Microbes could be a basis for the development of natural biological substitutes for the chemical fertilisers used by farmers on poor soils

A study supported by FAPESP has identified 522 genomes of archaea and bacteria associated with the roots and soil of two plant species native to the Brazilian montane savanna ecoregion known as campos rupestres (‘rocky meadows’).

Hundreds of micro-organisms hitherto unknown to science were identified, showing that the ecoregion is a natural biodiversity hotspot and that many new organisms have yet to be described and classified in Brazil.

The discovery could potentially be a basis for the development of natural biological substitutes for the chemical fertilisers used by farmers, especially those containing phosphorus.

First author of the article, Antônio Camargo, who conducted the study during his PhD research with a scholarship from FAPESP at the State University of Campinas’s Institute of Biology (IB-UNICAMP) in São Paulo state, said: “Phosphorus is normally present in the soil, but not always in a form that plants can use.

“Most of the micro-organisms we found make phosphorus soluble so that plants can absorb it.”

One of the plants, Vellozia epidendroides, lives in shallow soil, whereas another, Barbacenia macranta, was found growing on exposed rock. Both belong to the family Velloziacea. Specimens were collected in a private area adjacent to the Serra do Cipó National Park in Minas Gerais state.

A comparison of micro-organisms associated with plants found growing in soil and on rocks showed that they comprised different communities but shared many species. Several micro-organisms were highly specialised in phosphorus transport and conversion to the soluble form of the mineral, which plants can absorb.

Camargo, currently a researcher at the US Department of Energy’s Joint Genome Institute, where the genomes were sequenced, added: “Microbial communities also play an important role in supplying nitrogen, another essential plant nutrient.”

See also: Better soil health for less grazed pastures

phosphate fertiliser

Rafael Soares Correa de Souza, a corresponding author of the article, said: “Previous research focused on plants’ mechanisms for adapting to the harsh conditions of this montane savanna and often ignored micro-organisms.

“Our study shows that micro-organisms can play a key role in plant adaptation to the extreme conditions of this environment.

“In particular, they supply the phosphorus needed to fuel plant growth.”

The researchers expect their discoveries to contribute to the creation of products that replace chemical fertilisers based on phosphorus, one of the crop nutrients most widely used by Brazilian farmers.

More than half the phosphate fertiliser used in Brazil is imported, mainly from Morrocco but also from Russia, Egypt, China and the United States.

In addition to the dependence on imports, phosphate fertiliser pollutes water bodies, and its production is a source of greenhouse gas emissions, estimated at 1kg for every kilogram of fertiliser produced. Moreover, phosphorus is a non-renewable natural resource and hence finite.

the need for nature conservation

Biological fertilisers are already in use in Brazil. In the case of soybeans, they are the main source of nitrogen in 80% of the planted area.

A previous study estimated that the use of biological inoculants instead of nitrogen fertilisers could save USD10bn (~£8.12bn) per year.

Souza, a co-founder of biotech startup Symbionics, which develops next-generation biologics, said: “The study also underscores the need for conservation of Brazil’s ecosystems, which can supply many other Nature-based solutions like this one.”

As noted, campos rupestres are biodiversity hotspots with many exclusive species. They form mosaics totalling some 26,500km2 scattered across Brazil in biomes such as the Cerrado (savanna), Caatinga (semi-arid areas in the northeast) and Atlantic Rainforest. The main threats to these ecosystems are mining and cattle raising.

The researchers are now conducting studies to test the benefits of some of the micro-organisms found in croplands.

The study is published in ISME Journal.

A hammer and chisel were required to collect samples from the terrain where Barbacenia macranta lives, in this case, exposed rock. © Rafael Soares Correa de Souza/ GCCRC.