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 NH4+-N plus NO3--N captured by ion exchange resin (IER) bags, did not differ in plots treated with ambient (355 mu L L-1) and elevated (680 mu 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.