Genetics of dark respiration and its relationship with drought hardiness in coastal Douglas-fir

Genetic variation in respiration parameters, and the relationships between respiration and drought hardiness were investigated in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). Material included 3-year-old seedlings from 12 families grown under two treatments: control (well-watered) and drought (moderate drought the second growing season followed by severe drought the next year). Respiratory parameters measured were metabolic heat rate (q) and rate of CO2 production (RCO2). Calculated parameters were the ratio of metabolic heat rate to CO2 production rate (q/RCO2), specific growth rate (RSG), and Arrhenius temperature coefficients of metabolic heat (μq) and CO2 production (μCO2). Growth traits measured were third-year increments of seedling height and diameter. Means of respiration traits were generally less in the drought treatment than in the control, with the exception of μq, which increased under drought. Consistent increase in μq and decrease in μCO2 values in response to drought appear to suggest a differential influence of drought on the temperature dependence of ATP synthesis in catabolic reactions, and ATP breakdown in anabolic reactions or in futile cycles of dark respiration. Metabolic heat rates measured over a wide a range of temperatures (20 to 55°C) differed significantly between control and drought treatments for the most drought sensitive family, but not for drought hardy families. Variation among the 12 families in q (at 25°C) and μCO2 were significant (p<0.05) when families were grown in the control treatment. Family means for height increments (r2=0.43 to 0.58; p<0.05) related negatively to respiration and diameter increments related positively to respiration traits (r2=0.34 to 0.56; p<0.05). Temperature coefficient of CO2 production rate under control treatment was negatively associated with shoot damage (r2=0.34; p<0.05) suggesting that respiration traits may be useful for evaluating drought hardiness in this species.