AGRICULTURE REPORT - Carbon Dioxide and Crops

AGRICULTURE REPORT
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March 12, 2002: Carbon Dioxide and Crops

By George Grow

This is the VOA Special English AGRICULTURE REPORT.

Increasing levels of carbon dioxide gas in Earth’s atmosphere have been linked to warming of the Earth. Now,

American scientists say the rising carbon dioxide levels can interfere¹ with the ability of plants to use some forms
of the important element nitrogen. They say the higher levels of carbon dioxide have affected² plants everywhere
and are forcing changes in the use of agricultural fertilizer.

The Proceedings³ of the National Academy of Sciences reported the findings.

Carbon dioxide levels in Earth’s atmosphere have increased more than thirty percent during the past two
centuries. For years, scientists believed that rising levels of the industrial gas would help plants. Carbon dioxide
is necessary for photosynthesis⁴, the process in which green plants use sunlight to make energy.

However, recent studies found that plants cannot support the increased amounts of carbon dioxide. In
experiments, scientists increased carbon dioxide levels by as much as two -hundred percent. At first, the plants
used thirty percent more carbon. Yet a short time later, the rate of carbon processing dropped to just twelve
percent greater than normal.

Scientists at the University of California at Davis are studying how plants react to fertilizer products made with
nitrate and ammonium. Nitrate and ammonium are different forms of nitrogen. Nitrogen is necessary for
production of proteins and nucleic acids in plants. Many farmers add nitrogen-rich fertilizers to their crops.

In the new study, the scientists found that ammonium fertilizer is more effective than nitrate fertilizer when
carbon dioxide levels in the atmosphere are unusually high. The scientists grew wheat seedlings⁵ with either
nitrate or ammonium under different levels of carbon dioxide. They found that increased carbon dioxide levels
limited the processing of nitrate in the plants.

The scientists also found that the kind of nitrogen did not affect wheat growth when carbon dioxide was at a
normal level. However, this changed when they increased the gas to almost two times the normal atmospheric⁶
level. The seedlings treated with ammonium grew at a faster rate than those treated with nitrate.

The scientists say they had similar results using tomato plants.

This VOA Special English AGRICULTURE REPORT was written by George Grow.

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1 interfere   

v.(in)干涉，干预；(with)妨碍，打扰

参考例句：

• If we interfere, it may do more harm than good.如果我们干预的话，可能弊多利少。
• When others interfere in the affair,it always makes troubles. 别人一卷入这一事件，棘手的事情就来了。

2 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。

3 proceedings   

n.进程，过程，议程；诉讼(程序)；公报

参考例句：

• He was released on bail pending committal proceedings. 他交保获释正在候审。
• to initiate legal proceedings against sb 对某人提起诉讼

4 photosynthesis   

n.光合作用

参考例句：

• In apple trees photosynthesis occurs almost exclusively in the leaves.苹果树的光合作用几乎只发生在叶内。
• Chloroplasts are the structures in which photosynthesis happens.叶绿体就是光合作用发生的地方。

5 seedlings   

n.刚出芽的幼苗( seedling的名词复数 )

参考例句：

• Ninety-five per cent of the new seedlings have survived. 新栽的树苗95%都已成活。 来自《现代汉英综合大词典》
• In such wet weather we must prevent the seedlings from rotting. 这样的阴雨天要防止烂秧。 来自《现代汉英综合大词典》

6 atmospheric   

adj.大气的，空气的；大气层的；大气所引起的

参考例句：

• Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
• Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。