One of the fundamental questions in plant ecology is evaluating the physiological trade-offs that define trait syndromes or strategies.  Nitrogen (N) limits plant growth in many ecosystems and species differ in their ability to assimilate carbon per unit nitrogen (nitrogen use efficiency, NUE).  Several recent studies have focused on elucidating the biochemical basis of species differences in NUE, particularly species differences in N partitioning to various photosynthetic and non-photosynthetic protein pools.  While cell-wall protein has been found to vary by a factor of two across species, other non-photosynthetic pools including amino acids, nucleic acids and N-containing secondary compounds, remain poorly characterized and may further explain species differences in NUE.  In this study, we surveyed a suite of N-containing biochemical fractions in ten woody species, including four nitrogen-fixing species.   

Results/Conclusions

A multivariate analysis concluded that species differed mainly in soluble (photosynthetic) protein and nucleic acid content.  While the ten species allocated roughly the same proportion of leaf N to total protein, species differed in their allocation to soluble, thylakoid and cell wall protein.  However, there was no trade-off between these fractions: species with high cell wall protein also tended to have high soluble protein fractions.  Species with high soluble protein fractions had higher amounts of amino acids and nucleic acids and also displayed higher carboxylation capacity and light-use efficiency.  Thylakoid protein was also positively correlated with carboxylation capacity and light-use efficiency.  NUE was not significantly correlated with any N-containing fraction.