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| Web URL(s): | http://archive.lib.msu.edu/tic/rpr/1998/61825,%20U%20RI-Hull.PDF
Last checked: 04/19/2013
Requires: PDF Reader |
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| Publication Type:
| Report |
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| Material Type: | Manuscript |
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| Monographic Author(s): | Hull, Richard J.; Jiang, Zhongchun; Ruemmele, Bridget; Bushoven, John T. |
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| Author Affiliation: | Hull: Principal Investigator and Professor, Plant Physiology, University of Rhode Island; Jiang: Postdoctoral Research Associate; Ruemmele: Assoc. Prof., Turfgrass Improvement; and Bushoven: Graduate Research Assistant |
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| Monograph Title: | Increasing the Nitrogen Use Efficiency of Cool-Season Turfgrasses by Regulating Nitrate Metabolism: 1998 Progress Report, 1998. |
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| Publishing Information: | Kingston, Rhode Island: University of Rhode Island, Plant Sciences Department |
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| # of Pages: | 9 |
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| Collation: | [9] pp. |
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| Abstract/Contents: | "A long-standing paradox confronting turfgrass managers is the simple fact that high quality turf cannot be maintained without annual applications of nitrogen even when clippings are retained on the turf and no nitrogen is removed. This paradox is made all the more intriguing by recent research that shows very little nitrogen is lost from turf though nitrate leaching, ammonia volatilization or denitrification (usually less than 15% of that applied as fertilizer). Our research has shown that more than 2000 lbs. of nitrogen per acre can be recovered within the turf-soil ecosystem of long established turf. With that much nitrogen present in the turf environment, it would appear unlikely that additional applications are unnecessary. The answer to this paradox lies in the fact that in the spring when nitrogen is most needed by turfgrasses, soils are too cold to mineralize much of the organic nitrogen available. During the summer, when soil is warm and nitrogen becomes available, turfgrass roots are starved for energy because of high respiratory demands by the shoots due to elevated air temperatures. Warm-season turfgrasses do not experience this problem because their leaf respiration does not increase as much during hot weather. This research project is intended to find means for making cool-season turf more efficient in recovering soil nitrogen. One obvious approach would be to promote greater root development and less shoot growth. This would make the grass better able to absorb nitrate from a larger volume of soil while less energy is committed to rapid shoot growth. Plant growth regulators have been used to achieve this goal but their action is not long lasting and while they inhibit shoot growth they often fail to stimulate root development. We believe the location of nitrogen metabolism in turfgrasses may be the key to this problem. Most soil nitrogen is available to turfgrass roots as nitrate and is readily absorbed in that form. However, before nitrate-nitrogen can be assimilated into amino acids and proteins it first must be reduced to ammonium. This reduction of nitrate occurs in two steps or reactions: nitrate reduction (NR) and nitrate reduction (NiR). In roots, the eight electrons (e-) required for these two reactions comes from the reduction of sugars produced during photosynthesis and translocated to the roots. In leaves, most of the eight electrons come directly from photosynthetic reactions. The ammonium (NH4+) is assimilated directly into the amide-nitrogen of glutamine which is a five-carbon amino acid. The first reaction in this process is catalyzed by the enzyme nitrate reductase and this has been determined to be the rate limited step in the chain of reactions leading to nitrogen assimilation. If nitrate is reduced in the roots, amino acids are produced there and root growth is promoted. If roots are unable to reduce nitrates rapidly as it is absorbed from the soil, the nitrate can be transported to leaves where it will be reduced, assimilated into amino acids and stimulate shoot growth. When nitrate is reduced in leaves, photosynthetic products are diverted to shoot growth and away from roots. This lowered carbon flow to roots makes them even lass able to reduce nitrate so more is transported to leaves and shoot growth is further stimulated and roots are not. This is what normally happens when turf receives nitrate from the soil or fertilizers. The research conducted in this project will determine if the nitrate stimulation of shoot growth can be minimized by promoting nitrate reductase activity (NRA) within roots. We have found in all Kentucky bluegrass cultivars studied, NRA is often ten times more active in the leaves than in the roots. However, some cultivars (Liberty) did exhibit significantly greater NRA in their roots. We will determine if such cultivars produce greater root growth and if this contributes to more efficient nitrogen use. Currently we are extending this investigation to include diverse cultivars of perennial ryegrass and creeping bentgrass. Similar comparisons will be made and we will determine if greater root NRA correlates well with increased nitrogen use efficiency and field performance. We are also examining management practices that promote greater root growth (higher mowing heights, lower nitrogen frequency, infrequent but through irrigation, etc.) to determine if they contribute to greater root NRA. If this relationship between NRA in turfgrass roots and increased root growth is substantiated, efforts will be made to alter turfgrasses genetically to produce cultivars that have a more active nitrate reductase enzyme in their roots. This may produce turfgrasses that will utilize soil nitrate leaching from turf and produce turf with a larger, stronger root system that would be more tolerant of drought, and root feeding insects. This research could greatly increase the over-all efficiency of turfgrass management." |
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| Language: | English |
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| References: | 0 |
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| See Also: | See also related summary article, "Increasing the nitrogen use efficiency of cool-season turfgrasses by regulating nitrate metabolism", 1998 Turfgrass and Environmental Research Summary [USGA], 1998, pp. 23-24, R=61825. R=61825 |
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| Note: | Also appears as pp. 126-134 in the USGA Turfgrass Research Committee Reporting Binders for 1998.
"A Progress Report Prepared for the United States Golf Association"
"November 1998"
"Project Duration: 3 years (Feb. 1998 - Jan. 2001)
Tables |
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