Two plants commonly found in the northern region of Brazil - duckweed and "pasture killer" - have high potential to be used as a raw material for the production of bioenergy, indicate studies by researchers from the National Institute of Science and Bioethanol Technology - one of the INCTs supported by FAPESP and the National Council for Scientific and Technological Development (CNPq) in the State of São Paulo.

Laboratory tests revealed that the production of simple sugars by duckweed after the plant's biomass was subjected to a process called saccharification was greater than that of sugarcane, the main raw material for second generation ethanol today. The pasture forest grows very fast and may be a viable option for the production of bioelectricity in the Amazon region by burning the plant's biomass, without causing deforestation, the researchers evaluate.

The results of the studies were published in the journal Bioenergy Research.

"The "pasture killer" and duckweed could complement or be alternatives to sugar cane for the production of bioenergy", says Marcos Silveira Buckeridge, director of the INCT for Bioethanol and project coordinator to FAPESP Agency.

The researchers evaluated the composition and the potential for saccharification of the biomass of the two plants for the production of bioenergy. The results of the analyzes of five species of duckweed - Spirodela polyrhiza, Landoltia punctata, Lemna gibba, Wolffiella caudata and Wolffia borealis - revealed that three monosaccharides - glucose, galactose and xylose - constitute 51.4% of the plant cell wall .

The results also indicated that the duckweed biomass has low resistance to hydrolysis or saccharification. In this process, the lignocellulosic biomass is placed in contact with an enzymatic cocktail in order to transform the complex sugars present in the plant cell wall into simple sugars, which can be fermented by the yeasts to obtain second generation ethanol.

"Duckweed showed low resistance to hydrolysis, probably because it has almost no lignin", evaluates Buckeridge. Lignin is a macromolecule that, associated with hemicellulose and cellulose in the cell wall, has the function of providing rigidity, impermeability and resistance to biological and mechanical attacks on plant tissues.

The results of the analysis of the "pasture killer" (Senna reticulata species) revealed that almost 50% of the biomass of the leaves and stem of the plant is composed of pectins, hemicelluloses and cellulose. Lignin varied considerably between the organs of the plant, being more present in the roots (35%), leaves (10%) and stem (7%).

"When we analyzed the entire biomass of the plant we saw that it has an enormous amount of starch in the leaves, much greater than we have already found in other plants", compares Buckeridge.

The researchers also evaluated the effect of increased carbon dioxide (CO2) in the atmosphere on the composition of the biomass in the pasture. The results indicated that, although it did not significantly change the lignin composition in the cell wall, the high CO2 reduced the proportion of the macromolecule in the leaves and roots of the plant. In addition, the starch concentration in the leaves increased 31% and the saccharification of the plant's biomass improved by 47%.

"The pasture killer develops very well under high temperatures. That is why it is an interesting option for generating bioelectricity by burning the plant's biomass, especially in the northern region of the country," says Buckeridge.

Duckweed, in turn, also grows in all regions of the world. In addition to being an option for producing second generation ethanol - because it is easier to hydrolyze than sugarcane - the plant also serves to clean water, says the researcher.

"Another advantage of duckweed in relation to other crops that have been studied for the production of bioenergy is that it does not need land to be cultivated. Therefore, it does not compete with food production", says Buckeridge.

The article Senna reticulata: a viable option for bioenergy production in the Amazonian region (DOI: 10.1007 / s12155-020-10176-x), by Adriana Grandis, Bruna C. Arenque-Musa, Marina CM Martins, Thais Olivar Maciel, Rachael Simister , Leonardo D. Gómez and Marcos S. Buckeridge, can be read in the journal Bioenergy Research at https://link.springer.com/article/10.1007/s12155-020-10176-x.

And the article High saccharification, low lignin, and high sustainability potential make duckweeds adequate as bioenergy feedstocks (DOI: 10.1007 / s12155-020-10211-x), by Débora Pagliuso, Adriana Grandis, Eric Lam and Marcos S. Buckeridge, can be read in the same magazine at https://link.springer.com/article/10.1007/s12155-020-10211-x ..