Seasonal variations in whole-ecosystem BVOC emissions from a subtropical bamboo plantation in China

摘要

Isoprene and monoterpene emissions and environmental conditions were measured over a six month period in a Lei bamboo (Phyllostachys violascens) forest in a subtropical region in China. Isoprene and monoterpene emissions were measured using a relaxed eddy accumulation (REA) system on an above-canopy tower. From July to November of 2012, isoprene contributed 99.1% of terpenoid emissions. alpha-pinene, constituting 0.8% of total observed terpenoid emissions, was the only monoterpene for which a significant flux was detected. Emissions of the sesquiterpenes longifolene and alpha-cedrene were observed at very low rates. Isoprene and alpha-pinene emissions exhibited strong diurnal variations, with lower emissions in the morning and late evening, and the highest emissions around noon. BVOC peak emissions typically occurred a few hours after the noon PAR peak and coincided with the daily temperature peak. This behavior can be described reasonably well by the MEGANv2.1 biogenic emission model. During the campaign (i.e., from 7 July, 2012 to 19 Jan., 2013), the mean (and maximum) emission fluxes (mg m(-2) h(-1)) were 0.95 (1032) for isoprene, 0.010 (0.176) for alpha pinene, 0.001 (0.063) for longifolene, and 2.6 x 10(-4) (0.009) for alpha-cedrene, respectively. During the winter season, when the ground was covered by organic mulch to increase soil temperature and to increase the yield of bamboo shoot, there was no evident impact on BVOC emissions. The observed seasonal variation followed the general behavior predicted by the MEGANv2.1 model, with lower emissions associated with cooler conditions, but the magnitude of the emission decrease was greater than expected indicating driving variables are missing from the model. Emission factors, representing the emission expected for a Leaf Area Index of 5 at a temperature of 30 degrees C and PAR of 1500 mu mol m(-2) s(-1), during the peak growing season for this site were 0.008 mg m(-2) h(-1) for alpha-pinene and 3.3 mg m(-2) h(-1) for isoprene. The isoprene emission factor is similar to the value (3.6 mg m(-2) h(-1)) for this location in the MEGANv2.1 global biogenic emission model. A second bamboo plantation, containing Moso bamboo (Phyllostachys heterocycla), was investigated and found to have similar isoprene and monoterpene emission rates as Lei bamboo forest. The emission data obtained in this study are the first canopy-scale flux measurements reported for bamboo plantations and demonstrate the potential importance of bamboo isoprene emissions for regional ozone and organic aerosol production. (C) 2015 Elsevier Ltd. All rights reserved.