Effects of warming and elevated O3 concentrations on N2O emission and soil nitrification and denitrification rates in a wheat-soybean rotation cropland

Soil properties and fungal community jointly explain N2O emissions following N and P enrichment in an alpine meadow

Nutrient enrichment, such as nitrogen (N) and phosphorus (P), typically affects nitrous oxide (N2O) emissions in terrestrial ecosystems, predominantly via microbial nitrification and denitrification processes in the soil. However, the specific impact of soil property and microbial community alterations under N and P enrichment on grassland N2O emissions remains unclear. To address this, a field experiment was conducted in an alpine meadow of the northeastern Qinghai-Tibetan Plateau. This study aimed to unravel the mechanisms underlying N and P enrichment effects on N2O emissions by monitoring N2O fluxes, along with analyzing associated microbial communities and soil physicochemical properties. We observed that N enrichment individually or in combination with P enrichment, escalated N2O emissions. P enrichment dampened the stimulatory effect of N enrichment on N2O emissions, indicative of an antagonistic effect. Structural equation modeling (SEM) revealed that N enrichment enhanced N2O emissions through alterations in fungal community composition and key soil physicochemical properties such as pH, ammonium nitrogen (NH4+-N), available phosphorus (AP), microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN)). Notably, our findings demonstrated that N2O emissions were significantly more influenced by fungal activities, particularly genera like Fusarium, rather than bacterial processes in response to N enrichment. Overall, the study highlights that N enrichment intensifies the role of fungal attributes and soil properties in driving N2O emissions. In contrast, P enrichment exhibited a non-significant effect on N2O emissions, which highlights the critical role of the fungal community in N2O emissions responses to nutrient enrichments in alpine grassland ecosystems.

Elevated ozone decreases the multifunctionality of belowground ecosystems

Elevated tropospheric ozone (O₃ ) affects the allocation of biomass aboveground and belowground and influences terrestrial ecosystem functions. However, how belowground functions respond to elevated O₃ concentrations ([O₃ ]) remains unclear at the global scale. Here, we conducted a detailed synthesis of belowground functioning responses to elevated [O₃ ] by performing a meta-analysis of 2395 paired observations from 222 publications. We found that elevated [O₃ ] significantly reduced the primary productivity of roots by 19.8%, 16.3%, and 26.9% for crops, trees and grasses, respectively. Elevated [O₃ ] strongly decreased the root/shoot ratio by 11.3% for crops and by 4.9% for trees, which indicated that roots were highly sensitive to O₃ . Elevated [O₃ ] impacted carbon and nitrogen cycling in croplands, as evidenced by decreased dissolved organic carbon, microbial biomass carbon, total soil nitrogen, ammonium nitrogen, microbial biomass nitrogen, and nitrification rates in association with increased nitrate nitrogen and denitrification rates. Elevated [O₃ ] significantly decreased fungal phospholipid fatty acids in croplands, which suggested that O₃ altered the microbial community and composition. The responses of belowground functions to elevated [O₃ ] were modified by experimental methods, root environments, and additional global change factors. Therefore, these factors should be considered to avoid the underestimation or overestimation of the impacts of elevated [O₃ ] on belowground functioning. The significant negative relationships between O₃ -treated intensity and the multifunctionality index for croplands, forests, and grasslands implied that elevated [O₃ ] decreases belowground ecosystem multifunctionality.

Effect of gradual increase of atmospheric CO2 concentration on nitrification potential and communities of ammonia oxidizers in paddy fields

Currently, the influence of elevated atmospheric CO₂ concentration (eCO₂) on ammonia oxidation to nitrite, the rate-limiting step of nitrification in paddy soil, is poorly known. Previous studies that simulate the effect of eCO₂ on nitrification are primarily based on an abrupt increase of atmospheric CO₂ concentration. However, paddy ecosystems are experiencing a gradual increase of CO₂ concentration. To better understand how the nitrification potential, abundance and communities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) respond to eCO₂ in paddy ecosystems, a field experiment was conducted using the following two treatments: a gradual increase of CO₂ (EC, increase of 40 ppm per year until 200 ppm above ambient) and ambient CO₂ (CK). The results demonstrated that the EC treatment significantly (P < 0.05) stimulated the soil potential nitrification rate (PNR) at the jointing and milky stages, which increased by 127.83% and 27.35%, respectively, compared with CK. Furthermore, the EC treatment significantly (P < 0.05) stimulated the AOA and AOB abundance by 56.60% and 133.84%, respectively, at the jointing stage. Correlation analysis showed that the PNR correlated well with the abundance of AOB (R² = 0.7389, P < 0.001). In addition, the EC treatment significantly (P < 0.05) altered the community structure of AOB, while it had little effect on that of AOA. A significant difference in the proportion of Nitrosospira was observed between CO₂ treatments. In conclusion, the gradual increase of CO₂ positively influenced the PNR and abundance of ammonia oxidizers, and AOB could be more important than AOA in nitrification under eCO₂.

Biochar modulates mineral nitrogen dynamics in soil and terrestrial ecosystems: A critical review

Biochar, over the last two decades, has become the focal point of agro-environmental research given its unique functionality, cost-effectiveness and recyclability potentials. It has been studied intensively as an efficient scavenger for the decontamination of several organic and inorganic pollutants. However, the ability of biochar to modulate nitrogen (N) dynamics in soil and terrestrial ecosystems remains controversial. This work deliberates on the premise that biochar functionality enables maximizing N use efficiency by reducing the potential losses induced by volatilization/emission and runoff/leaching as well as stimulating available N inputs derived from symbiotic and nonsymbiotic biological nitrogen fixation (BNF) and N mineralization/retention. For this purpose, we carried out a critical review on different intriguing dimensions surrounding the potentiality of biochar to modulate the complicated reactions of soil N cycle with emphasis on its pros and cons. Previous studies in the literature have shown contradictory results with a noticeable significant effect of biochar toward stimulating available N inputs and reducing its losses under short-term laboratory experimentations. However, long-term field investigations have indicated minimal or negative effects in this regard. Furthermore, some of the experimentations lack appropriate controls or fail to account for inputs or losses associated with biochar particles. It is thus of great importance to contextualise lab-scale experimentations based on real field data to provide a holistic approach for understanding the complicated reactions responsible for modulating N cycle in the charosphere. Additionally, biochar functionalization should be highlighted in the foreseeable research to develop fit-for-purpose forms tailored in agro-environmental applications.

Effects of sulfoxaflor on greenhouse vegetable soil N2O emissions and its microbial driving mechanism

The wide application of pesticides ensures the safety of food production, but it also has a serious impact on soil ecosystem. Although sulfoxaflor as a pesticide has great potential for application due to its excellent insecticidal activity and low crossresistance, little is known about its soil environmental safety risks. In this study, the effects of sulfoxaflor on N₂O emissions and microorganisms in greenhouse vegetable soils were studied by indoor simulation culture experiments. Dynamic changes of soil main inorganic N and N₂O emission rate were tested, and the abundance and community of total bacteria and microorganisms related to N cycle were analyzed. The results indicated that soil microorganisms rapidly degraded sulfoxaflor, and the N₂O emissions rate and ammonium nitrogen (NH₄⁺-N) content significantly increased, while nitrate nitrogen (NO₃^--N) content was significantly decreased. Sulfoxaflor significantly changed the abundance and community of total bacteria, nitrite reducing and nitrous oxide reducing bacteria, but had no significant effect on ammoxidation microorganisms. The N₂O emission rate was positively correlated with gene abundance of denitrifying microorganisms. Under 65% soil maximum water holding capacity, sulfoxaflor may broke the dynamic balance of N₂O production and consumption in the denitrification process, which caused a significant increase in N₂O emission. Therefore, the application of sulfoxaflor had a certain effect on N cycling and utilization in greenhouse vegetable soil.