【正文】 oftime to read this book in class, doesn39。t mean that I　　cannot read it on myown know, I think I’ll give it a try.　　TPO10 – Lecture 3　　Narrator　　Listen to part ofa lecturein an Ecology Class.　　Professor　　So we’ve been talking about nutrients,the elementsin the environment that　　are essential for living organisms to develop, live a healthylife and reproduce.　　Some nutrients arequiet scarce。 therejust isn’t much ofthem in the　　 fortunatelytheyget nutrientsare used over　　and over in the environment,we call that a nutrient of the　　importance of nutrientsand their scarcity,nutrient recycling is one of the most　　significant ecosystem processesthat will cover in this course. The threemost　　important nutrient recyclesare thenitrogen cycle,the carbon cycle and the　　one we are going to talkabout today,the Phosphorus cycle.　　So thePhosphorus cycle has been studied a lot byecologists because like I　　said, Phosphorus cycle is a most important nutrientand it’s not so abundant.　　The largest quantities are found in rocks at the bottom ofthe ocean. How the　　Phosphorus get there? Well,let’s startwith the Phosphorus in rocks. The rocks　　get broken down into smaller and smaller particlesas theyare weathered.　　Theyare weathered slowly byrain and wind over long periods of time.　　Phosphorus is slowly released as the rocks are broken down and then it gets　　spread around into thesoil. Once it’s in the soil, plants absorb it through their　　roots.　　Student　　So that’s the reason people mine rocks that contain a lot ofPhosphorus tohelp　　the agriculture?　　Professor　　Hum, theymined the rock, artificially break it down and put the Phosphorus　　into the agricultural fertilizers. So humans can play a role in a first part of the　　Phosphorus cycle the breaking down of rocks and the spreading　　Phosphorus into the soil by speeding up the rate at which this natural process　　occurs. You see. Now after thePhosphorus is in the soil, plants use Phosphorus from the soil to when theydie, theydepose.　　And thePhosphorus is recycled back into the soil。 same thing with the　　animals that eatthose plants, or eat other animals thathave eatenthose　　plants. We call all ofthis – the land phase ofthe Phosphorus cycle. Buta lot　　of thePhosphorus in the soil getswashed away into riversby rain and melting　　snow. And so begins another phase of the anyone guess what it　　is called? Nancy　　Nancy　　Well, if the one is called the land phase, then thishas to be called thewater　　phase,right?　　Professor　　Yes, that’s such a difficult point isn’tit? In a normal waterphase, rivers　　eventuallyempty into oceans, and oncein the oceans, the Phosphorus gets　　absorbed by water plants like algae. Then fish eatsthe algae or eat other fish　　that have eaten those plants. Butthe water phase is sometime affected by　　excessive fertilizers. Ifnot all ofPhosphorus gets used by the cropsand larger　　amounts of Phosphorus getsinto the rivers. This could cause a rapid growth of　　waterplants in the river,which can lead to the waterwaste getting clogged with　　organisms, which can change theflow of the current studies are　　looking at these effectsand I reallydo hope we can find theway to dealwith　　this issue before these ecosystems are adverselyaffected. Ok? Ofcourse,　　another way that humans can interrupt thenormal process is fishing. The　　fishing industry helps bring Phosphorus back toland. In the normalwater　　phase the remaining Phosphorus makesits way,settlesto the bottomof the　　ocean and getsmixed into the ocean sediments. But remember,thisis a cycle.　　The Phosphorus at the bottom ofthe ocean has to somehow make its way　　back to thesurface, to pletethe cycle, tobegin the cycle all over again.　　After millions of years, powerful geological forces, like under watervolcanoes　　lift up the ocean sediments to form new land. When an under volcano pushes　　submerge rock to thesurface, a new island is created. Then over manymore　　years thePhosphorus reachrocks of thenew land begin to erode and the　　cycle continues.　　Guy　　What about, well, you said that thenitrogen cycle is also an important nutrient　　 thereis a lot ofnitrogen in the atmosphere, so Iwas wondering, is　　therea lot ofPhosphorus in the atmosphere too?　　Professor　　Good question, ’re right to guess thePhosphorus can end up in　　earth atmosphere. Itcan move from the land or from the oceans to the　　atmosphere, and vice versa. However,there’s just not as substantial amount of it there,like thereis with nitrogen, it’s a veryminimal