When it rains

The desert is normally a very dry place, which makes life in the soil very difficult. Recently we've had a LOT of rain during the monsoon season. This was the 2nd wettest September in Phoenix's history! What does this mean for the organisms living in the soil in the desert? What happens in the soil after it rains?

Chelsey samples the soil crust beneath a creosote.

Most of the rain we get in the Sonoran Desert is in small amounts. Even small rains can make a difference. The microscopic organisms in the soil, particularly the bacteria and fungi, will get active after a sprinkle. Most plants require bigger rains, though. That means that the soil crusts I mentioned in my last post can "wake up" quickly after even a small rain to begin photosynthesizing and respiring, but plants like the creosote in the picture here may not.

Soil microorganisms are responsible for a lot of important processes in the soil. They respire carbon dioxide into the atmosphere, they help recycling nitrogen and phosphorus for plants. If soil microorganisms respond to rain quickly, then so will carbon, nitrogen, and phosphorus cycling. After a rainfall, carbon dioxide release from the soil increases. Microbes take up and release nitrogen more quickly, and nitrogen compounds can be washed away with the water. So rain can make a lot of things happen in the soil!

The predictions for the Sonoran Desert is that climate change will cause the area to become dryer, with larger rain events that will happen more sporadically, delivering less rain overall. This has led many scientists to ask how the Sonoran Desert ecosystem will change in the future. If rain events have this big of an effect, how will the ecosystem respond to changes in the amount and frequency of rainfall?

Kelly uses a watering can to simulate rainfall.

A lot of research has investigated how the plants of desert communities respond to these changes. There may be changes in the amount plants are able to grow, as well as changes in the species that are able to survive. Much less is known about how the microscopic organisms in the soil will respond.

Some of our research investigates how the soil community changes when the timing and amount of precipitation changes. We use watering cans to make "fake" rainfall events that happen in different amounts and at different frequencies, and then look at how the invertebrates living in the soil respond. We will be able to help answer these questions to predict the future for soil communities in the Sonoran Desert.