A couple of studies (full text articles provided by NCBI) about potential agricultural futures.
The first one detailes the symbiotic relationships in the soil ecosystem that enrich soil quaility, enable nutrient fixation from a molecular biology viewpoint. Lightly touches on the possibility of targetet interventions (including genetical engineering) to enhance symbiotic relationships between plants and micro-organisms as a way to limit fertilizer inputs.
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')Genome Biol. 2003;4(1):201. Epub 2003 Jan 3.
Post-genomic insights into plant nodulation symbioses.
Gresshoff PM.
Department of Botany, School of Life Sciences, The University of Queensland, St,
Lucia, Brisbane, QLD 4072, Australia. p.gresshoff@botany.uq.edu.au
Several legume genes involved in establishing nitrogen fixation have been
discovered using functional genomics; when mutated, the genes affect symbioses,
and all encode receptor kinases. This provides long-awaited insights into a
complex plant-bacterium interaction and heralds the possibility of extending the
range of plants susceptible to nitrogen-fixing nodulation.
Publication Types:
Review
Review, Tutorial
PMID: 12540294 [PubMed - indexed for MEDLINE]
PeakOil is You
Post Green Revolution Agriculture
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Post Green Revolution Agriculture
by EnergySpin » Tue 09 Aug 2005, 23:40:59
Whole article can be read here
Abstract and Introduction ...
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')
Abstract
Several legume genes involved in establishing nitrogen fixation have been discovered using functional genomics; when mutated, the genes affect symbioses, and all encode receptor kinases. This provides long-awaited insights into a complex plant-bacterium interaction and heralds the possibility of extending the range of plants susceptible to nitrogen-fixing nodulation.
Nitrogen is essential for life
Plants are essential for life on this planet; they convert solar energy to chemical energy that we eventually use as food, fuel, feed and fiber. But plants can do this only if they have nitrogen, the most limiting element for the synthesis of proteins, amino acids, nucleotides and vitamins. Nitrogen is commonly assimilated as nitrate and modern agriculture is highly dependent on nitrate fertilizer, with global annual nitrate fertilizer costs exceeding US$300 million. Moreover, nitrate often contaminates ground water and surface streams, causing environmental and human health problems, at a cost that possibly exceeds several billion dollars.
Some plants are naturally able to acquire nitrogen from the air through a process called symbiotic nitrogen fixation. In broad terms, this process requires a close interaction between a soil bacterium, Rhizobium, and the roots of plants of the legume family (which includes soybeans, peas, beans and clovers, as well as thousands of other species found in a wide range of ecosystems). Rhizobium enters into a symbiosis in which both partners benefit from their interaction: the bacterium gains sugar from the plant, and the plant gains reduced nitrogen. For this reason, legumes tend to be very nutritious and serve as a direct protein source for many people and animals.
All the bacterial genes needed for symbiotic nitrogen fixation have been identified. Now, exciting progress is being made in elucidating the plant's contribution to this mutually beneficial interaction, with the identification of crucial signal transduction genes involved early in the response to Rhizobium. The major advances originate from the discovery of plant genes that, if mutated, affect the symbiotic function of the plant. This breakthrough was accomplished by applying functional genomic tools to classic plant mutation breeding, a fruitful marriage of old and new approaches. Precise genetic and developmental controls are required for the establishment of the complex interaction between bacterium and plant. Most significantly, when the legume root is stimulated by the appropriate bacterial partner it develops spherical, cylindrical or coral-like outgrowths, in which the bacterium is housed and where it accomplishes nitrogen fixation (the reduction of atmospheric N2 gas into NH3, which is subsequently assimilated by the plant to form glutamine). These structures are called 'nodules' and are produced from proliferating root cortex and the pericycle (a cell layer along the length of the root that is akin to pluripotent stem cells in animals and is normally involved in lateral root initiation).
Nodules are induced by bacterial lipo-chito-oligosaccharides called nodulation factors [1,2]. The invading Rhizobium differentiates into a nitrogen-fixing form within a highly specialized plant membrane, making the resultant 'symbiosome' and the entire nodule fascinating examples of 'cellular sociology' [3,4]. Such intimacy and specificity of interaction clearly require precise signaling and genetic regulation. Thanks to recent genomic advances we are now at the threshold of discovering significant numbers of genes involved in the process of nodulation and it may become possible to expand rhizobial symbiosis to other non-leguminous crop plants. Indeed the full impact on agricultural sustainability of such developments cannot be estimated at this point.
I have to point out that a recurrent theme in biological research today is that cooperative relationships are equally (if not more important) than antagonistic relationships. This article shows one such example (i.e. the symbiosis between legumes and fungi, and addresses strategies to extend this symbiotic relationship in nature.
The second article takes these ideas further and connect them to the effects (positive in the short term but negative in the long term) of the so called Green Revolution.
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')Plant Physiol. 2001 Oct;127(2):390-7.
Symbiotic nitrogen fixation and phosphorus acquisition. Plant nutrition in a world of declining renewable resources.
Vance CP.
United States Department of Agriculture Agricultural Research Service,
Department of Agronomy and Plant Genetics, University of Minnesota, 1991 Buford
Circle, St. Paul, MN 55108-6026, USA. vance004@tc.umn.edu
Publication Types:
Review
Review, Tutorial
PMID: 11598215 [PubMed - indexed for MEDLINE]
Whole article can be read here
A few excerpts
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')Although we can produce enough food to feed today's population, that achievement has come at the cost of an ever-increasing impact on Earth's sustainability. The striking increase in the use of nitrogen (N) and phosphorus (P) fertilizers between 1960 and 2000 by intensive agricultural practices has led to degradation of air and water quality (Bumb and Baanante, 1996; Pinstrup-Anderson et al., 1997; Tilman et al., 2001).
Can we feed the projected 8 to 9 billion people in 2040? Probably yes, but at an accelerated impact on sustainability and environmental quality (Waggoner, 1994; Trewavas, 2001). As currently practiced, agriculture will require an additional 40 and 20 Tg (1012 g or million metric tons) of N and P fertilizer, respectively, applied to agricultural soils to meet food production needs in 2040 (Table I; Bumb and Baanante, 1996; Frink et al., 1999). It is astounding that irrigation water equivalent to 10 times the flow of the Nile River will be required to meet these agricultural demands (Postel, 2001).
Grain crop yields until the 1930s were about 0.5 to 1.0 metric tons Ha-1, with N supplied primarily from crop rotations and manures ....anthropogenic addition of fixed N via fertilizer into intensive agriculture became common practice after 1945, increasing from 5 Tg in 1950 to 90 Tg in 2000 (Table I). Accompanying grain yield increased to about 7 metric tons Ha-1,
Why does anthropogenic addition of N by agriculture matter? A grain yield of 5 to 9 metric tons Ha-1 requires the addition of 200 to 300 kg N Ha-1 (Heichel, 1987; Peoples et al., 1995). The efficiency of N recovery by grain crops ranges from 35% to 75% with an average near 50% (Smil, 1999; Socolow, 1999). For example, N recovery by maize, which has a grain N content of 1.5%, is 39% for the first 100 kg of N fertilizer and only 13% for the second 100 kg ....A conundrum to the N issue is contrasting availability of N fertilizer for extensive agriculture as practiced in the developing world. Due to weak infrastructure, poor transportation, and high cost, N fertilizer is frequently unavailable for subsistence farmers, leaving N from intercropping legumes and other species capable of symbiotic N2 fixation as the only source of N. Note I have written elsewhere about this law of diminishing returns in agricultural fertilizer input and how the 3rd world is not dependent on fertilizers except for cash crops
...Plants have adopted two broad strategies that enhance N and P acquisition and use (Table II): (a) those directed toward improved acquisition or uptake, and (b) those targeted to conserve use...Because most legumes used by humans display all of these adaptive strategies, they are ideal for crop management schemes aimed at enhancing sustainability and buffering against the dependence on N and P fertilizer. .... Peterson and Russelle (1991) have estimated that properly managed alfalfa (Medicago sativa)-corn (Zea mays) rotations in the U.S. upper midwest (Corn Belt) could reduce fertilizer inputs by up to 25% without loss of production and give a realized net return of $70 to $90 million. Depending upon the management and cropping system, legume green manures have the potential to replace more than 100 kg N Ha-1 for a subsequent grain crop. This equates to a savings of between $60 to $90 Ha-1 in N fertilizer. The enhanced yield due to the rotation effect coupled to the savings in fertilizer expense offset most potential loss in income. Smil (1999) and Socolow (1999) estimate that the use of legumes and other N2-fixing associations accompanied by good agronomic practices (proper soil tests and fertilizer application) along with the use of germplasm having efficient N uptake could effectively save 20 Tg N year-1 (comparable savings could probably accrue for P use). Not only would a savings in N fertilizer occur with expanded use of legumes in intensive agriculture, but also the potential for N leaching into groundwater and volatilization of N into the atmosphere could be reduced because legume N is less susceptible to the chemical and physical conversions that lead to such losses. An unrecognized benefit of expanded use of N2-fixing species in agriculture is their contribution to carbon sequestration. The biological fixation of 90 Tg N year-1 (50% by legumes) is equivalent to sequestering an additional 770 to 990 Tg of carbon year-1.
....
The plant strategies identified in Table II as enhancing N and P acquisition or use are genetically controlled and subject to genetic improvement either through traditional plant breeding or through transgenic technology. ...Tantalizing results showing improved N and P acquisition obtained by overexpressing single genes involved in NO3- and PO4- uptake hold promise for future application.Evidence is accumulating that overexpression of selected individual genes involved in N and P acquisition can improve nutrient uptake. As the arsenal of plant genes involved in these processes expands, we will undoubtedly see more successful examples. Because of the urgent need for plant germplasm having improved N and P use efficiency, research programs that combine traditional plant breeding and transgenic technology will be imperative.
SYNOPSIS
The world is on the brink of a new agriculture, one that involves the marriage of plant biology and agroecology under the umbrella of biotechnology and germplasm improvement. Although N and P fertilizers will continue to play a major role in intensive agriculture, depletion of natural resources, loss of biodiversity, and long-term unsustainability necessitate alternative strategies be investigated and implemented to buffer against food insecurity and environmental degradation. Furthermore, because improved N and P use by plants has immediate and direct benefit in extensive agriculture in developing countries where access to fertilizers is limited, funding for research at international centers should be a high priority. The following recommendations deserve attention: (a) reemphasize the use of legumes and symbiotic N2 fixation to improve soil N and P fertility while reducing fossil fuel consumption and providing a source of dietary N; (b) develop intercropping schemes that foster efficient N and P use; (c) continue to isolate, characterize, and develop fundamental understanding of individual genes holding promise of application to improving N and P use; (d) enhance the expression of genes and increase the synthesis of gene products, such as those involved in transport of nutrients and exudation of organic acids, through both traditional plant breeding and transgenic technology and incorporate these traits into adapted germplasm; and (e) assess the factors limiting rhizobial and mycorrhizal interactions with plants with the goal of site- (region) specific inoculation.
I would appreciate it If the "usual suspects" (who shall rename un-named) respected my time in compiling this and did not start a flame on this thread.
"Nuclear power has long been to the Left what embryonic-stem-cell research is to the Right--irredeemably wrong and a signifier of moral weakness."Esquire Magazine,12/05
The genetic code is commaless and so are my posts.
The genetic code is commaless and so are my posts.
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EnergySpin - Intermediate Crude
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