Effect of nitrogen deficiency on biomass production, photosynthesis, carbon partitioning, and nitrogen nutrition status of Melaleuca and Eucalyptus species

Abstract

Genetic variation in response to N-deficiency between tropical woody plants was assessed by growing two species each of the genus Melaleuca (M. leucadendra and M. cajuputi) and Eucalyptus (E. camaldulensis and E. tereticornis) hydroponically at two levels of N. Biomass, N content and carbohydrate contents of various plant parts, leaf photosynthetic rate, and photo assimilate distribution were determined in all the plants at both control N (2.14 mM) and low N (0.36 mM) levels. Although the Eucalyptus genotype grew faster than Melaleuca under control conditions, the reduction of stem elongation and growth by N-deficiency was more severe in Eucalyptus species than in Melaleuca. In the same way as the effect on growth, N-deficiency reduced the photosynthetic rate and leaf area in all the species. The better performance at a low N level of Melaleuca compared with Eucalyptus species could be attributed to the lower reduction of either the photosynthetic rate (M. cajuputi) or the leaf area expansion (M. leucadendra). M. cajuputi had a higher leaf N concentration that was less affected by stress in this species than in the others. N-deficiency induced a better N use efficiency in the leaves of Melaleuca by enhancing significantly the photosynthetic rate per unit leaf N. In response to N-deficiency, all the plants except for M. cajuputi accumulated a remarkably higher concentration of sugars and starch in different organs like roots, stem, and leaves, but the partitioning of photoassimilates was directed preferentially to the growth of the roots in Eucalyptus compared to Melaleuca species. Although the relative rate of biomass accumulation was positively correlated with the N concentration of the plant in both genera studied, the associations were stronger and regression coefficients were higher in Eucalyptus than in Melaleuca, with the crossing points of their regression lines occuring between the values in the low N and control treatments. The total N content in the plant exhibited a stronger correlation with N absorption per unit root weight than with the root weight. These results suggest that Melaleuca species are more resistant than Eucalyptus to N-deficiency owing to the maintenance of (1) a higher ability of N uptake by roots, (2) higher source activity represented by either the photosynthetic rate or the leaf area, and (3) more efficient N utilization of the source activity at a low N level in the growth medium. © 2003 Taylor & Francis Group, LLC.