Arnold J. Bloom
 |
Department
of Vegetable Crops University of California at Davis Davis, CA 95616 (530) 752-1743 office |
Education
B.A.; Physics; Yale University; June, 1971
Ph.D.; Biology; Stanford University; January, 1979
Professional Experience
Research Associate
Landesanstalt fur Immissionschutz, Essen, Germany
July, 1971 - August, 1972
Research Associate
Institute of Arctic Biology, U. of Alaska, Fairbanks
September, 1978 - September, 1980
Research Botanist
Dept. of Botany, U. of California, Davis
October, 1980 - November, 1981
Assistant, Associate, Full Professor, and Chair
Dept. of Vegetable Crops, U. of California, Davis
December, 1981 - Present
Honors and Distinctions
Graduated cum laude, 1971
William Bates Traveling Fellow, 1971
NIH Training Grant Fellow, 1972 - 1976
Ph.D. with distinction, 1979
Plant Biology Distinguished Lecturer, UCLA, 1994
NSF Panel Member: Physiological Ecology & Population Biology 1983
NSF Panel Member: Biological Instrumentation 1989-1990
NSF Panel Member: Ecological & Evolutionary Physiology 1992-1996
NASA Science Working Group on the Space Station 1992-1996
DOE Panel Member: Photosynthesis in Nature 1993
Chair, Rockefeller Advisory Seminar, International Agriculture 1995
USDA Panel Member: Forest/Range/Crop/Aquatic Ecosystems 1996
NASA Panel Member: Space Biology 1998-2000
Research Interests
Nitrogen availability, low temperatures, and elevated carbon dioxide are interrelated environmental factors that strongly influence crop production.
Nitrogen is the inorganic nutrient that plants require in greatest quantity and that most frequently limits productivity in agricultural systems. To insure high yields, farmers in the U.S. apply over 11 million metric tons of nitrogen fertilizer annually; manufacture and distribution of this fertilizer account for over one-third of the total energy expended in agriculture.
Low soil temperatures not only inhibit all root metabolic functions, but can cause permanent damage. Many crops are chilling sensitive so that brief exposures to temperatures lower than 10°C result in significant losses. In California, low temperatures define the growing season for most vegetables.
Although elevated CO2 dramatically stimulates short-term carbon fixation in C3 plants, its effect on longer-term productivity is highly variable. Some vegetables such as tomato and cucumber suffer declining yields under elevated CO2, while others show only slight gains. With atmospheric concentrations of CO2 increasing by over 0.5% year and CO2 fertilization of greenhouse vegetables becoming more commonplace, elevated CO2 is no longer just a laboratory phenomenon.
Our research focuses
on the interrelations among these factors and addresses the following issues:
(a) influence of NH4+ and NO3¯ on root growth
and development, (b) chilling tolerance in tomato, and (c) effects of elevated
CO2 on plant carbon-nitrogen relations
A schematic of the nutrient flow system in which we estimated net ion uptake
by 36 plants. The main chamber is constructed from acrylic plastic and
has 36 cuvettes surrounded by a water jacket. For simplicity, only two
cuvettes are depicted on the left and details for one cuvette are shown
on the right.
Chilling Tolerance in Tomato
In a cultivated tomato (Lycopersicon esculentum), a brief exposure of the roots to chilling temperatures damaged root ammonium absorption and caused the shoots to wilt. Under the same treatment, a wild relative from high altitudes (Lycopersicon hirsutum) showed little change in ammonium absorption and the shoots did not wilt. In offspring from crosses between the two species, the chromosomal locations associated with these traits were identified. Ammonium absorption was associated with a location on chromosome 3. Shoot wilting after two hours at 4ºC was highly correlated with a location on chromosome 9. Recovery from wilting after six hours at 4ºC was associated with a location on chromosome 7. We are currently characterizing the genetics and physiology of these traits.
Additional crosses between the hybrid offspring and the cultivated tomato have been made. Genetic markers are allowing identification of individual plants in which the genetic material derives from the cultivated tomato except for the specific chromosomal locations associated with ammonium absorption or shoot wilting. In physiological studies, we are examining these individuals to determine the role of ammonium absorption and water movement in the overall chilling response of tomato and the relationship among root ion absorption, water movement, and growth.
This material is based upon work supported by the USDA NRI-CGP under Grant No. 2000-00647.
Inorganic N and Root Growth and Development
We study the mechanisms through which plant roots make appropriate adjustments to their morphology and physiology in response to fluctuating rhizosphere levels of ammonium (NH4+) and nitrate (NO3–). The soil environment is extremely heterogeneous; movement of substances through its discontinuous gaseous, liquid, and solid phases can be tortuous; and competition among soil organisms is intense. Nonetheless, plant roots locate and acquire soil nitrogen. Our experiments suggest the following:
Root growth depends on the absorption of exogenous nitrogen near the apex.
Cell division in the root apical meristem is more rapid under NH4+ nutrition.
Root nitrogen acquisition alters rhizosphere pH and redox potential.
Rhizosphere pH and redox potential regulate root cell proliferation and plasticity.
Schematic of a multi-barrel microelectrode. The 3 longer barrels are pulled
from thin-wall glass capillaries: one contains NH4+-selective liquid ion
exchanger, another contains NO3– exchanger, and the last contains
a salt solution and serves as a local reference electrode. The 4 shorter
barrels are pulled from solid glass rods.
A scanning electron micrograph showing the tip of a multi-barrel ion-selective
microelectrode. Each of the 3 barrels with holes is filled with a liquid ion
exchanger or salt solution. The total tip diameter to enclose the open barrels
is about 3 µm.
Stainless steel and glass root cuvette for the microelectrode experiments.
The cuvette is positioned on the stage of an inverted microscope, and the root
and microelectrode are viewed from below. A micromanipulator positions the
microelectrode tip at various distances from the root surface to measure ion
depletion around the root.
We have developed unique approaches for this work. A root extensiometer characterizes root mechanical properties in intact plants. Multibarrel ion-selective microelectrodes and redox microelectrodes measure the flux rates of several ions and redox potentials along a growing root. The proposed experiments will use maize seedlings because they have become a model system for root development and are amenable to the required mechanical manipulations.
Elevated Carbon Dioxide
Change in AQ (ratio of CO2 influx to O2 efflux) as a function of leaf internal
CO2 concentration when the nitrogen source for 16-d old wheat was shifted
from NH4+ to NO3–. The change in AQ is inversely related to the amount
of NO3– assimilated in the shoot. Plants were grown at ambient or
elevated CO2 conditions.
We recently confirmed in short-term leaf gas exchange measurements and
longer-term plant growth experiments that CO2 inhibits nitrate (NO3–)
assimilation. Our experiments so far have been limited to wheat. Were CO2
inhibition of NO3– assimilation common among plants, it would offer
a mechanistic explanation for several other unresolved phenomenon including
(a) plant acclimation to CO2, (b) CO2 inhibition of respiration, (c) the
localization of NO3– assimilation in the mesophyll of C4 species,
and (d) the central role of nitrogen availability in determining ecosystem
response to CO2 enrichment. Moreover, it suggests that rising CO2 levels
will have yet unforeseen effects upon nitrogen cycling in natural and managed
ecosystems because unassimilated NO3– may leach into groundwater
or increase nitrogen trace gas emissions.
We have also discovered that wheat leaves emit significant amounts of nitrous oxide (N2O), a greenhouse gas that has a radiative forcing potential approximately 250 times greater than CO2 and that contributes to stratospheric O3 degradation through photolysis in the upper atmosphere. The concentration of N2O in the atmosphere is increasing by approximately 0.27% annually. Our preliminary results indicate that leaf N2O emissions are associated with photoassimilation of NO3– in leaves. It is also likely that root NO3– assimilation produces N2O and that vascular land plants transpire the N2O that is generated by denitrification and nitrification in soils. Given the large quantities of NO3– assimilated by plants in the terrestrial biosphere, we estimate that plant N2O production could account for as much as 12% of the N2O generated.
Leaf N2O emissions will change with rising atmospheric CO2 concentrations because elevated CO2 inhibits NO3– photoassimilation, slows transpiration, and stimulates denitrification in the rhizosphere. Predicting the magnitude or even the direction of these changes is not currently possible because virtually nothing is known about relative importance of the factors that regulate leaf N2O emissions. The current research focuses on these issues.
This material is based upon work supported by the National Science Foundation under Grant No. 9974927.
Publications
Roy K, Bloom AJ, Söll D (1971) tRNA separations using benzolated DEAE-cellulose. In: Cantoni G, Davies D (eds) Procedures in Nucleic Acid Research. Harper and Row, New York, pp 524-541
Kuelske S, Bloom AJ (1973) Testing an area source model through application to an isolated area source and simultaneous concentration measurements. VDI Berlin 200:189-198
Chapin FS, III, Bloom AJ (1976) Phosphate absorption: adaptation of tundra graminoids to a low temperature, low phosphorus environment. Oikos 26:111-121
Zeiger E, Bloom AJ, Hepler PK (1978) Ion transport in stomatal guard cells: a chemiosmotic hypothesis. What's New in Plant Physiology 9:29-32
Bloom AJ (1979) Salt requirement for Crassulacean Acid Metabolism in the annual succulent, Mesembryanthemum crystallinum. Plant Physiol 63:749-753
Bloom AJ (1979) Diurnal ion fluctuations in the mesophyll tissue of the Crassulacean Acid Metabolism plant, Mesembryanthemum crystallinum. Plant Physiol 64:919-923
Bloom AJ, Troughton JH (1979) High productivity and photosynthetic flexibility in a CAM plant. Oecologia (Berl) 38:35-43
Gulmon SL, Bloom AJ (1979) C3 photosynthesis and high temperature acclimation of CAM in Opuntia basilaris Englem. and Bigel. Oecologia (Berl) 38:217-222
Bloom AJ, Mooney HA, Björkman O, Berry J (1980) Materials and methods for carbon dioxide and water exchange analysis. Plant Cell Environ 3:371-376
Bloom AJ, Chapin FS, III (1981) Differences in steady-state net ammonium and nitrate influx by cold and warm adapted barley varieties. Plant Physiol 68:1064-1067
Bloom AJ, Epstein E (1984) Varietal differences in salt-induced respiration in barley. Plant Sci Letts 35:1-3
Schulze E-D, Bloom AJ (1984) Relationship between mineral nitrogen influx and transpiration in radish and tomato. Plant Physiol 76:827-828
Bloom AJ (1985) Wild and cultivated barleys show similar affinities for mineral nitrogen. Oecologia (Berl) 65:555-557
Bloom AJ, Chapin FS, Mooney HA (1985) Resource limitation in plants—an economic analogy. Ann Rev Ecol Syst 16:363-92
Bloom AJ, Finazzo J (1985) The influence of ammonium and chloride on potassium and nitrate absorption by barley roots depends on time of exposure and cultivar. Plant Physiol 81:67-69
Bloom AJ (1986) Plant economics. Trends Ecol Evol 1:98-100
Bloom AJ (1986) Use nitrogen more effectively. American Vegetable Grower, Western Perspective 34:32-34
Chapin FS, Bloom AJ, Field CB, Waring RH (1987) Plant responses to multiple environmental factors. BioSci 37:49-57
Bloom AJ, Smart D (1987) Species variation in the absorption of mineral nitrogen. Proc Hydroponics Soc Am 8:104-113
Bloom AJ (1988) Ammonium and nitrate as nitrogen sources for plant growth. ISI Atlas of Science 1:55-59
Bloom AJ, Caldwell RM (1988) Root excision decreases nutrient absorption and gas fluxes. Plant Physiol 87:794-796.
Smart D, Bloom AJ (1988) The kinetics of ammonium and nitrate absorption in cultivated and wild species of Lycopersicon. Oecologia (Berl.) 76:336-340.
Bloom AJ (1989a) Continuous and steady-state nutrient absorption by intact plants. In: Torrey JG, Winship LJ (eds) Applications of Continuous and Steady-State Methods to Root Biology. Martinus Nijhoff Publishers, Dordrecht, 147-163.
Schachtman D, Bloom AJ, Dvorák J (1989) Salt-tolerant Triticum × Lophopyrum derivatives limit the accumulation of sodium and chloride ions. Plant Cell Environ 12:47-55.
Bloom AJ (1989b) Principles of instrumentation for physiological ecology. In: Pearcy RW, Ehleringer JR, Mooney HA, Rundel P (eds) Physiological Plant Ecology: Field Methods and Instrumentation. Chapman and Hall, New York, 1-13.
Bloom AJ, Caldwell RM, Finazzo J, Warner RL, Weissbart J (1989) Oxygen and carbon dioxide fluxes from barley shoots depend on nitrate assimilation. Plant Physiol 91:352-356.
Henriksen GH, Bloom AJ, Spanswick RM (1990) Measurement of net fluxes of ammonium and nitrate at the surface of barley roots using ion-selective microelectrodes. Plant Physiol 93:271-280.
Bloom AJ, Sukrapanna SS (1990) Effects of exposure to ammonium and transplant shock upon the induction of nitrate absorption. Plant Physiol 94:85-90.
Jackson LE, Bloom AJ (1990) Root distribution in relation to nitrogen availability in field-grown tomatoes. Plant Soil 128:115-126.
Smart DR, Bloom AJ (1991) Influence of root NH4+ and NO3¯ content on the temperature response of net NH4+ and NO3¯ uptake in chilling sensitive and chilling resistant Lycopersicon taxa. J Exp Bot 42:331-338.
Koch G, Bloom AJ, Chapin FS (1991) Ammonium and nitrate as nitrogen sources in two Eriophorum species. Oecologia Berlin) 88:570-573.
Amthor JS, Koch GW, Bloom AJ (1992) CO2 inhibits respiration in leaves of Rumex crispus L. Plant Physiol 98:757-760.
Bloom AJ, Sukrapanna SS, Warner RL (1992) Root respiration associated with ammonium and nitrate absorption and assimilation by barley. Plant Physiol 99:1294-1301.
Bloom AJ, Jackson LE, Smart DR (1993) Root growth as a function of ammonium and nitrate in the root zone. Plant Cell Environ 16:199-206.
Smart DR, Bloom AJ (1993) The relationship between kinetics of NH4+ and NO3¯ absorption and growth in the cultivated tomato (Lycopersicon esculentum Mill. cv. T5). Plant Cell Environ 16:259-267.
Kosola KR, Bloom AJ (1994) Methylammonium as a transport analog for ammonium in tomato (Lycopersicon esculentum). Plant Physiol 104:435-442.
Bloom AJ (1994) Crop acquisition of ammonium and nitrate. In: Boote KJ, Bennett JM, Sinclair TR, Paulsen GM (eds) Physiology and Determination of Crop Yield. ASA, CSA, SSSA, Madison, WI. 303-310.
Jackson LE, Bloom AJ (1994) Assessment of methylammonium as an analog for ammonium in plant uptake from soil. Plant Soil 164:195-202.
Kosola KR, Bloom AJ (1996) Chlorate as a transport analog for nitrate absorption by roots of tomato (Lycopersicon esculentum). Plant Physiol 110:1293-1299.
Evans RD, Bloom AJ, Sukrapanna SS, Ehleringer JR (1996) Nitrogen isotope composition of tomato (Lycopersicon esculentum Mill. cv T-5) grown under ammonium or nitrate nutrition. Plant Cell Environ 11:1317-1323
Bloom AJ (1996) Nitrogen dynamics in plant growth systems. Life Support Biosphere Sci 3:35-41.
Nicoulaud BAL, Bloom AJ (1996) Plant growth, urea absorption and assimilation under urea applied foliarly as the sole nitrogen source for tomato. J Am Soc Hort Sci 121:1117-1121.
Bloom AJ (1997) Nitrogen as a limiting factor: crop acquisition of ammonium and nitrate. In: Jackson LE (ed) Agricultural Ecology. Academic Press, San Diego, pp. 145-172.
Bloom AJ (1997) Interactions between inorganic nitrogen nutrition and root development. J Plant Nutri Soil Sci 160:253-259.
Bloom AJ, Randall LB, Meyerhoff PA, St. Clair DA (1998) The chilling sensitivity of root ammonium influx in a cultivated and wild tomato. Plant Cell Environ 21:191-199.
Colmer TD, Bloom AJ (1998) A comparison of net NH4+ and NO3– fluxes along roots of rice and maize. Plant Cell Environ 21:240-246.
Nicoulaud BAL, Bloom AJ (1998) Nickel supplements improve growth when foliar urea is the sole nitrogen source for tomato. J Am Soc Hort Sci 123:556-559.
Smart DR, Bloom AJ (1998) Investigations of ion absorption during NH4+ exposure: I. Relationship between H+ efflux and NO3– absorption. J Exp Bot 49: 95-100.
Bloom AJ (1998) Chapter 5. Mineral Nutrition. In: Taiz L, Zeiger E (eds) Plant Physiology, 2nd Edition. Sinauer Assoc., Sunderland, MA, pp. 103-124.
Bloom AJ (1998) Chapter 12. Assimilation of Mineral Nutrition. In: Taiz L, Zeiger E (eds) Plant Physiology, 2nd Edition. Sinauer Assoc., Sunderland, MA, pp. 323-345.
Smart DR, Ritchie K, Bloom AJ, Bugbee BB (1998) Nitrogen balances for wheat canopies (Triticum aestivum cv Veery 10) grown under elevated CO2. Plant Cell Environ 21:753-764.
Nicoulaud BAL, Bloom AJ (1998) Ammonium does not induce ammonium absorption in nitrogen sufficient tomatoes. J Amer Soc Hort Sci 123:787-790.
Taylor AR, Bloom AJ (1998) Ammonium, nitrate, and proton fluxes along the maize root. Plant Cell Environ 21:1255-1263.
Bloom AJ, Taylor AR (2000) Active ion transport in plants. In Kung S –D, Yang S –F, eds, Discoveries in Plant Science — Volume 3, Singapore, World Scientific, in press.
Truco MJ, Randall LB, Bloom AJ, St.Clair DA (2000) Detection of QTL associated with shoot wilting and root ammonium uptake under chilling temperatures in an interspecific backcross population from Lycopersicon esculentum × L. hirsutum. Theor. Appl. Genet., in press.