October 03, 2010

Genetically altered plants, algae and trees could sequester carbon

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BioScience journal invited several scientists with relevant expertise to contribute to this issue's Special Section on biological carbon sequestration.

Our authors have a range of perspectives on the topic. They include some (Christer Jansson and colleagues, and Steven H. Strauss and his coauthors) who are pursuing the prospects for genetically engineered trees that might one day contribute to amelioration of global warming—if they can meet safety requirements for testing. Richard Sayre outlines the possibilities for cultivating algae as biofuel feedstock. Others (Robert B. Jackson and Justin S. Baker, and Rattan Lal) analyze the big-picture ecological and economic constraints on expanding sequestration in forests and in soil generally through agriculture. Emily Boyd discusses societal understanding of the choices that large-scale enhanced biological carbon sequestration would necessarily bring, and considers how they could play into economic development.

Genetically Altered Trees and Plants Could Help Counter Global Warming Forests of genetically altered trees and other plants could sequester several billion tons of carbon from the atmosphere each year and so help ameliorate global warming. Researchers at Lawrence Berkeley National Laboratory and Oak Ridge National Laboratory, outlines a variety of strategies for augmenting the processes that plants use to sequester carbon dioxide from the air and convert it into long-lived forms of carbon, first in vegetation and ultimately in soil. Besides increasing the efficiency of plants' absorption of light, researchers might be able to genetically alter plants so they send more carbon into their roots—where some may be converted into soil carbon and remain out of circulation for centuries. Other possibilities include altering plants so that they can better withstand the stresses of growing on marginal land, and so that they yield improved bioenergy and food crops.

Photosynthetic assimilation of atmospheric carbon dioxide by land plants offers the underpinnings for terrestrial carbon (C) sequestration. A proportion of the C captured in plant biomass is partitioned to roots, where it enters the pools of soil organic C and soil inorganic C and can be sequestered for millennia. Bioenergy crops serve the dual role of providing biofuel that offsets fossil-fuel greenhouse gas (GHG) emissions and sequestering C in the soil through extensive root systems. Carbon captured in plant biomass can also contribute to C sequestration through the deliberate addition of biochar to soil, wood burial, or the use of durable plant products. Increasing our understanding of plant, microbial, and soil biology, and harnessing the benefits of traditional genetics and genetic engineering, will help us fully realize the GHG mitigation potential of phytosequestration.

The complete list of peer-reviewed articles in the October 2010 issue of BioScience is as follows:

Phytosequestration: Carbon Biosequestration by Plants and the Prospects of Genetic Engineering
Christer Jansson, Stan D. Wullschleger, Udaya C. Kalluri, and Gerald A. Tuskan

Opportunities and Constraints for Forest Climate Mitigation
Robert B. Jackson and Justin S. Baker

Managing Soils and Ecosystems for Mitigating Anthropogenic Carbon Emissions and Advancing Global Food Security
Rattan Lal

Microalgae: The Potential for Carbon Capture
Richard Sayre

Far-reaching Deleterious Impacts of Regulations on Research and Environmental Studies of Recombinant DNA-modified Perennial Biofuel Crops in the United States
Steven H. Strauss, Drew L. Kershen, Joe H. Bouton, Thomas P. Redick, Huimin Tan, and Roger A. Sedjo

Societal Choice for Climate Change Futures: Trees, Biotechnology, and Clean Development
Emily Boyd

Time Horizons and Extinction Risk in Endangered Species Categorization Systems
Jesse D'Elia and Scott McCarthy

The total C stock (i.e., organic and inorganic C) in terrestrial systems is estimated to be around 3170 gigatons (GT; 1 GT 5 1 petagram 5 1 billion metric tons )—2500 GT in the soil and 560 GT and 110 GT in plant and microbial biomass, respectively. Total C in the oceans is 38,000 GT . The soil C pool, which is 3.3 times the size of the atmospheric C pool of 760 GT, includes about 1550 GT of soil organic carbon (SOC) and 950 GT of soil inorganic carbon (SIC) (Lal 2004, 2008a). Of the C present in the world’s biota,99.9% is contributed by vegetation and microbial biomass; animals constitute a negligible C reservoir. The annual fluxes of C between the atmosphere and land, and atmosphere and oceans, are 123 and 92 GT, respectively. Therefore, 123 GT represents the photosynthetic C uptake, or the gross primary productivity (GPP), of the global terrestrial system. Approximately 60 GT of the GPP captured by plants through photosynthesis is returned to the atmosphere almost immediately through plant respiration. The remaining amount is the net primary productivity (NPP).

Microalgae: The Potential for Carbon Capture

There is growing recognition that microalgae are among the most productive biological systems for generating biomass and capturing carbon. Further efficiencies are gained by harvesting 100% of the biomass, much more than is possible in terrestrial biomass production systems. Micro-algae's ability to transport bicarbonate into cells makes them well suited to capture carbon. Carbon dioxide— or bicarbonate-capturing efficiencies as high as 90% have been reported in open ponds. The scale of microalgal production facilities necessary to capture carbon-dioxide (CO2) emissions from stationary point sources such as power stations and cement kilns is also manageable; thus, microalgae can potentially be exploited for CO2 capture and sequestration. In this article, I discuss possible strategies using microalgae to sequester CO2 with reduced environmental consequences.

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