Nannipieri et al. (2017) reviewed the principles concerning soil enzymology. They consider diverse soil elements to better understand the way soil components interact such as the interactions between microbial species, proteins, and clay mineral with DNA. The review identify the role of crucial biological molecules entrapped and adsorbed in soil. They argue that active cells in the soil release enzymes to reduce polymers to monomers. Dying microbial cells can also release these enzymes, which are then adsorbed and safeguarded against proteolysis to remain active. This activity is considered to be stable and extracellular, does not rely on the surviving microbial activity and can occur under aggressive conditions for microbial events. Existing enzyme assays fail to differentiate the events related to the stable and extracellular enzymes from events occurring because of microbial events. The inability to differentiate emerges because of the enzymes at the external surface of viable cells where the active locations extend into the extracellular setting and the intracellular enzymes. Human activities affect extracellular enzymes widely through soil moisture, and temperature alteration and the availability of nitrogen. While enzymes react to nitrogen in the soil, they do so based on soil pH, temperature, and moisture in addition to other factors such as the duration of nitrogen exposure, and the type of the soil. Besides, enzyme activities may not represent microbial events on-site since enzymes on soil surfaces such as organic substances, iron oxides, and clay particles can be stabilized for long periods. The events related to these stable abiontic enzymes may be unrelated to the viable or active microbial cells. In turn, this makes it difficult to interpret the way nitrogen inputs modify microbial functions. Single enzyme assays usually do not consider the importance of extracellular enzymes and different microorganisms in biogeochemical processes. The authors consider abiontic enzymes to be those that possess biological origins but cannot be controlled by viable cells. The rates of enzyme activities should be viewed as possible abiontic enzyme rates. These enzymes can thrive in stabilized forms on organic colloids, soil particles, or soil organic matter. Therefore, while these enzymes may not demonstrate the extant microbial activity, they may indicate the effect of the addition of nitrogen and other environmental factors during their synthesis.
The review also demonstrates the significance of the abiontic enzyme idea. Abiontic enzymes cause a significant part of the enzyme events measured in soil (Nannipieri et al., 2017). The activities comprise nearly 55 percent of the entire enzyme activity (Schimel et al., 2017). Schimel et al. (2017) states that while clays can adsorb these enzymes; this lowers the enzymes’ catalytic behavior and affects their protein conformation. Notably, abiontic enzymes can be found in stabilized forms mainly in two places, which are adsorbed to external or internal clay surfaces and in humic colloids through copolymerization, entrapment, or adsorption during the establishment of humic matter (Nannipieri et al., 2017). Scientists can use abiontic enzymes as biological elements to demonstrate soil quality and previous biological activity, determine management influence on soil, and represent the ability of soil to stabilize the organic matter (Utobo & Tewari, 2015). Stakeholders can also use the enzymes to confirm the changes in organic carbon before accurately measuring it with traditional techniques (Makoi & Ndakidemi, 2008). Studies have shown that abiontic enzymes are highly sensitive to pH changes and practices focused on managing soil (Adetunji et al., 2017). Stakeholders can use this feature as an effective biogeochemical element for computing ecological changes emerging because of soil acidification in settings that involve abiontic enzyme activities (Adetunji et al., 2017). According to Makoi and Ndakidemi (2008), pollution with heavy metals deters abiontic enzymes. When plants are exposed to soils polluted with these metals, their fragments do not indicate abiontic decay or enzyme activities. Abiontic enzymes are independent of live cells and the external effects on them. Besides, cellular control and regulation mechanisms do not affect them. A better understanding of the abiontic enzymes and factors that influence them can significantly enhance knowledge regarding the status of the soil ecosystem.
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Besides, soil enzyme activities affect the decomposition of organic matter in the soil and the long term carbon stabilization in soils. Innovations have expanded the measurement scale and advanced the basic knowledge of soil function and form. Examples include multi-enzyme assays, the development of algorithms that mimic enzyme activities, and the functional gene analysis. These technologies allow scientists to measure extracellular enzyme events, obtain genetic data on the activity and composition of microbial groups in the soil, and obtain information regarding the interactions between minerals and substrate in the soil. Accurately measuring soil enzyme kinetics, however, is a significant challenge (Hinckley et al., 2014). While these techniques are widespread and use possible enzyme activities as pointers of microbial function, they have numerous limitations (Nannipieri et al., 2017). According to Davidson et al. (2014), the existing measurement models lag behind the conceptual knowledge of soil enzyme kinetics and biogeochemical factors. Additionally, current models use enzyme assays that are not optimized, do not identify the different locations for specific enzyme activities, and equate enzyme activity to microbial activity (Nannipieri et al., 2017). New measurement models are required to integrate all the measurements. Modernizing the basic assumptions of the existing biogeochemical measurement models can significantly increase their accuracy.
References
Adetunji, A. T., Lewu, F. B., Mulidzi, R., & Ncube, B. (2017). The Biological activities of β- glucosidase, Phosphatase and Urease as Soil Quality Indicators: a Review. Journal of Soil Science and Plant Nutrition , 17 (3), 794–807. https://doi.org/10.4067/s0718- 95162017000300018
Davidson, E. A., Savage, K. E., & Finzi, A. C. (2014). A big-Microsite Framework for Soil Carbon Modeling. Global Change Biology , 20 (12), 3610–3620. https://doi.org/10.1111/gcb.12718
Hinckley, E.-L. S., Wieder, W., Fierer, N., & Paul, E. (2014). Digging Into the World Beneath Our Feet: Bridging Across Scales in the Age of Global Change. Eos, Transactions American Geophysical Union , 95 (11), 96–97. https://doi.org/10.1002/2014eo110004
Makoi, J. H., & Ndakidemi, P. A. (2008). Selected soil enzymes: examples of their potential roles in the ecosystem. African Journal of Biotechnology , 7 (3).
Nannipieri, P., Trasar-Cepeda, C., & Dick, R. P. (2017). Soil Enzyme Activity: a Brief History and Biochemistry as a Basis for Appropriate Interpretations and Meta-analysis. Biology and Fertility of Soils , 54 (1), 11–19. https://doi.org/10.1007/s00374-017-1245-6
Schimel, J., Becerra, C. A., & Blankinship, J. (2017). Estimating Decay Dynamics for Enzyme activities in Soils from different Ecosystems. Soil Biology and Biochemistry , 114 , 5–11. https://doi.org/10.1016/j.soilbio.2017.06.023
Utobo, E. B., & Tewari, L. (2015). Soil Enzymes as Bioidicators of Soil Ecosystem Status. Applied Ecology and Environmental Research , 13 (1). https://doi.org/10.15666/aeer/1301_147169
