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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >PHOTOSYNTHESIS AND CARBON ISOTOPE DISCRIMINATION IN BOREAL FOREST ECOSYSTEMS - A COMPARISON OF FUNCTIONAL CHARACTERISTICS IN PLANTS FROM THREE MATURE FOREST TYPES
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PHOTOSYNTHESIS AND CARBON ISOTOPE DISCRIMINATION IN BOREAL FOREST ECOSYSTEMS - A COMPARISON OF FUNCTIONAL CHARACTERISTICS IN PLANTS FROM THREE MATURE FOREST TYPES

机译：北方森林生态系统的光合作用与碳同位素判别-三种成熟林类型植物功能特性的比较。

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In this paper we compare measurements of photosynthesis and carbon isotope discrimination characteristics among plants from three mature boreal forest types (Black spruce, Jack pine, and aspen) in order to help explain variation in ecosystem-level gas exchange processes. Measurements were made at the southern study area (SSA) and northern study area (NSA) of the boreal forest in central Canada as part of the Boreal Ecosystem-Atmosphere Study (BOREAS), In both the NSA and the SSA there were significant differences in photosynthesis among the major tree species, with aspen having the highest CO2 assimilation rates and spruce the lowest, Within a species, photosynthetic rates in the SSA were approximately twice those measured in the NSA, and this was correlated with similar variations in stomatal conductance. Calculations of the ratio of leaf intercellular to ambient CO2 concentration (c(i)/c(a)) from leaf carbon isotope discrimination (Delta) values indicated a relatively low degree of stomatal limitation of photosynthesis, despite the low absolute values of stomatal conductance in these boreal tree species. Within each ecosystem, leaf Delta values were strongly correlated with life-form groups (trees, shrubs, forbs, and mosses), and these differences are maintained between years. Although we observed significant variation in the C-13 content of tree rings at the old Jack pine site in the NSA during the past decade (indicating interannual variation in the degree of stomatal limitation), changes in summer precipitation and temperature accounted for only 44% of the isotopic variance. We scaled leaf-level processes to the ecosystem level through analyses of well-mixed canopy air. On average, all three forest types had similar ecosystem-level Delta values (average value +/- standard deviation, 19.1 parts per thousand +/- 0.5 parts per thousand), calculated from measurements of change in the concentration and carbon isotope ratio of atmospheric CO2 during a diurnal cycle within a forest canopy. However, there were seasonal changes in ecosystem discrimination for aspen forests, while the evergreen conifer forests exhibited relatively constant discrimination values throughout the active growing season. [References: 58]
机译：在本文中，我们比较了三种成熟的北方森林类型（黑云杉，杰克松和白杨）的植物之间的光合作用和碳同位素歧视特征的测量值，以帮助解释生态系统水平气体交换过程的变化。作为加拿大北方生态系统-大气研究（BOREAS）的一部分，在加拿大中部寒带森林的南部研究区（SSA）和北部研究区（NSA）进行了测量。在NSA和SSA中，在主要树种之间的光合作用，其中白杨具有最高的CO2同化率，云杉最低。在一个树种内，SSA中的光合作用速率约为NSA中测量值的两倍，这与气孔电导率的类似变化相关。尽管气孔电导的绝对值较低，但根据叶碳同位素判别（Δ）值计算出的细胞间CO2与环境CO2浓度之比（c（i）/ c（a））表明，光合作用的气孔限制程度相对较低。在这些北方树种中。在每个生态系统中，叶片的Delta值与生命形态组（树木，灌木，Forb和苔藓）密切相关，并且这些差异在数年之间保持不变。尽管在过去的十年中，我们在NSA的老杰克松树站点观察到树木年轮的C-13含量有显着变化（表明气孔限制程度的年际变化），但夏季降水和温度的变化仅占44％同位素方差通过对混合良好的冠层空气进行分析，我们将叶片级过程扩展到了生态系统级。平均而言，这三种森林类型都具有相似的生态系统水平的Delta值（平均值+/-标准偏差，每千分之19.1 +/-千分之0.5），这是通过测量大气中浓度和碳同位素比的变化得出的森林冠层在昼夜循环中的二氧化碳。然而，白杨林的生态系统判别存在季节性变化，而常绿针叶林在整个生长期都表现出相对恒定的判别值。 [参考：58]

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