【摘要】 精确模拟冠层气孔导度(GS)对于评估区域蒸散具有重要意义。该研究选择两种常见的人工阔叶树种尾叶桉(Eucalyptusurophylla,外来种)和木荷(Schimasuperba,本地种)作为研究对象,利用K?stner法和修订的Penman-Monteith公式计算冠层平均气孔导度(分别定义为GS1和GS2)。研究还分析了环境因子对冠层脱耦联系数(Ω)的影响,并用其来评价两种方法模拟的冠层气孔导度的合理性。结果表明,两个树种冠层气孔导度均与气象条件耦合较好(尾叶桉:Ω=0.10±0.03,木荷:Ω=0.17±0.03)。主成分分析显示,光合有效辐射(PAR)以及水汽压亏缺(D)显著影响Ω的大小,而风速(u)的影响较小。单因素分析则发现各环境因子与Ω之间的相关性并不显著。边界线分析表明D和PAR的增加使得Ω最终趋向于一个与树种有关的稳定值(木荷≈0.20,尾叶桉≈0.05),而Ω随u的增加呈幂指数下降。与木荷相比,尾叶桉具有更高的气孔导度(尾叶桉和木荷的GS2年平均值分别为(33.42±9.37) mmol·m–2·s–1和(23.40±2.03) mmol·m–2·s–1),并且尾叶桉和木荷的GS1与GS2的线性拟合斜率分别为0.92 (R2≈0.70)和0.98 (R2≈0.76),表明GS1比GS2高估了冠层气孔导度。另外, GS1和GS2对水汽压亏缺的敏感性与参比气孔导度(GSiref, D=1 kPa时的气孔导度)的比值Pi与Ω紧密相关。根据统计,尾叶桉和木荷的GS1估计值在Ω=0.05–0.15 (83.1%的数据)和0.10–0.20 (47.8%的数据)之间时是相对可靠的。更多还原

【Abstract】 Aims Accurate simulation of canopy stomatal conductance(GS) is quite important for the assessment of regional evapotranspiration.Methods In this study, two planted broad-leaved tree species, Eucalyptus urophylla(exotic species) and Schima superba(native species), were chosen to estimate their GS with two different methods of K?stner(GS1) and inversed Penman-Monteith equation(GS2). The effect of environmental factors on canopy decoupling coefficient(Ω) was evaluated before they were adopted to assess the reasonability of GS simulated by the two methods.Important findings Results showed that the GS of the two tree species was well coupled with meteorological conditions(Ω = 0.10 ± 0.03 for E. urophylla and 0.17 ± 0.03 for S. superba). Principal component analysis showed that photosynthetically active radiation(PAR) and vapor pressure deficit(D) significantly dominated the variations of Ω, while the effect of wind speed(u) was very weak. Multivariate correlation analysis also found weak relations between those environmental factors and Ω. Boundary line analysis revealed that the increase of D and PAR would eventually force Ω approaching a constant value as determined by tree species(S. superba ≈ 0.20,E. urophylla ≈ 0.05), while Ω decreases exponentially with the increase of u. Compared with S. superba, E. urophylla has higher GS. The annual averages GS2 of E. urophylla and S. superba were(33.42 ± 9.37) mmol·m–2·s–1 and(23.40 ± 2.03) mmol·m–2·s–1, respectively. Linear fitting showed that the GS2/GS1 ratio of E. urophylla and S.superba was 0.92(R2 ≈ 0.70) and 0.98(R2 ≈ 0.76), respectively, implying the overestimated canopy stomatal conductance for GS1(p < 0.01). In addition, the ratio of the sensitivity of canopy stomatal conductance to vapor pressure deficit to stomatal conductance at D = 1 kPa(GSiref) for GS1 and GS2 is closely related to Ω. Based on the estimation, GS1 was relatively reliable when Ω = 0.05–0.15(83.1% of all the data) and 0.10–0.20(47.8% of all the data) for E. urophylla and S. superba.更多还原