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Keywords:

  • ammonium;
  • elevated CO2;
  • fine roots;
  • loblolly pine;
  • nitrate;
  • uptake kinetics

ABSTRACT

The nitrogen requirement of plants is predominantly supplied by NH4+ and/or NO3 from the soil solution, but the energetic cost of uptake and assimilation is generally higher for NO3 than for NH4+. We found that CO2 enrichment of the atmosphere enhanced the root uptake capacity for NO3, but not for NH4+, in field-grown loblolly pine saplings. Increased preference for NO3 at the elevated CO2 concentration was accompanied by increased carbohydrate levels in roots. The results have important implications for the potential consequences of global climate change on plant-and ecosystem-level processes in many temperate forest ecosystems.