R.
Ford Denison, Professor
Emeritus, UC Davis
From 1993 through
2002,
R. FORD DENISON taught crop ecology and conducted research at the
University of
California,
Davis, on topics ranging from
agricultural
sustainability to the evolution of
cooperation between microbes and plants. For most of this
time, he directed "the world's
youngest 100-year experiment" (LTRAS.ucdavis.edu),
tracking
the long-term trends that determine agricultural sustainability.
His work on symbiotic
nitrogen fixation, a possible
alternative to
nitrogen fertilizers, has led to a patent and publications
in
journals from Nature
to Field Crops Research. One
recent paper, "Darwinian
Agriculture: When Can Humans Find Solutions Beyond the Reach of
Natural
Selection?" points out
some limitations both of agricultural biotechnology and of agriculture
that mimics natural ecosystems. He has been interviewed on National
Public Radio, Science Update (AAAS), and DeutschlandRadio and has been an
invited speaker at international meetings and at institutions
from
Japan's National
Agricultural Research Center to the Scripps Institute of
Oceanography. He was educated at Harvard, Evergreen, and
Cornell, where he earned a Ph.D. in Crop Science, with postdoctoral and
sabbatical research at UC Davis, UCLA, Queen's University (Ontario),
Welsh Plant Breeding Station (Aberystwyth), and University of
Minnesota. His
research
has
been supported by NSF, USDA, and California's
Agricultural Experiment Station. This web page was last updated
May 2005, when he moved to the University of Minnesota.
Teaching
PLB 142. Ecology of Crop Systems (4) II. Denison. Lecture, 3
hours;
discussion, 1 hour. Prerequisite: Agricultural Systems and Environment
2 or Biological Sciences 1C; Math 16A or Physics 1A, or consent of
instructor.
Ecological processes governing the structure and behavior of managed
ecosystems.
Emphasis on mechanistic and systems views of the physical environment,
photosynthetic productivity, competition, adaptation, nutrient cycling,
energy relations and contemporary issues such as climate change.
PBI 225. Methods and Instrumentation for Crop and Soil Science
(3)
III. Denison, Hsiao, Hartz, Mitchell, Pettygrove, Scow & van
Kessel. Lecture, 1 hour; discussion, 1 hour; laboratory, 3 hours.
Prerequisite:
Basic knowledge of plant physiology, soil science, chemistry and
physics.
Theory and practice of in situ sampling and instrumentation methods for
crop science and related aspects of soil science (e.g. moisture and
fertility)
and laboratory analysis. Not offered every year.
Research

How does evolution based on
"selfish genes" maintain cooperation? We are trying to answer
this question for
rhizobia,
symbiotic bacteria that infect legume plants like alfalfa or soybean
and (to varying extents) supply them with nitrogen. Fixing
nitrogen is costly for rhizobia, so why haven't rhizobia that supply
their plant hosts with nitrogen (indirectly benefiting competing
rhizobia infecting the same plant) been completely displaced by
"ineffective" rhizobia? Why are ineffective rhizobia common
enough to be a problem in some
soils but not others? This research
may lead to practical applications, such as legume
crops that selectively enrich the soil with the
most-beneficial
local strains of rhizobia. This research may also be relevant to other
cases where symbiosis
breaks
down, as in coral bleaching. As time allows, I also hope to
explore other applications of modern evolutionary theory, pursuing some
of the ideas in our paper on Darwinian Agriculture. Steve Kaffka
has replaced me as Director
of
LTRAS,
but I remain interested in scientific approaches to the problem of
long-term sustainability,
especially
that of agriculture. To pursue my research objectives, I have
often
had to develop new tools, including mechanistic
computer
models and noninvasive scientific instruments, such as the nodule
oximeter or a laser-scanner (at right)
to
measure green leaf area index in the field.
Grants
Other recent grants on which I was principal investigator or co-PI
include:
Patent

- Method and Apparatus for Measuring Oxygen Concentration and its
Subsequent
Use in Estimating Nitrogen Fixation in Plants. D.B. Layzell, S.
Hunt,
G. Palmer, R.F. Denison. #5,096,294.
Publications
- E.T. Kiers, S.A. West, and R.F. Denison. 2005? Maintaining
cooperation in the legume-rhizobia symbiosis: identifying selection
pressures and mechanisms. In: J.
Sprent and E. James (eds.) Leguminous Symbioses. Kluwer Academic
Publishers (in press).
- Kong, A.Y., J. Six, D.C. Bryant, R.F. Denison, and C. van
Kessel.
2005. The relationship between carbon input, aggregation, and soil
organic carbon stabilization in sustainable cropping systems.
Soil
Science Society of America Journal (in press).
- R.F. Denison and E.T. Kiers. 2005. Sustainable crop
nutrition: constraints and opportunities. In: M. Broadley (ed.) Plant
Nutritional Genomics. Blackwell.
- Hasegawa, H., and R.F. Denison. 2005. Model
predictions of winter rainfall effects on N dynamics of winter wheat
rotation following legume cover crop or fallow. Field Crops
Research 91:251-261.

- R.F. Denison and E.T. Kiers. 2004. Why are
most rhizobia
beneficial to their plant hosts, rather than parasitic? (Invited
review.) Microbes
and Infection 6:1235-1239.
- R.F. Denison and E.T. Kiers. 2004. Lifestyle
alternatives
for rhizobia: mutualism, parasitism, and forgoing symbiosis.
(Invited review.) FEMS
Microbiology Letters 237:187-193.
- Denison, R.F., D.C. Bryant, and T.E.
Kearney. 2004. Crop
yields over
the
first
nine years of LTRAS, a long-term comparison of field crop systems in a
Mediterranean climate. Field
Crops Research
86:267-277.
- Martini, E.A., J.S. Buyer, D.C. Bryant, T.K. Hartz, and R.F.
Denison. 2004. Yield
increases during the organic transition: improving soil quality or
increasing
experience? Field
Crops Research 86:255-266.
- Okano, Y., K.R. Hristova, C. Leutenegger, L. Jackson, R.F.
Denison, B.
Gebreyesus, D. LeBauer, and
K.M. Scow. 2004. Effects of ammonium on the
population
size of ammonia-oxidizing bacteria in soil -- Application of real-time
PCR. Applied
and Environmental Microbiology 70:1008-1016.
- Kiers, E.T., R.A. Rousseau, S.A. West, and
R.F. Denison.
2003. Host
sanctions and the legume-rhizobium mutualism. Nature
425:78-81. Widely covered in scientific and popular press.
- Kinraide, T.B., and R.F. Denison. 2003. Strong
inference,
the way
of
science.
American Biology Teacher 65:419-424.
- Denison, R.F., E.T. Kiers, and S.A. West. 2003. Darwinian
Agriculture:
When can humans find solutions beyond the reach of natural
selection? Quarterly
Review of Biology 78:145-168. See updates
and commentary.
- Denison, R.F., C. Bledsoe, M. Kahn, F. O'Gara, E.L. Simms,and
L.S.
Thomashow.
2003. Cooperation in the rhizosphere and the "free rider" problem. Ecology
84:838-845.
- Denison, R.F., and Y. Okano. 2003. Leghemoglobin oxygenation
gradients
in alfalfa and yellow sweetclover nodules. Journal
of Experimental Botany 54:1085-1091.
- Kiers, E.T., S.A. West & R.F. Denison. 2002. Mediating
mutualisms:
the influence of farm management practices on the evolutionary
maintenance
of symbiont cooperation. Journal
of Applied Ecology 39:745-754.
- West, S.A., E.T. Kiers, I. Pen & R.F. Denison. 2002.
Sanctions
and mutualism stability: when should less beneficial mutualists be
tolerated? Journal
of Evolutionary Biology 15:830-837.
- West, S.A., E.T. Kiers, E.L. Simms & R.F. Denison.
2002.
Sanctions
and mutualism stability: why do rhizobia fix nitrogen? Proceedings
of the Royal Society, London 269:685-694.
- Denison, R.F. 2001. Meeting report: ecologists and molecular
biologists
find common ground in the rhizosphere. Trends
in Ecology and Evolution
16:535-536.
- Denison, R.F. 2000. Legume sanctions
and the evolution of
symbiotic cooperation by rhizobia.
American
Naturalist 156:567-576.
- Hasegawa, H.,
D.C. Bryant,
and R.F. Denison. 2000. Testing CERES model predictions of crop growth
and N dynamics, in cropping systems with leguminous green manures in a
Mediterranean climate. Field
Crops Res. 67:239-255.
- Hasegawa, H.,J.M. Labavitch, A.M. McGuire, D.C. Bryant, and R.F.
Denison.
1999. Testing CERES model predictions of N release from legume cover
crop
residue. Field
Crops Res. 63:255-267.
- Plant, R.E., A. Mermer, G.S. Pettygrove, M.P. Vayssieres, J.A.
Young,
R.O.
Miller, L.F. Jackson, R.F.
Denison, and K. Phelps. 1999. Factors
underlying
grain yield spatial variability in three irrigated wheat fields.
ASAE Transactions
42:1187-1202.
- Serraj, R., V. Vadez, R.F. Denison, and T.R. Sinclair. 1999.
Involvement
of ureides in nitrogen fixation inhibition in soybean. Plant
Physiol. 119:289-296.
- McGuire, A.M., D.C. Bryant, and R.F. Denison. 1998. Wheat yields,
nitrogen
uptake, and soil moisture following winter legume cover crop vs.
fallow. Agron.
J. 90:404-410.
- Denison, R.F. 1998. Decreased oxygen permeability: a universal
stress
response
in legume root
nodules. Bot. Acta 111:191-192.
- Jacobsen, K.R., R.A. Rousseau, and R.F. Denison. 1998. Tracing
the
path
of oxygen into birdsfoot trefoil and alfalfa nodules using
iodine
vapor. Bot.
Acta.
111:193-203. (cover article)
- Pettygrove,G.S., S.K. Upadhyaya, M.G. Pelletier, T.K. Hartz, R.E.
Plant,
and R.F. Denison. 1998. Tomato yield - color infrared photograph
relationships.
Proc. 4th Intl. Conf. Precision Agric., St. Paul, MN.
- Arrese-Igor,C., A.J. Gordon, F.R. Minchin, and R.F.
Denison.
1998.
Nitrate
entry and nitrite formation in the infected region of soybean nodules. J.
Exp. Bot. 9:41-48.
- Miller, R.O., G.S. Pettygrove, R.F. Denison, L. Jackson, M. Cahn,
R.
Plant, T. Kearney. 1998. Site specific relationships between flag leaf
nitrogen,
SPAD meter values and grain protein in irrigated wheat. Commun. Soil
Sci.
Plant Anal. 9:1381-1382.
- Denison, R.F., and R.
Russotti. 1997. Field estimates of
green leaf
area index using laser-induced chlorophyll fluorescence. Field
Crops Res. 52:143-150.
- Denison, R.F. 1997. Minimizing errors in LAI estimates from
laser-probe
inclined-point quadrats. Field
Crops Res. 51:231-240.
- Denison, R.F. 1997. Review of "Long-Term Experiments in
Agricultural
and Ecological Sciences." Field Crops Res. 54:74-75.
- Shimada, S., R. Rousseau, and R.F. Denison. 1997. Wavelength
options
for
monitoring leghemoglobin oxygenation gradients in intact legume root
nodules. J.
Exp. Bot. 48:1251-1258. (cover article)
- Denison, R.F., R.O. Miller, D. Bryant, A. Abshahi, and W.E.
Wildman.
1996.
Image processing extracts more information from color infrared aerial
photos.Calif.
Agric. 50(3):9-13 (cover article)
Denison, R.F., and B.L. Harter. 1995. Nitrate effects on nodule
oxygen
permeability and leghemoglobin
Nodule oximetry and computer
modeling.Plant
Physiol. 107:1355-1364. - Denison, R.F., and T.B. Kinraide.
1995. Oxygen-induced
membrane depolarizations
in legume root nodules: possible evidence for an osmoelectrical
mechanism
controlling nodule gas permeability. Plant
Physiol. 108:235-240
- Denison, R.F. 1995. Agricultural soil and crop practices.
McGraw-Hill Yearbook
of Science and Technology, pp. 6-9.
- Denison, R.F., J.F. Witty, and F.R. Minchin. 1992. Reversible O2-inhibition
of nitrogenase activity in attached soybean nodules. Plant
Physiol. 100:1863-1868.
- Denison, R.F., S. Hunt, and D.B. Layzell. 1992. Nitrogenase
activity, nodule
respiration, and O2
permeability following detopping of
alfalfa
and birdsfoot trefoil. Plant
Physiol. 98:894-900.
- Denison, R.F. 1992. Mathematical modeling of oxygen diffusion and
respiration
in legume root nodules. Plant
Physiol. 98:901-907.
- Denison, R.F., and D.B.
Layzell.
1991. Measurement of legume nodule respiration and O2
permeability by noninvasive spectrophotometry of leghemoglobin. Plant
Physiol.
96:137-143.
- Denison, R.F., D.L. Smith, T. Legros, and D.B. Layzell. 1991.
Noninvasive
measurement of internal oxygen concentration in field-grown soybean
nodules. Agron.
J. 83:166-169.
- Denison, R.F., and H.D. Perry. 1990. Seasonal growth rate
patterns for
orchardgrass and tall fescue on the Appalachian Plateau. Agron.
J. 82:869-873.

- Denison, R.F., J.M. Fedders, and C.B.S.
Tong. 1990. Amyloglucosidase digestion can overestimate starch
content
of plants. Agron.
J. 82:361-364.
- Denison, R.F. 1989. Implications of competitive inhibition in the
acetylene
reduction assay for dinitrogen fixation. Ann. Bot. 64:167-169.
- Denison, R.F., and R.S. Loomis. 1989. An
Integrative Physiological Model of Alfalfa Growth and Development.
Univ. Calif. Div. Agric.
Natural Resources, Publ. 1926, 73 pp.
- Denison, R.F., and P.S. Nobel. 1988. Growth
of Agave deserti without
current photosynthesis. Photosynthetica 22:51-57.

- Denison, R.F., P.R. Weisz, and T.R. Sinclair. 1988. Oxygen supply
to
nodules
as a limiting factor for symbiotic nitrogen fixation. p. 767-776. In:
R.J.
Summerfield (ed.) World Crops: Cool Season Food Legumes. Kluwer
Academic
Publishers, Dordrecht.
- Weisz, P.R., R.F. Denison, and T.R. Sinclair. 1985. Response to
drought
stress of nitrogen fixation (acetylene reduction) rates by field-grown
soybeans. Plant Physiol. 78:525-530.
- Sinclair, T.R., P.R. Weisz, and R.F. Denison. 1985. Oxygen
limitation
to
nitrogen fixation in soybean nodules. p. 797-806. In: R. Shibles (ed.)
Proceedings, World Soybean Conf. III. Westview Press, Boulder.
- Denison, R.F., and T.R. Sinclair. 1985. Diurnal and seasonal
variation
in dinitrogen fixation (acetylene reduction) rates by field-grown
soybeans.
Agron. J. 77:679-684.
- Denison, R.F., P.R. Weisz, and T.R. Sinclair. 1985. Variability
among
plants
in dinitrogen fixation Agron. J.77:947-950.
- Denison, R.F., P.R. Weisz, and T.R. Sinclair. 1983. Analysis of
acetylene
reduction rates of soybean nodules at low acetylene concentrations. Plant
Physiol. 73:648-651.
- Denison, R.F., T.R. Sinclair, R.W. Zobel, M.N. Johnson,
and G.M.
Drake.
1983. A nondestructive field assay for soybean
nitrogen fixation by
acetylene
reduction. Plant Soil 70:173-182.
- Denison, R.F. 1979. A 2K Symbolic Assembler for the
6502.
Self-published
manual recently reincarnated
on the web.
- Denison, R., B. Caldwell, B. Bormann, L. Eldred, C.
Swanberg,
and S.
Anderson. 1976. The effects of acid rain on nitrogen fixation in
western
Washington coniferous forests. Water Air Soil Pollut.
8:21-34.
Computer
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Education and Employment
History
- Professor and Agronomist, Department of Agronomy and Range
Science,
1993
to present (Assoc. Prof. 5/93-6/99).
- Plant Physiologist, USDA/ARS, Beckley WV. 1986 to 1993.
- Postgraduate Researcher, with P.S. Nobel, UCLA. 1985.
- Postdoctoral Research Agronomist, with R.S. Loomis, UC
Davis.
1982
to 1984.
- Ph.D., crop science, with T.R. Sinclair, Cornell
University,
1983.
(M.S., 1980).
- B.A., with ecology emphasis, The Evergreen State College,
1975.
- Another Harvard dropout.
Professional
Activities
- Member of the Editorial Board, Field
Crops Research, 1994-present
- Invited talks: Intl. Cong. N2 Fixation, European
N2 Fixation Congress, Amer.
Soc. Agron. national meeting, Nat. Agric. Res. Center (Japan), Scripps
Inst.
Oceanography,
Bodega Marine Lab., UC Berkeley Grad School Journalism, UCD Law School,
Calif.
Dept. Food & Agric., UCD Center Pop. Biol., Calif. Plant & Soil
Conf., etc.
- Annual guest lectures at UC Davis in graduate ecology and upper
division
crop evolution classes; departmental seminars at UC Davis and elsewhere.
- Chair of Agroecology Curriculum Review Committee, member College
Committee on Sustainable Agriculture.
- Grant reviews for USDA, NSF, NSERC, Swiss and Russian National
Science
Foundations, IPM program, etc.
- Webmaster for Environmental
Plant
Biology and Small Farm
Technology
websites.
New address
Ecology, Evolution and
Behavior
University of
Minnesota
1987 Upper Buford Circle
St. Paul, MN
55108
E-mail: First five
letters of my last name + 036 + umn.edu (you know where to put the @)