Research PR showcase! Vol.1: Enhancement of soil water retention

IRCAEB Director, Shinichiro Sawa

IROAST director Shinichiro Sawa is a researcher who utilizes Arabidopsis (known as a model plant for scientists) to conduct various research. In order to perform more practical and societally-relevant works, since moving his laboratory to Kumamoto University Prof. Sawa studies the prominent agricultural pest root-knot nematodes. Even though these nematodes infect many plant species, tomato plants are used in the laboratory to identify compounds secreted by the roots that attract and repel nematodes.

Grant-in-Aid for Scientific Research on Innovative Areas 2012-2017 “Information processing system of plant cell wall” Sawa laboratory research panel. Direction: Mitsuko Kudo, illustration: Hiroko Uchida.

With the recent founding of IRCAEB, our research activities have shifted to focus more on local collaborations and practical utilities. Have you heard of the newly published research by Prof. Shinya Hayami? Prof. Hayami is an expert in synthesizing very thin sheets of graphene oxide. Even though graphene oxide may sound very exotic, it is in fact modified from graphite found in pencil lead (which is mostly carbon and actually does not contain lead). Graphene is made from horizontally-bonded carbon layers, each only 1 atom thick. When these carbons are conjugated with –OH hydroxyl groups it is converted to graphene oxide.

The thickness of graphene oxide sheets is about 1 nano meter (10-9 meter), the lengths is about 1~10 milli meters, superficially it actually resembles powder more so than sheets. Graphene oxide is an excellent material known to be highly absorbent and is an electric insulator.

Above: Points of line intersections represent carbon atoms, which are omitted for brevity.

Graphene oxide is highly absorbent, and has even been reported to adsorb COVID-19 virus in a previous press release. Our experiment begins to explore the utility of graphene oxide’s absorbent property in agriculture.

Tomato seedlings were grown in 2 different types of soil, including regular soil and soil mixed with graphene oxide at the ratio of 0.1 mg per 1 L of soil. Experiments were conducted to test whether the water absorbent property of graphene oxide can enhance the soil water retention, and help plants to survive droughts. Tomato seedlings were grown in both soil types and watered normally for 14 days. Watering was stopped at day 15, and the tomato seedlings were observed over time to see if they tolerate draught stress. This rough preliminary experiment was conducted to test whether graphene oxide has the potential to be utilized as a soil additive in agriculture, and graphene oxide performed surprisingly well in protecting tomato seedlings against draught.

Right panel: Plants grown in soil mixed with graphene oxide showed extraordinary tolerance against draught.

It is easy to conceive that with such high water-retentive soil it may be possible to grow crop plants in arid area. However, in reality this is trickier than one would think. For example, polymers used in diapers are also highly absorbent, but they are so efficient that they do not release the absorbed water easily. When placed near plant roots, these polymers will likely pull water out from plants instead, making them not very useful in agriculture. On the other hand, it has been hypothesized that the water retention capacity of graphene oxide is gentle enough that plants may absorb the water off from it. Sprinkling charcoal in fields is a common practice in traditional agriculture. Since graphene oxide is essentially charoal, perhaps the benefits of charcoal in crop growth has been recognized longer than we thought. But just how exactly does charcoal help plant growth? IRCAEB strives to delineate these mechanisms, and expand upon them to enhance the soil properties in arid environments. We aim to improve the soil quality with safe and reliable materials, and continue to seek out conditions to effectively utilize graphene oxides for various environments and crop plants.

Above: It is thought that the –OH hydroxyl functional groups on graphene oxide help trap water molecules.

Graphene oxide may have other applications as well, for example it has been shown to adsorb and kill Covid-19 virus. Even though its precise anti-viral mechanisms remain unclear, currently face masks made from unwoven fabric coated with graphene oxide are being developed. This may become a more efficient personal protection equipment to help curb the Covid-19 pandemic. Similarly, whether graphene oxide can adsorb and kill plant-pathogenic fungi, thereby potentially be used to combat plant diseases are currently being explored.

IRCAEB hopes to understand how plants respond to charcoals traditionally used in agriculture and gardening, by standardize the atomic structure through the synthesis of graphene oxide. Field tests will be essential for accomplish these goals, and we hope to continue developing this technology with local farmers and growers in the Kumamoto prefecture.

Above: Graphene oxide suspension in water, its effects on plants remains to be explored.