title: Photosynthesis and transpiration ofPinus radiata D. Don under natural conditions in a forest stand.
abstract: Gas-exchange ofPinus radiata foliage was measured with climatised cuvettes under natural light in the sun-crown of 8 m tall trees in a forest stand. Measurement began during a period of drought (ψWS-8.2 bar, ψWe-10.5 bar) and continued after elimination of soil moisture-deficit by watering (ψWS-0.5 bar, ψWe-5.5 bar). Soil and air moisture-deficits severely restricted gas-exchange. Watering resulted in an immediate decline in stomatal resistance (rs) and an increase in net photosynthesis (PN) of 13%. A slower progressive gas-exchange recovery occurred additionally during the 10 days after watering leading to a further decline inrsto 3 s cm-1and an ultimate increase inPNof 38% when measured under comparable conditions at 8 mb v.p.d. Radiata pine had a high photosynthetic capacity with a measured maximumPNof 10.2 mg CO2dm-2h-1total needle surface (11.4 mg CO2g-1DM h-1).Optimum temperature forPNin March (late summer) occurred at ca. 18°C. Rate ofPNwas 95% saturated at irradiance of 900 μE m-2s-1and 50% saturated at only 270 μE m-2s-1. Radiata pine needles responded directly to changes in atmospheric humidity by adjusting their stomatal diffusive resistance. As a result, between 8 and 18 mb v.p.d.PNdeclined by 2.3% mb-1increase.
authors.affiliation: Forest Research Institute, P.O. Box 31-011, Christchurch, New Zealand.
authors.forename: Udo
authors.initials: U
authors.lastname: Benecke