Characterizing the Respiration of Stems and Roots of Three Hardwood Tree Species in the Great Smoky Mountains
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CER of small roots (d<0-8 mm) was measured with a newly developed system which allows periodic in situ measurements by using permanently installed flexible cuvettes. Temperature-adjusted CER of roots showed no diel variation. The moderate long-term changes occurred simultaneously in all species and size classes, suggesting that they were driven mostly by environmental factors. Mean root CER ranged from 0.5 to 4.0 nmol g-1 d.w. s-1. Rates were up to six times higher for fine roots (d<2.0 mm) than for coarse roots.
CER (per unit length) of boles (d>10 cm) and twigs (d<2 cm) was related to diameter by the function lnCER = a+DÂ·lnd, with D between 1.2 and 1.8. A new, scale-invariant measure of CER, based on D, facilitated comparisons across diameters. Q10 varied with the method of determination, and it was higher in spring (1.8-2.5) than in autumn (1.4-1.5) for all species. Daytime bole CER often fell below temperature-based predictions, likely due to transpiration. The reduction (usually <10%) was less pronounced at the drier site. Twig CER showed more substantial (often >Â±50%) deviations from the predictions. Deviations were higher in the canopy than in the understory. Mean bole maintenance respiration (at 20Â°C and d=20 cm) was 0.66, 0.43 and 0.50 Î¼mol m-1, while the volume-based growth coefficient was around 5, 6 and 8 mol cm-3 for BC, RM and RO, respectively.
In a controlled study, BC and RM seedlings were fumigated in open-top chambers with sub-ambient, ambient and twice-ambient levels of ozone. The twice-ambient treatment reduced stem CER in BC by 50% (p=0.05) in July, but there was no treatment effect in September or in RM. Ozone reduced root/shoot ratio and diameter growth in BC, and Pmax in both species.
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