Seasonal change in the temperature coefficientQ 10 for respiration of field-grown hinoki cypress (Chamaecyparis obtusa) trees

The effect of temperature upon nighttime respiration was examined on four different sized sample trees in a 17-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.) stand over two years. Seasonal changes inQ ₁₀ values and their responses to mean temperature were investigated. On the basis of the monthly relationships between nighttime respiration (r) and temperature inside a chamber (θ),r=r ₀exp (kθ), theQ ₁₀ value (=exp(10k)) was calculated. TheQ ₁₀ values were high (Q ₁₀≥3.0) in winter when mean air temperature was low, and gradually decreased toward summer (Q ₁₀≤1.5) through spring with increasing temperature. TheQ ₁₀ values were negatively correlated with mean air temperature. The response ofQ ₁₀ values to mean air temperature was described by a single equation, regardless of tree size. This result, which might be characteristic of this species, shows that respiration ofC. obtusa trees is promoted by slight increases of air temperature in winter season. On the other hand, temperature sensitivity of total respiration reduced during growing season when ambient temperature was high. These chaning temperature sensitivity according to seasons may depend on the seasonal change of the ratio of growth respiration to total respiration. It is concluded that changes in temperature due to changing seasons not only change respiration rate, but also change the response of respiration rate to temperature by shiftingQ ₁₀ values.