Nutrients213-page9

Nutrients213-page9 - plants. The Rhizobium bacteria that...

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Plant Nutrients and Soils - 9 Mineral cycling is affected by agricultural practices that leave soil open to wind and water erosion. Many feet of top soil can be washed away in floods or by wind, as documented in the 1930’s dustbowl era in United States dry land farming. Most agriculture relies on the use of added fertilizers to supply minerals that are not returned by nutrient cycling. (See ecology section for nutrient cycles in the ecosystem.) Fertilizers may be organic or inorganic. There are benefits and detriments to both. Any added fertilizer is potentially a water pollution problem since minerals leached from soil by rain or irrigation may wind up in waterways. In spite of adding fertilizers, soil depletion is a serious problem in agriculture. As discussed earlier, nitrogen-fixing bacteria are an important source of nitrogen for
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Unformatted text preview: plants. The Rhizobium bacteria that form root nodules in legumes are the best known nitrogen-fixing associates. Such bacteria can convert atmospheric nitrogen into ammonia, the first in a series of bacterial reactions that provides soluble nitrate ions for plant use. Each legume has a host-specific . Chemical signals (flavenoids) from legume roots stimulate to activate a set of bacterial Nod (nodule) genes that produce enzymes that affect root hair growth and formation of the plasma membrane infection thread as a means for the to invade the root cortex cells. Once within the cortex cells, Nod factors promote dedifferentiation and cell division to initiate the nodule formation. root nodules Nodule, xs...
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This note was uploaded on 01/08/2012 for the course BIO 213 taught by Professor Makina during the Fall '09 term at SUNY Stony Brook.

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