On geologic timescales, plant carbon isotope fractionation responds to precipitation similarly to modern plants and has a small negative correlation with pCO2
On geologic timescales, plant carbon isotope fractionation responds to precipitation similarly to modern plants and has a small negative correlation with pCO2
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DOI：
10.1016/j.gca.2019.11.023
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发表时间：
2020-02
影响因子：
5
通讯作者：
K. Schlanser;A. Diefendorf;D. Greenwood;K. Mueller;C. K. West;A. Lowe;J. Basinger;E. Currano;A. Flynn;H. Fricke;Jie Geng;H. Meyer;D. Peppe
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作者：
K. Schlanser;A. Diefendorf;D. Greenwood;K. Mueller;C. K. West;A. Lowe;J. Basinger;E. Currano;A. Flynn;H. Fricke;Jie Geng;H. Meyer;D. Peppe
叶片碳同位素分馏（Δleaf）对环境条件敏感，可以反映叶片气体交换对气候和环境因子的响应状态和演化。在现代植物中，水的可用性是Δleafacross网站的最强环境预测因子，这些网站在大气中经历相对均匀和低浓度的CO2（pCO 2）。生长室实验表明，现代植物的Δ叶也可以对pCO 2变化敏感。然而，在地质时期，它是不确定的Δ叶如何响应pCO 2和降水的变化。为了解决这个问题，我们从化石叶遗址收集了沉积物（岩石）样本，这些样本代表了从200到900 ppmV的pCO 2值范围，从新墨西哥州到高北极的40多个纬度，从晚白垩世到渐新世的4000万年。对于每个站点，大气CO2的碳同位素组成（δ 13 Catm），pCO 2，平均年降水量和平均年温度的约束从独立的代理。从沉积物样品中，我们提取了长链正烷烃（来自植物蜡的生物标志物）。然后测定沉积物中dn-C29和n-C31烷烃的碳同位素比值，计算Δ叶。结果表明，即使在控制了年平均降水量后，Δ叶与pCO 2仍呈负相关。叶片对CO2的Δ响应很小（-0.3 ± 0.09‰/100 ppmV），表明植物正在调整内部叶片CO2浓度以适应大气pCO 2浓度，可能是通过优化叶片气体交换来最大限度地增加碳摄入量，并最大限度地减少水分损失以应对环境条件。与先前对地质沉积物和活植物的研究类似，Δ leaf也与水的可用性呈正相关，并且在较小程度上对植物类型和可能的海拔高度敏感。因此，过去地质学中的Δ叶-pCO 2关系可能比现代研究中观察到的更为复杂，因此，排除了其作为apCO 2代用品的用途。
Leaf carbon isotope fractionation (Δleaf) is sensitive to environmental conditions and can provide insights into the state and evolution of leaf gas-exchange in response to climate and environment factors. In modern plants, water availability is the strongest environmental predictor of Δleafacross sites that experience relatively uniform and low concentrations of CO2in the atmosphere (pCO2). Growth chamber experiments show Δleafof modern plants can also be sensitive to changingpCO2. However, over geologic time, it is uncertain how Δleafhas responded to shifts inpCO2and precipitation. To address this problem, we collected sediment (rock) samples from fossil leaf sites that represent a range ofpCO2values from ∼200 to 900 ppmV, over 40 degrees of latitude from New Mexico to the High Arctic, and 40 million years spanning the Late Cretaceous to the Oligocene. For each site, the carbon isotope composition of atmospheric CO2(δ13Catm),pCO2, mean annual precipitation, and mean annual temperature were constrained from independent proxies. From sediment samples, we extracted long-chainn-alkanes (biomarkers derived from plant wax). We then measured the carbon isotope ratios of sediment-derivedn-C29andn-C31alkanes to calculate Δleaf. Results show a negative correlation between ΔleafandpCO2even after controlling for mean annual precipitation. The Δleafresponse topCO2is small (−0.3 ± 0.09‰/100 ppmV), suggesting plants are adjusting internal leaf CO2concentrations to atmosphericpCO2concentrations, likely by optimizing leaf gas-exchange to maximize carbon intake and minimize water loss in response to environmental conditions. Similar to previous studies of geologic sediments and living plants, Δleafwas also positively correlated with water availability and, to a lesser extent, sensitive to plant type and possibly altitude. As a result, the Δleaf–pCO2relationship in the geologic past may be more complex than observed in modern studies and therefore, precludes its use as apCO2proxy.