Progress 10/01/02 to 09/30/07
Outputs
This project is investigated several aspects of rhizosphere chemistry and biology. During the project we examined nutrient and carbon transfer among plants indigenous to the oak woodlands in the field and in a greenhouse setting. Using forb and grass mixtures in growth chambers we examined transfer of rubidium, arsenic, strontium, cesium, and nitrogen(15N) from plants treated with these elements to receiver plants. The donors and receivers were separated by a stainless steel mesh barrier with openings that excluded roots, but allowed fungal hyphae to grow across the separation. Levels in the receiver plants exceeded those in controls for all elements except strontium. These transfers were most likely mediated by fungal hyphae because roots could not pass through the stainless steel mesh and the likely hood of mass flow in the system was very remote. In the grass forb mixtures, transfer appears to be tied to plant phenology. In the field, we examined nitrogen and
rubidium transfers between grey pine and blue oaks, blue oaks and blue oaks and transfers from soil to Ponderosa pine. We found that nitrogen(15N) applied to oak seedlings was transferred to adjacent seedlings and to those seedlings separated from the treated seedling by a stainless steel mesh that prevents roots of the seedlings from interacting. Interestingly, the transfer was very irregular as some seedlings close to the labeled seedling received little isotopic nitrogen while those further away and even those across the stainless steel barrier to root penetration were enriched. We found irregular transfer of nitrogen and rubidium from soil to Ponderosa pine seedlings. Enrichment of nitrogen in eight replicate trees was quite variable, but significant transfer took place in late spring and early summer when the soils were very dry. Again these transfers were most likely due to hyphal transport as the treated soil was separated from the saplings by root-restrictive screens In
addition C (13C as CO2)_applied to the saplings was found in fungal hyphae in the soil separated from the roots by stainless steel screen. This confirms a bidirectional transfer from saplings to soil in compartments that were separated from bulk soil by root restrictive screens. Again this strongly suggests that N and C are transferred between the soil and saplings by hyphae. In separate laboratory studies we examined the reactions of manganese with humic substances and with chromium and the role of manganese dioxide minerals in oxidation processes that may occur in the rhizosphere and soil. As an extension of the previous study, the role of humic substances in the photo-oxidation of divalent manganese was also investigated. The role of plant polyphenols in nutrient nitrogen dynamics of acidic soils was studied using isotopic N and tannins extracted from several plants native to the pygmy forest of coastal California. Different tannins affected N transformations to a greater or lesser
extent.
Impacts
Mycorrhizal connections among plants may be very important with respect to the survival and establishment of oak-woodland species. Our studies on common mycorrhizal connections among plants in the oak-grass setting of the Sierra foothills will provide additional information on the ability to sustain this ecosystem in the face of environmental changes. The role of polyphenols in nitrogen dynamics is an important aspect of nutrient cycling in forests and the role of Mn in oxidation reactions is also an important control on chromium cycling.
Publications
- Hynes, M.M., Zasoski, R.J., Bledsoe, C.S. 2006. [In press] A new technique for quantification of fungal biomass: hyphal length without the use of an equation? USDA Forest Service General Technical Report PSW-GTR.
- Hynes, M.M., Zasoski, R.J., Bledsoe, C.S. 2006. Evaluation of hyphal biomass and diversity under oaks and pines in the lower Sierra Nevada foothills of Northern California. In Annual meetings abstracts [CD-ROM]. ASA, CSSA, and SSSA, Indianapolis, IN.
- Hynes, M.M., Zasoski, R.J., Bledsoe, C.S. 2006. A new technique for quantification of fungal biomass: hyphal length without the use of an equation? The 6th California Oak Symposium Abstracts, Rhonert Park, CA.
- Meding S. M., Bledsoe C. S., Horwath W. R., Zasoski R. J. 2006. Hyphal transfer of 15N-nitrate and rubidium between 2-3 yr established blue oak seedlings in an oak woodland of the California Sierra Nevada Foothills. Joint Meeting of the American Phytopathological Society, Canadian Phytopathological Society, Mycological Society of America, Quebec City, Quebec, Canada. July 29 through August 2nd. Poster.
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Progress 01/01/05 to 12/31/05
Outputs
This project is investigating the chemistry and biology of the rhizosphere. During the reporting period we examined nutrient transfer among three different oak species. Blue oak, live oak and white oak seedlings were grown in the field for two years and then treated with 15N. We examined the transfer between tops and roots as well as grasses and forbs growing between treated (donor) and receiver seedlings. In the field at our oak-woodland site we found that nitrogen and rubidium applied soil bait traps was transferred to adjacent ponderosa pine seedlings. In addition 13C applied to the seedlings was found in fungal hyphae in the bait traps. This confirms that hyphae can transfer N from the soil to the pine seedlings and transfer C from the seedling to the soil fungi. As we found in the previous year, the transfers were variable among the different seedlings, but the seedlings and hyphae were significantly enriched in either 15N or 13C.
Impacts
Mycorrhizal connections among plants may be very important with respect to the survival and establishment of oak-woodland species. Our studies on common mycorrhizal connections among plants in the oak-grass setting of the Sierra foothills will provide additional information on the ability to sustain this ecosystem in the face of environmental changes.
Publications
- Bledsoe, C. S., W. R. Horwath, R. J. Zasoski, X. He, M. Morris, M. Smith, X.Cheng, D. Southworth.2005. New Ideas: Ectomycorrhizal Diversity and Function in Oak Woodlands. Abstracts Soil Science Society of America Annual Meetings - Salt Lake City Utah. Nov 10-15, 2005.
- He,X.,C.S.Bledsoe, W.R. Horwath, R. J. Zasoski,. 2005. Foliar Uptake and Distribution of 15NH4+ and 15NO3- in Evergreen and Deciduous California Oak Seedlings in a Common Garden Experiment. Abstracts Soil Science Society of America Annual Meetings - Salt Lake City Utah. Nov 10-15, 2005.
- Hynes, M. M., S. M. Meding, and R. J. Zasoski. 2005. Transfer of 13C, 15N and K Analogues in Saplings of Pinus Ponderosa. Abstracts Soil Science Society of America Annual Meetings - Salt Lake City Utah. Nov 10-15, 2005.
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Progress 01/01/04 to 12/31/04
Outputs
This project is investigating the chemistry and biology of the rhizosphere. During the reporting period we examined nutrient transfer among grasses, forbs and blue oak seedlings. We investigated the transfers in the growth chamber and in the field. Nitrogen and rubidium transfers between grey pine and blue oaks, blue oaks to blue oak transfers and transfers from soil to Ponderosa pine were examined in the past year. In the field at our oak-woodland site we found that nitrogen applied to oak seedlings was transferred to adjacent seedlings and to those seedlings separated from the treated seedling by a stainless steel mesh that prevents roots of the seedlings from interacting. Interestingly, the transfer was very irregular as some seedlings close to the labeled seedling received little isotopic nitrogen while those further away and even those across the stainless steel barrier to root penetration were enriched. We also found irregular transfer of nitrogen from soil to
Ponderosa pine seedlings. Enrichment of eight replicate trees was quite variable, but transfer did take place in last spring and early summer when the soils were very dry.
Impacts
Mycorrhizal connections among plants may be very important with respect to the survival and establishment of oak-woodland species. Our studies on common mycorrhizal connections among plants in the oak-grass setting of the Sierra foothills will provide additional information on the ability to sustain this ecosystem in the face of environmental changes.
Publications
- Horwath, W.R., C.S. Bledsoe, R.J. Zasoski, and X. He. Influence of grasses on N movement in pine common etcomycorrhizal networks. Abstract # 4863. Abstracts, Annual Meeting of the American Agronomy Society. Seattle, WA Oct 31-Nov 4, 2004.
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Progress 01/01/03 to 12/31/03
Outputs
This project is investigating the chemistry and biology of the rhizosphere. During the report period we investigated the role of plant polyphenols on nutrient dynamics in acidic soils. We continue to examine nutrient transfer among grasses, forbs and blue oak seedlings. We investigated the rate of these transfers across a stainless steel mesh barrier permeable only to fungal hyphae. These transfers appears to have a strong tie to plant phenology. We continue to investigate the development of mycorrhizal fungi that contains a green fluorescent protein. Inserting a green fluorescent protein in the fungi would allow us to visualize fungal-specific connections among plants. An altered method of transforming the fungi appears to work and we are continuing with these studies. In the field at our oak-woodland site we found that nitrogen applied to saplings was transferred to adjacent saplings; however the removal of grasses between the saplings corresponded with a reduction
in transfer. Transfer was inferred from the isotopic composition of the saplings that were treated with 15-N.
Impacts
Mycorrhizal connections among plants may be very important with respect to the survival and establishment of oak-woodland species. Our studies on common mycorrhizal connections among plants in the oak-grass setting of the Sierra foothills will provide additional information on the ability to sustain this ecosystem in the face of environmental changes. The ability to trace fungal connections via a fluorescent protein would have a significant impact on the study of mycorrhizae in ecosystems.
Publications
- Kraus, T. E C., R. J. Zasoski, and R. A. Dahlgren. 2003 Tannins in Nutrient Dynamics of Forest Ecosystems- A Review. Plant and Soil 256:41-66.
- Kraus, T. E C., R. J. Zasoski, and R. A. Dahlgren. 2003 (in press) Fertility and pH Effects on Polyphenol and Condensed Tannin Concentrations in Foliage and Roots. Plant and Soil
- Kraus, T. E C., R. J. Zasoski, and R. A. Dahlgren. 2003.(in press) Tannin effects on Carbon and Nitrogen Dynamics in a Forest Soil. Soil Biol. Biochem.
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Progress 01/01/02 to 12/31/02
Outputs
This project is investigating the chemistry and biology of the rhizosphere. During the report period we investigated the role of mycorrhizal fungi in the transfer of nutrients between plants and the reactions of manganese with humic substances and with chromium. In growth chamber studies of forbe and grass mixtures we observed transfer of rubidium, cesium, and nitrogen from donor plants to receiver plants across a stainless steel mesh barrier. Arsenic was also transferred between the plants and appears to be a good analog for phosphorus. These transfers had to be via fungal hyphae because roots could not pass through the stainless steel mesh. We continue to investigate the development of mycorrhizal fungi that contains a green fluorescent protein. Inserting a green fluorescent protein in the fungi would allow us to visualize fungal-specific connections among plants. We are trying a new method that looks more promising than the previous techniques used last year.
Another aspect of the project investigated the role of manganese dioxide minerals in oxidation processes that may occur in the rhizosphere and soil. In this period, the role of humic substances in the photo-oxidation of divalent manganese was investigated and the role of the well- crystallized mineral pyrolusite was also investigated.
Impacts
This project is important for several reasons. Mycorrhizal connections among plants may be very important with respect to the survival and establishment of oak-woodland species. Our studies on common mycorrhizal connections among plants in the oak-grass setting of the Sierra foothills will provide additional information on the ability to sustain this ecosystem in the face of environmental changes. The ability to trace fungal connections via a fluorescent protein would have a significant impact on the study of mycorrhizae in wildland ecosystems. Manganese dioxide, the oxidized form of divalent manganese, can oxidize chromium (III) ion to the toxic chromium (VI) form. Knowing that divalent manganese can be oxidized by abiotic systems is an important contribution to the geochemistry of manganese and the redox cycle of chromium. The abiotic oxidation of manganese (II) to manganese (IV) is an important addition to information on the cycling of manganese. In light of the
current discussion of Cr levels in drinking waters, this research is very topical.
Publications
- Chung, J.B., and R.J. Zasoski. 2002 Oxidation of Cr(III) to Cr(IV) by Pyrolusite. Agric. Chem. Biotechnol. 45(3): 125-130.
- Nico, P. S. C. Anastasio and R.J. Zasoski. 2002. Rapid photo-oxidation of Mn(II) mediated by humic substances, Geochim Cosmo Chim Acta 66(23):4047-4056.
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Progress 01/01/01 to 12/31/01
Outputs
This project is investigating the chemistry and biology of the rhizosphere. During the report period we investigated the role of mycorrhizae in the transfer of nutrients between plants. The initial part of this effort was to make and evaluate containers that would allow us to demonstrate nutrient transfers between plants separated by fine stainless steel screens. We are using analogs of common soil ions (such as rubidium, strontium, arsenic, and cesium) that are that are applied to the soil or plants as a tracer to monitor uptake and movement. Our initial efforts found that 45-micron screens could exclude oak roots, but not grass roots. A 25-micron screen was able to exclude grass roots but not root hairs; therefore, an air gap between compartments is necessary to prevent nutrient transfer by root hairs between plants. Preliminary results using grasses and forbes found that fungal connections between two soils separated by the screens were numerous. It appeared that
Sr can be transferred across the screens within a week of application. We are also investigating the possibility of tracking fungal hyphae using a green fluorescent protein. Inserting a green fluorescent protein in a mycorrhizal fungi would allow us to visualize fungal-specific connections among plants. Another aspect of the project continues to investigate the role of manganese dioxide minerals in oxidation processes that may occur in the rhizosphere. In this period, the role of humic substances in the photo-oxidation of divalent manganese was investigated.
Impacts
Environmental Impacts: This project is important for several reasons. Mycorrhizal connections among plants may be very important with respect to the survival and establishment of oak-woodland species. Our studies on common mycorrhizal connections among plants in the oak-grass setting of the Sierra foothills will provide additional information on the ability to sustain this ecosystem in the face of environmental changes. The ability to trace fungal connections via a fluorescent protein would have a significant impact on the study of mycorrhizae in wildland ecosystems. Manganese dioxide, the oxidized form of divalent manganese, can oxidize chromium (III) ion to the toxic chromium (VI) form. Knowing that divalent manganese can be oxidized by abiotic systems is an important contribution to the geochemistry of manganese and the redox cycle of chromium. In light of the current discussion of Cr levels in drinking waters, this research is very topical.
Publications
- Chung, J. B., R.G. Burau, and R. J. Zasoski. 2001. Chromate Generation by Chromate Depleted Subsurface Materials. Water, Air and Soil Pollution. 128:407-417.
- Jaffe, B.A., and R.J. Zasoski. 2001. Soil pH and the activity of a palletized nematophagous fungus. Phytopath. 91(3): 324-330.
- Nico, P. S., and R. J. Zasoski. 2001. Mn(III) center availability as a rate controlling factor in the oxidation of phenol and sulfide on MnO2. Environ. Sci. Tech. 35: 3338-3343.
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Progress 01/01/00 to 12/31/00
Outputs
This project is investigating the chemistry and biology of the rhizosphere. The chemistry and mineralogy of the rhizosphere was examined by extracting and analyzing soil solutions from soil that had been cropped successively to grass and tomato. Our hypothesis is that successive cropping of the soil would approximate the near root conditions of the rhizosphere in the bulk soil. Soil solutions were obtained by centrifugation of moist soils and the solutions were analyzed for silica, aluminum, electrical conductivity and pH. Solutions from several acidic and alkaline soils were apparently supersaturated with respect the solid phase minerals that were present. Efforts to determine the activity of the dissolved ions have resulted in saturation indices that are closer to values expected for soil minerals. In another aspect of this project, we are continuing to investigate the effect of citrate, as a root exudate analog, on the dissolution of iron phosphates. In the last
year, we evaluated iron phosphate dissolution in stirred and unstirred solutions. We used changes in temperature as a means to approach equilibrium from both supersaturation and undersaturation solutions. As strengite dissolved the total iron in solution should be equal to the total phosphate in solution. In continuously shaken solutions, the difference between solution phosphate and solution iron is not as large as in the solution that were stirred intermittently. A third aspect of the project continues to investigate the role of manganese dioxide minerals in oxidation processes that may occur in the rhizosphere. In this period, the role of manganese (III) in the oxidation of sulfides and simple organic compounds was investigated. Addition of pyrophosphate to manganese dioxide suspensions resulted in a significant reduction in rate sulfide and phenol oxidation. Observed reductions in the oxidation rate for phenols and sulfides corresponded very well with the predicted free manganese
(III) levels and the model for oxidation developed for the oxidation of Cr(III). We are continuing to examine these relationships.
Impacts
This project is important for several reasons. Iron phosphates are arguably the most stable form of phosphate in soils. The rate at which iron phosphates dissolve and the level of dissolution has important consequences for plant growth the transport of phosphorus in soils. Chromium (VI) is toxic. If we understand the mechanisms that are responsible for converting the much less toxic chromium (III) ion to chromium (VI), the regulation and the natural levels of chromium expected in the environment will be better understood. In light of the current discussion of Cr levels in drinking waters, this research is very topical.
Publications
- Malunda, J. J.. 2000. Dissolution of synthetic strengite and synthetic variscite as a function of pH and citrate level. Ph.D. Thesis, Department of Land, Air and Water Resources. University of California, Davis.
- Nico, P.S., and R. J. Zasoski.. 2000. Importance of Mn(III) availability on the rate of Cr(III) oxidation on delta-MnO2. Environ. Sci. Tech. 34:3363-3367.
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Progress 01/01/99 to 12/31/99
Outputs
This project is investigating the chemistry and biology of the rhizosphere. The chemistry and mineralogy of the rhizosphere was examined by extracting and analyzing soil solutions from soil that had been cropped successively to grass and tomato. Our hypothesis is that successive cropping of the soil would approximate the near root conditions of the rhizosphere in the bulk soil. Soil solutions were obtained by centrifugation of moist soils and the solutions were analyzed for silica, aluminum, electrical conductivity and pH. Solutions from several acidic and alkaline soils were apparently supersaturated with respect the solid phase minerals that were present. We feel that part of the reason for the solutions being supersaturated is because pH values in these soil solutions were too high. Growing plants in the soil has demonstrable effects on soil pH. In initially acidic soils, rhizosphere pH increased, while in soils that were initially alkaline, rhizosphere pH
decreased. In another aspect of this project, we are continuing to investigate the effect of citrate, as a root exudate analog, on the dissolution of iron and aluminum phosphates. In the last year, we emphasized evaluating the rate of iron and aluminum phosphate dissolution. In suspensions containing iron and phosphates the rate of phosphate appearance was strongly correlated with the square root of time. The same relationship was found in aluminum phosphate suspensions, in spite of the fact that iron phosphate dissolves incongruently, while well aluminum phosphate dissolves congruently. A third aspect of the project continues to investigate the role of manganese dioxide minerals in chromium (III) oxidation to chromium (VI). In this period, the role of manganese (III) in the oxidation reaction was investigated. Addition of pyrophosphate to manganese dioxide suspensions resulted in a significant reduction in rate of chromium oxidation. The effect was evident at pyrophosphate levels as
low as five to seven micromoles per liter. This reduction in oxidation rate was observed at pH four, five, and six and corresponded very well with the predicted free manganese (III) levels. Some chromium oxidation continues when most of the manganese (III) is complexed. This and the fact that chromium oxidation occurs in the presence of manganese dioxide minerals that do not contain manganese (III), suggests that a second mechanism of oxidation exists. We are continuing to examine these relationships.
Impacts
Environmental Impacts: This project is important for several reasons. Chromium (VI) is toxic. If we understand the mechanisms that are responsible for converting the much less toxic chromium (III) ion to chromium (VI), the regulation and the natural levels of chromium expected in the environment will be better understood. This should lead to better regulation and management of chromium-rich sites.
Publications
- Nico, P.S., Wilcox, B. P. and Zasoski, R. J. 1999. Environmental cycling of chromium in the Sacramento River Area. Annual Meeting UCTSTRP, Santa Barbara Ca, April,
- McGahan, D. G., Zasoski, R. J. and Southard, R. J.. 1999. Rhizosphere and bulk soil solution comparison and mineral stability. Agron. Abst. p. 206.
- Malunda, J. J., and R. J. Zasoski. 1999. Effects of Citric Acid and pH on the dissolution of synthetic iron phosphate and aluminum phosphate. Agron. Abst. p. 209.
- Nico, P. S, and Zasoski, R. J. 1999. Importance of Mn(III) availability on Cr(III) oxidation by Birnessite. ACS National Meeting New Orleans. LA.
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Progress 01/01/98 to 12/01/98
Outputs
Investigations of iron and aluminum phosphate solubility in relation to pH and citrate levels continue with an emphasis on approaching equilibrium from supersaturation. The conditional stability of iron citrate complexes was also investigated for a Geothite-citrate system at pH 2, 4 and 6. None of the solutions appear to conform to the expected solubility or conditional stability constants. Modeling and analysis continue in this system. Rhizosphere samples are being generated for a number of California soils derived from different parent materials with different pH levels. Comparison of mineralogy and extractable ions have been compared and contrasted. Acidity does not affect clay mineralogy. Growth and uptake of arsenic and mercury by Zorro fescue as well as soil solution chemistry in mine overburden materials were evaluated in relation to lime, fertilizer, and organic amendments. Solution arsenic levels increased with phosphate additions and changed significantly
with respect to sampling time, lime applications, and organic matter additions. Plant growth responded to lime, fertilizer and organic matter additions as well. There were significant interactions among the treatments for both growth and solution levels of mercury and arsenic.
Impacts
(N/A)
Publications
- Vaast, Ph., E.P. Caswell-Chen and R.J. Zasoski. 1998. Influences of a root-lesion nematode, Pratylenchus coffeae, and two arbuscular mycorrhizal fungi, Acaulospora mellea and Glomas clarum on coffee (Coffee arabica L.). Biol. Fertil. Soils
- Vaast, P., R.J. Zasoski, and C.S. Bledsoe. 1998. Effects of Solution pH, temperature, nitrate/ammonium ratios, and inhibitors on ammonium and nitrate uptake by arabica coffee in short-term solution culture. J. Plant Nutrition, 21:1551-1564.
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- Heereman, D. A., V.P. Claassen, and R.J. Zasoski. 1998. Plant uptake and growth effects of As and Hg by Zorro Fescue as influenced by revegetation treatments on acidic andesite overburden. Agron. Abst.
- Heereman, D. A., V.P. Claassen, and R.J. Zasoski. 1998. Soil solution chemistry of acidic overburden material as influenced by lime, fertilizer and organic matter treatments. Agron. Abst. p. 203.
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Progress 01/01/97 to 12/01/97
Outputs
Investigations of iron and aluminum phosphate dissolution of in the presence of varying citrate concentrations continued with a focus on modeling. Since, strengite is postulated to be the stable solid phase P mineral in acidic soils, an ability to predict solution P levels is important. A BASIC computer program has been developed to predict solution phosphorus, and iron in relation to pH, and citrate levels. This program allows comparison among the experimental data,output from MINTEQA2 and the BASIC Model. Using published equilibrium constants for iron citrate complexes and for strengite solubility, the BASIC model does not duplicate the experimental data. MINTEQA2 also fails to predict solution phosphorus and iron concentrations. A sensitivity analysis of the strengite-citrate system is in progress. A technique for extraction of soil solution from moist soils using a heavy liquid has been adapted to our studies of rhizosphere and bulk soil solution chemistry in
acidified soils. Soils from several acidified areas have been collected and are being characterized. At one site, excessive ammonium applications resulted in soil pH levels of 3.8. Mineralogy of the clay fraction has changed little in these samples. Aluminum as a fraction of the exchangeable acidity is less than would be predicted for soils that have become acidic over geologic time periods. 1.
Impacts
(N/A)
Publications
- Claassen, V.P., R.J. Zasoski, and B.M. Taylor. 1996. A method of direct soil extraction and PCR amplification of endomycorrhizal fungal DNA. Mycorrhizae 6: 447-450.
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Progress 01/01/96 to 12/30/96
Outputs
Data from the previous study of mycorrhizae and nematode interactions is being submitted for publications. Research on iron and aluminum phosphate compounds continued and focus on the dissollution of iron phosphate. unlike aluminum phosphate, iron phosphate was not a congruent dissolution. Levels of solution iron were well below those of phosphate and the adsorption of iron on the solid phase strengite (iron phosphate) is one possibility which is being investigated. Modeling efforts with MINTEQA2 suggested that citric acid would significantly increased solution P levels for both /iron and aluminum phosphates with a maximum effect at pH 4 and 5 for strengite and variscite (aluminum phosphate). This was confirmed experimentally. In the presence of citrate, variscite solutions took 22 days to reach a steady state, while strengite reach steady state levels in 25 days. While greater dissolution took place in the presence of citrate, the system took longer to reach steady
state than when only an inert electrolyte was present.
Impacts
(N/A)
Publications
- MALUNDA, J. J. and ZASOSKI, R. J., Effect of Citric Acid on the Dissolution of Synthetic Strengtic and Variscited. Abstracts Western Soil Science Society Meetings. San Jose, CA June 24, 1996.
- VAAST, Ph., ZASOSKI, R.
- J., and BLEDSOE, C. S. 1997. Effects of Vesicular Arbuscular Mycorrhizal Inoculation at Different Soil P Availabilities on Growth and Nutrient Uptake of in vitro propagated coffee (Coffea arabica L.) Plants. Inpress.
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Progress 01/01/95 to 12/30/95
Outputs
Nematodes and mycorrhizae interactions with coffee nutrition and growth was examined. Strong interactions between the time of mycorrhizal infection and nematodes introduction as well as differences between nematode species were found. A second effort related to root exudates is the modelling the interactions of varisite with citrate. Citrate is being used as model root exudate which should enhance the dissolution of varisite. The computer program MINTEQ was used and modified to examine the interactions. Reactions for citrate and aluminum complexes were not part of the data base which was in the original MINTEQ version. Synthesized materials were characterized and found to conform to existing data for strengite and varisite. Kinetics of varisite dissolution in the presence and absence of citrate was apparently at equilibrium after seven days, however level of aluminum and phosphorus declined after 7 days. These solutions tested positively when plated on agar implying
that microbial growth was affecting the results. A second study under presumably sterile conditions found that equilibration in the presence of citrate enhanced dissolution, but attained equilibrium after 12 days. The ion activity product of the solutions to conform to published solubility criterion for varisite.
Impacts
(N/A)
Publications
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Progress 01/01/94 to 12/30/94
Outputs
Research on this project has progressed in three areas during the last year. Organic exudates generated by plant roots can modify the reactivity of metals in the rhizosphere. In one project we examined the interaction of manganese dioxide (birnessite) with chromium in the presence of oxalate, citrate and pyruvate. Chromium oxidation was depressed by the presence of oxalate and citrate and less so by the presence of pyruvate. This depression was attributed to the dissolution of birnessite by the organic acids which varied with pH. Chelation of metals by the organics is also a possibility which is under investigation. A second effort related to root exudates is the modeling of interactions of varisite and strengite with citrate and malate using the program MINTEQ. Citrate and malate are being used as model root exudates and should enhance the dissolution of the insoluble iron and aluminum phosphates. Previously synthesized materials were characterized and found to
conform to existing data for strengite and varisite. Mycorrhizae and nematode interactions on coffee roots has been a third aspect of our rhizosphere research. Techniques for axenic culture of enodomycorrhizae and coffee have been tried and were partially successful. Isolation and surface sterilization of spores from several difference VAM species was successful as judged by the lack of microbial growth on agar plates containing the treated spores. In vitro culture of the VAM and coffee was successful for 3 months, but the seedling peri.
Impacts
(N/A)
Publications
- CHUNG, J-B., AND R.J. ZASOSKI. 1994. Ammonium-potassium and ammonium-calcium exchange equilibria in bulk and rhizosphere soil. Soil Sci. Soc. Amer. J. 58:1368-1375.
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Progress 01/01/93 to 12/30/93
Outputs
During the last year this project has examined the interaction of native soils as media for revegetation by native plants on highway fill slopes. Decomposed granite has been characterized with regards to its ability to supply phosphorus and to grow plants and support mycorrhizae. Soil phosphorus has been fractionated and greenhouse studies have examined the availability of soils to supply P and to evaluate slow release phosphorus forms in two acid soils. The growth of lupin and native grass. Field trials have been established to examine the influence of mycorrhizae and added nutrients. Laboratory studies designed to evaluate the influence of root exudates on phosphorus availability are also in progress. Varasite and strengite have been synthesized and characterized as refractory compounds which are the residual form of phosphorus in acidic soils. Studies of rhizosphere interactions among mycorrhizae and nematodes are in progress. Coffee will be used as the test plant
in an acid soil from the Sierra Nevada mountains. Nitrogen relations in a strongly acidic soil have also been examined by applying labelled N to almond trees on drip irrigation. Root response to the strongly acid conditions is being evaluated by extracting fine roots from cores of varying acidity. The chemistry of acid mine drainage has also been evaluated for levels of toxic elements and pH as a part of a study to ameliorate and revegetate an abandoned sulfur/copper mine in the Sierra Nevada mountains.
Impacts
(N/A)
Publications
- ZASOSKI, R.J., and BURAU, R.G. 1993. Mechanisms of chromium redox reactions and transformation in rhizosphere and bulk soil. p 33-53. IN Reactions of Toxic Pollutants in Soil Systems. Annual Report of the Kearney Foundation of Soil Science.
- BURAU, R.G., CHUNG, J-B. and ZASOSKI, R.J. 1993. Chromate generation by subsurface material - in vitro study. Agron. Abst. 1993. p. 223.
- CHUNG, J-B. and ZASOSKI, R.J. 1993. Chromium speciation in Cr(III) Oxidation by Mn-oxides - in relation to the oxidation mechanism. Agron. Abst. 1993. p. 224.
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