Effect of nitrogen supply and irradiance on seedling survival and biomass in two evergreen, ericaceous species.

摘要

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-1N 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.