High levels of pollution are common in many cities in the world. A new study published on 9 November in Nature Communications has revealed the extent to which pollution is negatively affecting plant and animals populations (1). The findings allude to just some of the negative effects man-made pollution is having on ecosystems.
Reactive nitrogen compounds disrupt plant communities through soil deposition, however, the negative consequences may extend to higher trophic levels ― higher ranks in the food chain. The study, led by Dr Stuart Campbell from the Department of Animal and Plant Sciences of the University of Sheffield, suggests that plant-eating insects could influence the ability of leaves to absorb reactive nitrogen and act as a sink for atmospheric pollutants from human activity like smog.
In the past 50 years, there has been a 3-fold increase in the release of reactive nitrogen compounds, such as nitrogen oxides (NOx), into the atmosphere. In particular, nitrogen dioxide (NO2) is a dangerous pollutant known to cause severe health problems in humans but may also be having a cascading effect on plants and insects. In this way, reactive nitrogen compounds pose a significant threat to biodiversity. A number of studies have demonstrated a widespread decline in plant diversity owing to reactive nitrogen deposition in soils which alters soil chemistry.
Pollutants deposited in the soil are taken up by plants through their roots or absorbed directly from the atmosphere by their leaves. According to the study, leaves of plants exposed to increased levels of NO2 pollution ― similar to the levels measured in major cities ― produce more defensive chemicals, called “defensive metabolites.” Moreover, for the first time, the researchers have shown that insects feeding on these leaves demonstrate poor growth.
The team also looked at whether insects can influence the ability of plants to absorb NO2 from the environment. The authors suggest insects could be affecting the amount of pollution removed from the air by urban green spaces since the plants fed on by insects were found to absorb much less NO2. Furthermore, the ability of urban trees to absorb gaseous pollutants like NO2 seems to vary between species and locations, which could also be partly influenced by the behaviour of these leaf-feeding insects.
Insects are an important part of many ecosystems. They cycle nutrients, pollinate plants, disperse seeds, help maintain soil structure and fertility. In addition, many arthropods provide a major food source for numerous amphibians, reptiles, birds, mammals, as well as other insects. Therefore, the massive decline in insect populations is incredibly worrying and poses an enormous threat to the natural world and food sources.
This work is yet another example of the devastating effects that human-made pollutants from sources like combustion, construction, mining, and agriculture are having on the environment. A unified global effort is urgently needed to tackle these problems.
(1) Campbell, S.A. and Vallano., D.M. Plant defences mediate interactions between herbivory and the direct foliar uptake of atmospheric reactive nitrogen. Nature Communications (2018). DOI: 10.1038/s41467-018-07134-9