Trees take carbon dioxide from the atmosphere and store it in complex molecules (分子), releasing oxygen. The more photosynthesis (光合作用), the more carbon is locked away.
Carbon dioxide is a major driver of climate change, so the more that can be taken out of the atmosphere by plants, the better. With the warmer climate leading to a longer growing season, some researchers have suggested that more carbon dioxide would be absorbed by trees and other plants than in previous times. But a new study has changed this theory and could have profound effects on how we adapt to climate change.
The researchers at the Swiss Federal Institute of Technology studied the degree to which the timing of colour changes in autumn tree leaves was determined by the growth of the plants in the previous spring and summer.
Using data from the Pan European Phenology Project, which has tracked some trees for as long as 65 years, the researchers found in their long-term observational study that as the rate of photosynthesis increased, leaves changed colour and fell earlier in the year. For every 10%d increase in photosynthetic activity over the spring and summer growing season, trees shed their leaves, on average, eight days earlier.
This research shows that deciduous (每年落叶的) trees can only absorb a set amount of carbon each year and once that limit is reached, no more can be absorbed. At that point, leaves begin to change colour. This limit is set by the availability of nutrients, particularly nitrogen (氮气), and the physical structure of the plant itself, particularly the inner vessels which move water and dissolved nutrients around. Nitrogen is a key nutrient which plants need in order to grow, and it’s often the amount of available nitrogen that limits total growth. This is why farmers and gardeners use nitrogen fertilisers (肥料) to overcome this limitation.
It suggests that by 2100, when tree growing seasons are expected to be between 22 and 34 days longer, leaves will fall from trees between three and six days earlier than they do now.
8. What can we know from the first two paragraphs?
A.More carbon dioxide has been absorbed by plants than before. |
B.Higher temperature has an influence on plants’ growing season. |
C.Climate change can be solved naturally through photosynthesis. |
D.Plants can give off oxygen and molecules through photosynthesis. |
9. How many days earlier may leaves averagely fall with 20% increase in photosynthesis?
A.Eight days. | B.Sixteen days. |
C.Twenty-eight days. | D.Thirty-four days. |
10. What does the underlined word “vessels” mean in Paragraph 5?
A.Basins. | B.Wells. | C.Containers | D.Channels. |
11. What does the author mainly intend to inform us?
A.Nitrogen is an essential nutrient for plant growing. |
B.Warmer climate contributes to longer growing season. |
C.Farmers use fertilizers to increase the growth of plants. |
D.The amount of carbon plants absorb is limited in a year. |