Nitrogen is the most common element in the atmosphere. It is essential for plants to grow, so many gardeners add fertilisers to the soil or grow nitrogen fixing plants nearby.
Why is nitrogen important?
Nitrogen deficient plants are small and slow developers. They do not have the nitrogen needed to create the necessary genetic and structural materials to grow properly, which could limit the amount of carbon sequestered.
Tropical forests are important carbon sinks and can reduce the impact of climate change by removing carbon. However, scientists believe a shortage of nitrogen in the soil is affecting tropical forests around the world, with 0.69 billion tonnes of carbon dioxide (CO2) failing to be stored. This is the equivalent of two years of CO2 and other greenhouse gas emissions from the UK.
Researchers, led by scientists from the University of Leeds, published a study that shows the importance of nitrogen in tropical forests. They provide evidence that forests can rebound up to twice as fast after deforestation when their soils contain enough nitrogen.
The scientists chose over 76 different plots around Central America and monitored them for 20 years. They tested the role of nutrients by treating these plots differently. They fertilised some plots with nitrogen, others with phosphorus, and some with both. The scientists did not fertilise the remaining plots.
During the first 10 years, forests with more nitrogen in the soil rebounded at twice the rate than the other plots. These results are important because, according to lead author Wenguang Tang, ‘It suggests there are ways we can boost the capture and storage of greenhouse gases through reforestation by managing the nutrients available to trees.’
However, the scientists do not recommend fertilising forests, as fertilisers can have harmful side effects for the environment. This include nitrous oxide emissions. Instead, the researchers suggest restoring forests in areas that have enough nitrogen due to air pollution or planting nitrogen fixing trees.
What is nitrogen fixing?
Nitrogen fixing involves establishing other plants to add more nitrogen to the soil. These plants have bacteria living in root nodules that transfers nitrogen from the atmosphere to the soil. The nitrogen can then be taken up by other plants. Levels of nutrients in the soil, such as nitrogen, can affect a forests’ ability to effectively capture and store carbon.
There are numerous plants that can help introduce more nitrogen into soil naturally, such as gorse and alder. The researchers suggest planting trees from the legume family to help revitalise the soil, as legumes are nitrogen fixing plants.
