Fig 1.
(A) The effect of temperature on relative respiration (the fraction of respiration relative to 15°C) of common species including animals, microbes, and plants follows the Arrhenius exponential derivative (Q10) that ranges between 1.5 and 2.7 (see S1 Table for references). (B) The effect of temperature on relative stem respiration (t0 = 15°C and Rs0 = 390 μmol CO2 m-3 s-1) for P. integerrima, P. trichocarpa, and O. europea followed a single exponential trend between 1°C and 15°C (Q10 of 1.7 –pink line). A significant divergence from the predicted exponential respiration drop was observed for P. integerrima and O. europea near 0°C (red bar indicates differences at -2°C in an unpaired two-way t-test, p<0.005, df = 14). P. trichocarpa shows no significant divergence from the predicted exponential curve at low temperatures. (C) The percent deviation in respiration at -2°C for 15 tree species (mean ± SE of 5 replicates).
Fig 2.
(A) The temperature-respiration relations in P. integerrima stems during 5 hours of cooling from 15°C to -2°C (blue dots) and 3 hours of heating back to 15°C (orange dots) versus the values projected by the Arrhenius equation (dashed line). Asterisks denote respiration rates which significantly differ from the projected values (paired two-tailed t test, p<0.005, df = 7). (B) The percent deviation from the projected respiration at -2°C during three consecutive days in which statistical analysis showed no significant differences (Repeated measure ANOVA and Tukey HSD, p = 0.05, df = 10).
Fig 3.
Temporal changes in nonstructural carbohydrate (NSC) concentrations [mg cm-3] in stems after 0 (no chilling), 1, 2, and 3 hours of chilling of P. trichocarpa and P. integerrima stems (A)–soluble carbohydrates (SC), and (B)–starch.
Lower case letters denote significant differences between NSC levels in P. trichocarpa and upper case letters between NSC levels in P. integerrima (Repeated measure ANOVA and Tukey HSD, p = 0.05, df = 18).
Fig 4.
For 2005 to 2013 in the western US, (A) estimated median non-structural carbohydrate (NSC) consumption due to excess respiration and (B) range of variation (min–max) in NSC consumption due to excess respiration.