Geological Sciences, Stanford University, Stanford, CA, 94305, USA.
Plant Sciences, University of California at Davis, Davis, CA, 95616, USA.
New Phytol. 2019 Jul;223(1):40-49. doi: 10.1111/nph.15446. Epub 2018 Oct 10.
Anatomically preserved fossils allow estimation of hydraulic parameters, potentially providing constraints on interpreting whole-plant physiology. However, different organ systems have typically been considered in isolation - a problem given common mismatches of high and low conductance components coupled in the hydraulic path of the same plant. A recent paper addressed the issue of how to handle resistance mismatches in fossil plant hydraulics, focusing on Carboniferous medullosan seed plants and arborescent lycopsids. Among other problems, however, a fundamental error was made: the transpiration stream consists of resistances in series (where resistances are additive and the component with the largest resistance can dominate the behavior of the system), but emphasis was instead placed on the lowest resistance, effectively treating the system as resistances in parallel (where the component with the smallest resistance will dominate the behavior). Instead of possessing high assimilation capacities to match high specific stem conductances, it is argued here that individual high conductance components in these Paleozoic plants are nonetheless associated with low whole-plant productivity, just as can be commonly seen in living plants. Resolution of how to handle these issues may have broad implications for the Earth system including geobiological feedbacks to rock weathering, atmospheric composition, and climate.
解剖保存完好的化石可以估算水力参数，这可能为解释整株植物生理学提供限制。然而，不同的器官系统通常是孤立考虑的——这是一个问题，因为在同一植物的水力路径中，高导和低导成分通常不匹配。最近的一篇论文解决了如何处理化石植物水力中的阻力不匹配问题，重点关注石炭纪髓木种子植物和树状石松类植物。然而，除了其他问题之外，还犯了一个根本性的错误：蒸腾流由串联电阻组成（其中电阻是可加的，具有最大电阻的组件可以主导系统的行为），但重点是放在最低电阻上，实际上将系统视为并联电阻（其中具有最小电阻的组件将主导系统的行为）。这里认为，与高比茎导度相匹配的是个体高导组件，而不是个体高导组件，在这些古生代植物中，个体高导组件与低整株植物生产力相关，这与现代植物中常见的情况一样。解决这些问题的方法可能对地球系统具有广泛的影响，包括对岩石风化、大气组成和气候的地质生物反馈。
