Nitrogen fertilizer and Amorpha fruticosa leguminous shrub diversely affect the diazotroph communities in an artificial forage grassland

• Published in: The Science of the total environment 2020-04, Vol.711, p.134967-134967, Article 134967
• Main Authors: Xiao, Dan, Liu, Xin, Yang, Rong, Tan, Yongjun, Zhang, Wei, He, Xunyang, Xu, Zhihong, Wang, Kelin
• Format: Article
• Language: English
• Subjects: China; Ecosystem; Fabaceae; Fertilizer; Fertilizers; Fragile ecosystem; Grassland; Guimu-1 hybrid elephant grass; Legumes plantation; nifH gene; Nitrogen; Soil; Soil Microbiology
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.134967

[Display omitted] •N fertilization significantly decreased diazotroph abundance.•Amorpha fruticosa significantly increased diazotroph richness.•N fertilization and A. fruticosa reduced the competitive interactions among the diazotroph communities.•The rare taxa of diazotrophs can be a candidate for regulating N fixation in forage grass cultivation.•An effective N input from legume planting in forage grass cultivation is proposed. Soil diazotrophs have been known to be essential in biological nitrogen (N) fixation, which contributes to the sustainability of agricultural ecosystems. However, there remains an inadequacy of research on the effects of different N inputs from N fertilization and from symbiotic N fixation associated with legumes on the diazotroph communities in agricultural ecosystems. Hence, we investigated the variations in diazotroph abundance and community composition as well as the soil properties with different N inputs in the Guimu-1 hybrid elephant grass cultivation on karst soils in China. We conducted six different N treatments: control, Amorpha fruticosa planting at a spacing of 1.5 × 2 m (AFD1), A. fruticosa planting at a spacing of 1 × 2 m (AFD2), N fertilization (N), A. fruticosa planting at a spacing of 1.5 × 2 m with N fertilization (AFD1N), and A. fruticosa planting at a spacing of 1 × 2 m with N fertilization (AFD2N). Our results showed that the interaction between sampling time and N fertilization significantly affected the diazotroph abundance. In July, the diazotroph abundance significantly decreased in the N fertilization treatments: N, AFD1N, and AFD2N, compared to that in the control. The richness and Chao1 estimator of diazotrophs significantly increased in AFD2N and AFD1 correspondingly in December and July, relative to those in the control. Co-occurrence networks showed species-species interactions with high negative correlations that occurred more in the control than in the N input plots. The N input from N fertilization and legume planting directly increased the ammonium N and nitrate N and consequently affected the dissolved organic N and pH of the soil, thereby altering the diazotroph abundance and richness. Our findings demonstrated that both N fertilization and legumes could reduce the interspecific competition among diazotroph species by providing greater N availability in the forage grass.