Indices of plant N availability in an alpine grassland under elevated atmospheric CO2

The objective of this study was to estimate whether elevated atmospheric CO₂] alters plant N availability in a native high-elevation grassland in the Swiss Alps using two integrative, relatively non-disruptive methods. Estimates based on seasonal net plant N uptake, and those based on the amounts of NH ₄ ⁺ -N plus NO ₃ ^– -N captured by ion exchange resin (IER) bags, did not differ in plots treated with ambient (355 L L^–1) and elevated (680 L L^–1) CO₂] in either the second (1993) or third (1994) growing season under treatment with elevated CO₂]. The results of this study suggest that the effects of rising atmospheric CO₂] on plant N availability may be negligible in this grassland. The results also contrast the relatively large effects of elevated atmospheric CO₂] (increases and decreases) reported for highly disturbed artificial systems.