BOTANISTS may have to rewrite their textbooks following the discovery that some plants can turn themselves into compost when they die.
Like gardeners, botanists assumed only soil microbes can break down decaying plant matter into nitrates and nitrites. Now Charles Hipkin and his colleagues from the University of Wales in Swansea have discovered 15 legumes that generate nitrates and nitrites in their own tissue as they die.
Legumes have root nodules that harbour nitrogen-fixing microbes. These scavenge nitrogen from air and soil and enable it to be converted into amino acids. Self-composting species use these to make 3-nitropropionic acid.
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Hipkin鈥檚 team used a rare nitrogen isotope to track the metabolism of 3NPA in horseshoe vetch (Hippocrepis comosa), and showed that it is directly converted into nitrates and nitrites within the plant鈥檚 dying stems and leaves (Nature, vol 430, p 98).
鈥淚t鈥檚 a throughput from nitrogen in the air right through to nitrate in the soil,鈥� says Hipkin.