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Die weltweiten Kohlenstoffvorräte in den Böden übersteigen jene aus Pflanzen und Atmosphäre um das Dreifache. Organische Bodensubstanzen wie beispielsweise Humus spielen beim globalen Kohlenstoffkreislauf eine zentrale Rolle, da sie riesige Mengen an Kohlenstoff speichern und so der Klimaerwärmung entgegenwirken. Das Kyoto-Protokoll gestattet daher den unterzeichnenden Ländern, Böden und Wälder als sogenannte Kohlenstoffsenken an die Treibhausgas-Emissionen anzurechnen. Doch es ist weitgehend unbekannt, weshalb gewisse organische Bodensubstanzen während Jahrtausenden stabil bleiben, andere dagegen schnell zerfallen und wiederum Kohlenstoff freigeben. Die bisher verwendeten Erklärungsmodelle gehen davon aus, dass die Abbaugeschwindigkeit von der molekularen Struktur der organischen Bodensubstanz abhängig ist. Jetzt weist ein internationales Forschungsteam mit 14 Wissenschaftlern unter der Leitung von Michael Schmidt, Professor für Bodenkunde und Biogeographie an der Universität Zürich, in Nature nach, dass zahlreiche andere Faktoren die Abbaugeschwindigkeit von organischer Bodensubstanz beeinflussen.
Bodenumwelt bestimmt Abbautempo des Humus
«Das Abbautempo wird nicht von der molekularen Struktur der abgestorbenen Pflanzenreste bestimmt, sondern von der Bodenumwelt, in der der Abbau stattfindet», fasst Schmidt die neuen Resultate zusammen. So beeinflusst u.a. die physische Isolation der Moleküle oder die Tatsache, ob die Moleküle im Boden durch mineralische oder physikalische Strukturen geschützt sind, die Abbaugeschwindigkeit von organischen Bodensubstanzen. Auch die Bodenfeuchtigkeit spielt eine wichtige Rolle. Die Forschenden können weiter zeigen, dass es entgegen der Lehrmeinung keine Huminstoffe im Boden gibt und diese deshalb nicht für Modelle herangezogen werden dürfen.
Es braucht neue Experimente und Modelle
Wie Prof. Schmidt erklärt, müssen die Erkenntnisse nun für neue Experimente und Modelle genutzt werden. Dabei sollen nicht nur wie bis anhin die ersten Zentimeter des Bodens untersucht werden, sondern die gesamten oberen zwei bis drei Meter. Die Forscher machen in ihrem Artikel verschiedene Vorschläge, wie die Modelle zur Prognostizierung der Reaktion von Böden auf Veränderungen des Klimas, der Vegetation und der Landnutzung zu verbessern sind.
Die neuen Erkenntnisse werfen zudem ein kritisches Licht auf Bioengineering-Versuche mit stark Lignin-haltigen Pflanzen oder Pflanzenkohlen (Biochar), mit denen langfristig mehr Kohlenstoff im Boden gespeichert werden soll.
###
Literatur:
Michael W. I. Schmidt, Margaret S. Torn, Samuel Abiven, Thorsten Dittmar, Georg Guggenberger, Ivan A. Janssens, Markus Kleber, Ingrid Kögel-Knabner, Johannes Lehmann, David A. C. Manning, Paolo Nannipieri, Daniel P. Rasse, Steve Weiner & Susan E. Trumbore: Persistence of soil organic matter as an ecosystem property, in: Nature, 6 October, 2011, DOI: 10.1038/nature10386
Kontakte:
Prof. Dr. Michael Schmidt
Universität Zürich
Geographisches Institut
Tel. 41-44-635-51-40
E-Mail: michael.schmidt@geo.uzh.ch
Zusammenhang zwischen Boden als Kohlenstoffspeicher und globaler Erwärmung überdenken
2011-10-06
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