UVM Theses and Dissertations
Format:
Print
Author:
Anderson, Brandon H.
Dept./Program:
Plant and Soil Science
Year:
2004
Degree:
Ph. D.
Abstract:
The use of phosphatase enzymes has proven to be a reliable method for identifying organic P in soil and water samples. Three P substrates, 4-methylumbelliferyl phosphate (MUP), deoxyribonucleic acid (DNA) and potassium phosphate (KH₂PO₄), were used to compare the relative mobility and soil fixation affinity of orthophosphate monoesters, orthophosphate diesters and soluble inorganic P in (1) a soil column experiment and (2) a soil P adsorption test tube experiment. The total net quantity of 757.8 ug P 2L⁻¹ of orthophosphate diesters in the DNA columns leachate far exceeded the net quantity of orthophosphate monoesters in leachate from the MUP columns and soluble inorganic P in the leachate from the KH₂PO₄ columns, with 4.6 and 34.0 ug P 2L⁻¹, respectively.
Elevated concentrations of soluble inorganic P were detected in the first pore volume of leachate for all treatment columns. Also, high concentrations of orthophosphate monoesters and diesters within the first pore volume were collected from the DNA treated columns. Soil P adsorption of soluble organic and inorganic P in a test tube experiment yielded similar results - orthophosphate diesters from the DNA had a low affinity for soils. Also, soil test P and soil texture were found to be important variables in the correlation of organic and inorganic P adsorption. However in both experiments, high concentrations of other P compounds were identified in samples treated with organic P substrates, suggesting physical/enzymatic hydrolysis and/or displacement of native soil P.
In a separate experiment, twenty-three representative soils from the Champlain Valley of Vermont were selected to test the relationship between algal growth and commonly used P soil tests as well as two suggested tests for bioavailable P. Soils were either autoclaved or not prior to addition to flasks containing P starved algae in a nutrient solution without P. Compared to non-autoclaved samples, pretreatment in the autoclave provided close to 60% more algal available P, as indicated by increased algal growth. While algal growth in the presence of autoclaved soil was highly correlated with growth in the presence of non-autoclaved samples, correlations between algal numbers and soil tests were higher when samples were not autoclaved. In a subset of 6 out of the 23 soils, autoclaving resulted in significantly greater concentrations of soluble P, with 78% more orthophosphate monoesters, 60% more orthophosphate diesters and 54% more soluble inorganic P, than non-autoclaved samples.
Soil test P was better correlated with algal growth with a logarithmic regression model than with the simple linear model used by several other researchers. Olsen P was the most highly correlated with algal growth, with P extracted by Modified Morgan, Feoxide strip, and Bray-Kurtz 1, and Mehlich 3 generally similarly correlated with algal growth. Because of the sensitive nature of algal bioassays, batch cultures of algae grown with soil or sediment samples may be susceptible to inhibition/stimulation from chemical compounds indigenous to the sample that override the effect of the limiting nutrient. Inhibition of algal growth may have occurred with two soils relatively high in extractable Zn, which produced relatively low numbers of algae despite being very high in estimated available P by all extraction methods used. Removing those samples from the calculations dramatically improved correlations between soil test P and algal growth.
Elevated concentrations of soluble inorganic P were detected in the first pore volume of leachate for all treatment columns. Also, high concentrations of orthophosphate monoesters and diesters within the first pore volume were collected from the DNA treated columns. Soil P adsorption of soluble organic and inorganic P in a test tube experiment yielded similar results - orthophosphate diesters from the DNA had a low affinity for soils. Also, soil test P and soil texture were found to be important variables in the correlation of organic and inorganic P adsorption. However in both experiments, high concentrations of other P compounds were identified in samples treated with organic P substrates, suggesting physical/enzymatic hydrolysis and/or displacement of native soil P.
In a separate experiment, twenty-three representative soils from the Champlain Valley of Vermont were selected to test the relationship between algal growth and commonly used P soil tests as well as two suggested tests for bioavailable P. Soils were either autoclaved or not prior to addition to flasks containing P starved algae in a nutrient solution without P. Compared to non-autoclaved samples, pretreatment in the autoclave provided close to 60% more algal available P, as indicated by increased algal growth. While algal growth in the presence of autoclaved soil was highly correlated with growth in the presence of non-autoclaved samples, correlations between algal numbers and soil tests were higher when samples were not autoclaved. In a subset of 6 out of the 23 soils, autoclaving resulted in significantly greater concentrations of soluble P, with 78% more orthophosphate monoesters, 60% more orthophosphate diesters and 54% more soluble inorganic P, than non-autoclaved samples.
Soil test P was better correlated with algal growth with a logarithmic regression model than with the simple linear model used by several other researchers. Olsen P was the most highly correlated with algal growth, with P extracted by Modified Morgan, Feoxide strip, and Bray-Kurtz 1, and Mehlich 3 generally similarly correlated with algal growth. Because of the sensitive nature of algal bioassays, batch cultures of algae grown with soil or sediment samples may be susceptible to inhibition/stimulation from chemical compounds indigenous to the sample that override the effect of the limiting nutrient. Inhibition of algal growth may have occurred with two soils relatively high in extractable Zn, which produced relatively low numbers of algae despite being very high in estimated available P by all extraction methods used. Removing those samples from the calculations dramatically improved correlations between soil test P and algal growth.