Weniger CO2 aus dem Wald: Blätter vergammeln langsamer als gedacht

Gute Nachrichten: Ein wärmeres Klima beschleunigt die Zersetzung von Laubresten offenbar weniger als gedacht. Die aus diesem Prozess erwachsenden CO2-Emissionen wurden also höchstwahrscheinlich überschätzt. Das gab die Kansas State University am 2. Mai 2017 per Pressemitteilung bekannt:

Ecology team finds leaf litter has slower decomposition rate in warm temperatures than previously estimated

Kansas State University ecologists are part of an international team that found that the rate that microbes and invertebrates breakdown a leaf is not as sensitive to water temperature increases as once predicted. Walter Dodds took the photo of a decomposing leaf with shrimp in Valium Stream on Ilha Grande.

The time it takes for a leaf to decompose might be the key to understanding how temperature affects ecosystems, according to Kansas State University ecologists. Using leaf litter data in streams from 1,025 publications, a team of international stream ecologists, including Kansas State University’s Walter Dodds, university distinguished professor, and Lydia Zeglin, assistant professor, both in the Division of Biology, found average leaf litter decomposition rates are less than half of what the metabolic theory of ecology would predict. The research, which measured how sensitive leaf litter is to increases in temperature, is published in Global Change Biology. “The theory of how organisms respond to temperature says organisms will move at a faster rate at higher temperatures,” Dodds said. “That relationship for single organisms — whether it’s a lizard or bacterium — has a certain rate of increase with warmer temperatures. According to our study, the rate of decomposition will still happen faster with a rise in temperature, just not as fast as we expected.”

The team evaluated data from publications that measured leaf litter in streams and rivers and determined that leaf litter breakdown rates may increase 5-21 percent if the average water temperature warms about 1-4 degrees Celsius. This finding is counter to the metabolic theory estimates of a 10-45 percent increase with the same increase in temperature. Dodds said understanding the relationships among temperature, leaf decomposition and running water can help ecologists better predict how the carbon cycle will react with future climate adjustments. Since plant materials store a lot of the world’s carbon, and streams and rivers help transport plant material around the world, leaf litter decomposition in streams can be a big contributor to atmospheric carbon. According to Zeglin, when leaves fall in running water, they can be transported to the ocean, and as they move through the water they will breakdown more completely. If leaves enter the soil and are preserved, carbon from those leaves is more likely to be sequestered and not as easily release into the atmosphere as carbon dioxide.

“Streams put a good amount of CO2 into the atmosphere, so the rate that those leaves breakdown is an indicator of how much carbon goes into the atmosphere,” Dodds said. “The longer carbon is retained and stuck in leaves, as opposed to being respired as CO2 by either the microbes or the invertebrates that eat the leaves, the better.” By combining all the research data available and pulling out all the variables, the ecologists saw trends that indicated that organisms can adjust to changing environmental conditions and the breakdown rates may change slightly but shouldn’t shock the system. “To some degree, biological communities are going to adjust themselves to environmental change,” Dodds said. “Either the organisms will adapt to the changing temperature or different organisms that are effective at warmer temperatures will take their place. If those organisms change the rate that plant material is broken down, more CO2 will return to the atmosphere more quickly.”

The research team came up with the idea to extract data from thousands of already published studies and compare the breakdown rates of leaves from around the world at a National Science Foundation Long Term Ecological Research, or LTER, workshop. The data came from research papers on streams around the world, including LTER sites. The team found the papers using scholarly search engines such as Google Scholar or Web of Science. “This meta-analysis shows that while there is variation from site to site in the relationship between temperature and decomposition, the compilation of information from the work of thousands of individual scientists allows us to better understand the global trends,” Zeglin said.

Auch die Wildlife Conservation Society hatte am 2. Mai 2017 gute Nachrichten zu berichten. Eine ganze Reihe von Korallen kommen mit der Klimaerwärmung offenbar besser zurecht als zuvor angenommen:

Some – But Not All – Corals Adapting to Warming Climate

A new WCS study reveals evidence that some corals are adapting to warming ocean waters – potentially good news in the face of recent reports of global coral die offs due to extreme warm temperatures in 2016. The study appears in the latest issue of Marine Ecology Progress Series.

The study looked at responses to extreme temperature exposures in the same reefs over time, and found less coral bleaching in 11 of the 21 coral species studied. WCS Senior Conservation Zoologist Tim McClanahan, who has been studying coral responses to climate change since the extreme temperatures of the1998 El Nino, authored the study. The study took place in two marine national parks of Kenya. Looking at two similarly severe warming events in 1998 and 2016, McClanahan found that the number of pale and bleached coral colonies declined from 73 to 27 percent, and 96 to 60 percent in the two parks with different background temperatures. Most of this change was due to about half of the most common species that did not bleach strongly in 2016.  One rare species was, however, more sensitive than in 1998.

Bleaching takes place when stressed corals discharge beneficial algae that supply energy to corals causing them to turn pale or white and often starve. Worldwide, an estimated 60 percent of corals and 90 percent of coral species experienced bleaching due to unusually warm ocean water in 2016. McClanahan says: “This was a rare chance to study bleaching responses during two separate times with very similar conditions. Adaptation is evident for some of the more important reef building corals but, sadly, many species are not adapting, so this is a good news-bad news story.” But McClanahan warns: “Evidence for adaptation in the past is not evidence for adaptation in the future. Nevertheless, I suspect this adaptation to hot water started before my 1998 work and could have begun during the 1983 and 1988 El Niños, when coral bleaching was first observed in the region.”

Said Tim McClanahan: “Despite the many caveats and interpretation of these results, this study provides one of the first response-rate estimates for many common corals at the population level.  It therefore provides a basis for future studies and improving model predictions and the types of evaluations needed to address the future health of coral reefs.” Global awareness continues to grow about the immediate threats facing coral reef ecosystems, and a global commitment to address those threats. In February, at the Economist World Ocean Summit in Bali, Indonesia, the ‘50 Reefs’ initiative was launched by the Global Change Institute of the University of Queensland and the Ocean Agency. The initiative brings together leading ocean, climate and marine scientists to develop a list of the 50 most critical coral reefs to protect, while leading conservation practitioners are working together to establish the best practices to protect these reefs.