Root bacteria help reduce the environmental impact of rice cultivation

A Japanese study has identified some bacteria in rice roots that are responsible for nitrogen fixation and can spread in soil without fertilizers or pesticides. This helps the plant adapt and grow

by Matteo Cavallito

Rice is the staple food for more than a half  of the world’s population. Therefore, supporting rice yields makes a key contribution to global food security. Factors such as pesticides and chemical fertilizers are known to provide concrete help in this regard, but they also have clear environmental impacts. For these reasons, identifying hidden or underestimated natural resources that can positively impact the growth of these plants means opening up new prospects for sustainable and highly productive agriculture.

This is claimed, among others, by some Japanese scientists. In a study published in the journal Plant and Cell Physiology, in fact, they showed how rice plant that are grown without chemical input use the microbial communities associated with their roots to adapt to nutrient-poor soils.

Microbes help plants adapt to the soil

“Plants accommodate diverse microbial communities, termed the microbiome, which can change dynamically during plant adaptation to varying environmental conditions,” according to a study conducted by researchers at the Nara Institute of Science and Technology in collaboration with the University of Tokyo, the Tokyo Institute of Technology, Nagoya University, and Tohoku University.

“However, the direction of these changes and the underlying mechanisms driving them, particularly in crops adapting to the field conditions, are not well understood.”

To better understand these dynamics, the authors sequenced a specific gene in the plant and analyzed it using an artificial intelligence-based machine learning algorithm. In this way, they identified the presence of bacterial groups constantly enriched with nitrogen in an agricultural field not treated with fertilizers or pesticides. The microorganisms observed, they explained, were found to be crucial in ensuring high yields.

Nitrogen fixers proliferate in untreated fields

The study was conducted on particularly productive land that had been free of chemical inputs for over 70 years but nevertheless managed to achieve 60–70% of the yield measured in similar conventionallly managed fields. By monitoring the root microbiome for four growing seasons and comparing it with a nearby field treated with fertilizers, they observed a steady increase in nitrogen-fixing bacteria. These bacteria, they explain in a statement, seem to play a crucial role in providing nitrogen to plants without synthetic fertilizers.

Metagenomic analysis confirmed that the genes responsible for nitrogen fixation were significantly morabundant in the roots of plants grown in the unfertilized field.

The study also showed that the composition of these nitrogen-fixing communities changes depending on the different stages of growth. In the early vegetative stages, in particular, anaerobic bacteria are predominant, but as the plant matures, they give way to microaerophiles and aerobes. These changes appear to be a response to seasonal variations in soil oxygen and agricultural practices such as water drainage.

The goal: a more sustainable rice cultivation

The researchers conclude that the results of the study “provide valuable insights into the assembly of the rice root microbiome in nutrient-poor soil, which can aid in managing microbial homeostasis for sustainable agriculture.” This is an important milestone, especially in a scenario of climate changthat is impacting the quality of rice crops in Asia.

Understanding how rice maintains productivity with the support of microbes, in particular, help develop new strategies in precision agriculture. These include assessing the suitability of fields, monitoring the nutritional status of plants, and optimizing the use of fertilizers. But also, according to researchers, developing soil biostimulants, or specific microbial communities to promote crop yields.