The earth's ecosystems play a major role in relation to the carbon cycle and thus also the loss of carbon. Ecosystem respiration depends on the interaction between plants, animals, and microorganisms, such as bacteria and fungi, and this respiration depends to a large extent on temperature. In a new publication in the internationally recognised journal Nature Ecology & Evolution, researchers from, among others, the Department of Agroecology at Aarhus University have investigated the relationship between temperature and respiration from the earth's ecosystems.

"This is a topic of great importance for modeling of future climate change, but it is also an area where there has been a lack of empirical analysis on a large-scale level of the connection between temperature and respiration," says professor and head of department Jørgen E. Olesen.

210 different places on Earth

The relationship between temperature and respiration is typically described by an exponential relationship. The researchers have tested this by examining whether there are threshold values ??where this relationship no longer come into play. This is done across 210 globally distributed measuring points. At these sites, the exchange of CO₂ between ecosystem and atmosphere has been measured over longer periods.

“The 210 locations are spread globally, so we cover a comprehensive temperature range. And that means we have been able to find threshold values ??for both high and low temperatures in relation to the respiration of ecosystems. It is connected in such a way that when you are above or below a certain temperature, the ecosystems' metabolism no longer follow the exponential relationship,” says Jørgen E. Olesen.

In other words, researchers have found the sensitivity of ecosystems and their dependence on temperature. An example of how temperature affects ecosystems are permafrost areas where it is so cold that the temperature is below the threshold set by the researchers for ecosystems, that is, the ecosystems are put to sleep.

"However, if the temperature rises above the low threshold for microbial degradation in these permafrost areas, we risk that large stocks of labile carbon can be released," explains Jørgen E. Olesen. 

Time also plays a role

As part of the study, researchers have examined different time intervals, and it turns out that the longer the time period considered, the lower the sensitivity of ecosystems to temperature.

“We have used measurements from half an hour to a full year. And our results indicated that the annual respiration of ecosystems has a markedly lower temperature sensitivity compared to the variation at hourly basis. This shows that the influence of environmental factors on respiration varies with the time period. It plays an important role in relation to the earth's ability to retain carbon during climate change, which we are experiencing now and will experience in the future,” says Jørgen E. Olesen. 

For example, researchers have been able to see that it is the temperature that affects the activity of underground microbial groups in cold climates, while it is to a greater extent the limitation of water and nutrients that affects the activity in warmer climates.

The climate of the future

“In our study, we found temperature thresholds for when ecosystem respiration changes relative to a standard curve. But it is important to keep in mind that this kind of results need to be validated against many different ecosystem components as soon as detailed data collected over a long period of time is available. And it is also important to remember that man-made changes also affect the activity of ecosystems,” says Jørgen E. Olesen.

However, although the results in the future must be validated on the basis of far more data, the results of the study can still play an important role in including the global temperature thresholds in the description of climate change, and thus improve forecasts of climate change.