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Danforth attempts to improve water efficiency of bioenergy crop

© Shutterstock / Murilo MazzoSorghum growing against a blue sky.

Dr Ivan Baxter, principal investigator at the Donald Danforth Plant Science Center, is to lead a $16 million research programme to improve the water efficiency of sorghum, a widespread crop that has been championed as a source of sustainable bioenergy. 

  • The project, which has been funded by the US Department of Energy (DoE), will combine several engineering techniques to improve the water efficiency of sorghum cultivation. 
  • Agricultural crops account for around 70% of the world’s freshwater withdrawals, but the sector is struggling to access resources due to external factors such as climate change.
  • Sorghum has been proposed as a more sustainable source of bioenergy, but its inefficient use of water remains a challenge.

Baxter will lead a team of researchers from multiple institutions, including Stanford University, Washington State University and the Carnegie Institution for Science, in combining multiple engineering techniques to better understand sorghum’s water efficiency. The five-year project has been funded by the US Department of Energy’s Biosystems Design to Enable Safe Production of Next-Generation Biofuels, Bioproducts and Biomaterials programme, with a budget of $16 million. 

Improving the water efficiency of sorghum cultivation 

The researchers will begin their work by identifying the main limitations to sorghum’s water efficiency in three focus areas. These include the volume of water that can be acquired by the crop’s roots, the amount that is evaporated from its pores and the productivity of its photosynthetic carbon assimilation. 

By combining genetics, genomics and bioinformatics, they believe that they can pick out the specific genes that control each of these systems. With this information in hand, they plan to combine various biological engineering techniques – collectively referred to as synthetic biology – to control when each of these genes is activated. If successful, this will allow them to express beneficial genes while shutting down those that result in inefficiencies. 

Each new method that is developed will be trialled with both sorghum and a closely related plant known as Setaria viridis. Although it does not share sorghum’s exact genetics, the Setaria viridis will serve as an appropriately similar species for modelling each method as its faster growth cycle will enable a rapid testing process.

As Baxter explained: “Combining ‘design-build-test-learn’ cycles with parallel studies of model and crop species will enable rapid experimental iterations, leading to faster and substantial water use efficiency improvements in bioenergy feedstocks.” 

Freshwater scarcity threatens global agriculture 

Water is a vital resource for the growth of any crop, but changing weather patterns are severely reducing the availability and reliability of its supply. Rising temperatures are causing soil water content to fall below its natural levels, while simultaneously depleting the reservoirs that would typically serve to provide supplementary irrigation. 

Currently, agriculture accounts for around 70% of global freshwater withdrawals, with irrigated crops representing 20% of all cultivated land. The acceleration of climate change, combined with ongoing trends in population growth and urbanisation, is increasingly placing the sector’s water consumption under pressure as it is forced to compete with other uses. 

According to the World Bank, up to 40% of the water that is currently consumed by agricultural crops will have to be reallocated to other activities. Given that water scarcity is predicted to worsen across 80% of global croplands by 2100, such re-allocation presents a major challenge. 

Can sorghum provide a sustainable source of bioenergy? 

With rising concerns that we may be on the brink of a worldwide hunger crisis, the use of scarce water resources to produce bioenergy crops rather than food supplies has been subject to controversy.  

On the one hand, biomass is seen as an abundant and cost-effective resource that can be used to produce electricity as well as liquid, gaseous and solid fuels. Its proponents argue that the carbon sequestered during plant growth means that the emissions of biomass combustion are fully offset, making it a vital resource for delivering the global transition to net zero. 

Biomass critics, meanwhile, note that different feedstocks vary significantly in their decarbonisation potential. The use of woody biomass, for example, has been linked to deforestation, biodiversity loss, air pollution and reductions in carbon sequestration capacity. 

The International Energy Agency (IEA), for its part, has acknowledged that bioenergy is likely to be a considerable contributor to the net zero strategies of governments around the world. It warned that such strategies must not have a negative impact on biodiversity, freshwater systems, food security or quality of life. Ultimately, the IEA’s conclusion is that bioenergy can only be justified in cases where it effectively reduces lifecycle greenhouse gas emissions while avoiding unacceptable social, environmental or economic impacts. 

Sorghum has been identified as a potential candidate for meeting these conditions. It grows in annual cycles, meaning that its carbon reabsorption can be achieved far more quickly than when waiting for trees to grow. Its deep root system enables it to sequester more carbon than most plant species, and it can be grown on marginal or degraded land to avoid the displacement of vital food crops. Furthermore, sorghum has shown particular resilience to the drought conditions and extreme temperatures that are occurring more frequently as the climate changes. 

Selective breeding and improvements in agronomy have enabled researchers to increase sorghum yields, but the amount of biomass it can produce with a given amount of water has remained constant. This inefficient use of water is considered the main hurdle to sorghum’s use as a sustainable source of bioenergy, hence the focus of Baxter’s research. 

“To be economically viable and have environmental benefits, crops used for bioenergy production need to be grown where the supply of water is insufficient or too inconsistent to support production of traditional food crops”, he said, indicating his awareness of the strict criteria that must be met, if bioenergy is ever to provide a truly sustainable resource. 

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