School of Biology and Environmental Science, University College Dublin, Belfield, Dublin, Ireland.
PLoS One. 2013 Apr 10;8(4):e60614. doi: 10.1371/journal.pone.0060614. Print 2013.
The Triassic-Jurassic boundary (Tr-J; ∼201 Ma) is marked by a doubling in the concentration of atmospheric CO2, rising temperatures, and ecosystem instability. This appears to have been driven by a major perturbation in the global carbon cycle due to massive volcanism in the Central Atlantic Magmatic Province. It is hypothesized that this volcanism also likely delivered sulphur dioxide (SO2) to the atmosphere. The role that SO2 may have played in leading to ecosystem instability at the time has not received much attention. To date, little direct evidence has been presented from the fossil record capable of implicating SO2 as a cause of plant extinctions at this time. In order to address this, we performed a physiognomic leaf analysis on well-preserved fossil leaves, including Ginkgoales, bennettites, and conifers from nine plant beds that span the Tr-J boundary at Astartekløft, East Greenland. The physiognomic responses of fossil taxa were compared to the leaf size and shape variations observed in nearest living equivalent taxa exposed to simulated palaeoatmospheric treatments in controlled environment chambers. The modern taxa showed a statistically significant increase in leaf roundness when fumigated with SO2. A similar increase in leaf roundness was also observed in the Tr-J fossil taxa immediately prior to a sudden decrease in their relative abundances at Astartekløft. This research reveals that increases in atmospheric SO2 can likely be traced in the fossil record by analyzing physiognomic changes in fossil leaves. A pattern of relative abundance decline following increased leaf roundness for all six fossil taxa investigated supports the hypothesis that SO2 had a significant role in Tr-J plant extinctions. This finding highlights that the role of SO2 in plant biodiversity declines across other major geological boundaries coinciding with global scale volcanism should be further explored using leaf physiognomy.
三叠纪-侏罗纪界线（Tr-J；约 201 Ma）以大气 CO2 浓度加倍、气温上升和生态系统不稳定为标志。这似乎是由于中大西洋岩浆省的大规模火山活动，导致全球碳循环发生重大扰动。据推测，这种火山活动也可能向大气中输送了二氧化硫（SO2）。SO2 在导致当时生态系统不稳定方面所起的作用并没有得到太多关注。迄今为止，从化石记录中几乎没有直接证据表明 SO2 是导致此时植物灭绝的原因。为了解决这个问题，我们对保存在 Astartekløft 的九个植物床的保存完好的化石叶进行了形态叶分析，包括银杏类、本内苏铁类和松柏类。将化石分类群的形态响应与在受控环境室中用模拟古大气处理暴露的最接近的活等同分类群中观察到的叶片大小和形状变化进行了比较。现代分类群在用 SO2 熏蒸时，叶片的圆形度有统计学意义的增加。在 Astartekløft，化石分类群的相对丰度突然下降之前，也观察到它们的叶片圆形度也出现了类似的增加。这项研究表明，通过分析化石叶的形态变化，可以在化石记录中追踪大气 SO2 的增加。在调查的所有六个化石分类群中，相对丰度下降后叶片圆形度增加的模式支持了 SO2 在 Tr-J 植物灭绝中起重要作用的假设。这一发现强调，使用叶片形态学进一步探索与全球规模火山活动同时发生的其他主要地质边界的 SO2 在植物生物多样性下降中的作用。
