托福TPO5阅读真题文本翻译及答案Part1
Minerals and Plants
Research has shown that certain minerals are required by plants for normal growth and The soil is the source of these minerals, which are absorbed by the plant with the water from the Even nitrogen, which is a gas in its elemental state, is normally absorbed from the soil as nitrate Some soils are notoriously deficient in micro nutrients and are therefore unable to support most plant So-called serpentine soils, for example, are deficient in calcium, and only plants able to tolerate low levels of this mineral can In modern agriculture, mineral depletion of soils is a major concern, since harvesting crops interrupts the recycling of nutrients back to the
Mineral deficiencies can often be detected by specific symptoms such as chlorosis (loss of chlorophyll resulting in yellow or white leaf tissue), necrosis (isolated dead patches), anthocyanin formation (development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous Soils are most commonly deficient in nitrogen and Nitrogen-deficient plants exhibit many of the symptoms just Leaves develop chlorosis; stems are short and slender, and anthocyanin discoloration occurs on stems, petioles, and lower leaf Phosphorus-deficient plants are often stunted, with leaves turning a characteristic dark green, often with the accumulation of Typically, older leaves are affected first as the phosphorus is mobilized to young growing Iron deficiency is characterized by chlorosis between veins in young
Much of the research on nutrient deficiencies is based on growing plants hydroponically, that is, in soilless liquid nutrient This technique allows researchers to create solutions that selectively omit certain nutrients and then observe the resulting effects on the Hydroponics has applications beyond basic research, since it facilitates the growing of greenhouse vegetables during Aeroponics, a technique in which plants are suspended and the roots misted with a nutrient solution, is another method for growing plants without
While mineral deficiencies can limit the growth of plants, an overabundance of certain minerals can be toxic and can also limit Saline soils, which have high concentrations of sodium chloride and other salts, limit plant growth, and research continues to focus on developing salt-tolerant varieties of agricultural Research has focused on the toxic effects of heavy metals such as lead, cadmium, mercury, and aluminum; however, even copper and zinc, which are essential elements, can become toxic in high Although most plants cannot survive in these soils, certain plants have the ability to tolerate high levels of these
Scientists have known for some time that certain plants, called hyperaccumulators, can concentrate minerals at levels a hundredfold or greater than A survey of known hyperaccumulators identified that 75 percent of them amassed nickel, cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of Hyperaccumulators run the entire range of the plant They may be herbs, shrubs, or Many members of the mustard family, spurge family, legume family, and grass family are top Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of metals may afford some protection against plant-eating insects and microbial
Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals-an environmentally friendly approach known as This scenario begins with the planting of hyperaccumulating species in the target area, such as an abandoned mine or an irrigation pond contaminated by Toxic minerals would first be absorbed by roots but later relocated to the stem and A harvest of the shoots would remove the toxic compounds off site to be burned or composted to recover the metal for industrial After several years of cultivation and harvest, the site would be restored at a cost much lower than the price of excavation and reburial, the standard practice for remediation of contaminated For examples, in field trials, the plant alpine pennycress removed zinc and cadmium from soils near a zinc smelter, and Indian mustard, native to Pakistan and India, has been effective in reducing levels of selenium salts by 50 percent in contaminated
Paragraph 1: Research has shown that certain minerals are required by plants for normal growth and The soil is the source of these minerals, which are absorbed by the plant with the water from the Even nitrogen, which is a gas in its elemental state, is normally absorbed from the soil as nitrate Some soils are notoriously deficient in micro nutrients and are therefore unable to support most plant So-called serpentine soils, for example, are deficient in calcium, and only plants able to tolerate low levels of this mineral can In modern agriculture, mineral depletion of soils is a major concern, since harvesting crops interrupts the recycling of nutrients back to the
