Short-term legacy effects of rice season irrigation and fertilization on the soil bacterial community of the subsequent wheat season in a rice-wheat rotation system

Soil properties and microbial diversity are markedly enhanced by the long-term effects of organic fertilizers. However, the short-term impacts of inorganic and organic fertilizers vary in different agroecosystems, especially when combined with different irrigation conditions. Here, we examined the influence of different fertilizer types (NPK: mineral fertilizer, NPKM: mineral fertilizer plus organic fertilizer, NPKWS: mineral fertilizer plus straw) combined with different irrigation regimes (AWMID: shallow water layer, AWMOD: alternate wetting and moderate drying, AWSD: alternate wetting and severe drying) on the soil properties and bacterial communities at the wheat harvest stage of a one-year rice-wheat rotation system (RWRS), in the rice zone along the Yellow River of China. Our results revealed that the irrigation mode had a stronger impact on the soil properties, and bacterial community than the fertilizer regime, although most indicators did not differ significantly, probably owing to the short duration of the trial. Several low-abundance bacteria were recognized to be strongly (P < 0.05) influenced by different irrigation and fertilizer regimes in the RWRS using LEfSe analysis, but no definite trends were observed among the treatments. A co-occurrence network uncovered the modular clustering patterns of bacteria, which were significantly correlated with the available phosphorus content and some soil enzyme activities. Moreover, the denitrification, nitrite respiration, and sulfur respiration capacities of soil microbes were significantly improved in the mineral fertilizer combined with the alternate wetting and moderate drying treatment. In addition, the wheat yield did not significantly (P < 0.05) decrease after water-saving irrigation regime during the previous rice season. Further research is warranted to elucidate the long-term effects of partial substitution of chemical nitrogen with organic nitrogen and water-saving irrigation regimes on an RWRS.