Leaf angle responds to nitrogen supply in eucalypt seedlings. Is it a photoprotective mechanism?

We examined the adjustment of leaf angle (L θ) and foliar chlorophyll and xanthophyll chemistry in Eucalyptus nitens (Deane and Maiden) Maiden seedlings maintained in various nitrogen (N)-supply treatments over a 6-month period. Adjustment of L θ toward the vertical was greatest under conditions of foliar N deficiency and became incrementally more horizontal with increasing foliar N concentration. Photochemical efficiency (F v/F m) and quantum yield were lower in seedlings with low foliar N (low-N seedlings) in winter, but not in autumn. Low-N seedlings generally had low area-based chlorophyll concentrations and high xanthophyll-cycle conversion ratios, particularly during months of low temperature. Under mild temperature conditions, high concentrations of zeaxanthin and antheraxanthin were associated with lower electron transport rates (ETR). Incident light, F v/F m, ETR and total chlorophyll concentration were negatively correlated with L θ, with horizontal leaf orientation measured as 0° and vertical leaf orientation as 90°. Xanthophyll conversion ratio was positively correlated with L θ. Adjustments in L θ may play a role in photoprotection of E. nitens seedlings by assisting the leaf to balance its utilization and dissipation of energy. © 2006 Heron Publishing.