生物谷报道：科学家说，大气二氧化碳浓度的增加可能改变草原的性质，并减少它们作为牧场的价值。这项研究发表在了本周（9月4日）出版的《美国科学院学报》上。
该研究的主要作者、美国农业部农业研究局的植物生理学家Jack Morgan说，如果大气的二氧化碳浓度持续上升，非洲、哈萨克斯坦、墨西哥、蒙古、南亚和东南亚的重要牧区可能受到威胁。
Morgan和他的同事在美国科罗拉多州用于放牧牲畜的半干旱草原上建造了6个透明的舱。这些草原与发展中国家的许多草原拥有类似的气候和植物群。
其中3个舱的二氧化碳浓度和今天的浓度相同，而另外3个舱的浓度加倍。在5年的时间里，科学家发现二氧化碳浓度高的舱中的植物群发生了显著的变化。木本灌木繁盛起来，特别是一种称为冷蒿（Artemisiafrigida）的灌木。
Morgan告诉本网站说，在实验开始的时候，灌木只占了植被面积的不到1%，但是到了试验结束的时候，它们占了植被面积的10%。他说，木本灌木在高浓度的二氧化碳环境中胜过草的主要原因是由于它们的光合作用方法更适于高浓度的二氧化碳。Morgan还表示，主要的担心在于大多数家养牲畜不爱吃冷蒿这类植物，因此这类植物占了上风将让牧场质量变差。
南非国立生物多样性研究所的首席专家GuyMidgley告诉本网站说，已经有证据表明灌木入侵了世界的许多草原。
他说还不清楚二氧化碳是不是这种变化的主要驱动者。然而，Morgan的实验“提示了我们确实需要更认真地对待二氧化碳”。
Midgley还说，如果没有昂贵的机械干预，太多的灌木入侵可能将让南非无法兴办牧场。
Midgley和Morgan都同意，减少草原转型的一个可能方法是使用有控制的焚烧，这种方法能杀死灌木但是不会杀死草，另外还要防止过度放牧。过度放牧会让草减少，让更多的木本植物孳生。（援引科学与发展网）
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原始出处:
Published online before print September 4, 2007
Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0703427104
OPEN ACCESS ARTICLE
Ecology
Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe
( C3 | C4 | functional group | global change | semiarid grassland )
Jack A. Morgan *, Daniel G. Milchunas , Daniel R. LeCain *, Mark West , and Arvin R. Mosier ¶
*Rangeland Resources Research Unit and Northern Plains Area, Agricultural Research Service, United States Department of Agriculture, Fort Collins, CO 80526; Department of Forest, Rangeland, and Watershed Stewardship and Natural Resources Ecology Laboratory, Colorado State University, Fort Collins, CO 80523; and ¶Soil Plant Nutrient Research Unit, Agricultural Research Service, United States Department of Agriculture, Fort Collins, CO 80526
Edited by Harold A. Mooney, Stanford University, Stanford, CA, and approved July 25, 2007 (received for review April 13, 2007)
A hypothesis has been advanced that the incursion of woody plants into world grasslands over the past two centuries has been driven in part by increasing carbon dioxide concentration, [CO2], in Earth's atmosphere. Unlike the warm season forage grasses they are displacing, woody plants have a photosynthetic metabolism and carbon allocation patterns that are responsive to CO2, and many have tap roots that are more effective than grasses for reaching deep soil water stores that can be enhanced under elevated CO2. However, this commonly cited hypothesis has little direct support from manipulative experimentation and competes with more traditional theories of shrub encroachment involving climate change, management, and fire. Here, we show that, although doubling [CO2] over the Colorado shortgrass steppe had little impact on plant species diversity, it resulted in an increasingly dissimilar plant community over the 5-year experiment compared with plots maintained at present-day [CO2]. Growth at the doubled [CO2] resulted in an 40-fold increase in aboveground biomass and a 20-fold increase in plant cover of Artemisia frigida Willd, a common subshrub of some North American and Asian grasslands. This CO2-induced enhancement of plant growth, among the highest yet reported, provides evidence from a native grassland suggesting that rising atmospheric [CO2] may be contributing to the shrubland expansions of the past 200 years. Encroachment of shrubs into grasslands is an important problem facing rangeland managers and ranchers; this process replaces grasses, the preferred forage of domestic livestock, with species that are unsuitable for domestic livestock grazing.
全文下载：Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe
