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Continuous nitrogen (N) loading alters plant growth and subsequently has the potential to impact soil organic carbon (SOC) accumulation in salt marshes. However, the knowledge gap of photosynthesized carbon (C) allocation in plant-soil-microbial systems hampers the quantification of C fluxes and the clarification of the mechanisms controlling the C budget under N loading in salt marsh ecosystems. To address this, we conducted an N fertilization field observation combined with a 5 h 13C-pulse labeling experiment in a salt marsh dominated by Suaeda. salsa (S. salsa) in the Yellow River Delta (YRD), China. N fertilization increased net 13C assimilation of S. Salsa by 277.97%, which was primarily allocated to aboveground biomass and SOC. However, N fertilization had little effect on 13C allocation to belowground biomass. Correlation analysis showed that 13C incorporation in soil was significantly and linearly correlated with 13C incorporation in shoots rather than in roots both in a 0 N (0 g N m−2 yr−1) and +N (20 g N m−2 yr−1) group. The results suggested that SOC increase under N fertilization was mainly due to an increased C assimilation rate and more efficient downward transfer of photosynthesized C. In addition, N fertilization strongly improved the 13C amounts in the chloroform-labile SOC component by 295.26%. However, the absolute increment of newly fix 13C mainly existed in the form of residual SOC, which had more tendency for burial in the soil. Thus, N fertilization enhanced SOC accumulation although C loss increased via belowground respiration. These results have important implications for predicting the carbon budget under further human-induced N loading. • Newly fixed carbon allocation and turnover in a salt marsh were quantified in situ. • Nitrogen fertilization enhanced photosynthetic carbon fixation in salt marshes. • Increased newly fixed carbon in +N group mainly allocated in shoot and soil organic carbon. • Soil organic carbon accumulation was mainly benefited by greater shoot growth. • Nitrogen fertilization improved residual soil organic carbon and is favor for carbon sequestration. [ABSTRACT FROM AUTHOR]

Advanced slurry processing (anaerobic digestion, acidification and separation) is being promoted to generate renewable energy, reduce ammonia emissions and optimise storage and transport, respectively. However, these processes could affect slurry phosphorus (P) forms and bioavailability, and hence P dynamics in soil after application. This study investigated the effect of slurry processing, viz. separation, acidification and anaerobic digestion on P forms and distribution of cattle slurry, as well as P dynamics in soil following application of mechanically separated solid and liquid cattle slurry. The results showed that acidification and anaerobic digestion had little impact on TP distribution among particle fractions of slurry, but had substantial influence on P speciation and distribution. Acidification increased the dissolved inorganic-P (IP–H 2 O) proportion in cattle slurry, by reducing the mineral surface adsorbed (IP–NaHCO 3) and precipitated inorganic P (IP–HCl) proportion. Anaerobic digestion decreased OP-NaHCO 3 proportion by degradation and increased the IP-NaHCO 3 and IP-HCl proportion by adsorption and precipitation. Particles <63 μm accounted for over 65% of P present in cattle slurry. The above changes in whole slurry made by acidification and anaerobic digestion were dominated by the <63 μm fraction. Slurry-derived soluble inorganic-P in soil decreased with time, due to adsorption and microbial immobilisation. This decrease was slower in the soil amended with anaerobically digested slurry. Results suggest that anaerobic digestion and acidification change P speciation of separated solid and liquid slurry and the subsequent P dynamics in soil after application. • Acidification increased labile inorganic P in cattle manure by dissolution. • Anaerobic digestion increased labile inorganic P in cattle manure by degradation. • Particles <63 μm accounted for the majority of P present in cattle manure. • Anaerobic digestion increased mass proportion of the <63 μm particles. • Slurry processing controls soluble P in soil, but not the moderately labile P. [ABSTRACT FROM AUTHOR]

Microbial volatile organic compounds (VOCs) can suppress plant pathogens. Although fertilization strongly affects soil microbial communities, the influence of fertilization on microbial VOC-mediated suppression of pathogens has not been elucidated. Soil was sampled from a paddy field that had been subjected to the following treatments for 30 years: a no-fertilizer control, mineral fertilization (NPK), NPK combined with rice straw (NPK + S), NPK combined with chicken manure (70% NPK + 30% M). Then, within a laboratory experiment, pathogens were exposed to VOCs without physical contact to assess the impact of VOCs emitted from paddy soils on in vitro growth of the fungal rice pathogens: Pyricularia oryzae and Rhizoctonia solani. The VOCs emitted from soil reduced the mycelial biomass of P. oryzae and R. solani by 36–51% and 10–30%, respectively, compared to that of the control (no soil; no VOCs emission). Overall, the highest suppression of P. oryzae and R. solani was in the NPK and NPK + S soils, which emitted more quinones, phenols, and low alcohols than NPK + M soils. The abundances of quinones and phenols in the soil air were maximal in the NPK-fertilized soil because the low ratio of dissolved organic carbon and Olsen-P increased the population of key species such as Acidobacteriae, Anaerolineae, and Entorrhizomycetes. The abundance of alcohols was minimum in the NPK + S fertilized soil because the high SOC content decreased the population of Sordariomycetes. In conclusion, mineral fertilization affects bacterial and fungal VOC emissions, thereby suppressing the growth of R. solani and P. oryzae. [Display omitted] • NPK with straw and NPK fertilized soils had the highest rice pathogen suppression. • High suppression of P. oryzae was found in soils with a high organic C content. • High suppression of R. solani was found in soil with a low DOC:OlsenP ratio. • Quinones and phenols suppress the mycelial of rice pathogen. • Acidobacteria, Anaerolineae, and Sordariomycetes are key species affecting VOCs. [ABSTRACT FROM AUTHOR]