Some new things have come out that I would bring to your attention. Release of nitrous oxide from fertilized agriculture. An ‘emissions factor’ of about 1% of fertilizer nitrogen becoming nitrous oxide has been widely employed. New analysis by Shcherback et al. in Science supports that value. Previously it had come from a rather short list of studies. The ‘state of tropical carbon’ is now much better pinned down by Grace et al. in Global Change Biology. See also Achard et al. and Berenguer et al. in the same journal. Longer growing seasons mean more terrestrial productivity (carbon uptake) and they are caused both by +CO2 and +temperature. Keenan et al. in Nature Climate Change. You will recall that both temperature and CO2 increases are larger in El Nino years and smaller in La Nina. This appears to come at least in part from more rain (more productivity) during La Nina in water-limited lands in the southern Hemisphere. See Poulter et al. in Nature. Highly relevant because an El Nino appears increasingly likely in 2014, although it may not be as strong as 1997-1998. Meanwhile folks (like me) who study decomposition, the other half of the terrestrial carbon cycle, continue toiling away. I’ll wait on describing my toils until the journal reviewers have their way with several manuscripts now nearing completion. However, I want to mention an important aspect that we have so far failed to understand. Mycorrhizae are fungi that work together with plant roots. Sometimes they act like plain old decomposer fungi, other times very differently. They are a Big Deal in agriculture, which is another reason why I am bringing them up. I suppose we won’t understand decomposition well at all until all the players and their resources (like carbon and nitrogen) get combined in better studies. Won’t be easy, and it’s darn lucky that both of those elements have some isotopes we can work with. Predictions of the global carbon cycle are unlikely to get more accurate until decomposition research approaches the high standards already set by productivity (photosynthesis) research. Temperature, CO2 and nitrogen deposition are all increasing, and how those affect decomposition depends on interactions among a bunch of critters, especially fungi. Finally the CO2 satellite will go up in a couple of weeks. First one never made it, so good luck getting the launch shroud off this time.
They form a partnership with a plant; getting sugar from it in exchange for other nutrients. The big one they are known for is nitrogen. Plants can't use atmospheric/elemental nitrogen, and require it in other forms. The fungi can convert that elemental nitrogen into something a plant can use. Soy was an important crop in ancient China not for a food, but for its nitrogen fixing capabilities that refreshed the soil for other crops the next season. It was actually one of these fungi that grew with the soy roots doing the work.
It is a few specialized bacteria that fix atmospheric nitrogen, and not any fungi (that I know). The fungi do collect N and P from the soil (for the plant) and perhaps sometimes water as well. All in exchange for sugar from plant roots as TB said. Don't feel bad though - an agronomy professor (who shall remain unnamed) one told me that plants fix N through their stomates. Eww. One interesting aspect of fungi collecting N is that they don't only just do plain old decomposition, they kill small soil critters and digest them. This is probably more widespread than currently recognized, and I'd love to get some grad students roped into such research. All one needs is 15N stable isotope and a mass spec machine. Therefore, quite a lot of $$$ Anyway, that last Agaricus or Porcini you ate may have been a killer. Getting a bit tough to decide who is a vegetarian.
Each of the infrared absorbing gases poses difficulties, but methane perhaps the most. Sources and sinks are not know very accurately. Atmospheric concentrations can be measured, but it is hard to predict (or project) how it may change. Wetlands and flooded rice fields (for example) release methane to the atmosphere. Drier soils take it out of the atmosphere. There is a new study on the latter: Christian Juncher Jørgensen, et al. (2014) Net regional methane sink in High Arctic soils of northeast Greenland. Nature Geoscience doi:10.1038/ngeo2305 "Field measurements show methane uptake in all non-water-saturated landforms studied, with seasonal averages of − 8.3 ± 3.7 μmol CH4 m−2 h−1 in dry tundra and − 3.1 ± 1.6 μmol CH4 m−2 h−1 in moist tundra. The fluxes were sensitive to temperature, with methane uptake increasing with increasing temperatures." (from the abstract) They used satellite image analyses to scale up those local measurements. Can't say much more until I read the paper. But it certainly falls in the "good news" category that methane consumption increases with T.
In Geophysical Research Letters doi: 10.1002/2014JD022466 we read that CO2 energy absorption is less at higher elevations (Greenland, Antarctica, Tibet) because they are above a substantial portion of the (CO2 containing) atmosphere. Seems obvious once somebody says it, but I guess it is not in the global models yet.
