科學(xué)家說,，C4草本植物很可能是通過從熱帶森林天棚之下擴(kuò)散到更干燥的地區(qū)從而進(jìn)化了出來。這項(xiàng)結(jié)果可能有助于解釋C4光合作用的演化,，一些植物進(jìn)化出了這種更有效率的固定碳的途徑，從而在高溫,、低二氧化碳的環(huán)境下把二氧化碳分解成氧氣,。C4植物覆蓋了地球陸地面積的大約20%，包括重要的商業(yè)作物,，如玉米,、甘蔗和高粱，它的擴(kuò)散被認(rèn)為是地球歷史上最重要的事件之一,。
Erika Edwards和Stephen Smith把1230種草本植物的110萬多植物標(biāo)本的種系發(fā)生學(xué),、地理學(xué)、溫度和降雨量數(shù)據(jù)結(jié)合起來,，提出C4草本植物從密集的熱帶森林起源,，并擴(kuò)散到了零星的熱帶林地和稀樹草原系統(tǒng)。這組科學(xué)家指出,，C4植物過去已經(jīng)存在于炎熱的熱帶地區(qū),，并且在過去的3000萬年中，隨著植被從林蔭擴(kuò)散到更干燥,、陽光更充足的環(huán)境中而進(jìn)化出了C4光合作用途徑,。這組作者說，尚不清楚C4進(jìn)化的發(fā)生是由于陽光直射產(chǎn)生了更高的葉片溫度還是由于草本植物面臨的節(jié)約水的壓力增大,。（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS February 8, 2010, doi: 10.1073/pnas.0909672107
Phylogenetic analyses reveal the shady history of C4 grasses
Erika J. Edwardsa,1 and Stephen A. Smithb
aDepartment of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912; and
bNational Evolutionary Synthesis Center, Durham, NC 27705
Grasslands cover more than 20% of the Earth's terrestrial surface, and their rise to dominance is one of the most dramatic events of biome evolution in Earth history. Grasses possess two main photosynthetic pathways: the C3 pathway that is typical of most plants and a specialized C4 pathway that minimizes photorespiration and thus increases photosynthetic performance in high-temperature and/or low-CO2 environments. C4 grasses dominate tropical and subtropical grasslands and savannas, and C3 grasses dominate the world's cooler temperate grassland regions. This striking pattern has been attributed to C4 physiology, with the implication that the evolution of the pathway enabled C4 grasses to persist in warmer climates than their C3 relatives. We combined geospatial and molecular sequence data from two public archives to produce a 1,230-taxon phylogeny of the grasses with accompanying climate data for all species, extracted from more than 1.1 million herbarium specimens. Here we show that grasses are ancestrally a warm-adapted clade and that C4 evolution was not correlated with shifts between temperate and tropical biomes. Instead, 18 of 20 inferred C4 origins were correlated with marked reductions in mean annual precipitation. These changes are consistent with a shift out of tropical forest environments and into tropical woodland/savanna systems. We conclude that C4 evolution in grasses coincided largely with migration out of the understory and into open-canopy environments. Furthermore, we argue that the evolution of cold tolerance in certain C3 lineages is an overlooked innovation that has profoundly influenced the patterning of grassland communities across the globe.
