Rainforest mushrooms as weather makers

With the help of HZB’s x-ray microscope, MAXYMUS, MPIC
scientists in Mainz, Germany, recently decoded the methods
used by mushrooms and plants to influence Amazon rainforest
cloud formation. Organic substances condense on mushroom and
plant derived potassium salts resulting in production of
aerosol particles. On these, fog droplets form.
© Christopher Pöhlker / MPI für Chemie

Whereas in urban areas, soot or dust particles often double as condensation nuclei, in rain-forests, it is mainly organic evaporations from plants, which periodically trigger fog or cloud formation. Now, at HZB’s BESSY II, Max Planck Institute for Chemistry scientists have shown that inorganic salts also play a role in the process. It appears that tiny potas-sium salt particles make up the core of cloud condensation nuclei in the rainforest. These kinds of salts are evaporated by mushrooms and plants as a way of influencing the number of condensation nuclei and, by extension, affecting cloud formation and precipitation over the rainforest.

Christopher Pöhlker, a Ph.D. student in Dr. Ulrich Pöschl’s and Prof. Dr. Meinrat O. Andreae’s lab at the Max Planck Institute for Chemistry, recently made the discovery using a new aerosol analytical method at HZB’s BESSY II x-ray microscope, MAXYMUS, and at the Lawrence Berkeley National Laboratory’s synchrotron radiation source in California, USA.

Pöhlker examined organic aerosol particles that were collected from air filters and small, paper-thin plates in the untouched Brazilian rainforest north of Manaus, which allowed the chemist to precisely measure the particles’ potassium content. “We identified three different kinds of or-ganic aerosol particles and they all contained potassium salts,“ Pöhlker explains. “Our initial focus was on the organic material’s carbon, oxygen, and nitrogen content. But then, to our surprise, we found its potassium content to be extremely high – almost 20 percent!“ Internal structures inside the nanometer- to micrometer-size particles point to the fact that during oxidation and condensation of organic gas molecules, multi-phase processes also play a role – which involve different chemical phases like fog or cloud water and other gel-like organic substances. The results will help with the identification and quantification of the sources and impact of organic aerosol particles under pre-industrial conditions. This in turn can help scientists understand how the rainforest’s continental and regional climate works and its role in Earth’s “climate machine.“

Publication: Science 31st August 2012 “Biogenic potassium salt particles as seeds for secondary organic aerosol in the Amazon,”

Contact and further information:

Christopher Pöhlker: c.pohlker@­mpic.de; Tel.: 06131 305-6303

Dr. Ulrich Pöschl: u.poschl@­mpic.de; Tel.: 06131 305-6201