Abstract
Fungal denitrifiers play important roles in soil nitrogen cycling, but we have very limited knowledge about their distribution and functions in ecosystems. In this study, three types of arable soils were collected across different climate zones in China, including quaternary red clay soils, alluvial soils, and black soils. The composition and abundance of fungal nirK-containing denitrifiers was determined by MiSeq high-throughput sequencing and qPCR, respectively. Furthermore, a substrate-induced inhibition approach was used to explore N2O emissions from fungal denitrification. The results showed that the arable soils contained a wide range of nirK-containing fungal denitrifiers, with four orders and eight genera. Additionally, approximately 57.30% of operational taxonomic unit (OTUs) belonged to unclassified nirK-containing fungi. Hypocreales was the most predominant order, with approximately 40.51% of the total number of OTUs, followed by Sordariales, Eurotiales, and Mucorales. It was further indicated that 53% of fungal nirK OTUs were shared by the three types of soils (common), and this group of fungi comprised about 98% of the total relative abundance of the nirK-containing population, indicating that the distribution of fungal nirK-containing denitrifiers was quite homogenous among the soil types. These common OTUs were determined by multiple soil characteristics, while the composition of unique OTUs was manipulated by the specific properties of each soil type. Furthermore, fungal N2O emissions were significantly and positively correlated with fungal nirK abundance in the soils, whereas it was not clearly related to fungal nirK compositions. In conclusion, although the arable soils hosted diverse nirK-containing fungal denitrifiers, fungal nirK compositions were highly homogenous among the soil types, which could be a consequence of enduring agricultural practices. The abundance of fungal nirK-containing denitrifiers, rather than their composition, may play more significant roles in relation to N2O emission from fungal denitrification.
Highlights
Nitrogen cycling processes are crucial for the sustainability of ecosystems (Zumft, 1997; Ishii et al, 2011); among them, denitrification is important in soil nitrogen transformation and can cause nitrogen loss
We found that fungal nirK composition was quite homogenous among the three types of soils because their common operational taxonomic unit (OTU) accounted for approximately 53% of the total number of OTUs, and represented over 98% of the relative abundance of fungal nirK populations (Figure 2 and Table 2)
Our results showed that most of the common nirK-containing denitrifying communities belonged to Fusarium (Supplementary Figure S1B), which is known to be widely distributed in cultivated soils, rather than in natural soils (Mothapo et al, 2013; Silvestro et al, 2013)
Summary
Nitrogen cycling processes are crucial for the sustainability of ecosystems (Zumft, 1997; Ishii et al, 2011); among them, denitrification is important in soil nitrogen transformation and can cause nitrogen loss. Most studies targeted bacterial denitrifiers, and only few works involved fungal denitrifiers (Tiedje, 1994; Philippot et al, 2007; Mothapo et al, 2015). It was suggested that fungal denitrification may play an important role in soil nitrogen cycling (Shoun et al, 1992; Maeda et al, 2015). Our understanding of the fundamental processes that underlie the distribution patterns of soil fungal denitrifiers remains limited, despite some studies suggesting that Hypocreales, Sordariales, and Eurotiales might be the dominant nirK-containing fungi in forest and arable soil samples (Long et al, 2015; Chen et al, 2016; Novinscak et al, 2016)
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