Measuring and simulating crown respiration of Scots pine with increased temperature and carbon dioxide enrichment.

Acclimation to elevated atmospheric carbon dioxide concentration and temperature of respiration by the foliage in the crown of Scots pine (Pinus sylvestris) trees is measured and modelled. Starting in 1996, individual 20-year-old trees were enclosed in chambers and exposed to either normal ambient conditions (CON), elevated CO2 concentration (EC), elevated temperature (ET) or a combination of EC and ET (ECT). Respiration of individual leaves within the crown was measured in 2000. To extrapolate the response of respiration of individual leaves to the whole crown, a multi-layer model was developed and used to predict daily and annual crown respiration, in which the crown structure and corresponding microclimate data were used as input. Respiration measurements showed that EC led to higher Q10 values (4.6%) relative to CON, but lower basal respiration rates at 20 degrees C [R1.d(20)] (-7.1%) during the main growth season (days 120-240), whereas ET and ECT both reduced Q10 (-12.0 and -9.8%, respectively) throughout the year but increased R1.d(20) (27.2 and 21.6%, respectively) during the period of no-growth, and slightly reduced R1.d(20) (-1.7 and -2.8%, respectively) during the main growth season. Model computations showed that annual crown respiration increased: (1) by 16% in EC, with 92% of this increase attributable to the increase in foliage area; (2) by 35% in ET, with 66% related to the increase in foliage area and 17% to the rise in ambient temperature; and (3) by 27% in the case of ECT, with 43% attributable to the increase in foliage area and 29% to the rise in ambient temperature. Changed respiration parameters for individual leaves, induced by treatments, made only a small contribution to the annual crown respiration compared with the increased foliage area. The effects of changes in crown architecture and nitrogen distribution, caused by treatments, on the daily and annual course of crown respiration are discussed.