Independent and contrasting effects of elevated CO2 and N-fertilization on root architecture in Pinus ponderosa

Abstract

The effects of elevated CO2 and N-fertilization on the architecture of Pinus ponderosa Dougl. ex P. Laws & C. Laws fine roots and their associated mycorrhizal symbionts were measured over a 4-year period using minirhizotron tubes. The study was conducted in open-top field-exposure chambers located near Placerville, Calif. A replicated (3 replicates), 3×3 factorial experimental design with three CO2 concentrations [ambient air (∼354 μmol mol−1), 525 μmol mol−1, and 700 μmol mol−1] and three rates of N-fertilization (0, 100 and 200 kg ha−1 year−1) was used. Elevated CO2 and N treatment had contrasting effects on the architecture of fine roots and their associated mycorrhizae. Elevated CO2 increased both fine root extensity (degree of soil exploration) and intensity (extent that roots use explored areas) but had no effect on mycorrhizae. In contrast, N-fertilization had no effect on fine root extensity or intensity but increased mycorrhizal extensity and intensity. To better understand and model the responses of systems to increasing CO2 concentrations and N deposition/fertilization it is necessary to consider these contrasting root architectural responses.