Nitrogen has a greater influence than phosphorus on the diazotrophic community in two successive crop seasons in Northeast China

Abstract

Fertilizer-induced changes in soil nutrients regulate nitrogen (N) fixation in the terrestrial biosphere, but the influences of N and phosphorus (P) fertilization on the diazotroph communities in successive crop seasons were unclear. In this study, we assessed the effects of N and P (high vs. low doses) on the abundance and structure of N2-fixation communities after wheat and soybean harvest in a long-term (34 and 35 years) fertilization experiment. In both seasons, long-term N addition significantly decreased the abundance of nifH genes and 16S rDNA; in addition, high doses of N and P fertilizer decreased the richness of diazotrophs, whereas low doses did not. The proportion of the dominant genus, Bradyrhizobium, in the soybean season (86.0%) was higher than that in the wheat season (47.9%). Fertilization decreased diazotroph diversity and the relative abundance of Bradyrhizobium in the wheat season, but had insignificant effects in the soybean season. The addition of N, but not P, significantly changed the communities of both diazotrophs (at the genus level) and rhizobia (at the species level) in the two seasons. Soil pH was positively associated with nifH abundance and diazotrophic richness; soil NO3− content was negatively correlated with diazotrophic richness and positively correlated with diversity. Soil pH and NO3− content were the two main drivers shaping the soil diazotrophic community. Overall, long-term inorganic N had a greater influence than P on both diazotrophic abundance and community composition, and diazotrophic diversity was more clearly affected by fertilization in the wheat season than in the soybean season.

Effects of Nitrogen Input on Community Structure of the Denitrifying Bacteria with Nitrous Oxide Reductase Gene (nosZ I): a Long-Term Pond Experiment

“…Sediment samples were naturally air dried at room temperature and sieved through a 1-mm screen. The following seven physico-chemical parameters were measured: soil pH, NO 3 − content, NH 4 + , total nitrogen (TN), available phosphorus (AP), available potassium (AK), and organic matter (OM) [21]. All sediment properties were measured by the Analysis and Testing Center of the Chinese Academy of Agricultural Sciences (IEDA, CAAS, Beijing, China).…”

“…The nucleotide sequences of nosZ I were analyzed with the QIIME-1.9.1 pipeline. In short, low-quality sequences were discarded, and the remaining sequences were converted to amino acid sequences using the FunGene Pipeline of the Ribosomal Database Project [21]. The sequences that did not match the nitrousoxide reductase gene sequence were removed and the remaining high quality sequences were subsampled based on the lowest number of reads in a sample.…”

“…For alpha diversity, Shannon, Chao, and Shannon Even indices were calculated for each sample using the UPARSE pipeline [29]. For beta diversity, Bray-Curtis dissimilarities were calculated for the microbiota of all 30 samples using the R package vegan [21]. The Bray-Curtis dissimilarities were used for principal coordinate analysis (PCoA) and hierarchical clustering [30].…”

“…We used the term 'Differential genera' to refer to a genus that is found in signi cantly different proportions among ve groups. A phylogenetic tree was inferred of these differential genera using the neighbor joining method in MEGA v.6.1 and displayed using the iTOL (Interactive Tree Of Life, https://itol.embl.de/) together with data on the average relative abundances of genera [21]. The correlations between nosZ I communities (at genus level) and physico-chemical parameters were determined with redundancy analysis (RDA) using CANOCO 5.0.…”

“…As ecological functions tie up closely with microbial communities, the changes of microbial communities inevitably impact functions [19]. Soil studies have revealed that N addition decreased the population of microbial nitrogen xers [20], weakened the biological nitrogen xation capacity [21], and led to loss by denitri cation [22,23]. However, Kramer et al [24] found that the application of N in orchards signi cantly enhanced the activity and e ciency of soil denitri ers and reduced nitrate leaching.…”