Topographic Controls on Stomatal and Mesophyll Limitations to Photosynthesis in Two Subalpine Conifers
Topographic Controls on Stomatal and Mesophyll Limitations to Photosynthesis in Two Subalpine Conifers
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DOI：
10.1086/718050
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发表时间：
2022-01
影响因子：
2.3
通讯作者：
Jiemin Guo;D. Beverly;J. Mercer;C. Cook;B. Ewers;David G. Williams
中科院分区：
文献类型：
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作者：
Jiemin Guo;D. Beverly;J. Mercer;C. Cook;B. Ewers;David G. Williams
研究的前提。叶片气孔导度和叶肉导度限制光合作用，影响水分利用效率。很少有研究量化这些CO2扩散途径在自然条件下对成熟针叶树光合作用的相对限制。本文报道了两种落基山针叶树的气孔导度和叶肉导度在不同地形位置的季节性干燥过程中的变化。我们预测，地形对土壤水分有效性和能量平衡的控制将决定叶肉导度对针叶树光合作用的限制，并具有气孔和水力性状的不同模式。方法。利用叶片气体交换和碳同位素识别的同步测量方法，估算了落基山脉中部等水种黑松（Pinus contorta）和各水种恩格尔曼云杉（Picea engelmannii）树枝的气孔导度和叶肉导度。然后利用CO2响应曲线数据对光合作用(A)进行定量限制分析。关键的结果。气孔导度对光合作用的限制（42% ~ 67%）大于叶肉导度（5% ~ 17%），但两种针叶树的光合作用差异不显著。在中丘低坡位置，A、gs和gm在生长季节增加，尽管土壤湿度下降。相反，在较干燥的上山坡位置，生长季节土壤湿度的下降和气温的升高与gs的减少相关，而与A或gm无关。在生长季节，当气孔导度随水分限制而降低时，转基因调节在维持光合作用和提高植物水分利用效率方面发挥了潜在的重要作用。季节性干旱的持续转基因可能是针叶树在低资源生境中生存和保持竞争优势的重要机制。
Premise of research. Leaf stomatal and mesophyll conductances limit photosynthesis and influence water use efficiency. Few studies have quantified the relative limitations imposed by these CO2 diffusion pathways on photosynthesis in mature conifer trees under natural conditions. Here, we report observations of stomatal and mesophyll conductance changes during seasonal drying across contrasting topographic positions in two Rocky Mountain conifers. We predicted that topographic controls on soil water availability and energy balance would determine limitations to photosynthesis by mesophyll conductance across conifer species with contrasting patterns of stomatal and hydraulic traits. Methodology. Concurrent measurements of leaf gas exchange and carbon isotope discrimination were used to estimate stomatal (gs) and mesophyll (gm) conductance in branches of an isohydric species, lodgepole pine (Pinus contorta), and an anisohydric species, Engelmann spruce (Picea engelmannii), in the central Rocky Mountains. Quantitative limitation analysis of photosynthesis (A) was then performed using data from CO2 response curves. Pivotal results. Stomatal conductance imposed greater limitations on photosynthesis (42%–67%) than mesophyll conductance (5%–17%), but no significant differences in gm were observed between the two conifer species. At the mesic lower hillslope position, A, gs, and gm increased during the growing season despite declines in soil moisture. In contrast, at the drier upper hillslope position, declines in soil moisture and increases in air temperature during the growing season are correlated with reductions in gs but not with A or gm. Conclusions. Adjustments in gm played a potentially important role in sustaining photosynthesis and improving plant water use efficiency when stomatal conductance decreased with water limitation during the growing season at the research site. Sustained gm with seasonal drought may be an important mechanism allowing conifers to survive and maintain competitive dominance in low-resource habitats.