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Temperature response and acclimation of Coastal Douglas-fir fine root respiration in the laboratory and field Abbey, Tyler


The temperature response of Coastal Douglas-fir fine root respiration (RFR) was investigated with a laboratory based experiment and during field studies. In the laboratory, a reciprocal transplant experiment was carried out to assess the temperature response of biomass-specific RFR. Seedlings were moved from either 16 to 24°C or 24 to 16°C, to test for warm and cold acclimation, respectively. Following transfer, there was an elevation in RFR of all treatments. Neither this ’transfer effect’, nor the subsequent results provided evidence of an acclimation response. Over the 2004 and 2005 growing seasons, RFR was characterized at three stands that differ in age (55-y-old: Mature, 17-y-old: Young and 5-y-old: New). The results were interpreted for evidence of acclimation. Rates of RFR were low in spring 2004, however during that summer there was a significant and unexpected elevation in rate, at all sites. In 2005, rates began higher than the previous spring, indicating a possible ’carry-over effect’ from 2004. The seasonal increase in RFR observed in 2004 was not repeated in 2005. The New stand was the only site to show a pattern consistent with acclimation, although these results may have arisen due to summer drought or a decline in substrate availability. Sensitivity (i.e. Q₁₀) of RFR appeared to change with overall capacity in 2004, increasing from ~1.3 to 2.4 at all sites. In 2005, Q₁₀ values changed little over the growing season; however, there were greater site differences in this year. RFR in summer 2004 was much higher than most other published results for conifers. Given that there were no apparent methodological artifacts, it is suggested that because 2004 was such a hot and dry year, an endogenous stress reaction occurred in the trees and led to this result. With standing fine root biomass in May 2004 and a hypothetical mortality scenario, the measured rates of RFR were scaled to area to facilitate their comparison to ecosystem respiration (ER). The resulting model indicates that RFR may play an important role in maintaining levels of ER during drought years, when other less drought resistant components may have reduced activity.

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