Abstract
The agricultural imprints on soil microbial processes manifest at various timescales, leaving many temporal patterns to present slowly. Unfortunately, the lack of long-term continuous agricultural field sites in North America has left gaps in our understanding of agricultural management on biogeochemical processes and their controlling microbiota. Nitrification, ammonium oxidation by bacteria and archaea, is a critical control point in terrestrial nitrogen fluxes by oxidizing cationic ammonium to anionic nitrate, promoting nitrate leaching. Moreover, nitrous oxide is produced during nitrification, contributing to massive nitrous oxide emissions from fertilized agroecosystems. Nitrification is sensitive to many macro and micro-ecological filters, as nitrifiers are obligate aerobes and are sensitive to numerous non-growth substrates and metal ions. This study sought to understand the long-term implications of various rotation and fertilizer regimes on nitrification potential and nitrifying bacterial communities in the Morrow Plots (Urbana, IL). The Morrow Plots was established in 1876 and are the longest continuous field experiments in North America, making it the only site in America capable of assessing the impact of over 140 years of agricultural management on nitrification. The Morrow Plots contrasts fertilizer (manure, inorganic, unfertilized) and rotation (continuous corn, corn-soy, corn-oat alfalfa), allowing us to explore how conventional vs. regenerative agriculture practices impact nitrifier communities. The results of this study suggest that fertilizer and rotation interact to promote distinct bacterial nitrifier communities. Nitrification potential is highest in manure corn-oat-alfalfa plots, suggesting ammonium availability is not solely responsible for active nitrifier communities. Various soil chemical variables, like CEC, Mg, and Ca, significantly influenced nitrifier community beta-diversity, using 16S rRNA amplicon sequencing, suggesting long-term accumulation of specific cations diverge microbial community assembly. While this study only uses nitrification potential enzyme activity instead of isotope analyses, it sheds light on the importance of various physiochemical drivers on nitrification potential and communities. The results support the need for a more precise exploration of the mechanisms controlling field-scale nitrification rates over large temporal scales. Put together, this study supports the importance of long-term field sites for understanding agricultural manipulations of microbial biogeochemical cycling and sheds light on the micronutrients influencing nitrifier communities and potential activity.
Highlights
Soil nitrification, the aerobic oxidation of NH+4 to NO−2 and NO−3, is a critical control point in terrestrial nitrogen (N) cycling by modulating N-loss capacity from fertilized soils
Nitrification data is reported in Supplementary Table 1
Two-way ANOVA analyses (Table 1) concluded that potential nitrification was significantly influenced by fertility [2-Way ANOVA: F(2, 37) = 29.8442, P < 0.0001], TABLE 1 | Two-way analysis of variance (ANOVA) table for model assessing the influence of long-term fertility (MLP, inorganic fertilizers (IN), UF) and rotation (CC, corn and soybean rotation (CS), corn-oats-alfalfa rotation (COA)) on natural log transformed nitrification potential (NP) activity in the Morrow Plots
Summary
The aerobic oxidation of NH+4 to NO−2 and NO−3 , is a critical control point in terrestrial nitrogen (N) cycling by modulating N-loss capacity from fertilized soils. Agronomic management practices may directly impact nitrifiers, through manipulation of nitrifier growth, or indirectly through the alteration in their soil physiochemical habitat. The lack of long-term agricultural experiments within North America which contrast regenerative (organic fertilizers and tri-rotational regimes) and intensive (synthetic fertilizers and monocultures) practices, limits the ability to investigate long-term management-driven shifts in nitrifying communities and activities. The Morrow Plots long-term agricultural experiment, established in 1867 at the University of Illinois Urbana-Champaign, contrasts conventional with regenerative practices presenting the opportunity to study the relationship between soil nitrifying potential, agronomic management strategies, and soil physiochemical factors. Longterm factorial experiments can be used to evaluate the impacts of fertilizer and rotational management strategies on nitrogen biogeochemistry in order to understand if nitrogen losses in industrial systems can be mitigated with regenerative practices. Understanding anthropogenic disruption in nitrification will assist in the optimization of agronomic management strategies, ensuring the sustainability and protection of soil resources
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