Crumb Trail
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Wednesday, April 12, 2006
 

When it was recently discovered that plants emit methane I lamented that everything I know is wrong. One after another all my solid bits of knowledge turn out to be nonsense as new discoveries are made. The good scientist is happy when this happens, happy to have better information, comforted by the march of progress or something. I try, but it isn't comfortable, it's irritating. I have to take myself out behind the wood shed sometimes for a bracing lecture on the method and how this is all to the good. It happened again.

Until recently it was generally believed that the most important source of nitrogen for plants was inorganic nitrogen. However, researchers funded by the Biotechnology and Biological Sciences Research Council (BBSRC) from the University of Lancaster and the Institute of Grassland and Environmental Research (IGER) have found that not only can organic nitrogen be directly taken up by plants it is also used differently by different species, enabling nitrogen sharing and biodiversity.

By tagging organic nitrogen with stable isotopes researchers have challenged the long held idea that organic nitrogen has to be first converted into an inorganic form before the plants can use it. Their findings have significant implications in unfertilised, low-productivity grasslands where organic nitrogen often appears in greater concentrations than inorganic forms.

Professor Richard Bardgett, lead researcher at the University of Lancaster explained: "This research provides important new information about what happens to organic nitrogen in real ecosystems in real time. Tagging amino acids also revealed that different plant species prefer different sources of organic nitrogen. These preferences may be a way for plants and microbes to avoid competition with their neighbours for nitrogen when it is in very short supply, effectively enabling them to share nitrogen and maintain biodiversity."

This is just a brief press release. There's no useful detail, and the focus at the Institute of Grassland and Environmental Research (IGER) is on untilled swards, but it would seem that there are also implications for cropped lands that seek to amend soils using organic matter. If different plant species prefer different sources of organic nitrogen then a grower would want to match sources to crop species for best effects.

Update:

gaaahh! It seems that we also have anaerobic oxidation of methane.

Why did it take until now to identify this process? The main reason is probably that it proceeds at much lower rates than the anaerobic oxidation of other organic compounds or of hydrogen sulphide with nitrate. So the process is evident only in anoxic environments with low concentrations of oxidizable substrates other than methane, and with low levels of sulphate and high levels of nitrate. Such conditions prevail in anoxic freshwater habitats contaminated with agricultural run-off and in contaminated groundwater. The nitrate-dependent anaerobic oxidation of methane is predicted to occur mainly close to the oxic–anoxic interface, where in the oxic phase ammonia is oxidized to nitrate with oxygen by nitrifying (nitrate-forming) microorganisms. Nitrate then diffuses into the anoxic sediments saturated with methane, which is produced microbially from the degradation of cellulose and other plant material (Fig. 2). The interface is generally characterized by steep chemical gradients, which occur within millimetres and mask the process of the anaerobic oxidation of methane with nitrate.

posted by back40 | 4/12/2006 10:14:00 AM

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