Physiological Correlates of Variation in Nitrogen-Use Efficiency in Two Contrasting Sugarcane Cultivars
- Subasinghe Ranjith and
- Frederick C. Meinzer
The efficiency of N utilization in photosynthesis and dry matter production (NUE) is an important crop performance criterion. Our objectives were to characterize the magnitude and physiological correlates of variation in NUE in the C4 grass, sugarcane (Saccharum spp. hybrid). Two genotypes known to differ with regard to their resistance to drought and salinity stress were grown in solution culture in a glasshouse at three levels of N availability (0.1, 1.0, and 10 mM N). Photosynthetic gas exchange, dry matter accumulation, carboxylase activity, chlorophyll content, leaf N status, and plant-water relations characteristics were evaluated. Leaf water potential and plant hydraulic conductance decreased as applied N was reduced from 10 to 0.1 mM. At a given leaf N status, NUE was always significantly higher in the stress-resistant genotype (H69-8235) than in the susceptible genotype (H65-7052). However, a large genetic difference in dry weight accumulation at a given level of external N supply was observed only at 10 mM applied N. Higher NUE in H69-8235 was strongly associated with greater relative partitioning of leaf N to chlorophyll and ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco). The fraction of leaf N partitioned to the photosynthetic apparatus increased with declining N content in both genotypes. Photosynthetic and dry matter-based NUE were not entirely consistent with each other because growth was more sensitive than photosynthesis to N stress. It may be possible to further improve the already high NUE of C4 grasses by screening genotypes for differences in partitioning of leaf N into components of the photosynthetic apparatus such as chlorophyll and Rubisco.
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