Manure application effects on subsoils: Abundant taxa initiate the diversity reduction of rare bacteria and community functional alterations

Manure application is a significant agriculture practice that can affect the microbial community structure in both topsoil and subsoil. However, how the abundant and rare taxa in the soil profile respond to surface manure application and their ecological roles at different soil depths remain unknown. Based on a soil mesocosm experiment, we used amplicon sequencing and high-throughput quantitative-PCR array to characterize the bacterial community composition and functional traits across soil profiles. Results showed that the relative abundance and diversity of rare taxa increased in the topsoil but decreased in the 40–60 cm soil, where the relative abundance of abundant taxa increased after manure application. Evidence from network analysis, niche width and 16S rRNA operon (rrn) copy number suggest that abundant taxa in subsoils had a greater competitivity for resource mining than rare taxa. Regarding resource utilization strategies, microbial communities under manure treatment preferred to utilize recalcitrant carbon (C) and inorganic phosphorus (P) in the topsoil and labile carbon and organic phosphorus in the subsoil compared with non-manure application. Random Forest regression analysis indicated the relatively greater contribution of abundant taxa to C degradation and fixation in subsoils. These results imply that the manure application effect on microbial resource mining in subsoils is mainly driven by abundant bacteria due to the lower competitiveness of rare taxa for the C sources leached above. Overall, This study linked community functions with the ecological role of abundant and rare taxa in the context of environmental disturbances at different soil depths and shed light on the potential ecological risks of diversity reduction of subsoil rare bacteria

Unveiling the role of dissolved organic matter on phosphorus sorption and availability in a 5-year manure amended paddy soil

Dissolved organic matter (DOM) is an active component of organic manure that is widely used in agroecosystems to increase nutrient availability and consequently enhance crop yields. However, the ways in which soil DOM characteristics are influenced by organic manure and how it contributes to crop yield and soil P availability remains unclear. Here, we conducted a 5-year field experiment and demonstrated that partial replacement of chemical P fertilizer with swine manure could maintain high rice yield and soil available P levels and increase P fertilizer use efficiency (PUE) in comparison to chemical fertilization, even when the total P input was reduced. This suggests that organic manure application can significantly mobilize soil P and increase P availability. Structural equation modeling analysis indicated that the soil pH and humification degree of DOM, rather than DOM content, directly decreased maximum P adsorption capacity. The combined results of the optical spectroscopy and ultrahigh-resolution mass spectroscopy obtained from the laboratory validation experiment based on the DOM-removed soil demonstrated that manure-derived DOM competing with P for adsorption was one of the main reasons for the increase in soil P availability and that the effective DOM components were N-containing lignins, tannins, and condensed polycyclic aromatics with higher O/C and lower H/C ratios. Overall, our results provide solid evidence that soil DOM characteristics are influenced by manure application and facilitate soil P availability, which could help guide the sustainable P management and manure application in agroecosystems

Transgenic expression of delta-6 and delta-15 fatty acid desaturases enhances omega-3 polyunsaturated fatty acid accumulation in Synechocystis sp PCC6803

Background: Polyunsaturated fatty acids (PUFAs), which contain two or more double bonds in their backbone, are the focus of intensive global research, because of their nutritional value, medicinal applications, and potential use as biofuel. However, the ability to produce these economically important compounds is limited, because it is both expensive and technically challenging to separate omega-3 polyunsaturated fatty acids (omega-3 PUFAs) from natural oils. Although the biosynthetic pathways of some plant and microalgal omega-3 PUFAs have been deciphered, current understanding of the correlation between fatty acid desaturase content and fatty acid synthesis in Synechocystis sp. PCC6803 is incomplete. Results: We constructed a series of homologous vectors for the endogenous and exogenous expression of Delta 6 and Delta 15 fatty acid desaturases under the control of the photosynthesis psbA2 promoter in transgenic Synechocystis sp. PCC6803. We generated six homologous recombinants, harboring various fatty acid desaturase genes from Synechocystis sp. PCC6803, Gibberella fujikuroi and Mortierella alpina. These lines produced up to 8.9 mg/l of alpha-linolenic acid (ALA) and 4.1 mg/l of stearidonic acid (SDA), which are more than six times the corresponding wild-type levels, at 20 degrees C and 30 degrees C. Thus, transgenic expression of Delta 6 and Delta 15 fatty acid desaturases enhances the accumulation of specific omega-3 PUFAs in Synechocystis sp. PCC6803. Conclusions: In the blue-green alga Synechocystis sp. PCC6803, overexpression of endogenous and exogenous genes encoding PUFA desaturases markedly increased accumulation of ALA and SDA and decreased accumulation of linoleic acid and gamma-linolenic acid. This study lays the foundation for increasing the fatty acid content of cyanobacteria and, ultimately, for producing nutritional and medicinal products with high levels of essential omega-3 PUFAs.Background: Polyunsaturated fatty acids (PUFAs), which contain two or more double bonds in their backbone, are the focus of intensive global research, because of their nutritional value, medicinal applications, and potential use as biofuel. However, the ability to produce these economically important compounds is limited, because it is both expensive and technically challenging to separate omega-3 polyunsaturated fatty acids (omega-3 PUFAs) from natural oils. Although the biosynthetic pathways of some plant and microalgal omega-3 PUFAs have been deciphered, current understanding of the correlation between fatty acid desaturase content and fatty acid synthesis in Synechocystis sp. PCC6803 is incomplete