Could land-based early photosynthesizing ecosystems have bioengineered the planet in mid-Palaeozoic times?
Could land-based early photosynthesizing ecosystems have bioengineered the planet in mid-Palaeozoic times?
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DOI：
10.1111/pala.12187
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发表时间：
2015-09-01
期刊：
影响因子：
2.6
通讯作者：
Raven, John A.
中科院分区：
文献类型：
--
作者：
Edwards, Dianne;Cherns, Lesley;Raven, John A.
奥陶纪和志留纪是古地理、火山作用和气候变化方面的主要地质活动时期，其中最后一次是在希尔南提(晚奥陶世)达到顶峰的一系列冷期和冰川。达里维连(中奥陶世)隐孢子的出现标志着陆地上高等植物的出现。对后续岩石中的直接化石(巨型和微型化石)和一些间接证据的关键调查表明，存在藻类、细菌、蓝藻、真菌、可能的地衣、隐芽植物和底层管状植物。如今，类似的光合作用和分解作用也出现在隐花盖层(CCS)中，例如生物结皮，只是苔藓植物取代了隐芽植物(基生胚芽植物)，而维管植物则消失了。因此，现存的CCS为全球碳、氮固定和防止侵蚀做出了重大贡献，为早期陆地植被对岩石圈和大气的影响提供了一个很好的类比。作为评估奥陶纪-志留纪影响的先决条件，特别考虑了气候模型者使用的参数，回顾了一些非生物因素对现存隐形地被植物生长和存活的影响及其环境影响。这些因素包括光合作用有效辐射、紫外线辐射、温度、水、氧、二氧化碳、氮、磷、铁、表面粗糙度和反照率。一项对这种植被促进的风化性质和程度的调查得出结论，与目前根部维管植物的风化深度相比，这种植被的风化深度有限，对二氧化碳排放的影响很小。由于奥陶系-志留纪CCS的全球净生产力很可能低于今天，尽管有机碳中的一小部分难处理物质将导致陆地生物量更快的周转，我们得出结论，长期有机碳埋藏的可能性降低了。因此，由于碳埋藏，大气中氧气的增加和二氧化碳的减少将是非常有限的。
The Ordovician and Silurian periods were times of major geological activity as regards palaeogeography, volcanism and climate change, the last of these evidenced by a series of cooling episodes and glaciations that climaxed in the Hirnantian (Late Ordovician). The presence of cryptospores in the Darriwilian (Middle Ordovician) marked the advent of higher plants on land. A critical survey of direct (mega- and microfossils) and some indirect evidence in succeeding rocks indicates the presence of algae, Bacteria, Cyanobacteria, Fungi, probable lichens, cryptophytes and basal tracheophytes. Similar associations of photosynthesizers and decomposers occur today in cryptogamic covers (CCs), for example biological crusts, except that bryophytes replace cryptophytes (basal embryophytes) and tracheophytes are absent. Thus, extant CCs, which make significant contributions today to global carbon and nitrogen fixation and prevention of erosion, provide an excellent analogue for the impacts of early land vegetation on both lithosphere and atmosphere. As a prerequisite to assessing impacts in Ordovician-Silurian times, with particular consideration of parameters used by climate modellers, the effects of a number of abiotic factors on the growth and survival of extant cryptogamic ground covers and their environmental impacts are reviewed. Factors include photosynthetically active radiation, ultraviolet radiation, temperature, water, oxygen, carbon dioxide, nitrogen, phosphorus, iron, surface roughness and albedo. A survey of the nature and extent of weathering facilitated by such vegetation concludes that it was limited based on depth of weathering when compared with that from rooted tracheophytes today, with minor effects on carbon dioxide drawdown. As global net productivity from Ordovician-Silurian CCs was very probably lower than today, and while the small fraction of intractable material in their organic carbon would have resulted in a more rapid turnover of terrestrial biomass, we conclude that there was decreased possibility of long-term organic carbon burial. Hence, there would have been very limited increase in atmospheric oxygen and decrease in carbon dioxide resulting from carbon burial.