Optimum Nutrient Concentrations and CND Scores of Mature White Spruce Determined Using a Boundary-Line Approach and Spatial Variation of Tree Growth and Nutrition

ABSTRACT

Standards of optimum nutrition are not readily available for mature trees of the Canadian boreal forest. The objective of this study was to determine foliar nutritional standards for white spruce for all major nutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn)] using critical values (CVA) and compositional nutrient diagnosis (CND). Trees were sampled at two locations in Ontario and Quebec to cover a gradient of soil fertility levels. A boundary-line approach was used in combination with quadratic regression models to estimate the relationship between growth and foliar-nutrient concentrations or CND scores when free of the effects of interacting environmental factors. White spruce optimum nutrition ranges were computed from significant relationships (P ≤ 0.10) for N, P, K, Ca, and Mn concentrations and for N, P, and K CND scores. Optimum concentrations for first-year needles were 12.3, 1.9, 7.3, 6.5, and 0.39 mg g⁻¹ for N, P, K Ca, and Mn, respectively, whereas optimum CND scores were 0.17, −1.65, −0.40, and −0.30 for N, P, K, and Ca, respectively. Samples from a broader range of environmental conditions will be required in order to establish standards for all major nutrients and to ascertain toxicity levels of most nutrients.

Keywords:

• white spruce
• nutritional standards
• compositional nutrient diagnosis (CND)
• boundary-line approach

ACKNOWLEDGEMENTS

The research was supported in part by the Fonds Québécois de la Recherche sur la Nature et les Technologies (FQRNT), the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Centre of Excellence on Sustainable Forest Management Network (SFMN). We are also thankful to the Petawawa Research Forest and Forêt d'Enseignement et de Recherche du Lac Duparquet, which provided access to their facilities.

Notes

∗Mn data from Petawawa only (n = 160).

∗ Analysis based on Petawawa data only.

^∇ Model-predicted tree growth, expressed as a percentage of the model's maximum growth, at the limits of the nutritional range.

⁺ Calculation of nutritional threshold is prohibited for underlined values.

∗ Analysis based on Petawawa data only.

^#Regression coefficients are presented only if the quadratic coefficient “a” is statistically significant (p < 0.1).

^∇ Model-predicted tree growth, expressed as a percentage of the model's maximum growth, at the limits of the nutritional range.

⁺ Calculation of nutritional threshold is prohibited for underlined values.

∗Analysis based on Petawawa data only.