Nitrogen loading of Eucalyptus globulus seedlings: nutritional dynamics and influence on morphology and root growth potential

Abstract

Achieving successful outplanting of trees on increasingly harsher sites is a global concern. In Chile, for example, new Eucalyptus globulus plantations are being targeted to poorer, low fertility sites where additional stresses often negatively affect seedling performance during the first field season. Nitrogen-loading during the later stages of nursery production can, however, significantly improve seedling physiological performance on harsher sites by increasing plant growth and nutrient storage reserves for subsequent root growth after outplanting. Maximizing these benefits, and applying the concept of loading throughout the entire crop cycle, requires a better understanding of nitrogen (N) dynamics. Thus, for container E. globulus, considered one of the most important plantation species worldwide, we evaluated the effects of increasing N supply (50 to 600 mg N L-1) on seedling morphological traits, biomass production, root growth potential, and foliar N. After 15 weeks of N application, seedlings showed an increase in all growth variables evaluated up to 300 mg N L-1, whereas higher rates allowed luxury consumption. Modeling growth responses revealed, however, an apparent ammonium antagonism with other macronutrient cations suggests that high rates of this N-form may negate the potential benefits of N-loading, or that other modifications to the fertilizer solution may promote additional growth at higher N rates. Foliar N concentration, which was easily and accurately measured with a leaf chlorophyll meter, showed a gradient from basal to apical leaves suggesting a strong translocation of N in E. globulus seedlings. Our results suggest nursery management that supplies 300 mg L-1 of N through the entire growing season could improve seedling nutritional status, morphological attributes, and growth of new roots, attributes that may improve establishment on low fertility sites.