The abundance of nitrogen cycle genes and potential greenhouse gas fluxes depends on land use type and little on soil aggregate size

Abstract

Soil structure is known to influence microbial communities in soil and soil aggregates are the fundamental ecological unit of organisation that support soil functions. However, still little is known about the distribution of microbial communities and functions between soil aggregate size fractions in relation to land use. Thus, the objective of this study was to determine the gene abundance of microbial communities related to the nitrogen cycle and potential greenhouse gas (GHG) fluxes in six soil aggregate sizes (0-0.25, 0.25-0.5, 0.5-1.0, 1-2, 2-5, 5-10 mm) in four land uses (i.e. grassland, cropland, forest, young forest). Quantitative-PCR (Q-PCR) was used to investigate the abundance of bacteria, archaea and fungi, and functional guilds involved in N-fixation (nifH gene), nitrification (bacterial and archaeal amoA genes) and denitrification (narG, nirS, and nosZ genes). Land use leads to significantly different abundances for all genes analysed, with the cropland site showing the lowest abundance for all genes except amoA bacteria and archaea. In contrast, not a single land use consistently showed the highest gene abundance for all the genes investigated. Variation in gene abundance between aggregate size classes was also found, but the patterns were gene specific and without common trends across land uses. However, aggregates within the size class of 0.5-1.0 mm showed high bacterial 16S, nifH, amoA bacteria, narG, nirS and nosZ gene abundance for the two forest sites but not for fungal ITS and archaeal 16S. The potential GHG fluxes were affected by land use but the effects were far less pronounced than for microbial gene abundance, inconsistent across land use and soil aggregates. However, few differences in GHG fluxes were found between soil aggregate sizes. From this study, land use emerges as the dominant factor that explains the distribution of N functional communities and potential GHG fluxes in soils, with less pronounced and less generalized effects of aggregate size.

Microbial Extracellular Polymeric Substances: Ecological Function and Impact on Soil Aggregation

“…For many decades, the microbial communities inside different classes of aggregates have been investigated using several techniques and experimental designs ( Blaud et al, 2012 , 2017 ; Davinic et al, 2012 ; Zhang et al, 2018 ). Many studies determined the microbial community inside the different aggregate sizes in different agriculture management systems ( Sessitsch et al, 2001 ; Mummey and Stahl, 2004 ; Kravchenko et al, 2014 ); however, no studies evaluated the microbial community responsible for the aggregation.…”

Polyester Microplastic Mitigated NH3 Volatilization from a Rice–Wheat Rotation System: Does Particle Size or Natural Aging Effect Matter?

“…Moreover, MPs in soils altered soil structures relevant to N cycling . For instance, as recently reported by Liang et al, MPs decreased the stability of soil aggregates, which potentially promoted soil N loss . In addition, as one of the important determinants for NH 3 volatilization, NH 4 + –N concentration in MPs-polluted soil was only 44.3% and 21.3% of that in the control .…”

Impact of Cover Crop Monocultures and Mixtures on Organic Carbon Contents of Soil Aggregates

“…The tremendous diversity and size variations in different soil aggregate classes, in terms of their orientation, distribution, architectural complexity, and physicochemical features, create highly favorable and distinct microhabitats for microbial communities that could determine the functioning and resilience of soil ecosystems to environmental and climatic factors [25,26]. Therefore, considering the positive role of cover crops in soil health, it is important to study their role in influencing the OC contents of different soil aggregate-size classes [27]. Cover crops that are grasses or legumes may influence the structural properties of the soils, including the OC contents of different soil aggregate-size classes.…”