Photosynthetic nitrogen- and water-use efficiency of acacia and eucalypt seedlings as afforestation species

The ecophysiological traits of acacia and eucalypt are important in assessing their suitability for afforestation. We measured the gas-exchange rate, the leaf dry mass per area (LMA) and the leaf nitrogen content of two acacia and four eucalypt species. Relative to the eucalypts, the acacias had lower leaf net photosynthetic rate (P-N), lower photosynthetic nitrogen-use efficiency (PNUE), higher water-use efficiency (WUE), higher LMA and higher leaf nitrogen per unit area (N-area). No clear differences were observed within or between genera in the maximum rate of carboxylation (V-cmax) or the maximum rate of electron transport (J(max)), although these parameters tended to be higher in eucalypts. PNUE and LMA were negatively correlated. We conclude that acacias with higher LMA do not allocate nitrogen efficiently to photosynthetic system, explaining why their P-N and PNUE were lower than in eucalypts.