EFFECTS OF ELEVATED CO2 AND N FERTILIZATION ON FINE-ROOT DYNAMICS ANDFUNGAL GROWTH IN SEEDLING PINUS-PONDEROSA

The effects of elevated CO2 and N fertilization on fine root growth of Pinus ponderosa Dougl. ex P. Laws. C. Laws., grown in native soil in open-top held-exposure chambers at Placerville, CA, were monitored for a 2-year period using minirhizotrons. The experimental design was a r eplicated 3 x 3 factorial with a treatment missing; plants were expose d to ambient (approximate to 365 mu mol mol(-1)) air or ambient air pl us either 175 or 350 mu mol mol(-1) CO2 and three levels of N addition (0, 100 and 200 kg ha(-1) year(-1)). By the second year, elevated CO2 increased fine root occurrence and root length while N fertilization had no effect. The CO2 x N interactions were not significant. Neither elevated CO2 nor N fertilization altered fine root diameter. Fine root mortality was increased by increasing soil N but was reduced in eleva ted CO2. Highest fine root mortality occurred during summer and was lo west during winter. Elevated CO2 increased mycorrhizal and fungal occu rrence earlier than N fertilization. (C) 1997 Elsevier Science B.V.