Phosphorus regulates ecosystem carbon dynamics after permafrost thaw

<p>The ecosystem carbon (C) dynamics after permafrost thaw depends on more than just climate change since soil nutrient status may also impact ecosystem C balance. It has been advocated that the potential nitrogen (N) release upon permafrost thaw could promote plant growth and thus offset soil C loss. 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 permafrost thaw sequence (constituted by four thaw stages, <em>i</em>.<em>e</em>., non-collapse and 5, 14, and 22 years since collapse) with an in-situ fertilization experiment (included N and P additions at the level of 10 g N m^-2 yr^-1 and 10 g P m^-2 yr^-1, respectively) in a Tibetan swamp meadow to evaluate ecosystem C-nutrient interactions upon permafrost thaw. Our results showed that changes in soil P availability rather than N availability played an important role in regulating the increases in gross primary productivity and the decreases in net ecosystem exchange along the thaw sequence. The fertilization experiment further confirmed that P addition had stronger effects 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.</p>