Nitrogen enhanced photosynthesis of Miscanthus by increasing stomatal conductance and phosphoenolpyruvate carboxylase concentration

Miscanthus is one of the most promising bioenergy crops with high photosynthetic nitrogen-use efficiency (PNUE). It is unclear how nitrogen (N) influences the photosynthesis in Miscanthus. Among three Miscanthus genotypes, the net photosynthetic rate (P (N)) under the different light intensity and CO2 concentration was measured at three levels of N: 0, 100, and 200 kg ha(-1). The concentrations of chlorophyll, soluble protein, phosphoenolpyruvate carboxylase (PEPC), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, leaf anatomy and carbon isotope discrimination (Delta) in the leaf were analyzed to probe the response of photosynthesis in Miscanthus genotypes to N levels. P (N) in all genotypes rose significantly as N application increased. The initial slope of response curves of P (N) to C (i) was promoted by N application in all genotypes. Both stomatal conductance and C (i) were increased with increased N supply, indicating that stomatal factors played an important role in increasing P (N). At a given C (i), P (N) in all genotypes was enhanced by N, implying that nonstomatal factors might also play an important role in increasing P (N). Miscanthus markedly regulated N investment into PEPC rather than the Rubisco large subunit under higher N conditions. Bundle sheath leakiness of CO2 was constant at about 0.35 for all N levels. Therefore, N enhanced the photosynthesis of Miscanthus mainly by increasing stomatal conductance and PEPC concentration.