Temperate Plant Phenology
Phenology is the timing of growth and reproductive activity within a year, and it can vary greatly among plant species, populations, and even individuals. In temperate forests (characterized by moderate temperatures), many forest-floor plants expand their leaves and flower before the trees that form the forest’s upper layer (the canopy) begin leaf expansion. The consequence is that these plants do most of their growing and reproducing in temperatures that are far colder than those experienced by the canopy trees during the same life stages. Many studies have shown that this timing is actually advantageous to the forest-floor plants. Once the leaves of the trees fill in the open spaces, very little sunlight sometimes as little as 1 percent-gets through to the forest floor. Thus, the forest-floor plants’ growth and reproduction would be even more limited by light availability than they are by cool temperatures.
In most temperate species, it appears that temperature and photoperiod (day length) are the main factors determining plant phenologies. It is important to realize that temperature plays its role in a particular way. It is generally the sum of temperatures experienced over some period of time and not the temperatures on a particular day that determines the timing of leaf expansion. In cold years, then, leaf expansion is delayed. Plants, like other organisms, often use photoperiod as a reliable predictor of the average temperature. If they relied exclusively on temperature, a warm spell in midwinter would typically cause many plants to expand their leaves. By using temperature as a cue, plants can respond to an early spring by expanding their leaves early, but because they also use photoperiod as a cue, this response is limited. These plants, in other words, respond to environmental fluctuations, but they do so cautiously.
As the example of temperate forest-floor plants suggests, there are at least two main types of factors that act on plant phenologies: non-biological factors limiting growth-such as the timing of killing frosts (frosts cold enough to kill plants) or seasonal droughts-often determine the beginning or end of growth episodes (or both), but biological factors-in particular, competition for light or water-are also quite important for many species.
This observation raises an interesting question: why do the canopy trees in temperate forests wait so long before expanding their leaves? Why don’t they use the early spring to add to their growth, as the forest-floor plants do? There are a number of selective forces affecting the timing of leaf expansion. First, the canopy is elevated. Temperatures in the treetops can be considerably colder than those at ground level. Thus, leaf expansion for trees occurs later on the calendar. but it may not really be much later in terms of average temperature. Second, late frosts are a common occurrence. Leaves on trees are much more vulnerable to frost damage than are those on forest-floor plants, because the latter are partly sheltered by the trees and because the ground-level temperatures are higher. Third, all enzymes (substances that facilitate chemical reactions) used for plants metabolism have different defined temperature ranges over which they can operate, and they are most efficient at particular temperatures. Enzymes adapted for peak functioning at warm temperatures are unlikely to be efficient in the early spring; it is possible that earlier leaf expansion might reduce the total year’s growth of the trees, not increase it. Finally, many temperate-zone trees are wind-pollinated, and pollination in most of these species occurs while the trees are leafless. The presence of leaves earlier in the season would be likely to limit pollen transfer.
The phenologies of temperate forest-floor plants are actually more complex than we have implied so far. Most of the plants in northeastern North America have phenologies like those described here, but there are others that are able to capture and use light at other times. Some species can use light flecks on the forest floor to grow during the summer months. Still others use the additional light available in autumn, when some canopy species have begun shedding their leaves.
1
Phenology is the timing of growth and reproductive activity within a year, and it can vary greatly among plant species, populations, and even individuals. In temperate forests (characterized by moderate temperatures), many forest-floor plants expand their leaves and flower before the trees that form the forest’s upper layer (the canopy) begin leaf expansion. The consequence is that these plants do most of their growing and reproducing in temperatures that are far colder than those experienced by the canopy trees during the same life stages. Many studies have shown that this timing is actually advantageous to the forest-floor plants. Once the leaves of the trees fill in the open spaces, very little sunlight sometimes as little as 1 percent-gets through to the forest floor. Thus, the forest-floor plants’ growth and reproduction would be even more limited by light availability than they are by cool temperatures.
According to paragraph 1, which of the following is true about the phenology of temperate forests?
Factual Information Questions事实信息题
AGrowth and reproduction of forest-floor plants are limited more by cool temperatures than by the availability of light.
BCanopy trees grow and reproduce in temperatures far colder than those in which forest-floor plants do at the same stages
CLeaf expansion takes place in canopy trees later than in forest-floor plants.
DThe timing of growth and reproductive activity is more advantageous to canopy trees than it is to forest-floor plants.
2
In most temperate species, it appears that temperature and photoperiod (day length) are the main factors determining plant phenologies. It is important to realize that temperature plays its role in a particular way. It is generally the sum of temperatures experienced over some period of time and not the temperatures on a particular day that determines the timing of leaf expansion. In cold years, then, leaf expansion is delayed. Plants, like other organisms, often use photoperiod as a reliable predictor of the average temperature. If they relied exclusively on temperature, a warm spell in midwinter would typically cause many plants to expand their leaves. By using temperature as a cue, plants can respond to an early spring by expanding their leaves early, but because they also use photoperiod as a cue, this response is limited. These plants, in other words, respond to environmental fluctuations, but they do so cautiously.
The word “cautiously” in the passage is closest in meaning to
Vocabulary Questions词汇题
Acarefully
Bappropriately
Cpartially
Deffectively
3
In most temperate species, it appears that temperature and photoperiod (day length) are the main factors determining plant phenologies. It is important to realize that temperature plays its role in a particular way. It is generally the sum of temperatures experienced over some period of time and not the temperatures on a particular day that determines the timing of leaf expansion. In cold years, then, leaf expansion is delayed. Plants, like other organisms, often use photoperiod as a reliable predictor of the average temperature. If they relied exclusively on temperature, a warm spell in midwinter would typically cause many plants to expand their leaves. By using temperature as a cue, plants can respond to an early spring by expanding their leaves early, but because they also use photoperiod as a cue, this response is limited. These plants, in other words, respond to environmental fluctuations, but they do so cautiously.
According to paragraph 2, which of the following aspects of temperature has the greatest influence on the timing of leaf expansion?
Factual Information Questions事实信息题
AThe sum of temperatures over a certain number of days
BThe coldest temperature reached during winter
CThe difference between the high and low temperatures on a particular day
DThe amount of temperature fluctuation in a given period
4
As the example of temperate forest-floor plants suggests, there are at least two main types of factors that act on plant phenologies: non-biological factors limiting growth-such as the timing of killing frosts (frosts cold enough to kill plants) or seasonal droughts-often determine the beginning or end of growth episodes (or both), but biological factors-in particular, competition for light or water-are also quite important for many species.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
Sentence Simplification Questions句子简化题
APlant phenologies are affected both by non-biological factors, which often determine the beginning or end of growth episodes, and by biological factors such as competition for light or water.
BThe example of temperate forest-floor plants suggests that killing frosts or seasonal droughts, as well as competition for light or water, can determine the beginning or end of growth episodes.
CThe example of temperate forest-floor plants suggests that there are at least two main types of factors that act on plant phenologies as well as many other less important factors.
DThe relatively greater importance for many plant phenologies of non-biological factors as compared with biological factors is indicated by the example of temperate forest-floor plants
5
This observation raises an interesting question: why do the canopy trees in temperate forests wait so long before expanding their leaves? Why don’t they use the early spring to add to their growth, as the forest-floor plants do? There are a number of selective forces affecting the timing of leaf expansion. First, the canopy is elevated. Temperatures in the treetops can be considerably colder than those at ground level. Thus, leaf expansion for trees occurs later on the calendar. but it may not really be much later in terms of average temperature. Second, late frosts are a common occurrence. Leaves on trees are much more vulnerable to frost damage than are those on forest-floor plants, because the latter are partly sheltered by the trees and because the ground-level temperatures are higher. Third, all enzymes (substances that facilitate chemical reactions) used for plants metabolism have different defined temperature ranges over which they can operate, and they are most efficient at particular temperatures. Enzymes adapted for peak functioning at warm temperatures are unlikely to be efficient in the early spring; it is possible that earlier leaf expansion might reduce the total year’s growth of the trees, not increase it. Finally, many temperate-zone trees are wind-pollinated, and pollination in most of these species occurs while the trees are leafless. The presence of leaves earlier in the season would be likely to limit pollen transfer.
The word “peak” in the passage is closest in meaning to
Vocabulary Questions词汇题
Aprecise
Bnormal
Coptimum
Dsuccessful
6
This observation raises an interesting question: why do the canopy trees in temperate forests wait so long before expanding their leaves? Why don’t they use the early spring to add to their growth, as the forest-floor plants do? There are a number of selective forces affecting the timing of leaf expansion. First, the canopy is elevated. Temperatures in the treetops can be considerably colder than those at ground level. Thus, leaf expansion for trees occurs later on the calendar. but it may not really be much later in terms of average temperature. Second, late frosts are a common occurrence. Leaves on trees are much more vulnerable to frost damage than are those on forest-floor plants, because the latter are partly sheltered by the trees and because the ground-level temperatures are higher. Third, all enzymes (substances that facilitate chemical reactions) used for plants metabolism have different defined temperature ranges over which they can operate, and they are most efficient at particular temperatures. Enzymes adapted for peak functioning at warm temperatures are unlikely to be efficient in the early spring; it is possible that earlier leaf expansion might reduce the total year’s growth of the trees, not increase it. Finally, many temperate-zone trees are wind-pollinated, and pollination in most of these species occurs while the trees are leafless. The presence of leaves earlier in the season would be likely to limit pollen transfer.
According to paragraph 4. why does the common occurrence of late frosts affect the timing of leaf expansion in canopy trees but not in forest-floor plants?
Factual Information Questions事实信息题
ABecause the leaves of forest-floor plants respond better to cold temperatures than the leaves of canopy trees do
BBecause the enzymes of forest-floor plants are not as efficient at warm temperatures as the enzymes of canopy trees are
CBecause the leaves of forest-floor plants are far more protected from direct exposure to late frosts than the leaves of canopy trees are
DBecause the leaves of forest-floor plants recover more easily from damage done by late frosts than do the leaves of canopy trees
7
This observation raises an interesting question: why do the canopy trees in temperate forests wait so long before expanding their leaves? Why don’t they use the early spring to add to their growth, as the forest-floor plants do? There are a number of selective forces affecting the timing of leaf expansion. First, the canopy is elevated. Temperatures in the treetops can be considerably colder than those at ground level. Thus, leaf expansion for trees occurs later on the calendar. but it may not really be much later in terms of average temperature. Second, late frosts are a common occurrence. Leaves on trees are much more vulnerable to frost damage than are those on forest-floor plants, because the latter are partly sheltered by the trees and because the ground-level temperatures are higher. Third, all enzymes (substances that facilitate chemical reactions) used for plants metabolism have different defined temperature ranges over which they can operate, and they are most efficient at particular temperatures. Enzymes adapted for peak functioning at warm temperatures are unlikely to be efficient in the early spring; it is possible that earlier leaf expansion might reduce the total year’s growth of the trees, not increase it. Finally, many temperate-zone trees are wind-pollinated, and pollination in most of these species occurs while the trees are leafless. The presence of leaves earlier in the season would be likely to limit pollen transfer.
Paragraph 4 suggests that early leaf expansion could reduce the yearly growth of trees in temperate forests by
Inference Questions推理题
Adecreasing the effectiveness of wind pollination
Bnegatively affecting the metabolisms of these trees
Cforcing these trees to expend more energy on leaf production
Dnarrowing the range of temperatures over which these trees’ enzymes operate
8
The phenologies of temperate forest-floor plants are actually more complex than we have implied so far. Most of the plants in northeastern North America have phenologies like those described here, but there are others that are able to capture and use light at other times. Some species can use light flecks on the forest floor to grow during the summer months. Still others use the additional light available in autumn, when some canopy species have begun shedding their leaves.
Why does the author mention that “Some species can use light flecks on the forest floor to grow during the summer months”?
Rhetorical Purpose Questions修辞目的题
ATo make the point that phenologies of temperate forest plants differ significantly from phenologies of plants in other settings
BTo explain why growth and reproduction of forest-floor plants occur during different seasons
CTo support the idea that most plants in northeastern North America have phenologies like those already described
DTo give an example of a northeastern North American phenology that is less common than the ones previously described
9
In most temperate species, it appears that temperature and photoperiod (day length) are the main factors determining plant phenologies. [■]It is important to realize that temperature plays its role in a particular way. [■]It is generally the sum of temperatures experienced over some period of time and not the temperatures on a particular day that determines the timing of leaf expansion. In cold years, then, leaf expansion is delayed. [■]Plants, like other organisms, often use photoperiod as a reliable predictor of the average temperature. [■]If they relied exclusively on temperature, a warm spell in midwinter would typically cause many plants to expand their leaves. By using temperature as a cue, plants can respond to an early spring by expanding their leaves early, but because they also use photoperiod as a cue, this response is limited. These plants, in other words, respond to environmental fluctuations, but they do so cautiously.
Look at the four squaresthat indicate where the following sentence could be added to the passage
Moisture, which is significant in a tropical habitat, is not as significant for temperate species.Insert Text Questions句子插入题
Where would the sentence best fit？Click on a square sentence to the passage.
10
Among temperate forest plant species, phenology-the timing of growth and reproductive activity-can vary greatly
Prose Summary Questions概要小结题
Select 3 answers
AMost forest-floor plants expand their leaves and flower before canopy trees begin leaf expansion, because sunlight becomes largely unavailable to them after the trees are covered with leaves
BFactors such as seasonal droughts and the arrival of killing frosts largely determine growth periods for certain plant species; for others, only factors such as competition for water are of real importance.
CCanopy trees, unlike forest-floor plants, depend on enzymes in the chemical reactions associated with reproduction and leaf expansion but at some temperatures these enzymes reduce growth
DIn most temperate plant species, phenology is determined mainly by temperature combined with day length, which allows adjustment in response to early or late springs.
ECanopy trees wait to begin leaf expansion, since treetops are colder than forest floors and more exposed to frost; trees’ metabolisms need warmth to function well, and early leafing can limit pollination
FBecause many forest-floor plants flower in summer rather than in spring, and some begin leaf expansion in autumn, phenologies of forest-floor plants must be more complex than those of canopy trees.
