Abstract
Paddy soils distribute widely from temperate to tropical regions, and are characterized by intensive nitrogen fertilization practices in China. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in soil nitrification, but little is known about their biogeographic distribution patterns in paddy ecosystems. Here, we used barcoded pyrosequencing to characterize the effects of climatic, geochemical and spatial factors on the distribution of ammonia oxidizers from 11 representative rice-growing regions (75–1945 km apart) of China. Potential nitrification rates varied greatly by more than three orders of magnitude, and were significantly correlated with the abundances of AOA and AOB. The community composition of ammonia oxidizer was affected by multiple factors, but changes in relative abundances of the major lineages could be best predicted by soil pH. The alpha diversity of AOA and AOB displayed contrasting trends over the gradients of latitude and atmospheric temperature, indicating a possible niche separation between AOA and AOB along the latitude. The Bray–Curtis dissimilarities in ammonia-oxidizing community structure significantly increased with increasing geographical distance, indicating that more geographically distant paddy fields tend to harbor more dissimilar ammonia oxidizers. Variation partitioning analysis revealed that spatial, geochemical and climatic factors could jointly explain majority of the data variation, and were important drivers defining the ecological niches of AOA and AOB. Our findings suggest that both AOA and AOB are of functional importance in paddy soil nitrification, and ammonia oxidizers in paddy ecosystems exhibit large-scale biogeographic patterns shaped by soil pH, geographic distance, and climatic factors.
Highlights
Paddy ecosystems are essential components of the global agricultural systems, accounting for 75% of the worldwide rice production (Nicolaisen et al, 2004), and provide food to more than 50% of the world’s population (Wang et al, 2014)
We found that Nitrosomonas can be present in relatively higher abundance in either strongly acidic soils or in alkaline soils (Figure 2B). All these findings provided broad-scale evidence for the principal role of soil pH in structuring the ecological niches occupied by specific ammonia-oxidizing archaea (AOA) and AOB lineages in paddy soils, which is tightly associated with the pH-impacted nitrification activity as measured by Potential Nitrification Rates (PNR)
By pyrosequencing the ammonia-oxidizing microorganisms in water-logged paddy soils collected from 11 major rice-growing regions in China, this study comprehensively demonstrated that paddy soil ammonia oxidizers are not randomly distributed over space, they do exhibit large-scale biogeographic patterns similar to those of the well-documented macro organisms
Summary
Paddy ecosystems are essential components of the global agricultural systems, accounting for 75% of the worldwide rice production (Nicolaisen et al, 2004), and provide food to more than 50% of the world’s population (Wang et al, 2014). As an anthropogenic aquatic ecosystem, paddy fields are characterized by intensive rice cropping practices (Hu et al, 2012), which received high levels of nitrogenbased fertilizers over the last decades, resulting in significant disturbance of the nitrogen-cycling processes (Bowatte et al, 2006). Autotrophic nitrification is a pivotal process of the global nitrogen cycle (Galloway et al, 2008), exerting significant control over the balance between relatively immobile ammonium and more mobile nitrite and nitrate, and is crucial for plant nitrogen availability and rice productivity. There have been a large body of studies reporting the widespread occurrence of nitrification in the surface layers of water-logged paddy soils (Nicolaisen et al, 2004; Wu et al, 2011), considerable uncertainty remains about how environmental factors will affect nitrification processes in paddy soils
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