Effects of elevated CO 2 and N fertilization on fine root dynamics and fungal growth in seedling Pinus ponderosa

Abstract

The effects of elevated CO 2 and N fertilization on fine root growth of Pinus ponderosa Dougl. ex P. Laws. C. Laws., grown in native soil in open-top field-exposure chambers at Placerville, CA, were monitored for a 2-year period using minirhizotrons. The experimental design was a replicated 3 × 3 factorial with a treatment missing; plants were exposed to ambient (≈ 365 μmol mol −1) air or ambient air plus either 175 or 350 μmol mol −1 CO 2 and three levels of N addition (0, 100 and 200 kg ha −1 year −1). By the second year, elevated CO 2 increased fine root occurrence and root length while N fertilization had no effect. The CO 2 × N interactions were not significant. Neither elevated CO 2 nor N fertilization altered fine root diameter. Fine root mortality was increased by increasing soil N but was reduced in elevated CO 2. Highest fine root mortality occurred during summer and was lowest during winter. Elevated CO 2 increased mycorrhizal and fungal occurrence earlier than N fertilization.