EXPANSION OF C4 ECOSYSTEMS AS AN INDICATOR OF GLOBAL ECOLOGICAL CHANGE IN THE LATE MIOCENE
EXPANSION OF C4 ECOSYSTEMS AS AN INDICATOR OF GLOBAL ECOLOGICAL CHANGE IN THE LATE MIOCENE
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DOI：
10.1038/361344a0
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发表时间：
1993-01-28
期刊：
影响因子：
64.8
通讯作者：
QUADE, J
中科院分区：
文献类型：
--
作者：
CERLING, TE;WANG, Y;QUADE, J
在植物使用的三种不同的光合作用途径中，最常见和最原始的途径是C3途径，或卡尔文循环，其特点是最初的二氧化碳羧化形成磷酸甘油酸，一种3碳酸。C3植物的碳同位素组成（deletaC-13）在-23至-35‰之间变化，平均约为-26‰。几乎所有的树木，大多数灌木，草本植物和牧草，以及凉爽季节的草和莎草都使用C3通道。在C4途径（哈奇- slack循环）中，二氧化碳最初与磷酸烯醇丙酮酸结合形成4-碳酸苹果酸或天冬氨酸，它们被转运到束鞘细胞，在那里二氧化碳被释放并用于卡尔文循环反应1-4。C4植物的碳同位素组成范围约为-10至-14‰，现代植物平均约为-13‰1。暖季草和莎草是最丰富的C4植物，尽管C4光合作用在大约20个科中被发现5。第三种光合作用途径CAM结合了C3和C4途径的特点。CAM植物，包括许多多肉植物，具有中等碳同位素组成，也适应水和二氧化碳胁迫的条件。在现代全球生态系统中，C4植物具有重要的组成部分，主要分布在热带稀树草原、温带草原和半荒漠灌丛地。对来自古土壤的古植被和来自牙釉质化石的古饮食的研究表明，从700万到500万年前开始，旧世界和新世界的C4生物量迅速扩大。我们认为C4生物量的全球扩张可能与较低的大气二氧化碳水平有关，因为当大气中二氧化碳浓度较低时，C4光合作用比C3光合作用更有利。
THE most common and the most primitive pathway of the three different photosynthetic pathways used by plants is the C3 pathway, or Calvin cycle, which is characterized by an initial CO2 carboxylation to form phosphoglyceric acid, a 3-carbon acid. The carbon isotope composition (deletaC-13) of C3 plants varies from about -23 to -35 parts per thousand1-3 and averages about -26 parts per thousand. Virtually all trees, most shrubs, herbs and forbs, and cool-season grasses and sedges use the C3 pathway. In the C4 pathway (Hatch-Slack cycle), CO2 initially combines with phosphoenol pyruvate to form the 4-carbon acids malate or aspartic acid, which are translocated to bundle sheath cells where CO2 is released and used in Calvin cycle reactions1-4. The carbon isotope composition of C4 plants ranges from about -10 to -14 parts per thousand, averaging about -13 parts per thousand for modern plants1-3. Warm-season grasses and sedges are the most abundant C4 plants, although C4 photosynthesis is found in about twenty families5. The third photosynthetic pathway, CAM, combines features of both C3 and C4 pathways. CAM plants, which include many succulents, have intermediate carbon isotope compositions and are also adapted to conditions of water and CO2 stress. The modern global ecosystem has a significant component of C4 plants, primarily in tropical savannas, temperate grasslands and semi-desert scrublands. Studies of palaeovegetation from palaeosols and palaeodiet from fossil tooth enamel indicate a rapid expansion of C4 biomass in both the Old World and the New World starting 7 to 5 million years ago. We propose that the global expansion of C4 biomass may be related to lower atmospheric carbon dioxide levels because C4 photosynthesis is favoured over C3 photosynthesis when there are low concentrations of carbon dioxide in the atmosphere.