马占相思人工林净二氧化碳交换和碳同位素通量

应用稳定碳同位素技术，对马占相思人工林冠层受光和遮荫叶片的碳同化率(A_net)和叶面积指数(L)进行加权，将叶片水平的¹³C甄别率(Δ_i)扩展至冠层光合甄别率(Δ_canopy)，测定光合固定和呼吸释放的碳同位素通量及其净交换通量.结果表明：Δ_canopy的日变化明显，日出前和中午出现较低值(18.47‰和19.87‰)，而日落前达到最大(21.21‰)；秋季末期(11月)至翌年夏季，Δ_canopy逐步升高，年平均为(20.37±0.29)‰.不同季节自养呼吸(日间叶片呼吸除外)和异养呼吸释放CO₂的碳同位素比率(δ¹³C)平均值分别为(-28.70±0.75)‰和(-26.75±1.3)‰，春季林冠夜间呼吸CO₂的δ¹³C最低(-30.14‰)，秋季末期最高(-28.01‰).马占相思林与大气的CO₂碳同位素通量在春季和夏季中午时峰值分别为178.5和217 μmol·m^-2 ·s^-1·‰，日均值分别为638.4 和873.2 μmol·m^-2·s^-1·‰.冠层叶片吸收CO₂的碳同位素通量较呼吸释出CO₂的碳同位素通量高1.6～2.5倍，表明马占相思林日间吸收大量CO₂，降低空气CO₂浓度，具有改善环境的良好生态服务功能.

Net CO_2 exchange and carbon isotope flux in Acacia mangium plantation

By using stable carbon isotope technique,the leaf-level ~(13)C discrimination was integrated to canopy-scale photosynthetic discrimination(Δ_(canopy) through weighted the net CO_2 assimilation(A_(net)) of sunlit and shaded leaves and the stand leaf area index(L)in an A.mangium plantation,and the carbon isotope fluxes from photosynthesis and respiration as well as their net exchange flux were obtained.There was an obvious diurnal variation in Δ_(canopy) being lower at dawn and at noon time(18.47‰ and 19.87‰,respectively) and the highest(21.21‰) at dusk.From the end of November to next May,the Δ_(canopy) had an increasing trend,with an annual average of(20.37±0.29)‰.The carbon isotope ratios of CO_2 from autotrophic respiration(excluding daytime foliar respiration)and heterotrophic respiration were respectively(-28.70±0.75)‰ and(-26.75±1.3)‰ in average.The δ~(13) of nighttime ecosystem-respired CO_2 in May was the lowest(-30.14‰),while that in November was the highest(-28.01‰).The carbon isotope flux of higher than that of CO_2 emitted from respiration,suggesting that a large sum of CO_2 was absorbed by A.mangium,which decreased the atmospheric CO_2 concentration and improved the environment.