Extracellular Enzymes of Soils Under Organic and Conventional Cropping Systems: Predicted Functional Potential and Actual Activity

Abstract

Conventional cropping systems (CCSs) rely heavily on large-scale and intensive crop production, using mechanical tillage and synthetic inputs such as chemical fertilizers and pesticides. While these methods can be economically beneficial, they can also be environmentally destructive. Organic cropping systems (OCSs), on the other hand, offer a more sustainable approach with less harmful effects on the environment. CCSs exhibit higher prevalence rates compared to OCSs. This means that there is less research on soil processes in organic fields and the impact of these processes on soil quality. In this study, we aim to assess the functional potential of soils by analyzing their ability to transform carbon, nitrogen, phosphorus, and sulfur. We use shotgun sequencing data to predict the activities of enzymes involved in these cycles. These predictions are then compared to the actual enzyme activity measured in the soil. The objects of study are samples of Chernozem soil from fields cultivated for 11 years using the OCS method and 20 years using the CCS method. It was found that the chemical properties of the studied soils differed significantly in terms of total carbon and total and available nitrogen and phosphorus. Except for phosphorus, the concentration of these elements was significantly higher in the CCS than in the OCS. We assessed the quality of the soils by measuring their enzymatic activities. A comparison of the two cropping systems showed that the activities of the enzymes involved in the C, N, P, and S cycles were, on average, 2.91, 1.89, 1.74, and 1.86 times higher in the CCS than in the OCS, respectively. A two-way PERMANOVA showed that the cropping system was the main variable (F = 14.978, p p < 0.01). We used shotgun sequencing to identify functional genes involved in C, N, P, and S metabolism, as well as genes encoding the measured soil enzymes. Compared to the OCS, the CCS soils had a higher relative abundance of genes involved in N-conversion (log2(FC) +0.22), C-conversion (log2(FC) +0.14), P-conversion (log2(FC) +0.47), and S-conversion (log2(FC) +0.24). At the same time, we found no significant differences between the systems in the relative abundance of genes encoding the measured soil enzymes. Thus, the comparison of the two cropping systems studied showed that the soil microbiome in the CCS has a greater functional potential to support biogeochemical cycles of the key biogenic elements than in the OCS. In addition, this study links the data on the representation of functional genes with the actual activity of enzymes. Based on the results, it would be helpful to focus more specifically on actual enzyme activity or to combine several indicators to obtain a more accurate understanding of soil quality.

Keywords

• hydrolyzing enzymes
• nutrient cycling
• nitrogen-rich fertilizers
• soil organic matter
• soil phosphorous