Scientists have known that climate influences soil chemistry—and, in particular, soil pH, a measure of acidity or alkalinity. In dry climates, soil is alkaline; in wet climates, it’s acidic.

But what has remained unknown is just how soil pH changes between wet and dry climates. A new analysis sheds light on that mystery, revealing that the shift occurs abruptly, right at the boundary between wet and dry conditions. The findings appear in the journal Nature.

soil pH map
This global map of soil pH shows acidic areas in red and alkaline regions in blue. (Credit: UCSB)

“We found that if you go to wet climates—places where you might expect to find a forest, whether in the high latitudes or in the Amazon—the pH is acidic,” says lead author Eric Slessarev, a PhD student in the department of ecology, evolution, and marine biology at the University of California, Santa Barbara. “If you go to dry climates, the pH is alkaline. This is what we expected. But our analysis was able to confirm that…