Listen to part of a lecture in an ecology class.
So we've been talking about nutrients, the elements in the enviroment that are essential for living organisms to develop, live a healthy life and reproduce.Some nutrients are quite scarce; there just isn't much of them in the environment.But fortunately, they get recycled.When nutrients are used over and over in the environment, we call that a nutrient cycle.Because the importance of nutrients and their scarcity, nutrient recycling is one of the most significant ecosystem processes that will cover in this course.The three most important nutrient recycles are the Nitrogen cycle, the Carbon cycle, and the one we are going to talk about tody, the Phosphorous cycle.
So the phosphorous cycle has been studied a lot by ecologists because like I said phosphorous is an important nutrient and is not so abundant.The largest quantities is found in rocks at the bottom of the ocean.
How dose Phosphorous get there?Well, let's start with the Phosphorous in rocks.The rocks gets broken down into smaller and smaller particles as they are weathered.They are weathered slowly by rain and wind over a long periods of time.Phosphorous is slowly released as the rocks are broken down and it gets spread around into the soil.Once it's in the soil, plants absorb it through their roots.
So that's the reason people mine rocks that contain a lot of Phosphorous to help the agriculture?
Aha, the mine the rock artificially brake it down and put the phosphorous into the agriculture fertilizers.So humans can play a role in the first part of Phosphorous cycle.They braking down of rocks and spreading the Phosphorous into the soil by speeding up the rate at which this nature process occurs. You see.
Now after the Phosphorous is in the soil, plants grow, they use phosphorous from soil to grow; and when they die, they decompose.And the Phosphorous is recycled back into the soil, the same thing with the animals that eat those plants, or eat other animals that have eaten those plants.We call all of this the land phase of the Phosphorous cycle.But a lot of the Phosphorous in the soil gets washed away into rivers by rain and melting snow; and so begins another phase of the cycle.Can any one guess what it's called? Nancy.
Well, if the one is called the land phase, then this has to be call the water phase, right?
Yes, that's such a difficult point, isn't it?In a normal water phase, rivers eventually empty into oceans and once in the oceans, the Phosphorous gets absorbed by water plants like algae.Then fish eats the algae, or eat other fish that have eaten those plants.
But the water phase is sometimes effected by excessive fertilizers.If not all of the phosphorous gets used by the crops and large amounts of phosphorous gets into the rivers, this could course a rapid growth of water plants in the river, which can lead to the water ways getting clogged with organisms, which can change the flow of the water.Several current studies are looking at these effects and I really do hope we can find the way to deal with this issue before these ecosystems are adversely affected. OK?
Of course, another way that humans can interrupt the normal process is fishing.The fishing industry helps bring Phosphorus back to land.In the normal water phase the remaining Phosphorus makes its way, settles to the bottom of the ocean and gets mixed into the ocean sediments.But remember, this is a cycle.The Phosphorus at the bottom of the ocean has to somehow make its way back to the surface, to complete the cycle, to begin the cycle all over again.
After millions of years, powerful geological forces like underwater volcanos lift up the ocean sediments to form new land.When a underwater volcano pushes submerge rock to the surface, a new island is created.Then over many more years the phosphorous reach rocks of the new land begin to erode, and the cycle continues.
What about, well, you said that the Nitrogen cycle is also an important nutrient cycle.And there is a lot of nitrogen in the atmosphere, so I was wondering, is there a lot of Phosphorous in atomosphere too?
Good question, George.You are right to guess the Phosphorous can end up in the earth's atomosphere.It can move from the land from the oceans to the atomosphere and vice versa.However there's just not substantial amount of it there, like there is with Nitrogen. It's a very minimal quantity.
这是一道主旨题。在 lecture 的开头教授提到有些营养元素在自然界中的量不多，主要靠循环来得到充分利用，借此引出了 nutrient cycle 这个概念，并且全文接下来都围绕这个内容讲述，所以答案应该选 D。
地铁路线：乘坐地铁2号线至春熙路站 （E1口出） 下车，或者东门大桥站 （D1口出） 下车，向东大街方向直走约300米到达。乘坐地铁3号线至春熙路站 （E1口出） 下车，向东大街方向直走约600米到达。
地址： 南京市秦淮区中山东路532号金蝶科技园 H1幢308号（林客社 内）
公交路线：5路 34路 34路区间 36路 55路 59路 y5路夜间 17路 65路 115路 118路 y17路夜间
公交路线：101路 10路 12路 203路 214路 215路 223路 29路 3路 85路 M112路 M191路 M192路 N3路 P100路(定制公交请预约) 高快巴士200号线 高快巴士20路 高快巴士863号线到地王大厦下，步行431米即可到达。