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DO ELEVATED CO2 AND N FERTILIZATION ALTER FINE ROOT-MYCORRHIZAE RELATIONSHIPS IN PINUS PONDEROSA?
Tingey, D T., D L. Phillips, AND M G. Johnson. DO ELEVATED CO2 AND N FERTILIZATION ALTER FINE ROOT-MYCORRHIZAE RELATIONSHIPS IN PINUS PONDEROSA? Presented at 17th North American Forest Biology Workshop, Pullman, WA, July 15-19, 2002.
Despite extensive studies on the response of plants to elevated CO2, climate change and N deposition, little is known about the response of roots and mycorrhizae in spite of their key role in plant water and nutrient acquisition. The effects of elevated CO2 and N fertilization on Pinus ponderosa fine ( 2 mm diameter) roots and their associated mycorrhizae were monitored over a 4-yr period using a minirhizotron camera system. The trees were grown in native soil in open-top field-exposure chambers at Placerville, CA. The study was a 3x3 factorial with three levels of CO2 (ambient, [~350 ppm] air or ambient air enriched with either 175 or 350 ppm CO2) and three levels of N fertilization (0, 100 and 200 kg ha-1 yr-1, applied annually) and three replicates, except the middle CO2 and middle N treatment was omitted. Soil exploration, measured as fine root occurrence (proportion of frames containing roots) and rooting intensity (length of fine roots in frames containing roots) increased under elevated CO2, but was unaffected by N fertilization. The decline in fine root occurrence during the latter part of the study was off-set by an increase in mycorrhizal occurrence. Mycorrhizal occurrence increased with time and increased with both elevated CO2 and N fertilization. However, the ratio of mycorrhizal occurrence/fine root occurrence, a measure of relationship between fine roots and mycorrhizae, showed no change with elevated CO2 but increased with N fertilization. Under elevated CO2 fine root occurrence increased providing additional infection sites; consequently, mycorrhizae occurrence increases in proportion to the increase in fine roots. In contrast, N fertilization increased root branching, without increasing the amount of fine roots, thereby providing more sites for mycorrhizal infection.
Record Details:Record Type: DOCUMENT (PRESENTATION/ABSTRACT)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL HEALTH AND ENVIRONMENTAL EFFECTS RESEARCH LABORATORY
WESTERN ECOLOGY DIVISION