Trade-off Between Light- and Nitrogen-use Efficiency in Canopy Photosynthesis

Abstract

If the light-use efficiency (LUE) of species in a canopy is constant, canopy photosynthesis (CP) is proportional to the number of photons (Φ) absorbed by the canopy (CP=LUE×Φ). Likewise, if nitrogen-use efficiency (NUE) is constant, canopy photosynthesis is proportional to the amount of total leaf nitrogen (LN) (CP=NUE×LN). We applied these concepts to monospecific and mixed (1:1) stands of annuals ( Abutilon theophrasti and Ambrosia artemisiifolia ) at two stages, established in an ambient (360 μl l -1 ) or elevated (700 μl l -1 ) CO 2 atmosphere. In both>CO 2 concentrations, across the two species, daily canopy photosynthesis gave strong linear regressions with zero intercepts both against the number of absorbed photons and against total leaf nitrogen in the canopy. Doubling CO 2 increased LUE by 20–80% and NUE by 20–100%. LUE tended to be higher in Ambrosia than in Abutilon, and also higher in the later stage of canopy development than in the younger stage. Interference by Abutilon increased the LUE of Ambrosia. On the other hand, NUE tended to be higher in Abutilon than in Ambrosia , and to be higher in younger than in later stages. Interference by Abutilon decreased the NUE of Ambrosia. Thus, there are trade-offs (negative correlations) between LUE and NUE, which result from differences in leaf nitrogen per unit leaf area and from differences in leaf area development in the canopy. LUE increased with increasing leaf nitrogen concentration, while NUE increased with increasing light availability in the canopy.Copyright 1998 Annals of Botany Company