生物谷報(bào)道：科學(xué)家說,，大氣二氧化碳濃度的增加可能改變草原的性質(zhì)，并減少它們作為牧場(chǎng)的價(jià)值,。這項(xiàng)研究發(fā)表在了本周（9月4日）出版的《美國(guó)科學(xué)院學(xué)報(bào)》上。
該研究的主要作者,、美國(guó)農(nóng)業(yè)部農(nóng)業(yè)研究局的植物生理學(xué)家Jack Morgan說,，如果大氣的二氧化碳濃度持續(xù)上升，非洲,、哈薩克斯坦,、墨西哥、蒙古,、南亞和東南亞的重要牧區(qū)可能受到威脅,。
Morgan和他的同事在美國(guó)科羅拉多州用于放牧牲畜的半干旱草原上建造了6個(gè)透明的艙。這些草原與發(fā)展中國(guó)家的許多草原擁有類似的氣候和植物群,。
其中3個(gè)艙的二氧化碳濃度和今天的濃度相同,，而另外3個(gè)艙的濃度加倍。在5年的時(shí)間里,，科學(xué)家發(fā)現(xiàn)二氧化碳濃度高的艙中的植物群發(fā)生了顯著的變化,。木本灌木繁盛起來，特別是一種稱為冷蒿（Artemisiafrigida）的灌木,。
Morgan告訴本網(wǎng)站說,，在實(shí)驗(yàn)開始的時(shí)候，灌木只占了植被面積的不到1%,，但是到了試驗(yàn)結(jié)束的時(shí)候,，它們占了植被面積的10%,。他說，木本灌木在高濃度的二氧化碳環(huán)境中勝過草的主要原因是由于它們的光合作用方法更適于高濃度的二氧化碳,。Morgan還表示,，主要的擔(dān)心在于大多數(shù)家養(yǎng)牲畜不愛吃冷蒿這類植物，因此這類植物占了上風(fēng)將讓牧場(chǎng)質(zhì)量變差,。
南非國(guó)立生物多樣性研究所的首席專家GuyMidgley告訴本網(wǎng)站說,，已經(jīng)有證據(jù)表明灌木入侵了世界的許多草原。
他說還不清楚二氧化碳是不是這種變化的主要驅(qū)動(dòng)者,。然而,，Morgan的實(shí)驗(yàn)“提示了我們確實(shí)需要更認(rèn)真地對(duì)待二氧化碳”。
Midgley還說,，如果沒有昂貴的機(jī)械干預(yù),，太多的灌木入侵可能將讓南非無法興辦牧場(chǎng)。
Midgley和Morgan都同意,，減少草原轉(zhuǎn)型的一個(gè)可能方法是使用有控制的焚燒,，這種方法能殺死灌木但是不會(huì)殺死草，另外還要防止過度放牧,。過度放牧?xí)尣轀p少,，讓更多的木本植物孳生。（援引科學(xué)與發(fā)展網(wǎng)）
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原始出處:
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.
全文下載：Carbon dioxide enrichment alters plant community structure and accelerates shrub growth in the shortgrass steppe
