Alternatively, models fundamentally imply that NPP and you may plants C regarding northern permafrost part have raised historically (2) and can still boost in the long term (this research)

₂ for RCP4.5 were between 1.9% and 15.4% increase in NPP per 100-ppmv CO₂ before saturation, which is generally consistent with syntheses of free-air exchange CO₂ enrichment (FACE) experiments (mean of 13% globally) (29). Thus, there is the need for FACE experiments in the northern permafrost region to better constrain model responses to enhance atmospheric CO₂ in the region. In this study, the model with the least sensitivity (TEM6) was the only model in the sensitivity analysis for which C uptake was limited by plant N dynamics. Because the CO₂ response of the northern permafrost region is expected to be damped by N limitation (30, 31), it is important for earth system models to make progress in implementing N limitation to more effectively constrain analyses of the permafrost carbon–climate feedback.

Although the response to CO₂ fertilization is the primary reason for increases in C storage simulated by the models, models did exhibit substantial sensitivity of NPP to changes in air temperature. In recent decades, increasing temperatures appear to have increased plant biomass in tundra (32, 33), although some recent studies indicate that the long-term trend of greening in tundra may be experiencing a reversal in this decade (34, 35). Some analyses suggest that productivity in boreal forest regions has decreased in recent decades (36). It is important to recognize that there are some potentially important interactions of the NPP response to both changes in atmospheric CO₂ and temperature. For example, models that include N dynamics can predict increases in NPP in response to warming because of increased nitrogen availability released as a consequence of increased HR in response to warming (37), which may work against the N limitation of NPP to enhanced atmospheric CO₂. (mais…)