Photosynthesis and respiration ofPinus pumila needles in relation to needle age and season

Rates of net photosynthesis and dark respiration were measured for detached needles ofPinus pumila trees growing on the Kiso mountain range in central Japan in 1987. Dependency of photosynthesis on light and temperature was examined in relation to needle age and season. The light saturation point of net photosynthesis was lower in 3- and 4-yr-old needles than that in current (flushed in 1987), 1- and 2-yr-old needles.P _nmax, net photosynthetic rates at 1000 μmol m⁻² s⁻¹ and 15°C, of needles from 1- to 4-yr-old generally decreased with needle age.P _nmax of 1- to 4-yr-old needles became higher in August than in other months, andP _nmax of current needles did so in September. Current needles showed high respiration rates (at 15°C) only in August. Optimum air temperatures for net photosynthesis at 1000 μmol m⁻² s⁻¹ were between 10 and 15°C for current and 1-yr-old needles. The temperature coefficient of dark respiration rates was 2.3–3.3 for current needles from August to October, and 2.2 for 1-yr-old needles in mid-July.