Nitrogen deposition limits photosynthetic response to elevated CO2 differentially in a dioecious species

Sexual dimorphisms of dioecious plants are important in controlling and maintaining sex ratios under changing climate environments. Yet, little is known about sex-specific responses to elevated CO2 with soil nitrogen (N) deposition. To investigate sex-related physiological and biochemical responses to elevated CO2 with N deposition, Populus cathayana Rehd. was employed as a model species. The cuttings were subjected to two CO2 regimes (350 and 700 mu mol mol(-1)) with two N levels (0 and 5 g N m(-2) year(-1)). Our results showed that elevated CO2 and N deposition separately increased the total number of leaves, leaf area (LA), leaf mass, net photosynthetic rate (P (n)), light saturated photosynthetic rate (P (max)), chlorophyll a (Chl a), and chlorophyll a to chlorophyll b ratio (Chl a/b) in both males and females of P. cathayana. However, the effects on LA, leaf mass, P (n), P (max), Chl a and Chl a/b were weakened under the combined treatment of elevated CO2 and N deposition. Males had higher leaf mass, P (n), P (max), apparent quantum yield (I broken vertical bar), carboxylation efficiency (CE), Chl a, Chl a/b, leaf N, and root carbon to N ratio (C/N) than did females under elevated CO2 with N deposition. In contrast to males, females had significantly higher levels of soluble sugars in leaves and greater starch accumulation in roots and stems under the same condition. The results of the present work imply that P. cathayana females are more responsive and suffer from greater negative effects on growth and photosynthetic capacity than do males when grown under elevated CO2 with soil N deposition.