Saturday, 15 July 2006

Increasing Long Term Soil Carbon Sequestration in Agriculture and Forestry: The Role of Phytoliths.

Leigh A. Sullivan and Jeff Parr. Southern Cross Univ, 1 Military road, Lismore, Australia

Terrestrial carbon sequestration is fundamental to the global carbon cycle and is being utilised to counter increases in anthropogenic carbon dioxide emissions. Although soil organic carbon dominates the terrestrial carbon cycle in terms of total quantity, the long term sequestration of soil organic carbon in the Holocene was relatively low (<1 % of net primary production). Consequently there is a viewpoint that soil has a low carbon storage potential and hence only a relatively minor role to play in countering anthropogenic carbon dioxide emissions. Long term (decades to millennia) soil organic carbon sequestration mechanisms are currently thought to be mainly due to the physical protection of chemically recalcitrant organic matter within clays. Recent research is presented here to show that some forms of soil organic carbon (e.g. that occluded in phytoliths) are not readily physically accessible to the agents responsible for decomposition and that these forms also play a major role in long term soil organic carbon sequestration. Phytoliths (literally ‘plant rocks') are silicified features that form as a result of biomineralization within plants. The occlusion of carbon within phytoliths has been recently found to be an important process in the long-term sequestration of terrestrial carbon (Parr & Sullivan, 2005). Moreover, relative to the other soil organic carbon constituents, the carbon occluded in phytoliths (PhytOC) is highly resistant against decomposition. Although comprising < 10 % of the total carbon pool in contemporary topsoils (with ages of < 200 years), the resistance of this carbon fraction against decomposition processes resulted in this carbon fraction comprising 70 % of the total carbon pool in the buried topsoils after decomposition for 3,000 years in soils under grasslands. The carbon in phytoliths is sequestered over the geological time scale rather than the anthropological. Experimental and modelled data presented here indicates that the long term carbon sequestration potential of soil can be increased considerably in areas under managed vegetation (e.g. crops) by the adoption of simple agronomic and silvicultural practices. Reference: Parr J.F., L.A. Sullivan, Soil Biol. Biochem. 37, 117 (2005).

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