Case Studies

Fertilisers can make plants weaker, sicker

On top of causing soil damage and environmental problems from run-off, nitrogen-based fertilisers have now been shown to reduce a plant community’s resistance to fungal diseases.

Researchers warn that prolonged use of artificial fertilisers can lead to the extinction of the most resistant plant species in a community, meaning that the remaining species are in fact more susceptible to diseases.

In experimental field trials, the China-Australia research tested the biodiversity resilience of an isolated plant community in a native alpine meadow situated 3500m altitude in the Qinghai-Tibetan Plateau.

“In this diverse and pristine ecosystem, we have established that extended fertilisation of soils not only alters the structure of natural plant communities, it also exacerbates pathogen emergence and transmission,” the researchers from Fudan University in Shanghai and Flinders University in Adelaide conclude.

The 20-hectare experimental meadow, which has been spared from yak grazing now for 20 years, contains a rich and diverse plant community.

Professor Corey Bradshaw, Matthew Flinders Fellow in Global Ecology at Flinders University, says that this is one of the ways in which monocultures common in food cropping succumb to sudden outbreaks of severe disease.

“Our research from last year (2016) showed conclusively that having more species in an ecosystem provides a sort of insurance policy against disease for any given species, because of what’s known as the ‘dilution effect’,” Professor Bradshaw says.

“This means that when there are a lot of species in any given area, the chance of passing a disease pathogen from an infected individual to a neighbour of the same species is lower, so the entire community benefits from an overall lower prevalence and severity of diseases.”

The project’s leader, Professor Shurong Zhou of Fudan University, says the latest research published today found one of the main mechanisms of this disease-dilution effect.

“Adding fertilisers makes certain species outcompete others, leaving the overall biodiversity of a system lower and more susceptible to disease,” Professor Zhou says.

“In other words, while some species benefit from adding nitrogen, the overall effect at the community level could be worse because the surviving species end up being more diseased.”

Professor Bradshaw adds: “These experiments provide powerful information about how species diversity maintains ecosystem function, and how agriculture and other human interventions can accelerate ecosystem degradation.”

Source: Flinders University