The Jasper Ridge CO[sub 2] Project: First-year biomass from micro-ecosystem for climate change analysis (MECCA) experiments

Elevated atmospheric CO[sub 2] stimulated photosynthesis but produced a mixed pattern of biomass responses in natural California grassland. In artificial ecosystems with six single species growing on low-fertility serpentine soil, addition of 20 g m[sup [minus]2] of N, P, and K led to dramatic increases in annual net primary production (NPP) (mean increase > 500%) and consistent decreases in root fraction. Elevated CO[sub 2] (ambient plus 350 [mu]mol mol[sup [minus]1]) had almost no effect on annual NPP at natural nutrient levels, but stimulated biomass production by a mean of 15% with added nutrients. Root fraction did not change consistently with elevated CO[sub 2].