Elevated CO sub(2) and O sub(3) effects on fine-root survivorship in ponderosa pine mesocosms

• Published in: Oecologia Vol. 160; no. 4; pp. 827 - 837
• Main Authors: Phillips, Donald L, Johnson, Mark G, Tingey, David T, Storm, Marjorie J
• Format: Journal Article
• Language: English
• Published: 01-07-2009
• Subjects: Pinus ponderosa
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-009-1339-4

Atmospheric carbon dioxide (CO sub(2)) and ozone (O sub(3)) concentrations are rising, which may have opposing effects on tree C balance and allocation to fine roots. More information is needed on interactive CO sub(2) and O sub(3) effects on roots, particularly fine-root life span, a critical demographic parameter and determinant of soil C and N pools and cycling rates. We conducted a study in which ponderosa pine (Pinus ponderosa) seedlings were exposed to two levels of CO sub(2) and O sub(3) in sun-lit controlled-environment mesocosms for 3years. Minirhizotrons were used to monitor individual fine roots in three soil horizons every 28days. Proportional hazards regression was used to analyze effects of CO sub(2), O sub(3), diameter, depth, and season of root initiation on fine-root survivorship. More fine roots were produced in the elevated CO sub(2) treatment than in ambient CO sub(2). Elevated CO sub(2), increasing root diameter, and increasing root depth all significantly increased fine-root survivorship and median life span. Life span was slightly, but not significantly, lower in elevated O sub(3), and increased O sub(3) did not reduce the effect of elevated CO sub(2). Median life spans varied from 140 to 448days depending on the season of root initiation. These results indicate the potential for elevated CO sub(2) to increase the number of fine roots and their residence time in the soil, which is also affected by root diameter, root depth, and phenology.