Arnold J. Bloom

 Department of Plant Sciences
 Mailstop 3
 University of California at Davis
 Davis, CA 95616

 (530) 752-1743 office
 (530) 752-7482 laboratory
 (530) 752-9659 fax


MOOC (massive open online course) at



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 Plant Sciences, 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
Department Chair: Department of Vegetable Crops 1997-2002
President, Davis Chapter: Agricultural Honor Society 2002-2004
UCís Faculty Rep.: Federal Demonstration Partnership 2002-2007
Ceres Corporation: Consultant 2005-2007
Plant, Cell & Environment: Editorial Review Board 2006-present
Wilbur-Ellis Corporation: Expert Witness 2006
J. Sci. Food & Agric.: Associate Editor 2008-2010
Science Reviewer: Climate Literaracy & Energy Awareness Network 2010
Head Editor: Climate Change Collection, Encyclopedia of Earth 2011

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) chilling tolerance in tomato, and (b) effects of elevated CO2 on plant carbon-nitrogen relations.

Chilling Tolerance in Tomato

Cultivated tomato is a classic example of a chilling-sensitive species for which temperatures below 6°C, but above freezing, inflict significant injury. In contrast, wild relatives native to the Andes thrive at chilling temperatures. A process that differs between these two groups is root-shoot signaling: upon exposure to cold soils that impede water movement, roots of chilling-tolerant species generate signals that flow through xylem sap and prompt stomatal closure, whereas roots of chilling-sensitive species seem to lack such signals, and shoots continue to transpire and suffer wilting.

In a backcross population between chilling-sensitive and -tolerant tomato species, a quantitative trait locus (QTL) on chromosome 9 (stm9) had the largest effect on shoot turgor maintenance under root chilling, explaining over 30% of phenotypic variance. Near-isogenic lines (NILs) were used to map stm9 within a 2.7 cM region (genome of the chilling-tolerant species has not yet been sequenced, and the number of genes in this region is not known). Analysis of xylem sap from paired NILs for stm9 and their response to artificial xylem sap implicated certain small molecules as a signal. The proposed research will characterize plant responses to these small molecules and will begin to determine the role of this signaling mechanism for belowground stress.

Elevated Carbon Dioxide

Plants, with few exceptions, acquire most of their N as the inorganic ions ammonium and nitrate. I have developed a wide range of methods to assess ammonium and nitrate absorption from the rhizosphere, their translocation through a plant, and their assimilation into organic N compounds. These methods all confirm that atmospheric CO2 enrichment severely inhibits nitrate assimilation in the shoots of most plant species.

One mechanism responsible for this inhibition involves photorespiration. Photorespiration, contrary to popular opinion, is not a wasteful process. It enhances sequentially a) NADP+ reduction in the chloroplast, b) malate export from the chloroplast, c) NADH availability in the cytoplasm, and d) reduction of nitrate; to nitrite, the first step of nitrate assimilation. Rising atmospheric levels of CO2 decrease photorespiration and thereby limit shoot nitrate assimilation.

The relationship among CO2 enrichment, photorespiration, and nitrate assimilation explains a wide range of phenomena.



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, pp. 411-421.

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.101:1082-1092.

Bloom, A. J., and Holbrook, N. M. (2001) United Kingdoms. Plant Physiology 126:952-955.

Smart DR, Bloom AJ (2001) Wheat leaves emit nitrous oxide during nitrate assimilation. Proceedings of the National Academy of Sciences USA 98:7875-7878.

Bloom AJ, Smart DR, Nguyen DT, Searles PS (2002) Nitrogen assimilation and growth of wheat under elevated carbon dioxide. Proceedings of the National Academy of Sciences USA 99:1730-1735.

Bloom AJ (2002) Chapter 5. Mineral Nutrition. In: Taiz L, Zeiger E (eds) Plant Physiology, 3rd Edition. Sinauer Assoc., Sunderland, MA, pp 67-86.

Bloom AJ (2002) Chapter 12. Assimilation of Mineral Nutrients. In: Taiz L, Zeiger E (eds) Plant Physiology, 3rd Edition. Sinauer Assoc., Sunderland, MA, pp 259-282.

Bloom AJ, Meyerhoff PA, Taylor AR, Rost TL (2002) Root development and absorption of ammonium and nitrate from the rhizosphere. J Plant Growth Regulation 21:416-431.

Bloom AJ, Rost TL (2002) Root structure and function. Journal of Plant Growth Regulation 21:245-246.

Gutschick V.P. & Bloom A.J. (2003) Crossroads of animal, plant, and microbial physiological ecology. BioSciences 53:256-259.

Searles PS, Bloom AJ (2003) Nitrate photoassimilation in tomato leaves under short-term exposure to elevated carbon dioxide and low oxygen. Plant Cell & Environment 26: 1247-1255.

Cousins AB, Bloom AJ (2003) Influence of elevated CO2 and nitrogen nutrition on photosynthesis and nitrate photoassimilation in maize (Zea mays L.). Plant Cell & Environment 26: 1525-1530.

Bloom AJ, Zwieniecki MA, Passioura JB, Randall LB, Holbrook NM, St. Clair DA (2004) Water relations under root chilling in a sensitive and tolerant tomato species. Plant Cell & Environment 27:971-979.

Rachmilevitch S, Cousins AB, Bloom AJ (2004) Nitrate assimilation in plant shoots depends on photorespiration. Proceedings of the National Academy of Sciences USA 101:11506-11510.

Cousins AB, Bloom AJ (2004) Oxygen consumption during leaf nitrate assimilation in a C3 and C4 plant: the role of mitochondrial respiration. Plant Cell & Environment 27:1537-1545.

Epstein E, Bloom AJ (2005) Mineral Nutrition of Plants: Principles and Perspectives. 2nd Edition. Sinauer Associates, Sunderland, MA, 405 pp.

Volder A, Smart DR, Bloom AJ, Eissenstat DM (2005) Rapid decline in nitrate uptake and respiration with age in fine lateral roots of grape: implications for root efficiency and competitive effectiveness. New Phytologist 165:493-501.

Bloom AJ (2005) Coordination between roots and shoots. In NM Holbrook, MA Zwieniecki, eds, Long-Distance Transport in Plants. Academic Press, San Diego, CA, pp 241-256.

Goodstal FJ, Kohler GR, Randall LB, Bloom AJ, St. Clair DA (2005) A major QTL introgressed from wild Lycopersicon hirsutum confers chilling tolerance to cultivated tomato (Lycopersicon esculentum). Theoretical and Applied Genetics: 111:898-905

Bloom AJ (2006) Chapter 5. Mineral Nutrition. In: Taiz L, Zeiger E (eds) Plant Physiology, 4th Edition. Sinauer Assoc., Sunderland, MA.

Bloom AJ (2006) Chapter 12. Assimilation of Mineral Nutrients. In: Taiz L, Zeiger E (eds) Plant Physiology, 4th Edition. Sinauer Assoc., Sunderland, MA.

Bloom AJ, Frensch J, Taylor AR (2006) Influence of inorganic nitrogen and pH on the elongation of maize seminal roots. Annals of Botany 97:867-873.

Rost TL, Bloom AJ (2006) Root structure and function. Annals of Botany 97:837-838.

Bloom AJ (2006) Rising carbon dioxide concentrations and the future of crop production. Journal of the Science of Food and Agriculture 86:1289-1291.

Bloom AJ (2009) Responses of crop plants to rising atmospheric carbon dioxide concentrations. California Agriculture 63:67-72.

Foyer CH, Bloom AJ, Queval G, Noctor G (2009) Photorespiratory metabolism: genes, mutants, energetics, and redox signaling. Annual Review of Plant Biology 60:455-484.

Volder A, Anderson LJ, Smart DR, Bloom AJ, Lakso AN, Eissenstat DM (2009) Estimating nitrogen uptake of individual roots in container- and field-grown plants using a 15N-depletion approach. Functional Plant Biology 36:621-628.

Bloom AJ (2010) Global Climate Change: Convergence of Disciplines. Sinauer Assoc., Sunderland, MA, 420 pp.

Bloom AJ (2010) Chapter 5. Mineral Nutrition. In: Taiz L, Zeiger E (eds) Plant Physiology, 5th Edition. Sinauer Assoc., Sunderland, MA. pp. 107-130.

Bloom AJ (2010) Chapter 12. Assimilation of Mineral Nutrients. In: Taiz L, Zeiger E (eds) Plant Physiology, 5th Edition. Sinauer Assoc., Sunderland, MA. pp. 341-368.

Bloom AJ, Burger M, Asensio JSR, Cousins AB (2010) Carbon dioxide enrichment inhibits nitrate assimilation in wheat and Arabidopsis. Science 328: 899-903.

Bloom AJ (2010) Energetics of nitrogen acquisition. In: Foyer C, Zhang H (eds) Nitrogen Metabolism plants in the Post-Genomic Era. Vol. 2: Whole plant perspectives of nitrogen metabolism and network signalling processes in plants. Blackwell, Chichester UK, pp. 63-82.

Bloom AJ, Asensio JSR, Randall L, Rachmilevitch S, Cousins AB, Carlisle EA (2012) CO2 enrichment inhibits shoot nitrate assimilation in C3 but not C4 plants and slows growth under nitrate in C3 plants. Ecology 93:355-367.

Bloom AJ, Randall L, Taylor AR, Silk WK (2012) Deposition of ammonium and nitrate in the roots of maize seedlings supplied with different nitrogen salts. Journal of Experimental Botany 63:1997-2006.

Bloom AJ (2012) Integrated whole organism physiology. In: Hastings A, Gross L (eds) Encyclopedia of Theoretical Ecology. UC Press, Berkeley, CA, pp. 376-381.



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