John L Darcy, Steven K Schmidt, Joey E Knelman, Cory C Cleveland, Sarah C Castle, Diana R Nemergut

Current models of ecosystem development hold that low nitrogen availability limits the earliest stages of primary succession, but these models were developed from studies conducted in areas with temperate or wet climates. Global warming is now causing rapid glacial retreat even in inland areas with cold, dry climates, areas where ecological succession has not been adequately studied. We combine field and microcosm studies of both plant and microbial primary producers and show that phosphorus, not nitrogen, is the nutrient most limiting to the earliest stages of primary succession along glacial chronosequences in the Central Andes and central Alaska. We also show that phosphorus addition greatly accelerates the rate of succession for plants and for microbial phototrophs, even at the most extreme deglaciating site at over 5000 meters above sea level in the Andes of arid southern Peru. These results challenge the idea that nitrogen availability and a severe climate limit the rate of plant and microbial succession in cold-arid regions and will inform conservation efforts to mitigate the effects of global change on these fragile and threatened ecosystems.