The worldwide system of nitrogen

Systems thinking is a way of looking at things that recognizes the importance of interactions between parts. It is often contrasted with reductionism where the assumption is if we learn about the parts we can put the parts together to understand the whole. The study I found today is a clear example of why we need more systems thinking.

Zheng and colleagues (2025) did a meta analysis of 30 years worth of studies from across the globe. What they found is that climate change is changing the nitrogen cycle in significant ways. And, there are multiple effects. Let’s start with why this matters. Nitrogen is essential for plant growth, but excess nitrogen can result in algal blooms which can be toxic.

Higher levels of carbon dioxide result in higher growth rates. However, plants actually end up diluting their nitrogen content when they are growing with high levels of CO2. This means that if there is high CO2 and the plants are growing faster, they do not take up more nitrogen as a result. Since nitrogen is part of making protein, the plants end up with lower levels of protein. This can then impact the nutritional quality of the plants, which has the potential to impact humans and other animals.

Rising temperatures are clearly problematic for nitrogen. Key crops like maize have reduced production in warmer temperatures. On the other hand, soil microbes, which breakdown nitrogen compounds, are more active in warmer temperatures. As a result there is increased air and water pollution because the nitrogen compounds like ammonia, nitrous oxides, and nitrates that the bacteria release end up in the air and water.

Too much rain, may increase plant growth, but it can also increase the activity of the soil microbes. So it can result in both increased nitrogen uptake and increased nitrogen breakdown. Too little rain, on the other hand, can reduce productivity and decrease soil microbe activity.

Clearly then, we need to look at nitrogen as part of a complex system. It is influenced by several different factors that all have nuanced impacts. Looking at any one part of the system runs the risk of missing impacts because they are masked by something else. But, this would certainly be a much more complicated diagram than the ones I remember learning.