Christopher J. Matocha

Nitrogen Fertilization Suppresses Soil Phenol Oxidase Enzyme Activity In No-tillage Systems

Phenol oxidase is associated with the carbon cycle and its presence in soil environments is important to the formation of humic substances. Little effort has been made to integrate the response of phenol oxidases with soil management. We investigated phenol oxidase activity on a Maury silt loam (fine, mixed, mesic Typic Paleudalfs) soil after 33 years of imposed tillage and N fertilization treatments. Particle size fractions were investigated independently to help identify the location of the enzyme. Phenol oxidase activity was 1.7 times greater (P < 0.01) in no-tillage (NT) compared with moldboard plow (MP) in the control treatment (0 kg N ha−1), consistent with the known effects of tillage. The phenol oxidase was located primarily in the silt fraction, followed by the clay and sand in the NT. In NT, N fertilization (336 kg N ha−1) had a marked negative effect on soil phenol oxidase activity, showing a 38% decrease (P < 0.01) despite the increase in soil organic carbon (SOC). In contrast, MP plots were relatively insensitive to applied N rate. Phenol oxidase activity was related negatively to dissolved inorganic nitrogen (DIN) (r = −0.49, P < 0.1), SOC (r = −0.49, P < 0.1) and dissolved organic carbon (r = −0.51, P < 0.1) in NT. This research provides new information about the response of phenol oxidase enzymes to long-term N fertilization in NT and MP systems. These findings suggest that manipulating the application rates of fertilizer N in soils under NT will make it possible to impact phenol oxidase activity.

Fragipan Horizon Fragmentation in Slaking Experiments with Amendment Materials and Ryegrass Root Tissue Extracts

Slaking experiments were conducted of fragipan clods immersed in solutions of poultry manure, aerobically digested biosolid waste (ADB), fluidized bed combustion byproduct (FBC), D-H2O, CaCO3, NaF, Na-hexa-metaphosphate, and ryegrass root biomass. The fragipan clods were sampled from the Btx horizon of an Oxyaquic Fragiudalf in Kentucky. Wet sieving aggregate analysis showed significantly better fragmentation in the NaF, Na-hexa-metaphosphate, and ryegrass root solutions with a mean weight diameter range of 15.5–18.8 mm compared to the 44.2–47.9 mm of the poultry manure, ADB, and FBC treatments. Dissolved Si, Al, Fe, and Mn levels released in solution were ambiguous. The poor efficiency of the poultry manure, ADB, and FBC treatments was attributed to their high ionic strength, while the high efficiency of the NaF, Na-hexa-metaphosphate, and rye grass root solutions to their high sodium soluble ratio (SSR). A slaking mechanism is proposed suggesting that aqueous solutions with high SSR penetrate faster into the fragipan capillaries and generate the critical swelling pressure and shearing stress required to rupture the fragipan into several fragments. Additional fragmentation occurs in a followup stage during which potential Si, Al, Fe, and Mn binding agents may be released into solution. Field experiments testing these findings are in progress.

Erratum: Catalyzed Synthesis of Zinc Clays by Prebiotic Central Metabolites

A correction to this article has been published and is linked from the HTML version of this paper. The error has been fixed in the paper.

Catalyzed Synthesis of Zinc Clays by Prebiotic Central Metabolites

How primordial metabolic networks such as the reverse tricarboxylic acid (rTCA) cycle and clay mineral catalysts coevolved remains a mystery in the puzzle to understand the origin of life. While prebiotic reactions from the rTCA cycle were accomplished via photochemistry on semiconductor minerals, the synthesis of clays was demonstrated at low temperature and ambient pressure catalyzed by oxalate. Herein, the crystallization of clay minerals is catalyzed by succinate, an example of a photoproduced intermediate from central metabolism. The experiments connect the synthesis of sauconite, a model for clay minerals, to prebiotic photochemistry. We report the temperature, pH, and concentration dependence on succinate for the synthesis of sauconite identifying new mechanisms of clay formation in surface environments of rocky planets. The work demonstrates that seeding induces nucleation at low temperatures accelerating the crystallization process. Cryogenic and conventional transmission electron microscopies, X-ray diffraction, diffuse reflectance Fourier transformed infrared spectroscopy, and measurements of total surface area are used to build a three-dimensional representation of the clay. These results suggest the coevolution of clay minerals and early metabolites in our planet could have been facilitated by sunlight photochemistry, which played a significant role in the complex interplay between rocks and life over geological time.