Can moss help remove nitrogen pollution from the soil?

A while ago, I told you about soil biological crusts, and how they are an important part of nutrient cycling in deserts. One of the main parts of crusts that I'm interested in is moss.

Soil biotic crust dominated by moss (the green fuzzy stuff)

Moss is really neat, because it can tolerate the very harsh conditions that are common in the desert. They can survive being desiccated (almost completely dried out), extreme heat, and freezing. As soon as conditions improve, they perk right up! That means that when it rains, moss can quickly "wake up" and start exchanging nutrients with the soil and water. (You can see how quickly dry moss "wakes up" after I add water in the video below.) Other, larger plants are not able to respond to rain quite so quickly.

Here in Arizona's Sonoran Desert around Phoenix, we receive a fair amount of nitrogen from air pollution. That means that soil inside the city of Phoenix has more nitrogen than soil outside the city. A lot of our research tries to understand what happens to that nitrogen that's deposited by air pollution. Nitrogen can fertilize plants (which is why you might put it on your yard or garden), but too much of it can cause a problem, both for human health and for the ecosystem's health!

I was curious whether moss might be able to take up some of that extra nitrogen from pollution. Because it can "wake up" so quickly after rain, we wanted to know whether moss can take up some of that nitrogen, even if larger plants can't!

To answer our question, we sampled moss, and the soil beneath it, from different places in and around Phoenix. We sampled from both inside the city (where nitrogen pollution is a bigger problem) and rural areas to the east and west of Phoenix (where nitrogen pollution is less of a problem).

Undergraduate research student, Jessica, sampling moss.

We measured the amount of nitrogen in the moss and soil, so that we could learn whether moss takes up the extra nitrogen when it's in the soil. If moss nitrogen is higher where soil nitrogen is higher inside the city from pollution, it would suggest that moss is taking up the extra nitrogen in the soil. If moss nitrogen is the same across all of the sites, regardless of the amount of soil nitrogen, it would suggest that moss is not able to take up the extra nitrogen.


What did we learn? In our samples, there was more nitrogen in the soil inside the city of Phoenix (as expected), and the moss growing on that soil was also higher in nitrogen. That suggests that moss can take up nitrogen from pollution.

Moss nitrogen increases as soil nitrogen increases. The extra nitrogen inside the city of Phoenix ("core") compared to rural areas to the east and west is probably from nitrogen pollution.

However, moss is much less abundant inside the city where N pollution is a problem. Moss are sensitive to pollution and human disturbance, so they have a more difficult time surviving inside the city.

Moss is less abundant inside the city of Phoenix ("core") compared to the rural areas to the west and east.

So what does all of this mean? Moss can take up extra nitrogen from pollution, but because there is less moss where the pollution occurs, they aren't going to solve the problem. We need to help preserve the fragile moss crusts in order for them to help deal with the nitrogen pollution!

The results of this experiment are published in the article: Ball, B. and Alvarez Guevara, J. The nutrient plasticity of moss-dominated crust in the urbanized Sonoran Desert. Plant and Soil.