little surface litter ever makes it to the soil. Austin and Vivanco (2006) screened out no, some (UV-B) or all solar radiation to see how it affected leaf litter breakdown on the soil surface. They found that screening UV-B and total solar radiation reduced decomposition by 33 and 60%! Again, most of the decomposition they observed was due to photo-oxidation, not breakdown by mirco- or macroorganisms. This process has been recognized, but still it runs counter to the standard model. Similar experiments at places like the CPER and analysis of big data sets like LIDET and CIDET should give us good information about how important photo-oxidation is at different sites. In the meantime, the main thing I take from this work is that if we're interested in following the carbon, we need to look belowground!

Austin, A.T., and L. Vivanco, 2006: Plant litter decomposition in a semi-arid ecosystem controlled by photodegradation. Nature, 442, 555-558.

Organic cropping systems cover less than three percent of farmland area, but acreage devoted to organic agriculture is growing by 12% per year and proceeds are growing by over 20% per year, making organic agriculture the fastest growing segment of US agriculture (Lotter 2003). In order to be certified Organic, use of genetic engineering, ionizing radiation, and application of sewage sludge are prohibited. Nutrients must be managed solely using tillage and cultivation practices, crop rotations, cover crops and animal and crop waste materials. Use of organic fertilizers will impact soil carbon stocks, but how much? How will the turnover of added carbon differ from SOM under conventional farming? Marriott and Wander (2006a, b) have recently published a couple of papers that investigate these questions. Both papers demonstrate that manure-legume- and legume-based organic systems increase soil C content across multiple fractions (whole soil [14% in 10 yrs!], POM, fPOM, iPOM). Interestingly the legume system lead to greater POM C enrichment and less POM N enrichment than the manure-legume system. I wonder how much this added OM impacts retention of mineral N...

An observation: seeing these two closely related papers with similar data from the same set of sites published in such close succession makes me wonder about our scientific system ostensibly structured to advance knowledge that simultaneously encourages scientists to parse one story into two parts.

Lotter, D. W. 2003. Organic agriculture. Journal of Sustainable Agriculture 21:59-128.

Marriott, E. E., and M. M. Wander. 2006a. Total and Labile Soil Organic Matter in Organic and Conventional Farming Systems. Soil Science Society of America Journal 70:950-959.

Marriott, E. E., and M. M. Wander. 2006b. Qualitative and quantitative differences in particulate organic matter fractions in organic and conventional farming systems. Soil Biology & Biochemistry 38:1527-1536.

Peer review is a foundation for scientific progression. Just like other interactions between people, it has its problems (cronyism, vendettas, sloth). But when peer review works well, it enables science to move forward conservatively and collectively. Email and the web have streamlined the jobs of editors, but what else might these tools lead to regarding peer review? Nature is currently running a web debate to discuss the issue (click here; subscription required).

I personally look forward to the day of more informal pre-publication via the web. The journal Biogeosciences (along with other EGU journals) has tried this using a new type of article called a 'discussion' paper. Papers are raplidly assessed for merit and, if acceptible, published on the web site. The review process is more open, with reviews posted to the web site too, with comments welcomed. After the review, the articles are published in the regular print and on-line journals. Apparently commentary on papers have been limited, so results are mixed: people seem to like the idea, but don't add much to the discussion. According to one of the Nature arcicles, this two stage, open review discourages inferior submissions.

Say you were asked to develop an index for aridity - how would you do it? I would use some measure of precipitation relative to evapotranspiration (i.e., water deficit)? What if climate data weren't available? Plant species composition is a good indicator and their photosynthetic pathways (C3 vs. C4 vs. CAM) are too. So too is 13C water-use-efficiency. What if you were looking for historical information for which there were no climate obsrevations or plant material? 18-O information from bioapatite (teeth and bones) has been used, but the relationship between 18-O and aridity is confounded because 18-O in some animals varies with aridity. An article in today's PNAS describes a the relationship between 18-O-derived aridity proxies and water deficit from 9 evaporation insensitive animals and 6 evaporation sensitive animals. There is a strong positive relationship between water deficit and the enamel-rain water 18-O difference. This information could be used to produce better aridity proxies in the region, provided the source of bioapatite could be identified. The interesting thing is that the authors can't identify a behavioral or physioligical mechanisms (panter vs. sweater, grazer vs. browser, large vs. small) to explain the difference. All in all rather obscure, but a nice sleuth job.

Levin, N.E., Cerling, T.E., Passey, B.H., Harris, J.M., Ehleringer, J.R., 2006. A stable isotope aridity index for terrestrial environments. Proceedings of the National Academy of Sciences. 103, 11201-11205.

The Amazonian black earth - Terra Preta - soils are something of a mystery. They are very rich soils (15%C compared with <2% in surrounding soils) that are unevenly distributed throughout Amazonia. The increased fertility is evident via huge improevments to nutrient supply and retention of added nutrients. The fertility doesn't seem to decline with cultivation either. The origin of Terra Preta soils is uncertain, but the current idea is that they are anthropogenic soils that were developed by some type of human influence. They could have been areas that received special attention to build soil fertility or possibly repositories for organic wastes (will outhouse sites be the Terra Preta soils of the future?). A recent short communication in SBB (Ponge et al. 2006) discusses the potential for earthworms to process charcoal to enhance soil fertility. Their research has shown that earthworms prefer mixtures of charcoal and soil mineral particles to either alone, and that the composition of the resultant products are similar to the "relative volume of components of the soil matrix, including plant tissues at varying stages of decomposition, mineral particles of varying size and nature, aggregates of varying colour, size and shape." Further, dark humus samples from modern shifting cultivation plots were mainly comprised of P. corethrurus fecal pellets. Field experiments demonstrated that introduction of earthworms enabled incorporation of charcoal and manioc peels into the soil, increasing soil fertility without cost.

So, score one more for the lowly earthworm! I for one am anxious to learn more about the qualities of Terra Preta soils.

Ponge, J.-F., Topoliantz, S., Ballor, S., Rossi, J.-P., Lavelle, P., Betsch, J.-M., Gaucher, P., 2006. Ingestion of charcoal by the Amazonian earthworm Pontoscolex corethrurus: A potential for tropical soil fertility. Soil Biol. Biochem. 38, 2008-2009.

For more info about Terra Preta soils, click here.

Maldives - The presidents of the Oceanfront Real Estate Professionals Guild and the Small Island Developing States Network jointly announced the formation of a new partnership, the Tropical Resources Expansion and Development Coalition, with the intention of investing $37B to support land conservation, ocean fertilization, and deep-ocean CO2 pumping in order to reduce atmospheric carbon dioxide concentrations to 1990 levels. This expendiature is widely viewed as a response that will more than offset the land conversion/forest burning program supported by a consortium of historically arid countries, Arctic fruit growers, Antarcticans, and warm water shipping interests. This investment is expected to exacerbate the dispute between Advocates for Warmer World and the International Conservative Climate Coalition, who between them accoutn for the bulk of the $500B spent thus far to control the climate.

For more see: Parson, E.A., 2006. Reflections on Air Capture: the political economy of active intervention in the global environment: An Editorial Comment. Clim. Change. 74, 5-15.

Keith, D.W., Ha-Duong, M., Stolaroff, J.K., 2006. Climate Strategy with Co2 Capture from the Air. Clim. Change. 74, 17-45.

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?