关键词: CO₂浓度, 马尾松, 净光合速率, 气孔导度, 单萜烯释放速率, 开顶式气室

Abstract:

【Objective】Biogenic volatile organic compounds(BVOCs)are the main components of volatile organic compounds (VOCs) in the atmosphere and one of the key compounds of vegetation that affect the environment and climate. With the intensification of the global climate change, the research on BVOCs emission by plants under increasing CO₂ levels has gained a considerable interest. Effects of the elevated CO₂ concentrations on photosynthetic characteristics and monoterpene emission rate in Masson pine (Pinus massoniana) seedlings were studied to improve the understanding of the response mechanism of plant BVOC emissions to the climate change.【Method】According to the atmospheric CO₂ concentrations in different carbon emission scenarios reported in the Intergovernmental Panel on Climate Change (IPCC) fifth assessment report, 1-year-old Masson pine seedlings were fumigated with CO₂ concentration gradients, consisting of ambient air (437 μmol/mol,CK), 550 μmol/mol, 750 μmol/mol, and 1 000 μmol/mol in 12 open-top chambers (three replicated chambers for each), from September 10th to November 20th, 2017. The elevated CO₂ concentrations were maintained for 9 hours per day from 08:00 to 17:00. In the middle of October and November, the net photosynthetic rate and stomatal conductance of Masson pine seedlings were measured in ambient air from 09:00 to 11:30. Pine needles were collected for a chlorophyll determination. Monoterpene emissions of Masson pine seedlings were also sampled in the middle of October and November using a dynamic headspace adsorption sampling method with 200 mL/min for 30 min; all sampling experiments were carried out during 09:00-11:30 and 13:30-15:30. Monoterpene samples were collected through Tenax-TA glass tubes (Mesh 60/80) and analyzed using TDS-GC/MS. 【Result】Chlorophyll a and chlorophyll b of the plant seedlings exposed to 750 μmol/mol and 1 000 μmol/mol CO₂ for 60 days were both significantly lower than those under CK, and the total chlorophyll content decreased by 17.54% and 29.82%, respectively. However, the difference was not significant when fumigation was performed for 30 days. When measured in ambient air, the net photosynthetic rate and stomatal conductance of Masson pine seedlings treated with 60-day CO₂ enrichment was significantly lower than those under CK; however, there was also no significant difference when treated for 30 days. In addition, the total chlorophyll content of Masson pine seedlings was positively correlated with the leaf net photosynthetic rate significantly. Monoterpene emissions by Pinus massoniana were decreased by the elevated CO₂ after 60-day fumigation; the emission rate reached the lowest at the concentration of 1 000 μmol/mol, with a decrease of 19.43% (fumigated for 30 days) and 59.62% (fumigated for 60 days). After 60-day treatment, the monoterpene emission rate of P. massoniana seedlings was significantly and positively correlated to the leaf net photosynthetic rate and stomatal conductance.【Conclusion】With the extension of fumigation time,the photosynthetic acclimation of P. massoniana was revealed; the decline in monoterpene emissions may be attributed to the decrease in stomatal conductance under the condition of elevated CO₂ concentration.

Key words: CO₂ concentration, Pinus massoniana, net photosynthetic rate, stomatal conductance, monoterpene emission rate, Open-Top Chamber (OTCs)