环境变化对几个树种在北方田间条件下气体交换的影响

The Effects of Environmental Variables on Gas Exchange of Several Tree Species Under Boreal Field Conditions

关键词:  树种  气体交换  净二氧化碳同化率  气孔导度  光合作用  光流动量  气温  蒸气压差

Key words:  tree species  gas exchange  net CO₂ assimilation  stomatalconductance  photosynthesis  photosynthetic photon flux density  air temperature  vapor pressure deficit

摘要:

1994年和1995年夏季在加拿大Saskatchewan省Prince Albert市北部森林测定环境条件对欧洲杨(Populus tremuloides Michx.),胶杨(Populus balsamifera L.),榛子(Corylus cornuta Marsh.),短叶松(Pinus banksiana Lamb.)和黑云杉(Picea mariana(Mil)BSP)气体交换的影响。气体交换率的测定使用便携式气体交换系统(LI-6200)。结果表明光合作用光流动量(PPFD)、气温(Ta)、蒸气压差(VPD)和体内二氧化碳浓度(Ci)均对气体交换有显著影响,但对不同树种影响程度不同。在大气二氧化碳浓度(Ca)和相对稳定的气温和蒸气压差下,欧洲杨比短叶松和黑云杉有较高光饱和点、同化量子产量(H)、在饱和PPFD下最高同化率(Pm)和较低的光补偿点(LCP)。对欧洲杨树,幼龄树比老龄树有较高光合能力,且生长季早期光合能力比后期高。欧洲杨和短叶松的气孔导度(gs)随PPFD增加而增加。但黑云杉gs不受PPFD影响。在高光强下(PPFD>1000μmol·m^-2 s^-1),欧洲杨幼树被光叶片比曝光叶片表现较低的净二氧化碳同化率(A)、gs和暗呼吸(Rd)。短叶松和黑云杉Pm、H和Rd没有统计上差异。在高光强下,当气温从15℃增至35℃时,欧洲杨A和gs增加,黑云杉的降低,而短叶松没有明显变化。欧洲杨A和gs最高值的适宜的气温是24℃~29℃,短叶松是22℃~28℃,黑云杉是21℃~27℃。VPD明显影响欧洲杨、短叶松和黑云杉的气体交换,A和gs均随VPD降低而增高。短叶松和黑云杉当年生树枝A通常比一年龄和二年龄树枝低。两个针叶树种一年龄和二年龄树枝的气体交换没有明显差异。A-Ci反应的斜率(即羧化效率(CE))取决于PPFD、树种和树龄。一般情况下,CE遵循以下模式:欧洲杨 > 胶杨 > 榛子 > 短叶松,欧洲杨幼树 > 老树。总的结果表明尽管Ci、Ta和VPD改变光合作用效率,但光是最主要的因子。在高光强下,影响气体交换的环境因子是气温和蒸气压差。

Abstract:

The influence of environmental conditions on gas exchange of aspen (Populus tremuloides Michx.), balsam poplar (Populus balsamifera L.), hazelnut (Corylus cornuta Marsh.), jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill) BSP) was examined during the summers of 1994 and 1995 in the boreal forest near Prince Albert, Saskatchewan, Canada.Gas exchange rates were measured with a portable gas exchange system.The results showed that there were significant effects of photosynthetic photon flux density (PPFD), air temperature (Ta), vapor pressure deficit (VPD) and internal CO₂ concentration (Ci) on gas exchange. The effects differed among the different species. Under ambient CO₂ concentrations (Ca), and relatively constant Ta and VPD, aspen showed a higher light saturation point, quantum yield of assimilation (H), and maximum assimilation at saturating PPFD(Pm), and a lower light compensation point (LCP) than either jack pine or black spruce. In aspen, the photosynthetic capacity was higher in younger trees than in older trees, and was higher in the earlier growing season than in the later growing season. Stomatal conductance (gs) increased with increasing PPFD for both aspen and jack pine. There was no obvious effect of PPFD on gs for black spruce. Under high light (PPFD >1000 μmol m^-2 s ^-1), young aspen leaves from shaded canopy positions showed lower net CO₂ assimilation (A), gs and dark respiration (Rd) than sun leaves from exposed canopy positions. There were no statistical differences in Pm, H and Rd between jack pine and black spruce. Under high light, as Ta increased from 15℃ to 35℃, A and gs increased for aspen, decreased for black spruce and were not obviously influenced for jack pine.Net assimilation rate and gs were highest in the Ta range of 24℃~29℃ for aspen, 22℃~28℃ for jack pine and 21℃~27℃ for black spruce.The effect of VPD on gas exchange was significant for aspen, jack pine and black spruce which showed that A and gs increased with decreasing VPD. The current year shoots usually showed lower A than those of 1-and 2-year old shoots for jack pine and black spruce. There was no difference in gas exchange between 1-and 2-year old shoots in either conifer species. The initial slopes of the A-Ci responses (i.e., carboxylation efficiency (CE)) were PPFD dependent and differed among species and tree ages. In general, CE followed the pattern:aspen > balsam poplar > hazelnut > jack pine, and young aspen > old aspen. The overall results indicated that light was the major determinant of photosynthetic rate, although the rate was modified by Ci, Ta and VPD. Under high light, the major environmental influences on gas exchange were Ta and VPD.