no sp Assessment of Nitrogen Fluxes to Air and Water from Site Scale to Continental Scale | We assessed nitrous oxide (N2O) emissions at shoulder and foot-slope positions along three sloping sites (1.6-2.1%) to identify the factors controlling the spatial variations in emissions. The three sites received same amounts of total nitrogen (N) input at 170 kg N ha−1. Results showed that landscape positions had a significant, but not consistent effect on N2O fluxes with larger emission in the foot-slope at only one of the three sites. The effect of soil inorganic N (NH4+ + NO3−) contents on N2O fluxes (r2 = 0.55, p < 0.001) was influenced by water-filled pore space (WFPS). Soil N2O fluxes were related to inorganic N at WFPS > 60% (r2 = 0.81, p < 0.001), and NH4+ contents at WFPS < 60% (r2 = 0.40, p < 0.01), respectively. Differences in WFPS between shoulder and foot-slope correlated linearly with differences in N2O fluxes (r2 = 0.45, p < 0.001). We conclude that spatial variations in N2O emission were regulated by the influence of hydrological processes on soil aeration intensity.

International audience | Human urine concentrates 88% of the nitrogen and 50% of the phosphorus excreted by humans, making it a potential alternativecrop fertilizer. However, knowledge gaps remain on the fate of nitrogen in situations favouring NH3 volatilization and on theavailability of P from urine in soils. This study aimed at identifying the fate of nitrogen and phosphorus supplied by human urinefrom source separation toilets in a calcareous soil. To this end, a spinach crop was fertilized with 2 different doses of human urine and compared with a synthetic fertilizer treatment and an unfertilized control. The experiment was conducted in 4 soil tanks (50-cm depth) in greenhouse condi-tions, according to a randomized block scheme. We monitored soil mineral nitrogen over time and simulated nitrogen volatiliza-tion using Hydrus-1D and Visual Minteq softwares. We also monitored soil phosphorus pools, carbon, nitrogen and phosphorus(CNP) in microbial biomass, soil pH and electrical conductivity. Only an excessive input of urine affected soil pH (decreasing itby 0.2 units) and soil conductivity (increasing it by 183%). The phosphorus supplied was either taken up by the crop or remainedmostly in the available P pool, as demonstrated by a net increase of the resin and bicarbonate extractable P. Ammonium seemedto be nitrified within about 10 days after application. However, both Visual Minteq and Hydrus models estimated that more than50% of the nitrogen supplied was lost by ammonia volatilization. Overall, our results indicate that direct application of urine to acalcareous soil provides available nutrients for plant growth, but that heavy losses of volatilized nitrogen are to be expected. Ourresults also question whether long-term application could affect soil pH and salinity.

Freshwater wetlands are natural sinks of carbon; yet, wetland conversion for agricultural uses can shift these carbon sinks into large sources of greenhouse gases. We know that the anthropogenic alteration of wetland hydrology and the broad use of N-fertilizers can modify biogeochemical cycling, however, the extent of their combined effect on greenhouse gases exchange still needs further research. Moreover, there has been recent interest in wetlands rehabilitation and preservation by improving natural water flow and by seeking alternative solutions to nutrient inputs. In a microcosm setting, we experimentally exposed soils to three inundation treatments (Inundated, Moist, Drained) and a nutrient treatment by adding high nitrogen load (300 kg ha⁻¹) to simulate physical and chemical disturbances. After, we measured the depth microprofiles of N₂O and O₂ concentration and CO₂ and CH₄ emission rates to determine how hydrological alteration and nitrogen input affect carbon and nitrogen cycling processes in inland wetland soils. Compared to the Control soils, N-fertilizer increased CO₂ emissions by 40% in Drained conditions and increased CH₄ emissions in Inundated soils over 90%. N₂O emissions from Moist and Inundated soils enriched with nitrogen increased by 17.4 and 18-fold, respectively. Overall, the combination of physical and chemical disturbances increased the Global Warming Potential (GWP) by 7.5-fold. The first response of hydrological rehabilitation, while typically valuable for CO₂ emission reduction, amplified CH₄ and N₂O emissions when combined with high nitrogen inputs. Therefore, this research highlights the importance of evaluating the potential interactive effects of various disturbances on biogeochemical processes when devising rehabilitation plans to rehabilitate degraded wetlands.

Although fertilization plays an important role in determining the contents of soil dissolved organic matters or water-extractable organic matter (DOM, WEOM), knowledge regarding the dynamics, biodegradability, and microbial community shifts of WEOM in response to different fertilization treatments is very limited, particularly in rice–wheat cropping soil. Thus, in the present study, we performed biodegradation experiments using WEOM extracted from samples of soil that had been subjected to four different fertilization treatments: unfertilized control (CK), chemical fertilizer (CF), 50% chemical fertilizer plus pig manure (PMCF), and 100% chemical fertilizer plus rice straw (SRCF). UV spectrum and fluorescence 3D excitation–emission matrix analyses applied to investigate the chemical composition of WEOM revealed that all examined WEOMs were derived from microbial activity and the dominant portion comprised humic acid-like compounds. After the incubation, 31.17, 31.63, 43.47, and 33.01% of soil WEOM from CK, CF, PMCF, and SRCF treatments, respectively, were biodegraded. PMCF- derived WEOM had the highest biodegradation rate. High-throughput sequencing analyses performed to determine the microbial community before and after the incubation indicated that Sphingomonas, Bacillus, and Flavisolibacter were the predominant bacterial genera in the original inoculum derived from the four fertilization treatments. Following biodegradation, we observed that the dominant bacteria differed according to fertilization treatments: Curvibacter (43.25%) and Sphingobium (10.47%) for CK, Curvibacter (29.68%) and Caulobacter (20.00%) for CF, Azospirillum (23.68%) and Caulobacter (13.29%) for PMCF, and Ralstonia (51.75%) for SRCF. Canonical correspondence analysis revealed that, shifts in the microbial community were closely correlated with pH and specific UV absorbance at 254 nm. We speculated that the inherent traits of different WEOM and the properties of soil solutions under different fertilization treatments shaped the soil microbial community structure, thereby influencing the biodegradation of WEOM.

Increased reactive nitrogen (N) loadings to terrestrial ecosystems are believed to have positive effects on ecosystem carbon (C) sequestration. Global “hot spots” of N deposition are often associated with currently or formerly high deposition of sulphur (S); C fluxes in these regions might therefore not be responding solely to N loading, and could be undergoing transient change as S inputs change. In a four-year, two-forest stand (mature Norway spruce and European beech) replicated field experiment involving acidity manipulation (sulphuric acid addition), N addition (NH4NO3) and combined treatments, we tested the extent to which altered soil solution acidity or/and soil N availability affected the concentration of soil dissolved organic carbon (DOC), soil respiration (Rs), microbial community characteristics (respiration, biomass, fungi and bacteria abundances) and enzyme activity. We demonstrated a large and consistent suppression of soil water DOC concentration driven by chemical changes associated with increased hydrogen ion concentrations under acid treatments, independent of forest type. Soil respiration was suppressed by sulphuric acid addition in the spruce forest, accompanied by reduced microbial biomass, increased fungal:bacterial ratios and increased C to N enzyme ratios. We did not observe equivalent effects of sulphuric acid treatments on Rs in the beech forest, where microbial activity appeared to be more tightly linked to N acquisition. The only changes in C cycling following N addition were increased C to N enzyme ratios, with no impact on C fluxes (either Rs or DOC). We conclude that C accumulation previously attributed solely to N deposition could be partly attributable to their simultaneous acidification.

Atmospheric nitrogen (N) deposition has a significant influence on soil organic carbon (SOC) accumulation in forest ecosystems. Microbial residues, as by-products of microbial anabolism, account for a significant fraction of soil C pools. However, how N deposition affects the accumulation of soil microbial residues in different forest biomes remains unclear. Here, we investigated the effects of six/seven-year N additions on microbial residues (amino sugar biomarkers) in eight forests from tropical to boreal zone in eastern China. Our results showed a minor change in the soil microbial residue concentrations but a significant change in the contribution of microbial residue-C to SOC after N addition. The contribution of fungal residue-C to SOC decreased under low N addition (50 kg N ha⁻¹ yr⁻¹) in the tropical secondary forest (−19%), but increased under high N addition (100 kg N ha⁻¹ yr⁻¹) in the temperate Korean pine mixed forest (+21%). The contribution of bacterial residue-C to SOC increased under the high N addition in the subtropical Castanopsis carlesii forest (+26%) and under the low N addition in the temperate birch forest (+38%), respectively. The responses of microbial residue-C in SOC to N addition depended on the changes in soil total N concentration and fungi to bacteria ratio under N addition and climate. Taken together, these findings provide the experimental evidence that N addition diversely regulates the formation and composition of microbial-derived C in SOC in forest ecosystems.

Anaerobically digested and composted sewage sludge (CSS) has been suggested to be a slow-release fertilizer in forestry and an alternative to quick-release inorganic fertilizers. The effects of CSS with or without added carbohydrate on inorganic nitrogen availability and on soil animals were tested in two Norway spruce plantations. Half of the seedlings were individually fertilized with CSS, and the rest were left as controls. Solid sucrose was added to half of the fertilized and untreated seedlings. Soil samples were taken in the autumn in the first and the second year after the treatments. CSS increased soil NH4–N (2100%), the proportion of soil NO3–N, and the N concentration of spruce needles. CSS greatly reduced the abundances of enchytraeids, tardigrades and collembolans, but increased the proportion and abundance of bacterial-feeding nematodes irrespective of carbohydrate addition. A better stabilization method needs to be developed before CSS can be used as a forest fertilizer.

Exposure of aquatic organisms to micro- and nano-sized plastic debris in their environment has become an alarming concern. Besides having a number of potentially harmful impacts for individual organisms, plastic particles can also influence the phenotype and performance of their offspring. We tested whether the sperm pre-fertilization exposure to nanoplastic particles could affect offspring survival, size, and swimming performance in the European whitefish Coregonus lavaretus. We exposed sperm of ten whitefish males to three concentrations (0, 100 and 10 000 pcs spermatozoa⁻¹) of 50 nm carboxyl-coated polystyrene spheres, recorded sperm motility parameters using computer assisted sperm analysis (CASA) and then fertilized the eggs of five females in all possible male-female combinations. Finally, we studied embryonic mortality, hatching time, size, and post-hatching swimming performance of the offspring. We found that highest concentration of plastic particles decreased sperm motility and offspring hatching time. Furthermore, sperm exposure to highest concentration of plastics reduced offspring body mass and impaired their swimming ability. This suggests that sperm pre-fertilization exposure to plastic pollution may decrease male fertilization potential and have important transgenerational impacts for offspring phenotype and performance. Our findings indicate that nanoplastics pollution may have significant ecological and evolutionary consequences in aquatic ecosystems.

Rice field has been traditionally considered as a nonpoint source of reactive nitrogen (N) for the environment, while it, with surrounding ditches and ponds, also contributes to receiving N inputs from atmosphere and waterbodies and intercepting N outputs from rice field. However, a comprehensive assessment of the N source or sink of rice field for the environment is lacking. Here, we conducted the 3-year systematic observations and process-based simulations of N budget at the Jingzhou site in Central China. We identified the roles of rice field and evaluated the opportunities for shifting its role from N source (i.e., outputs > inputs) to sink (i.e., outputs ≤ inputs). Rice field was found to be a N source of 24.2–28.7 kg N ha⁻¹ for waterbodies (including surface and ground waters), but a N sink (2.2–8.8 kg N ha⁻¹) for the atmosphere for the wet and normal year climatic scenarios. The “4R-nutrient stewardship” (i.e., using the right type of N fertilizers, at right rate, right time, and in right place) applied in rice field was sufficient for the source-to-sink shift for the atmosphere for dry year climatic scenario, but needed to implement together with improvements of irrigation and drainage for waterbodies. Furthermore, with the combination of these improved management technologies, rice field played a role as a N sink of up to 22.8 kg N ha⁻¹ for the atmosphere and up to 2.0 kg N ha⁻¹ for waterbodies, along with 24% decrease in irrigation water use and 21% decrease in N application rate without affecting rice yield and soil fertility. Together these findings highlight a possibility to achieve an environmental-friendly rice field by improving agricultural management technologies.

The explosion of the Deepwater Horizon (DWH) oil platform resulted in large amounts of crude oil and dispersant Corexit 9500A® released into the Gulf of Mexico and coincided with the spawning season of the oyster, Crassostrea virginica. The effects of exposing gametes and embryos of C. virginica to dispersant alone (Corexit), mechanically (HEWAF) and chemically dispersed (CEWAF) DWH oil were evaluated. Fertilization success and the morphological development, growth, and survival of larvae were assessed. Gamete exposure reduced fertilization (HEWAF: EC201 h = 1650 μg tPAH50 L− 1; CEWAF: EC201 h = 19.4 μg tPAH50 L− 1; Corexit: EC201 h = 6.9 mg L− 1). CEWAF and Corexit showed a similar toxicity on early life stages at equivalent nominal concentrations. Oysters exposed from gametes to CEWAF and Corexit experienced more deleterious effects than oysters exposed from embryos. Results suggest the presence of oil and dispersant during oyster spawning season may interfere with larval development and subsequent recruitment.