Effect of nitrogen supply and irradiance on seedling survival and biomass in two evergreen, ericaceous species
Abstract:Ericaceous species are important competitors in many northern conifer plantations. Nitrogen (N) fertilization of forests can reduce the cover of ericaceous species, but whether this is a direct effect of N or an indirect effect of increased shade from fertilized trees is debated. To address this question, the growth and photosynthetic characteristics of two evergreen ericaceous species were studied in response to N fertilization and irradiance in a controlled environment. Salal ( Gaultheria shallon Pursch) seedlings were grown with 10, 100 or 250 mg l −1 N [+ phosphorus (P) and potassium (K)] under 0% or 60% shade. Evergreen huckleberry ( Vaccinium ovatum Pursch) seedlings were grown with 10 or 250 mg l −1 N (+PK), and with 250 mg l −1 N+K only under 0 or 50% shade. Salal survival decreased with increasing N supply, but shoot biomass was greatest in the 100 mg l −1 N treatment. Shade had no effect on salal survival, but shoot biomass was greater in shade. Survival of evergreen huckleberry grown in sun decreased with increasing N supply (+PK); however, survival of shaded plants was unaffected by N supply. Biomass of evergreen huckleberry shoots was greatest with 250 mg l −1 N (+PK) and was unaffected by irradiance. Shoot:root ratios increased with N supply and shade in both species. Rates of net photosynthesis in salal were unaffected by N treatment, and were higher in shaded plants. Chlorophyll concentrations in evergreen huckleberry increased with N supply, and were greatest in shade plants. It is suggested that fertilization of these ericaceous species with high levels of N reduces root growth which increases plant mortality under water stress. Shoot growth of plants surviving this stress is improved by fertilization.
Document Type: Research Article
Affiliations: Centre for Forest Biology, University of Victoria, STN CSC, Victoria, B.C., V8W 3N5, P.O. Box 3020, Canada
Publication date: 2004-12-01