Soil aggregates impact nitrifying microorganisms in a vertisol under diverse fertilization regimes

Abstract

Ammonia oxidizers (ammonia-oxidizing archaea (AOA) and bacteria (AOB)), nitrite oxidizers (e.g., Nitrobacter and Nitrospira) and comammox Nitrospira play important roles in the nitrogen cycle in agroecosystems, yet their activities and abundance in soil microhabitats under environmental disturbances remain unclear. In this study, we collected samples from treatment plots in a field experiment established in 2010 in a lime concretion black soil in central China to investigate the effects of varying inorganic and organic fertilizer managements in a wheat-maize crop rotation, in order to investigate the impacts on the abundance and activities of ammonia and nitrite oxidizers inhabiting different microenvironments in soil, represented by three soil aggregate size fractions. The treatments were: control without fertilizer (CK), chemical fertilization (NPK), NPK and straw (NPKS), NPKS and pig manure (NPKSP) or cow manure (NPKSC). The potential nitrite oxidation activity (PNO) and soil nutrients (soil carbon, nitrogen and phosphorus content) were the highest in the microaggregates, followed by those in the macroaggregates and silt+clay fractions in all the plots. Both the ammonia and nitrite oxidizers were more abundant in the macroaggregates and microaggregates than in the silt+clay fractions. A two-way analysis of variance (ANOVA) indicated that the soil aggregate size had a significant influence on the abundance of ammonia and nitrite oxidizers and the soil nutrients. We also found a significant positive correlation between PNO and the nitrite oxidizer and AOA abundance. In addition, the abundances of the ammonia oxidizers (AOA and AOB) and nitrite oxidizers (Nitrobacter and Nitrospira)were positively correlated with each other. Overall, the soil aggregates with a higher inorganic nutrient and organic carbon content may provide a better protective microenvironment to guard against environmental disturbances and facilitate the inhabitation of ammonia and nitrite oxidizers, which cooperate in the nitrogen cycling process.

Microscale heterogeneity of the soil nitrogen cycling microbial functional structure and potential metabolism

“…The direct effect from fertilization on the overall nitrogen cycling community could be hindered (or overlapped) by the microhabitat variation. Indeed, microorganisms in the face of nutrient selection pressure will promote changes in their taxonomic composition (Neumann et al ., 2013; Jiang et al ., 2014; Liao et al ., 2018; Han et al ., 2020) and soil aggregates providing spatially heterogeneous niches for microbes to occupy (Wilpiszeski et al ., 2019).…”

“…Soil potential nitrification activity (PNA) was gauged as described by Han et al . (2020). Briefly, ∼3.0 g soil was incubated in 30 ml of 10 mM NaClO 3 (to inhibit nitrite‐oxidation) with 2 mM (NH 4 ) 2 SO 4 (ammonium sulfate) with gentle shaking (180 rpm) at 28°C.…”

“…Microbial transformation of N is often depicted as a cycle within soils that requires interaction among microorganisms that carry out N 2 ‐fixation, nitrification (including ammonia oxidation and nitrite oxidation), ammonification, anammox, denitrification, dissimilatory nitrite reduction to ammonia, dissimilatory and assimilatory nitrate reduction (Kuypers et al ., 2018). Although the diversity and community composition of N‐cycling microbes have been studied extensively in terrestrial ecosystems, most have focused on a single step of the N transformation process (e.g., Zehr et al ., 2003; Zhang et al ., 2012; Nie et al ., 2015; Shan et al ., 2016; Han et al ., 2017), particularly nitrification and denitrification (He et al ., 2007a; Shen et al ., 2008; Kong et al ., 2010; Jones and Hallin, 2010; Jiang et al ., 2014; Han et al ., 2020). However, the coordinative interaction among the abundance, metabolic potential and taxonomic composition of overall N‐cycling functional guilds remains elusive in agricultural soils.…”

Soil microbial biomass and oxy-hydroxides contribute to aggregate stability and size distribution under different land uses in the Central Andes

“…Most recent studies on soil aggregates and microbial processes measure soil microbial properties and processes within the aggregates separated through the wet sieving method (Xiao et al 2017;Tian et al 2019;Han et al 2020;Li et al 2020;Vazquez et al 2020). This technique simulates aggregate stability and size distribution caused by re-wetting events and slacking that take place after rain or irrigation (Elliott 1986;Kemper and Rosenau 1986;Cambardella and Elliott 1993).…”

Soil aggregate size influences the impact of inorganic nitrogen deposition on soil nitrification in an alpine meadow of the Qinghai–Tibet Plateau

“…Soil aggregates, which are the soil particles combined with organic and inorganic matter (Six, Elliott & Paustian, 2000), are conventionally divided into macro-aggregates (>0.25 mm) and micro-aggregates (<0.25 mm) (Tisdall & Oades, 1982). Most previous studies of soil aggregates have focused on carbon sequestration or mineralization in areas that have experienced land use changes (Rabbi et al, 2015) and areas in tillage systems (Xie et al, 2017), while the research regarding nitrogen-related processes, such as nitrification, is insufficient (Han et al, 2019;Hoffmann, Schloter & Wilke, 2007;Nishio & Furusaka, 1970). Jiang et al (2015) separated the soil into three aggregate fractions, including large macroaggregates (>2 mm), small macroaggregates (0.25-2 mm) and inter-aggregate soil and space (<0.25 mm), and found soil aggregates showed a remarkable effect on potential nitrification activity and ammonia oxidizers in an acidic soil.…”