Summary Temperature acclimation of respiration may contribute to climatic adaptation and thus differ among populations from contrasting climates. Short‐term temperature responses of foliar dark respiration were measured in 33‐yr‐old trees of jack pine (Pinus banksiana) in eight populations of wide‐ranging origin (44–55°N) grown in a common garden at 46.7°N. It was tested whether seasonal adjustments in respiration and population differences in this regard resulted from changes in base respiration rate at 5°C (R5) or Q10 (temperature sensitivity) and covaried with nitrogen and soluble sugars. In all populations, acclimation was manifest primarily through shifts in R5 rather than altered Q10. R5 was higher in cooler periods in late autumn and winter and lower in spring and summer, inversely tracking variation in ambient air temperature. Overall, R5 covaried with sugars and not with nitrogen. Although acclimation was comparable among all populations, the observed seasonal ranges in R5 and Q10 were greater in populations originating from warmer than from colder sites. Population differences in respiratory traits appeared associated with autumnal cold hardening. Common patterns of respiratory temperature acclimation among biogeographically diverse populations provide a basis for predicting respiratory carbon fluxes in a wide‐ranging species.

Needle CO 2 exchange, structure and defense traits in relation to needle age in Pinus heldreichii Christ ± a relict of Tertiary flora AbstractmPinus heldreichii Christ is a long-lived, slowgrowing Tertiary relict from the Balkans. In this study we evaluated the physiological characteristics of eight needleage classes of P. heldreichii grown at the Arboretum of the Institute of Dendrology in Ko Ârnik, Poland. At the end of the growing season, current-year foliage had the highest rates of mass-based light-saturated net photosynthesis (Asat) of 33.5 nmol CO2 ? g ±1 ? s ±1 . Asat decreased with needle age, but older needle classes retained from approximately 62 to 26% of the current needles' rate. The relationship between leaf N and chlorophyll a concentration among all needleage classes was highly significant (r = 0.96, P = 0.0006). The variation in Asat of 1-to 7-year-old needles was linearly related to needle N concentration (r = 0.98, P = 0.0001). Needle dark respiration rates among these needle age classes ranged from 0.8 to 2.2 nmol ? g ±1 ? s ±1 and decreased with needle age and nitrogen concentration. Total phenols and glucose concentrations increased linearly with needle age. A similar pattern was observed in acid buffering capacity and the pH of tissue homogenates. The water content ranged from 62% for the current needles to 51% for the 6-year-old needles. Greater investment in leaf structural tissue and increased chemical defense is associated with higher structural cost of older needles and may reduce their photosynthetic activity. Significant declines in water and nitrogen content with needle age and an increase in content of phenolics is most likely a defense adaptation of P. heldreichii related to the species' long-lived leaves.

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