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Next Generation Carbon Bio-Sequestration Solutions

Sequestration Using Phytolith Occluded Carbon PhytOC
The global potential for bio-sequestration via phytolith carbon
(from bamboo and/or other similar grass crops) is
estimated to be ~1.5 billion t-e-CO2 y-1

Plantstone Pty Ltd is a research and development company thats primary focus is a soil organic carbon fraction that has previously been overlooked i.e. Phytolith organic carbon or PhytOC. The name plantstone refers to the silica bodies (pictured on the left) found in many plant species particularly grasses. They are also known as phytoliths and/or plant opal. The occlusion of carbon within phytoliths (literally ‘plant rocks’ formed by silicification within plants) has been recently found to be an important process in the long term sequestration of terrestrial carbon. The rate of both phytolith production and phytolith occluded carbon sequestration (termed ‘PhytOC’) varies widely between plant types and varieties1,4 . At Plantstone Research and Development we are working on increasing the potential of this process to help counter via agronomic and silvicultural means anthropogenic carbon dioxide emissions. We hold IP on procedures for plant breeding, carbon quantification and for the practical application of this process as well as both granted AUS Patent 2005279679, US Patent 7927884B2 and pending international patent applications on the use of these procedures for the purpose of carbon sequestration and carbon trading.

Current terrestrial approaches to enhancing terrestrial carbon sequestration include land use changes such as conversion of cultivated land to forest or grassland, or a change of tillage practices. Limitations of these approaches include 1) the period of carbon sequestration enhancement which lasts only for a few decades5, 2) the enhanced sequestered carbon is ‘stored’ at risk of desequestration by fire, disease, or future landuse reversion2, and 3) hidden CO2 emission ‘costs’ such as those associated with increased nitrogen fertiliser use or irrigation6. In contrast, carbon sequestered inside phytoliths is both chemically and physically protected by silica coatings and is secure against decomposition over a millennial time-scale relative to most other forms of soil organic matter (Fig. 1).

What is the potential of cultivation of crops and forests with enhanced PhytOC yields for increasing global carbon sequestration? The current global PhytOC sequestration estimates (between 0.4 – 0.9 g C m-2 yr-1)1 indicate that the global rate of carbon geosequestration by PhytOC production is between 0.05 and 0.12 Pg C yr—1. This represents up to 32% of the estimated current global terrestrial carbon sequestration rate6, but only 3.4 % (i.e. 3.2 Pg C yr—1) due to anthropogenic emissions5. However the rate of phytolith occluded carbon sequestration varies widely between plant types1 and it is likely that the PhytOC sequestration rate of many plant types could be increased considerably by selection or genetic manipulation and agronomic management as this trait has not been selected for previously. Indeed, the amount of carbon sequestered in phytoliths as a proportion of that fixed by plants is minor. For example, in the case of sugar cane, the PhytOC sequestration rate only represents ~0.3% of the dry above-ground biomass production. If the global PhytOC sequestration rate was enhanced on the land surface area that is either arable or forested (i.e. 4.6 x 1013 m2), and hence influenced by active land management, by the use of crops and forests with PhytOC production rates equivalent to for example, sugar cane with 18.1 gC m-2 yr-1, then this enhanced PhytOC process would be sequestering 0.83 Pg C yr—1, which is 26 % of the current total atmospheric increase of carbon as CO2.  This indicates a considerable potential for management aimed at enhancing the PhytOC carbon sequestration in crops and trees to contribute to global efforts aimed at the suppression of atmospheric CO2 concentrations.

The selection of enhanced PhytOC production in crops should not appreciably interfere with normal yields and value of those crops. For example, even if the PhytOC yield of sugar cane was increased by an order of magnitude, the amount of carbon available above-ground for other purposes such as sugar production would only decrease from 99.7% to 97%.  Whilst an increase in PhytOC yields of this magnitude would be likely to have only a relatively small effect on sugar yield, it would greatly increase long term soil carbon sequestration rates. The management of vegetation for enhanced PhytOC carbon sequestration would complement other land management practices for enhancing terrestrial carbon sequestration such as improved cropland management, improved grassland management, and improved forestry management, at negligible expense to the existing yields and productivity of those crops, pastures, or forests.

References list

1 J. F. Parr, L.A. Sullivan,  Soil Biol. Biochem. 37, 117 (2005).

2Post, W. M., K.C., Kwon, Glob. Change Biol. 6, 317 (2000).

3Skjemstad, J. O., P. Clarke, J.A. Taylor, J. M. Oades, S.G. McClure, Aust. J. Soil Res. 34, 251 (1996).

4Nable, R.O., J.G. Paull, B. Cartwright, Ann. Bot. 66, 83 1990.

5Post, W.M., R.C. Izaurralde, J.D. Jastrow, B.A. McCarl, J.E. Amonette, V.L. Bailey, P.M. Jardine, T.O. West, J. Zhou, BioScience 54, 895 (2004).

6Schlesinger, W.H., Nature 348, 232 (1990).