Results from linear regressions of the effects of ecosystem factors (permafrost presence (top), biome (middle) and soil C:N ratio (bottom)) on the relationship between summer air temperature and summer GPP. Standardized slopes reflect the effect of 1 s.d. (z-score) of summer temperature on C flux (also in units of s.d.). Error bars denote 95% confidence intervals, indicating consistent positive or negative relationships when not overlapping with the dashed zero line. Sample sizes (n = number of sites) are presented above each bar for each group. On average, GPP (negative scale; top) increases in warmer years regardless of permafrost presence but markedly less so in N-rich (soil C:N ratio < 15) systems, which have significantly lower rates of CO2 uptake during warmer years (bottom).
