Suitability of selected enzyme assays as future soil quality indicators Public Deposited

http://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/ft848v58f

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  • Deforestation, intensive agriculture and chemical use all can cause long-lastingn negative impacts on soil health. With all the vital functions that soils perform and the potential for further soil degradation, it is important that standards of soil quality or soil health be implemented. Soil aggregation is considered to be a good measure of soil quality because aggregation influences ecosystem function. Erosion, pollution, overgrazing, cultivation, land clearing and compaction negatively impact aggregation. Activities of the microbial biomass, fungi and bacteria, promote aggregation; any measure of soil quality should reflect this relationship. This project used enzyme assays as a surrogate indicator of microbial biomass. It was hypothesized that soil with a higher percentage of macroaggregates would maintain and stabilize soil enzyme activity by increasing the amount of potential habitat for the microbial biomass, and offer greater potential to protect abiontic enzymes. The activity of soil enzymes show a rapid response to changes in management practices which makes them useful indicators of future soil health. This study tested the feasibility of using a microwave stress test (MWES) to gauge a soil's ability to protect enzymes from stressing factors. Two enzyme assays were chosen for this work, arylsulfatase and fluorescein diacetate hydrolysis (FDA). Soils were sampled and tested from agricultural soils under conventional management, clearcut forest sites and undisturbed forest sites. Enzyme activity for both assays was consistently lower for the agricultural soils than for the forest soils. The clearcut forest sites had activity approaching that of the undisturbed forest sites. This suggests that the resident microbial population can recover following a negative impact after a few years. Activity for the stressed forest soils fell to levels that were near those of the unstressed agricultural soils. It appears that enzyme activity in the agricultural soils is largely associated with the mineral fraction of agricultural soils, whereas in forest soils a greater amount is associated with organic matter. It also suggests that the abiontic enzymes associated with organic matter are more vulnerable to stresses such as MWES than are those on the mineral surfaces of the soil. Arylsulfatase activity was found to be too variable under developed MWES protocol to be of use. Testing protocol for FDA is still being developed.
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