nitrogen Fixation – a deep dive (From 2)

I previous posts I wrote to the need for continuous supply of nitrogen from the air - through the nitrogen-fixing organisms - to ensure forest garden's fertility. The question is how kvävefixerana share the nitrogen they catch up to other plants?

The answer is that it takes place in two different ways. The majority is made available by dead plant parts like roots, leaf, twigs etc.. In most dead plant parts is nitrogen rather tightly bound and may only after degradation converted to a form that plants can take, Thus, either in the form of ammonium (NH₄₊), who are happy to stick to the ground- and humus particles and thus not so readily leached or in the form of nitrate (NO_3-), which is readily soluble and easily leached out if it is not taken up by vegetation at once [2]. The division between ammonium nitrogen and nitrate nitrogen in the foliage varies greatly between species. Smalbladig silverbuske (Elaeagnus angustifolia) for example, has been found to contain water soluble nitrogen directly rinsed from the leaves when they fall down in the autumn. Other, most speaker (Alnus spp.) contains more tightly bound nitrogen which first need to be broken down, a process that will take four years or longer [4]. This degradation occurs both using the decomposer and a variety of bacteria. Since the breakdown takes its time, it may in other words, take a number of years before the nitrogen from kvävefixerarna will benefit other plants. But as each year kvävefixerarna included in the system increases the nitrogen content in the soil and this process can continue for decades [1].

Another, more direct transfer of nitrogen from kvävefixerarna to other plants occurs by excretion of nitrate from the roots. This nitrogen is sent (in theory) via a direct link from kvävefixeraren recipient. The link consists of fungal hyphae, Thus, microscopic threads that can be likened to roots, though in much smaller size. These form networks between all sorts of plants, both those which are related, but also between plants belonging to different families [5]. As a thank you to send the mushrooms nitrogen (and other nutrients) between the trees, the little carbohydrates. To find out this has planted a nitrogen-fixing and non-nitrogen-fixing plant in a pot and separated them using a very fine mesh that only fungal hyphae can grow through. Later measured the amount of nitrogen that was transferred from the one to the other plant with the aid of a neurotransmitter. Obviously, this is an oversimplification of how it looks in reality, but by performing this experiment could show that it can actually be a transfer of nitrogen between two totally unrelated plants.

In the second, not entirely realistic experiments have attempted to quantify exactly how much nitrogen kävefixerarna can contribute to their neighbors. The first transmission method by dead plant parts were then to 45-185 kg of nitrogen per hectare per year, while the direct transmission accounted for 35-45 kg of nitrogen per hectare per year, or somewhere in between 18 and 50% the indirect and slower nitrogen transfer [4]. To put it all in context, we can compare with the nitrogen needs of a mature apple tree, which amounts to about 42 kg of nitrogen per hectare per year for fruiting and vegetative growth [6]. In reality, however, there is not the same conditions in a laboratory and the amount of nitrogen that can be captured from the atmosphere depends on a number of crucial factors. More on what it is about in the next post.

References

[1] Brady, N.C. and R.R. Because, The nature and properties of soils. Upper Saddle River, N.J.: Prentice Hall, 2002.
[2] Santi, C., D. Bogusz, and C. Franche, Biological nitrogen fixation in non-legume plants. Annals of botany, 111(5): p. 743-67, 2013..
[4] Roggy, J.C., A. Moiroud, R. flew, and A.M. domains, Estimating N transfers between N2~-fixing actinorhizal species and the non-N2~-fixing Prunus avium under partially controlled conditions. BIOLOGY AND FERTILITY OF SOILS, 39: p. 312-319, 2004.
[5] He, X.-H., C. Critchley, and C. Bledsoe, Nitrogen Transfer Within and Between Plants Through Common Mycorrhizal Networks (NMCs). Critical Reviews in Plant Sciences, 22(6): p. 531-567, 2003.
[6] Board of Agriculture, fertilization- and kalkningsråd orchard 2004, 2004. http://www2.jordbruksverket.se/webdav/files/SJV/trycksaker/Pdf_jo/jo04_5.pdf.