Differences in carbon and nitrogen metabolism between male and female Populus cathayana in response to deficient nitrogen

Sexual dimorphism occurs regarding carbon and nitrogen metabolic processes in response to nitrogen supply. Differences in fixation and remobilization of carbon and allocation and assimilation of nitrogen between sexes may differ under severe defoliation. The dioecious species Populus cathayana was studied after two defoliation treatments with two N levels. Males had a higher capacity of carbon fixation because of higher gas exchange and fluorescence traits of leaves after severe long-term defoliation under deficient N. Males had higher leaf abscisic acid, stomatal conductance and leaf sucrose phosphate synthase activity increasing transport of sucrose to sinks. Males had a higher carbon sink than females, because under N-deficient conditions, males accumulated >131.10% and 90.65% root starch than males in the control, whereas females accumulated >40.55% and 52.81%, respectively, than females in the control group. Males allocated less non-protein N (NNon-p) to leaves, having higher nitrogen use efficiency (photosynthetic nitrogen use efficiency), higher glutamate dehydrogenase (GDH) and higher leaf GDH expression, even after long-term severe defoliation under deficient N. Females had higher leaf jasmonic acid concentration and NNon-p. The present study suggested that females allocated more carbon and nitrogen to defense chemicals than males after long-term severe defoliation under deficient N.