Phosphorus regulates ecosystem carbon dynamics after permafrost thaw

Abstract:

The stability of carbon (C) in permafrost ecosystems after thaw depends on more than just climate change since soil nutrient status may also determine ecosystem C dynamics. It has been advocated that the potential nitrogen (N) release from thawing permafrost could promote vegetation production and thus regulate permafrost C-climate feedback. However, compared with the widely accepted C-N interactions, little is known about the potential role of soil phosphorus (P) availability. Here we combined two-year field observations along a thermokarst-induced thaw sequence with an in-situ fertilization manipulative experiment to evaluate the effects of changes in soil N and P availability on ecosystem C dynamics after permafrost thaw. We observed that gross primary productivity (GPP) increased, net ecosystem exchange (NEE) decreased gradually, whereas ecosystem respiration (ER) did not exhibit significant change along the thaw sequence. We also found that soil N availability exhibited an initial increase and a subsequent decline, whereas soil P availability increased progressively along the thaw sequence. The changes in soil P availability were positively associated with the dynamics of GPP after permafrost thaw, while soil N availability not. The fertilization experiment confirmed that P addition had a stronger effect on plant growth than N addition in this permafrost ecosystem. These two lines of evidence highlight the crucial role of soil P availability in altering the trajectory of permafrost C cycle under climate warming.