Article Information: Kittredge, H.A., Cannone, T., Funk, J., and Chapman, S.K. (2018) Soil respiration and extracellular enzyme production respond differently across seasons to elevated tmerpatures. Plant and Soil 425 (1-2): 351-361. https://link.springer.com/article/10.1007/s11104-018-3591-z
Microscopic Organisms with a BIG role
Microbes play an important role in every ecosystem. Involved in almost every nutrient cycle, this large group of tiny organisms include bacteria, fungi, algae, and protozoa. You can find them everywhere: the soil, the air, on living things, you name it! Though very tiny, they are able to control how an entire ecosystem functions.
Soil microbes are an essential part of the carbon and nitrogen cycles, and can have a big impact on climate change. When organisms die, they get broken down by decomposers like bacteria and other small critters. As they do this, they respire (release) carbon dioxide (CO2) back into the atmosphere, in a process called decomposition. Warming global temperatures due to climate change could increase the rate of this process, which would release more CO2 into the atmosphere!
During decomposition, microbes also add nitrogen from dead plants and animals back into the soil. They produce ammonia (NH3), which goes through the nitrification process. When nitrification is not completed, nitrous oxide (N2O), could be released into the atmosphere. Both CO2 and N2O are potent greenhouse gases. Because these gases play such a big role in climate change, it’s important to understand how they might be further impacted by warming temperatures!
Carbon and Decomposition
There are two types of carbon that we need to know when talking about decomposition: labile and recalcitrant carbon. Labile carbon is broken down very quickly by microbes during decomposition, while recalcitrant carbon is broken down very slowly, and could take many years! The speed of recalcitrant carbon decomposition determines how much carbon is stored in an ecosystem. The more it’s broken down, the more carbon is released into the atmosphere at CO2!
Microbial decomposition in soils is done with the help of extracellular enzymes. Extracellular enzymes, exoenzymes for short, are released by cells and live outside of that cell to do their jobs. They help out with many different biological processes, including decomposition. In fact, exoenzymes catalyze (speed up) the first step in decomposition. There are certain enzymes that could tell us if labile or recalcitrant carbon is being broken down. Looking at these exoenzymes can tell us a lot about how ecosystems are responding to rising temperatures.
A team from Villanova University wanted to looked at how rising temperatures impacted soil microbes. To do this, they set up a warming experiment at Ridley Creek State Park, a temperate deciduous forest, just outside of Philadelphia, Pennsylvania, using passive warming chambers. Ridley Creek is unique, in that there are very high rates of nitrogen deposition, meaning that nitrogen is being added the the ecosystem. Because of the location of the park, it is possible that air pollution from Philadelphia is the cause of these high rates.
The experiment at Ridley Creek was set up for three and a half years; during that time, the researchers took soil samples and measured soil respiration rates across all seasons to see how warming impacted “temperature-sensitive” enzymes and soil respiration, keeping in mind the high levels of nitrogen in the ecosystem!
Enzymes Interactions are Tricky!
The study found that different seasons had different impacts on microbial activity! In the Fall and Winter, both soil respiration rates and the enzyme involved in decomposing recalcitrant carbon were lower than in expected in the warming chambers, though not changed in the Summer and Spring. Interestingly, this result was not expected due to the fact that higher temperatures are generally thought to increase soil respiration rates, and in turn, decomposition. After three and half years of warming, carbon storage was not impacted!
The results of the study show two things: 1) seasonal differences could play a big role in how enzymes respond to warming, and 2) microbes are tricky to understand. Though there was little change in enzyme activity related to decomposition, the enzyme involved in acquiring nitrogen was almost double, meaning that the high rates of nitrogen could have changed how the enzymes responded to warming!
The Take Home Message
The most important message here is how important microbes are for ecosystem processes. Though tiny, they can tell us a lot about how ecosystems might respond to change, and that it’s not all black and white. Different seasons and different factors can cause tricky interactions, impacting microbial activity!
Microbes are tiny organisms with a big role: regulating the different nutrient cycles that keep our ecosystems functioning. Though this study does not show a change in carbon storage at Ridley State Park, it shows us the need for more studies on how microbes respond to warming across different seasons, which would give us a better understanding of how carbon sinks might be impacted by climate change.
- Kittredge, H.A., Cannone, T., Funk, J., and Chapman, S.K. (2018) Soil respiration and extracellular enzyme production respond differently across seasons to elevated tmerpatures. Plant and Soil 425 (1-2): 351-361. https://link.springer.com/article/10.1007/s11104-018-3591-z
- Romero-Olivares AL, Allison SD, Treseder KK (2017) Decomposition of recalcitrant carbon under experimental warming in boreal forest. PLoS ONE 12(6): e0179674. https://doi.org/10.1371/journal.pone.0179674