Table_3_A Review of C4 Plants in Southwest Asia: An Ecological, Geographical and Taxonomical Analysis of a Region With High Diversity of C4 Eudicots.pdf

Southwest Asia is climatically and topographically a highly diverse region in the xeric belt of the Old World. Its diversity of arid habitats and climatic conditions acted as an important area for the evolution and diversification of up to 20 (of 38 known) independent Eudicot C4 origins. Some of these lineages present unique evolutionary strategies like single-cell functioning C4 and C3–C4 switching mechanisms. The high diversity of C4 taxa in Southwest (SW) Asia is also related to the presence of seven phytogeographic zones including the Irano-Turanian region as a center of diversification of many Caryophyllales lineages and the Somali-Masai region (Southern Oman and Yemen) as a center of diversification for C4 Monocots. Nevertheless, the C4 flora of SW Asia has not received detailed attention. This paper presents a comprehensive review of all known C4 species in the area based on a literature survey, own floristic observations, as well as taxonomic, phylogenetic and herbarium data, and δ13C-isotope ratio analysis. The resulting checklist includes a total number of 923 (861 native, of which 141 endemic, and 62 introduced) C4 species, composed of 350 Eudicots and 509 Monocots, most of which are therophytic and hemicryptophytic xerophytes with pluriregional and Irano-Turanian distribution. Two hundred thirty-nine new δ13C-isotope ratios of C4 and C3 plants, as well as some taxonomic changes are presented. An analysis of the distribution of the three main C4 plant families (Chenopodiaceae, Poaceae, and Cyperaceae) in the region in relation to climatic variables indicates that the increase of C4 species follows more or less a latitudinal gradient similar to global patterns, while separate taxonomic groups seem to depend on specific factors as continentality (Chenopodiaceae), average annual temperature (Cyperaceae), and the presence of summer precipitation (Poaceae). An increase of C4 Eudicots in W-E direction even in similar longitudinal belts is explained by a combination of edaphic and climatic conditions. The provided data should encourage a deeper interest in the evolution of C4 lineages in SW Asia and their adaptation to ecological and climatical conditions and awaken interest in the importance of local C4 crops, the conservation of threatened C4 taxa, and awareness of human impacts on the rapid environmental changes in the region.

西南亚地处旧世界干旱带，是气候与地形多样性极高的区域。其多样的干旱生境与气候条件，是已知38个独立真双子叶植物（Eudicot）C4光合起源中多达20个的演化与分化的重要场所。这些演化支中部分拥有独特的演化策略，例如单细胞功能型C4途径以及C3-C4切换机制。西南亚（SW Asia）C4植物类群的高度多样性，还与7个植物地理区的存在密切相关：其中伊朗-图兰植物区（Irano-Turanian region）是诸多石竹目（Caryophyllales）演化支的分化中心，而索马里-马赛植物区（涵盖阿曼南部与也门）则是C4单子叶植物（Monocots）的分化中心。然而目前学界对西南亚的C4植物区系尚未开展细致研究。本文基于文献调研、自主的植物区系观测、分类学与系统发育学数据、标本馆馆藏资料以及碳13同位素（δ13C-isotope）比值分析，对该区域内所有已知C4物种进行了全面综述。最终生成的名录共收录923种C4植物（其中本土种861种，含141个特有种；归化种62种），包含350种真双子叶植物与509种单子叶植物，其中多数为具有多区分布与伊朗-图兰分布型的一年生旱生植物与隐芽旱生植物。本文还提供了239个C3与C4植物的全新碳13同位素比值数据，以及部分分类学修订内容。对该区域三大C4植物科——藜科（Chenopodiaceae）、禾本科（Poaceae）以及莎草科（Cyperaceae）的分布与气候变量的关联分析显示：C4物种的丰富度大致遵循与全球模式相似的纬度梯度变化；而不同分类类群则受特定因子调控：大陆度影响藜科，年均温影响莎草科，夏季降水则影响禾本科。即便在相似经度带内，真双子叶C4植物的丰富度也呈现由西向东递增的趋势，这一现象可由土壤与气候条件的共同作用加以解释。本文提供的数据将有助于推动学界对西南亚C4演化支的演化过程及其对生态与气候条件的适应机制开展更深入的研究，同时唤起学界对本土C4作物价值、受威胁C4类群保护工作的重视，并提升人们对人类活动影响该区域快速环境变化的认知。