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Physiological Correlates of Variation in Nitrogen-Use Efficiency in Two Contrasting Sugarcane Cultivars

Sugarcane Res. Inst., Uda Walawe, Sri Lanka
Hawaii Agric. Res. Center, 99-193 Aiea Heights Drive, Aiea, HI 96701

^* Corresponding author (E-mail: meinzer{at}hawaii.edu).

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.

Received for publication May 14, 1996.

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