The effect of CO2 concentration on carbon isotope discrimination during photosynthesis in Ginkgo biloba: implications for reconstructing atmospheric CO2 levels in the geologic past
The effect of CO2 concentration on carbon isotope discrimination during photosynthesis in Ginkgo biloba: implications for reconstructing atmospheric CO2 levels in the geologic past
复制标题
DOI：
10.1016/j.gca.2022.09.033
复制
发表时间：
2022-10
影响因子：
5
通讯作者：
Mason A. Scher;R. Barclay;A. Baczynski;Bryton A. Smith;J. Sappington;Lily Bennett;Suvankar Chakraborty;Jonathan P. Wilson;J. Patrick Megonigal;S. Wing
中科院分区：
文献类型：
--
作者：
Mason A. Scher;R. Barclay;A. Baczynski;Bryton A. Smith;J. Sappington;Lily Bennett;Suvankar Chakraborty;Jonathan P. Wilson;J. Patrick Megonigal;S. Wing
一些实验和对自由生活植物的观察发现，大气中二氧化碳浓度(PCO2)的增加与C3植物在光合作用(Δ13C)过程中对13C的辨别能力增加直接相关。这种相关性的倒置形式已被用来估计地质过去(即C3植物替代物)的二氧化碳含量，但很少有实验工作来确定在更自然的环境中以及在与深部地质记录相关的一系列二氧化碳含量中，二氧化碳作为区分驱动因素的相对重要性。在这里，我们报道了一项探索银杏中pCO2和Δ13C之间关系的实验。银杏是一种长期用于推断过去二氧化碳水平的植物，因为现存的银杏与银杏化石具有很强的相似性，而且银杏化石中保存着来自全球变暖气候晚期中生代和新生代时期的角质层。我们在大气二氧化碳(∼425ppm)和高水平(∼600、∼800和∼1000ppm)下对银杏进行了三年的种植，同时测量了空气(δ13Cair)和叶片(δ13Caf)的碳同位素组成(Ci/Ci)、内外CO2浓度比(Ci/Ci)、最大同化速率(Amax)、碳氮比(C：N)和单位面积叶片质量(LMA)。PCO_2与Δ_(13)Cleaforci/Ca无显著相关性，但与Amax、LMA、C/N比呈正相关。Δ13叶没有随着pCO2的增加而增加，这可能是因为缺乏Inci/Ca的变化，较厚的叶片减缓了CO2通过叶片扩散到叶肉细胞的速度，较高的max驱动了细胞内CO2的更快消耗和/或淀粉、脂类或其他具有不同同位素组成的化合物的相对比例的变化。我们的结果，以及许多不同类型C3植物中关于Δ13叶的文献数据的汇编，表明Δ13叶不会随着pCO2的增加而持续增加。相反，有各种各样的反应，无论是积极的还是消极的，与分类群或生长形式没有明显的关系，但可能反映了在较高的二氧化碳浓度下叶片结构、气孔反应和AMAX的变化。考虑到活体植物中Δ13Cave和pCO2之间的复杂关系，我们认为化石植物的Δ13Cave不能可靠地替代古大气中的pCO2。
Some experiments and observations of free-living plants have found that increasing atmospheric concentration of CO2(pCO2) is directly correlated with increasing discrimination against13C during photosynthesis (Δ13C) in C3 plants. The inverted form of this correlation has been used to estimatepCO2in the geological past (i.e. the C3 plant proxy), but there has been little experimental work to establish the relative importance ofpCO2as a driver of discrimination in more natural settings and over a range ofpCO2relevant to the deep-time geologic record. Here we report on an experiment exploring the relationship betweenpCO2and Δ13C inGinkgo biloba, a plant long used to infer past CO2levels because of the strong similarity of extant to fossilGinkgoand the abundance ofGinkgofossils with preserved cuticle from late Mesozoic and Cenozoic periods of warm global climate.We grewGinkgo bilobaplants for three years under ambientpCO2(∼425 ppm) and elevated levels (∼600, ∼800, and ∼ 1000 ppm) while measuring the carbon isotope composition of air (δ13Cair) and leaves (δ13Cleaf) as well as the ratio of internal to external CO2concentration (ci/ca), maximum photosynthetic assimilation rate (Amax), C:N ratio, and leaf mass per area (LMA). We found no significant relationship betweenpCO2and Δ13Cleaforci/ca. We did find a direct correlation ofpCO2withAmax, LMA, and C:N ratio. The lack of increase in Δ13Cleafwith risingpCO2may result from the lack of change inci/ca, thicker leaves that slow the rate of diffusion of CO2through the leaf to mesophyll cells, higherAmaxthat drives more rapid consumption of intracellular CO2and/or changes in the relative proportions of starches, lipids or other compounds that have distinct isotopic compositions.Our results, along with a compilation of data from the literature on Δ13Cleafin many different types of C3 plants, suggest that Δ13Cleafdoes not consistently increase with increasingpCO2. Rather, there is a diversity of responses, both positive and negative, that are not clearly related to taxonomic group or growth form but may reflect changes in leaf structure, stomatal response andAmaxunder higherpCO2. Given the complex relationship between Δ13CleafandpCO2in living plants we consider Δ13Cleafof fossil plants to be an unreliable proxy for paleo-atmosphericpCO2.