Nature often demonstrates the following regularity: products, synthesized by some microbes, are consumed by others with an "appetite". Here is a typical example: bacteria, residing in benthic sediments of bogs and rice-fields or in the intestines of ruminants, constantly excrete methane (CH₄) into the atmosphere. But this gas has "consumers"-it is oxidized by metanotrophic bacteria of forest soils. However, if in the latter case we observe large concentrations of nitrogen compounds, they suppress an oxidizing activity of the given metanotrophs. Therefore, of great interest is a work of a group of scientists from Russia and Germany, who, for the first time, proved that both the efficiency of bacterial oxidation of methane and an extent of nitrogen influence on the corresponding process depend on the species of trees growing in the forest. The journalist Nataliya Reznik told about these studies with

reference to a publication in the journal Doklady RAN (RAS Reports), No. 1, Vol. 447, 2012, on the pages of electronic edition of Science and Technologies of Russia-STRF.ru.

Methane is second in significance gas, participating in creation of hothouse effect, and that is why scientists are searching for methods of minimizing its influence. Specialists from the Institute of Forest named after V. Suka-chev, RAS SB, the Siberian Federal University (Krasnoyarsk), Lomonosov Moscow State University and Max Planck Institute for Terrestrial Microbiology (Marburg, Germany) are carrying out experiments for a number of years, trying to elucidate a role of some natural factors in fixation of methane. The work has been supported by the RFFR, RF Ministry of Education and Science, US Civilian Research and Development Foundation (CRDF) and Alexander von Humboldt Foundation (Germany).

In the focus of attention of international community are soil microorganisms, which annually remove from the atmosphere approximately 30 mln t of hothouse gases, which makes up 6-10 percent of its annual outflow (disappearance). Methane easily penetrates into the struc-turized forest soil, to places, inhabited by methano-trophs. As was mentioned above, CH₄ consumption by these organisms depends on the nitrogen content: in case of its abundance, bacterial activity decreases. Meanwhile, contamination by compounds of this element, caused by industrial discharges and climate warming, becomes more and more evident. And so, specialists are constantly worried by the problem of nitrogen influence on methane fixation in different forest soils.

In 1971-1972, staff members of the laboratory of soil science under the Institute of Forest, RAS SB, laid an experimental plot, 50 km away from the north-west of Krasnoyarsk. Without mixing different species, they compactly planted spruce, pine, cedar, aspen, birch and larch, i.e. practically all main forest-forming species of Siberia, and already for four decades are studying processes of excretion and fixation of hothouse gases. In 2006, the senior research assistant of this institute Oleg Menyailo, Dr. Sc. (Biol.), in cooperation with colleagues from Germany, demonstrated: different arboreal species differently affect CH₄ oxidation activity in soil-the highest level was observed under arboreal species, the lowest-in fir-groves.

Russian and German scientists verified how atmospheric methane oxidation activity is affected by different concentrations of nitrate and ammonia salts under trees of four species. They took samples of grey forest soils from under common spruce, larch, aspen and birch. The samples were incubated in the presence of CH₄ and ammonia sulphate or potassium nitrate. Three days later, the developers determined the methane oxidation level. As a result, it was for the first time established: ammonia salts suppress CH₄ consumption speed stronger than nitrates, which in low concentrations even stimulate the activity of methanotrophs. The most interesting thing is that an inhibiting effect of nitrogen compounds depends on tree species, from under which is taken the soil. The lowest is observed under spruce, and the highest-under birch. Thus, in case of 50 mg/kg concentration of ammonia salts, CH₄ oxidation activity in birch-groves decreases by two thirds.

Earlier Oleg Menyailo with coauthors established that specific composition of methanotrophs on all experimental plots was identical. But arboreal species affect a lot of soil processes, especially nitrogen fixation and mineralization. Microorganisms, residing under conifers, seize this element very rapidly, hence, their compounds do not accumulate in the soil. "Perhaps, differences in immobilization speed of nitrogen mineral forms under different arboreal species cause a dissimilar effect of nitrogen addition on the activity of methanotrophs", presupposes Menyailo.

It should be exphasized that by suppressing the capacity of soil microorganisms to fix methane, nitric contamination strengthens the hothouse effect. However, assessing the consequences of such contamination of the soil, it is necessary to take into account predominant arboreal species and the main form of nitrous compound.

N. Reznik, Russian Scientists Have Learned What Happens With Methane Under Trees.- Electronic Edition of "Science and Technologies of Russia-STRF.ru", December 24, 2012

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Prepared by Sergei MAKAROV