Research interests

My research and teaching efforts have been dealing with soil-plant interactions controlling nutrient availability and the biocycling of heavy metals, with special emphasis on rhizospheric processes influencing the biogeochemistry of forest and agriculture ecosystems. Currently, I focus on the reciprocal effects of soil-plant interactions in ecosystems under different environmental stress. This research area is a multidisciplinary in its approach and is at the forefront of international research areas. This is because about 10-40 % of net carbon assimilation of plants is invested in root activities such as root respiration and exudates. These high inputs of matter and energy cause substantial (bio-) chemical and biological changes, including microbial activities that are up to one magnitude higher than in bulk soil. Major scientific contribution related to rhizosphere.

1) Linked processes such as plant uptake, roots with their associated biota, high organic matter and acidity produced in the rhizosphere are the driving force for enhancing mineral weathering in soils. Specially, the preferential dissolution of minerals at the soil-root interface and the associated cation release to solution could be expected to affect nutrient availability in the vicinity of living-plant roots and thus to increase biological uptake. This finding also emphasizes the pedogenic significance of the rhizosphere zone and the role of roots as dynamic weathering agents.

2) The quantity and quality of organic matter in the rhizosphere regulate the reciprocal relationships between soil and roots with their associated biota. However, the biogeochemical role of organic matter in the rhizosphere still remains, as an area in which more future research is needed.

3) We, therefore, stress the fact that conventional tests using bulk soil give no information about root-induced changes in the rhizosphere due to the coexistence of soil and roots and the associated microorganisms. We also conclude that if relationships are to be established between soil chemistry and tree response, soil must be studied at the rhizospheric soil scale. The study of rhizospheric processes will provide a key in addressing emerging issues like the prediction of soil quality, trace element mobility, bioremediation of contaminated soils and soil-plant relationships in a changing environment. Such a problem calls for a multidisciplinary group of scientists with strong background in soil chemistry, soil microbiology, soil physics, soil ecology, and plant physiology.

Current research

Fieldwork
The fieldwork is being conducted in the North (Flakaliden) and South (Skogaby) of Sweden. The experimental work started in 1999 with a financial support from the Swedish council SJFR (Dnr 23 .0173/98). The aim of this field project is to develop a conceptual model to assess nutrient availability in the mineral soil-root system. During the past 2-3 years, we conducted extensive field work for soil sampling; installing homogeneous soil bag (HSB), test-mineral bags (TMB) and undisturbed soil columns in two different sites located in the northern and southern parts of Sweden. The manipulated treatments are control, irrigation and irrigation with fertilization. In this project, the HSB technique is used to allow the in situ monitoring of processes in the rhizosphere. One important aim of this investigation is to quantify the dissolution rate of soil minerals and index pure minerals such as plagioclase and apatite. The number of the HSB and TMB installed is sufficient for at least nine years sampling retrievals. The use of TMB is an activity within the framework of the SJFR (Sweden)-INRA (France) cooperative research program (projects – fd SJFR 990.0634/99 and Formas 23.0/2001-1268). The HSB and TMB also are applied in a third site in France for comparisons.

I believe that the use of the well defined technique HSB, where field soil variability is strongly reduced, should enable us to interpret the changes over time in the soil and mineral bags due to field treatments and the presence or absence of growing roots.

Research proposals under review
1) Role of Biotic and Abiotic Processes Occurring at the Soil-Root Interface on Forest Sustainability
Submitted by: George Gobran, Göran Ågren and Roger Finlay

2) Title: Novel Approach for Assessing the Impact of Land-uses on the Biocycling of Heavy Metals in Different Terrestrial Ecosystems
Submitted by: George Gobran, Bert Allard and Maria Greger

To: The Swedish council FORMAS
 

Publications

Scientific publications

50. Huang, P.M. and G.R. Gobran. 2005. Biogeochemistry of Trace Elements in the Rhizosphere. Elsevier (In press).

49.  Gobran, G.R., M-P Turpault, and F. Courchesne. 2005. Contribution of rhizospheric processes to mineral weathering in forest soils. In: PM Huang and GR Gobran (Eds.), Biogeochemistry of Trace Elements in the Rhizosphere. Elsevier 2005 (In press).

48. Shtangeeva, J.V-P.Laiho, H.Kahelin, and G.R.Gobran. 2004. Improvement of phytoremediation effects with help of different fertilizers. Soil Sci. Plant Nutr. 50: 885-889.

47. Selim, H.M., G.R. Gobran, X. Guan, and N. Clarke. 2004. Mobility of sulfate in forest soils: Kinetic modeling. J. Environ. Qual. 33:488-495.

46. Gobran, G.R., N. Lepp, D.C. Adriano, L. Bergström, R. Finlay, A. Iskandar, E. Lombi, S. McGrath, T. Punshon, M. Selim, O. Selinus and W. Wenzel (eds.). 2003. Conference proceedings of the International Conferences of Biogeochemistry of Trace Elements (6 volumes), 7th ICOBTE 2003 June 15 -19, 2003. http://www-conference.slu.se/7thICOBTE/index.htm

45. Selim, H.M., G.R. Gobran, X. Guan, and N. Clarke. 2003. Kinetic modeling of sulfate transport in a forest soil. In Geochemical and Hydrological Reactivity of Heavy Metals in Soils."  Selim, H.M. and W.L. Kingery (eds.), CRC Press, pp 259.

44. Gobran, G.R., W.W. Wenzel and E. Lombi, (eds.) 2001. Trace Elements in the Rhizosphere CRC Press, pp 321.
http://www.crcpress.com/us/product.asp?sku=1535+++&dept%5Fid=1

43. Lombi, E., W.W. Wenzel, G.R. Gobran and D.C. Adriano. 2001. Dependency of phytoavailability of metals on indigenous and induced rhizosphere processes: a review. In "Trace Elements in the Rhizosphere" (eds.) CRC Press, pp 3-24.

42. Fenn, L.B. and G.R. Gobran. 1999. Willow Tree Productivity on Fertilizer Solutions Containing Various Ca/Al Ratios. Nutrient Cycling in Agroecosystems, 53:121-131.

41. Gobran, G.R., S. Clegg and F. Courchesne.1999. The Rhizosphere and Trace Element Acquisition in Soils. In "Fate and Transport of Heavy metals in the Vadose Zone." Selim, H.M. and A. Iskander and H.M. (eds), CRC Press LLC.

40. Eriksson, E, A. Göransson and G. Gobran. 1998. Effects of alumium on growth and nutrition in birch seedlings under magnesium- or calcium-limiting growth conditions. Pflanzenernähr. Bodenk., 161:653-660.

39. Gobran, G.R., H. M. Selim, H. Hultberg and I. Anderson. 1998. Description of Sulfate Adsorption-Desorption and movement in a Swedish Forest Soil. Water, Air and Soil Pollution, 108:411-424.

38. Gobran, G.R., S. Clegg and F. Courchesne. 1998. Rhizospheric Processes Influencing the Biogeochemistry of Forest Ecosystems. Biogeochemistry 42:107-120.

37. Clarke, N., X. Guan and G.R. Gobran. 1997. Modified method for the determination of quickly reacting aluminium. Eur. J. Soil Sci. 48:553-556.

36. Clegg, S. and G.R. Gobran. 1997. Rhizospheric P and K In Forest Soil Manipulated with Ammonium Sulfate and Water. Can. J. Soil Sci. 77:525-533.

35. Clegg, S., G.R. Gobran and X. Guan. 1997. Rhizosphere Chemistry in an Ammonium Sulphate and Water Stressed Norway Spruce (Picea abies (L.) Karst.) Forest. Can. J. Soil Sci. 77:515-523.

34. Gobran, G. R., F. Courchesne and A. Dufresne. 1997. Relationships between sulfate retention and release, solution pH and DOC in the Gårdsjön soils. In: "Experimental Reversal of Acid Rain Effects", edited by H. Hultberg and R. A. Skeffington, John Wiley & Sons, Ltd..

33. Andersson, F., Ågren, G.I., Gobran, G.R. & Hallbäcken, L. 1997. Critical points in forest ecosystem understanding determining the predictability of primary production. In: Führer, E. & Berger, R. (eds.) Proceedings of the 1st EFERN-pleanry meeting held October 19th - 22nd 1996 in Vienna. Forstliche Schriftenreihe, Univ. f Bodenkultur, Wien, Vol 10. pp. 5-18. http:://efern.boku.ac.at

32. Courchesne, F. and G.R. Gobran. 1997. Mineralogy of bulk and rhizosphere soil in a Norway spruce stand. Soil Sci. Soc. Am. J. 61:1245-1249.

31. Clarke, N., X. Guan, S. Clegg and G.R. Gobran. 1996. Principal Component Analysis a Useful Method in the Study of Soil Chemical Processes. Norwegian Forest Research Institute (NISK), Ås, Norway. 47.14, 30pp.

30. Gobran, G. R. and S. Clegg. 1996. A conceptual model for nutrient availability in the Soil-Root System. Can. J. Soil Sci. 76:125-131.

29. Fenn, L.B., G.R. Gobran and I.Al-Windi. 1995. Willow tree growth on ammonium-based fertilizer solutions containing various Ca++/Al+++ retios. In "Nutrient uptake and cycling in forest ecosystem, ed. Nilsson, L:O, R.F. Huttl, U.T. Johansson and P. Mathy, EC Ecosystem research report No 21:113-121.

28. Ericsson, T., A. Göransson, H. Van Oene and G.R. Gobran. 1995. Interactions between Aluminium, calcium and magnesium - Impacts on nutrition and growth of forest trees. Ecological Bulletins 44:191-196.

27. Courchesne, F., Gobran, G.R., and Dufresne, A. 1995. The Role of Humic Acid on Sulfate Retention and Release in a Podzol. Water Air Soil Pollut. 85:1813-1818.

26. Clegg, S. and Gobran, G. R. 1995. Effects of aluminium on growth and root reactions of phosphorus Betula pendula seedlings. Plant and Soil 168-169:173-178.

25. Gobran, G.R., L.B. Fenn, H. Persson and I. Al-Windi. 1993. Nutritions resposnse of Norway spruce and willow to varying leveles of calcium and aluminum. Fertilizer Research 34:181-189.

24. Clegg, S., Clarholm, M. and Gobran, G. 1993. Can phosphorus availablity be manipulated in forest soils? In: Experimental manipulations of biota and biogechemical cycling in ecosystems. Ecosystems resarch reort No. 4. Eds. Rasmussen, L., Brydges, T. and Mathy, P. pp 202-204

23. Gobran G. R. and E. Tipping. 1993. Modelling the chemistry of humic-rich soil leachates. Applied Geochemistry Suppl. Issue No. 2, 121-124.

22. Alwindi, I., G.R. Gobran, and H. Persson. 1992. Ameliorative effects of calcium on aluminum-stressed tree species. In "Root Ecology and its Practicla Applications, H. Persson and M. Sobotik (eds.) - Verein fur Wurzelforsung, A-9020 Klagenfurt.

21. Gobran G. R. and Clegg S. 1992. Relationship between TOC and SO4-2 in soil and waters. The Science of the Total Environment 117/118:449-461.

20. Persson, H., I. Al-Windi, G.R. Gobran and L.B. Fenn. 1991. Effect of increasing Ca on NH4 absorption and growth of Norway spruce (Picea abies L.). In Plant roots and their environment, B.L. McMicheal and H. Persson, eds., pp 649.

19. Fenn, L. B., G. R. Gobran and G. I. Ågren. 1991. Nitrogen changes in forest litter after fertilization with calcium-urea. Soil Sci. Soc. Am. J. 55:509-514.

18. Fenn, L.B.., G.R. Gobran, H. Persson and I. Al-Windi. 1990. Beneficial Use of Soluble Calcium in Stimulating Plant Growth: II. Annual species. In "Above- and below-ground interactions in forest trees in acidified soils. CEC - Air pollution research report 32.

17. Gobran, G.R., L.B. Fenn, H. Persson and I. Al-Windi. 1990. Beneficial Uses of Soluble Calcium in Stimulating Plant Growth: II. Forest Species. In "Above- and below-ground interactions in forest trees in acidified soils. CEC - Air pollution research report 32.

16. Gobran, G. R. and G. I. Ågren. 1989. Significance of changes in Kc values for Ca-Al exchange and its effects on soil and water acidification predictions. Ecological Modelling, 44:165-175.

15. Gobran, G. R. and S. I. Nilsson. 1988. Effects of forest floor leachate on sulfate retention in a spodosol soil. J. Environ. Qual. 17:235-239.

14. Gobran, G. R. and E. Bosatta. 1988. Base cation depletion rate as a measure of soil sensitivity to acidic deposition: theory. Ecological Modelling 40:25-36.

13. Fenn, L. B., S. Miyamoto and G. Gobran. 1987. Guayule seedling response to nitrogen fertilizers. Fertilizer Research 11:113-121.

12. Miyamoto, S., T. Riley, G. Gobran, and J. Petticrew. 1986. Effects of saline water irrigation on soil salinity, pecan tree growth and nut production. Irrig Sci 7:83-95.

11. Miyamoto, S., G. R. Gobran and K. Piela. 1985. Salt effects on seedling growth and ion uptake of three pecan rootstock cultivars. Agron. J. 77:383-388.

10. Gobran, G. R. and S. Miyamoto. 1985. Gypsum dissolution in aqueous salt solutions. Soil Science. 140:89-93.

9. Miyamoto, S., K. Piela and G. R. Gobran. 1984. Salt effects on transplant mortality, growth and rubber yields of guayule. Irrig. Sci. 5:275-284.

8. Miyamoto, S. and G. Gobran. 1983. Assessment and potential remedies of salinity problems in pecan orchards of the middle Rio Grande. Proc. West Pecan Conf.; New Mexico State Univ. Las Cruces, New Mexico, U. S. A., Herrera, E. (ED.), P.1-24.

7. Dufey, Joseph E., Tarek H. Sheta, George R. Gobran and Henri Laudelout. 1982. Dispersion of chloride, sodium and calcium ions in soils as affected by exchangeable sodium. Soil Sci. Soc. Am. J., 46:47-50.

6. Gobran, George R. 1982. Analysis of soil and plant with special emphasis on sewage sludge amended soils: bibliographic study. SL/69/82, XII/ENV/12/82, Commission of the European Communities, Brussels, Belgium.

5. Gobran, George R., Joseph E. Dufey and Henri Laudelout. 1982. The use of gypsum for preventing soil sodification: Effect of gypsum particle size and location in the profile. Journal of Soil Science, 33:309-316.

4. Sheta, Tarek H., George R. Gobran, Joseph E. Dufey and Henri Laudelout. 1981. Sodium-calcium exchange in Nile Delta soils: single values for Vanselow and Gaines & Thomas selectivity coefficients. Soil Sci. Soc. Am., 45:749-753.

3.Gobran, G.R. 1980. Exchange equilibria and salt transport through Egyptian soils and gypsum amendment. Ph.D. thesis, the Catholic University of Louvain (UCL), Louvain-La-Neuve, Belgium.

2. Kharbousch, M. A., A. A. El-Ghonomy and G. Ragheb Gobran. 1975. Socio-ecological studies of the fungal flora in the Egyptian deserts: 1. The sociological relations of the fungal flora to the siliceous sand deposit north of Wadi-El-natrun. Zb1.Bakt.Abt. II, Bd. 130, S. 131-143. 1.Gobran, G.R. 1975. Phosphorus behavior in soils of Nile and Marine origin. M.S. thesis, Alexandria University, Alexandria, Egypt.

List of Theses produced under my supervision

1. Guan, X. 1995. Organic Matter Influences on Soil-Solution Chemistry, Ion Transport and Nutrient Availability in Forest Soils Department of Ecology and Environmental Research, Swedish University of Agricultural Sciences. ISBN No. 91-576-5059-4. Report No. 83. ISSN 0348-422x. ISRN SLU-EKOMIL-R-83--SE

2. Clegg, S.. 1996. Rhizospheric Nutrient Availability and Tree Root Reactions in a Changing Environment. Doctoral thesis, Swedish University of Agricultural Sciences, Uppsala. Acta Universitatis Agriculturae Sueciae, Silvestria 5.

3. Guan, X. 1997. Nutrient Availability in Forest Soils. Rhizospheric and sequential leaching studies. Doctoral thesis, Swedish University of Agricultural Sciences, Uppsala. Acta Universitatis Agriculturae Sueciae, Silvestria 36.