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Scagel, C.F., and Christian P. Andersen. 1997. Seasonal changes in root and soil respiration of ozone exposed ponderosa pine grown in different substrates. New Phytologist 136:627-643.

Exposure to ozone (O3) has been shown to decrease the allocation of carbon to tree roots. Decreased allocations of carbon to roots might disrupt root metabolism and rhizosphere organisms. The effects of soil type and shoot O3 exposure on below-ground respiration and soil microbial populations were investigated using container-grown ponderosa pine (Pinus ponderosa Laws.) growing in a low-nutrient soil, or a fertilizer-amended organic potting media, and exposed to one of the three levels of O3 for two growing seasons in open-top exposure chambers. A closed system, designed to measure below-ground respiratory activity (CO2 production, O2 consumption and RQ-Respiration Quotient: (CO2:O2)of plants growing in pots, was used monthly to monitor below-ground respiration of 3-yr.-old ponderosa pine.

Although seasonal differences were detected, CO2 production (Ámol h-1g-1 total root d.wt) and RQ(CO2:O2) increased with increasing O3 exposure level. Seasonal patterns showed increased respiration rates during periods of rapid root growth in spring and early fall. Respiration quotient tended to decrease during known periods of active root growth in control seedlings, but a similar response was not observed in O3-treated seedlings. Responses to O3 were greatest in the soil-grown plants, which had a lower fertility level than media-grown plants. Although root d. wt was decreased, root:shoot ratios did not change in response to O3. Soil-grown plants had higher root-shoot ratios than media-grown plants, reflecting the lower fertility of soil.

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