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.) France). Material included 3- year-old seedlings from 12 families grown under two treatments: control (we ll-watered) and drought (moderate drought the second growing season followe d by severe drought the next year). Respiratory parameters measured were me tabolic heat rate (q) and rate of CO2 production (R-CO2) Calculated paramet ers were the ratio of metabolic heat rate to CO2 production rate (q/R-CO2), specific growth rate (R-SG) and Arrhenius temperature coefficients of meta bolic heat (mu(q)) and CO2, production (mu(CO2)) Growth traits measured wer e third-year increments of seedling height and diameter. Means of respiration traits were generally less in the drought treatment th an in the control, with the exception of mu(q), which increased under droug ht. Consistent increase in mu(q) and decrease in mu(CO2) values in response to drought appear to suggest a differential influence of drought on the te mperature dependence of ATP synthesis in catabolic reactions, and ATP break down in anabolic reactions or in futile cycles of dark respiration. Metabol ic heat rates measured over a wide a range of temperatures (20 to 55 degree s 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 degrees C) and mu(CO2) were sig nificant (p<0.05) when families were grown in the control treatment. Family means for height increments (r(2)=0.43 to 0.58; p<0.05) related negatively to respiration and diameter increments related positively to respiration t raits (r(2)=0.34 to 0.56; p<0.05). Temperature coefficient of CO2 productio n rate under control treatment was negatively associated with shoot damage (r2=0.34; p<0.05) suggesting that respiration traits may be useful for eval uating drought hardiness in this species. (C) 2000 Elsevier Science B.V. Al l rights reserved.