摘要：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 the re 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 (Φ), 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 young er 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>1 000 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 difference s in Pm, Φ 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, an d 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 exchan ge were Ta and VPD.%1994年和1995年夏季在加拿大Saskatchewa n省Prince Albert市北部森林測定環境條件對歐洲楊(Populus tremuloides Michx.), 膠楊(Populus balsamifera L.),榛子(Corylus cornuta Marsh.),短葉松(Pin us banksiana Lamb.)和黑云杉(Picea mariana (Mill) BSP)氣體交換的影響.氣體交換率的測定使用便攜式氣體交換系統(LI-6200).結果表明光合作用光流動量(PPFD)、氣溫(Ta)、蒸氣壓差(VPD)和體內二氧化碳濃度(Ci)均對氣體交換有顯著影響,但對不同樹種影響程度不同.在大氣二氧化碳濃度(Ca)和相對穩定的氣溫和蒸氣壓差下,歐洲楊比短葉松和黑云杉有較高光飽和點、同化量子產量(Φ)、在飽和PPFD下最高同化率(Pm)和較低的光補償點(LCP).對歐洲楊樹,幼齡樹比老齡樹有較高光合能力,且生長季早期光合能力比后期高.歐洲楊和短葉松的氣孔導度(gs)隨PPFD增加而增加.但黑云杉gs不受PPFD影響.在高光強下(PPFD>1 000 μmol*m-2s-1),歐洲楊幼樹被光葉片比曝光葉片表現較低的凈二氧化碳同化率(A)、gs和暗呼吸(Rd).短葉松和黑云杉Pm、Φ和Rd沒有統計上差異.在高光強下,當氣溫從15℃增至35℃時,歐洲楊A和gs增加,黑云杉的降低,而短葉松沒有明顯變化.歐洲楊A和gs最高值的適宜的氣溫是24℃～29℃,短葉松是22℃～28 ℃,黑云杉是21℃～27℃.VPD明顯影響歐洲楊、短葉松和黑云杉的氣體交換,A和gs 均隨VPD降低而增高.短葉松和黑云杉當年生樹枝A通常比一年齡和二年齡樹枝低.兩個針葉樹種一年齡和二年齡樹枝的氣體交換沒有明顯差異.A-Ci反應的斜率(即羧化效率(CE))取決于PPFD、樹種和樹齡.一般情況下,CE遵循以下模式:歐洲楊>膠楊>榛子>短葉松, 歐洲楊幼樹>老樹.總的結果表明盡管Ci、Ta和VPD改變光合作用效率,但光是最主要的因子 .在高光強下,影響氣體交換的環境因子是氣溫和蒸氣壓差.
