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Global potent greenhouse gas nitrous oxide (N2O) emissions from soil are accelerating, with increases in the proportion of reactive nitrogen emitted as N2O, i.e., N2O emission factor (EF). Yet, the primary controls and underlying mechanisms of EFs remain unresolved. Based on two independent but complementary global syntheses, and three field studies determining effects of acidity on N2O EFs and soil denitrifying microorganisms, we show that soil pH predominantly controls N2O EFs and emissions by affecting the denitrifier community composition. Analysis of 5438 paired data points of N2O emission fluxes revealed a hump-shaped relationship between soil pH and EFs, with the highest EFs occurring in moderately acidic soils that favored N2O-producing over N2O-consuming microorganisms, and induced high N2O emissions. Our results illustrate that soil pH has a unimodal relationship with soil denitrifiers and EFs, and the net N2O emission depends on both the N2O/(N2O + N2) ratio and overall denitrification rate. These findings can inform strategies to predict and mitigate soil N2O emissions under future nitrogen input scenarios.

When composite honeycomb sandwich structures are subjected to low energy impacts, the upper panel or the honeycomb core often suffers large damages, which are invisible, but affects the structural safety. To achieve non‐destructive detection of these damages, an epoxy resin film (ERF) was designed as a functional coating to display the internal failure features on structure surface. The effect of low energy impacts on the damage modes of the ERF was first investigated, and then the correspondence between the ERF damage characteristics and the structural internal failure was established. Simulation and experimental results showed that with the increase of impact energy, cracks on the ERF expanded from the radial radiation with a small extension range to the circumferential pattern with an increased damage area. Meanwhile, localized delamination appeared inside the upper panel, while the degree of flexure and crushing damage to the core continued to increase. Based on the analysis of the crack extension pattern of the ERF and the damage state of the upper panel and honeycomb core, a specific link between the ERF crack characteristics and the internal damages to the sandwich structure was obtained, which might offer a novel non‐destructive testing method for composite impact damages. Highlights: Low energy impact damage in honeycomb sandwich structures was a concern.Impact damage response of epoxy resin film on sandwich composites was studied.Crack extension of the film showed a particular change from radial to annular.Specific link between film crack and sandwich structure damage was established.The results would be helpful for damage detection in sandwich composites. [ABSTRACT FROM AUTHOR]

Effects of plasma treatment distance on the adhesion properties of carbon fiber composites were investigated, and the association between the distribution of surface physical characteristics on the composites and their bonding properties was discussed. After plasma treatment at different distances, surface morphology of the bonding area was obtained and the roughness distribution model was established. The change in surface physical characteristics directly influences the wettability of the bonding surface and the tensile shear strength (TSS) of the bonded components. When the TSS showed an increase by 19.47% at the treatment distance of 15 mm, metallographic images indicated that the bonding layer was integrated with the composites and the joint in the component was dominated by cohesive failure. When the TSS showed a decrease by 30.72% at the treatment distance of 5 mm, metallographic images indicated that voids and delamination were introduced in the bonding layer and fiber tearing failure mode appeared in the plasma etched area. Moisture‐heat resistance of the bonded components was also considered and a noticeable increase in water absorption was observed in the case of excessive treatment at the distance of 5 mm, which was also related to the distribution of physical characteristics induced by the plasma treatment. Highlights: Surface characteristic distribution of plasma‐modified composites was analyzed.State of resin and fibers on composite surface varied with the treatment distance.Semi‐annular plasma treatment traces appeared in the roughness distribution.The high roughness in the distribution played a key role in bonding properties.Performance degradation due to close treatment was also distribution‐dependent. [ABSTRACT FROM AUTHOR]

Soil organic carbon (C) is the largest active C pool of Earth's surface and is thus vital in sustaining terrestrial productivity and climate stability. Arbuscular mycorrhizal fungi (AMF) form symbioses with most terrestrial plants and critically modulate soil C dynamics. Yet, it remains unclear whether and how AMF–root associations (i.e., mycorrhizae) interact with soil minerals to affect soil C cycling. Here we showed that the presence of both roots and AMF increased soil dissolved organic C and reactive Fe minerals, as well as litter decomposition and soil CO2 emissions. However, it reduced mineral‐associated C. Also, high‐resolution nanoscale secondary ion mass spectrometry images showed the existence of a thin coating (0.5–1.0 μm thick) of 56Fe16O− (Fe minerals) on the surface of 12C14N− (fungal biomass), illustrating the close physical association between fungal hyphae and soil Fe minerals. In addition, AMF genera were divergently related to reactive Fe minerals, with Glomus being positively but Paraglomus and Acaulospora negatively correlated with reactive Fe minerals. Moreover, the presence of roots and AMF, particularly when combined with litter addition, enhanced the abundances of several critical soil bacterial genera that are associated with the formation of reactive minerals in soils. A conceptual framework was further proposed to illustrate how AMF–root associations impact soil C cycling in the rhizosphere. Briefly, root exudates and the inoculated AMF not only stimulated the decomposition of litter and SOC and promoted the production of CO2 emission, but also drove soil C persistence by unlocking mineral elements and promoting the formation of reactive minerals. Together, these findings provide new insights into the mechanisms that underlie the formation of reactive minerals and have significant implications for understanding and managing soil C persistence. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) significantly contribute to plant resource acquisition and play important roles in mediating plant interactions and soil carbon (C) dynamics. However, it remains unclear how AMF communities respond to climate change. We assessed impacts of warming and precipitation alterations (30% increase or decrease) on soil AMF communities, and examined major ecological processes shaping the AMF community assemblage in a Tibetan alpine meadow. Our results showed that warming significantly increased root biomass, and available nitrogen (N) and phosphorus (P) in soil. While precipitation alterations increased AMF abundances, they did not significantly affect the composition or diversity of AMF communities. In contrast, warming altered the composition of AMF communities and reduced their Shannon–Wiener index and Pielou's evenness. In particular, warming shifted the AMF community composition in favor of Diversisporaceae over Glomeraceae, likely through its impact on soil N and P availability. In addition, AMF communities were phylogenetically random in the unwarmed control but clustered in warming plots, implying more deterministic community assembly under climate warming. Warming enhancement of root growth, N and P availability likely reduced plant C‐allocation to AMF, imposing stronger environmental filtering on AMF communities. We further proposed a conceptual framework that integrates biological and geochemical processes into a mechanistic understanding of warming and precipitation changes' effects on AMF. Taken together, these results suggest that soil AMF communities may be more sensitive to warming than expected, highlighting the need to monitor their community structure and associated functional consequences on plant communities and soil C dynamics under the future warmer climate. [ABSTRACT FROM AUTHOR]

Aim: Ammonia‐oxidizing archaea (AOA) and bacteria (AOB) are the primary agents for nitrification, converting ammonia (NH4+) into nitrate (NO3−) and modulating plant nitrogen (N) utilization and terrestrial N retention. However, there is still lack of a unifying framework describing the patterns of global AOA and AOB distribution. In particular, biotic interactions are rarely integrated into any of the conceptual models. Location: World‐wide. Time period: 2005–2016. Major taxa studied: Ammonia‐oxidizing archaea and ammonia‐oxidizing bacteria. Methods: A meta‐analysis and synthesis were conducted to obtain a general picture of global AOA and AOB distribution and identify the primary driving factors. A microcosm experiment was then conducted to assess effects of relative carbon to nitrogen availability for heterotrophic microbes on AOA and AOB in two distinct soils. A mesocosm experiment was further carried out to characterize the effects of plant roots and their arbuscular mycorrhizal fungi (AMF) on AOA and AOB abundances using hyphae‐ or root‐ingrowth techniques. Results: Our meta‐analysis showed that soil carbon to nitrogen (C/N) ratios explained the most variance in AOA and AOB abundances, although soil pH had a significant effect. Experimental results demonstrated that high cellulose and mineral N inputs increased total microbial biomass and microbial activities, but inhibited AOA and AOB, suggesting microbial inhibition of AOA and AOB. Also, AMF and roots suppressed AOA and AOB, respectively. Main conclusions: Our study provides convincing evidence illustrating that relative carbon to nitrogen availability can predominantly affect the abundances of AOA and AOB. Our experimental results further validate that biotic competition among plants, heterotrophic microbes and ammonia oxidizers for substrate N is the predominant control upon AOA and AOB abundances. Together, these findings provide new insights into the role of abiotic and biotic factors in modulating terrestrial AOA and AOB abundances and their potential applications for management of nitrification in an increasing reactive N world. [ABSTRACT FROM AUTHOR]

Highlights In this paper, a mortise‐and‐tenon structural design was introduced into composite maintenance to create a new type of joint between the repair patches and the parent structure, where both the patches and the structure were carbon fiber composites. Effects of different joints, including step‐lap and mortise‐and‐tenon‐lap joints, on the bending failure of the repaired composites were simulated and then verified through experiments. Results showed that compared with the traditional step‐lap method, the mortise‐and‐tenon connection changed the direction of damage extension from a simple single path to complex multiple paths, which effectively inhibited the damage expansion and enhanced the structural damage tolerance. Therefore, the flexural strength of the repair with the new joint was improved by 19.9%. However, the mortise‐and‐tenon‐lap joint resulted in a poor moisture‐heat resistance of the repaired structure. Interestingly, although the flexural strength of the mortise‐and‐tenon repair decreased by 10.45% after the hygrothermal treatment, it was still higher than that of the step‐lap repair without hygrothermal treatment. A novel joint, mortise‐and‐tenon, was introduced into composite maintenance. Damage extended along multiple paths in the new joint and was inhibited. Flexural strength of the repair was higher than that of traditional step‐lap repair. [ABSTRACT FROM AUTHOR]

Soil acidification caused by acid deposition and N fertilization can significantly affect the composition and activity of microbial communities in acidic soils. However, whether and how acidification affects soil microorganisms and microbial‐mediated carbon (C) dynamics in alkaline soils are less known. Based on a 7‐year (2016–2023) acid addition experiment in an alkaline grassland (pH > 8) on the Loess Plateau in Northwest China, we examined the effects of soil acidification on soil fungal and bacterial communities and their C metabolism. Unexpectedly, our results showed that soil acidification mainly reduced fungal diversity, rather than bacterial diversity, possibly because acidification led to soil NH4+ accumulation and decreased plant diversity. Also, soil acidification reduced forb but increased grass biomass, and enhanced root production and turnover rate. Laboratory incubation experiments showed that changes in the microbial community and soil properties jointly promoted microbial decomposition of soil organic C (SOC), with more promotion for the decomposition of labile C (i.e. glucose) (+68.4%) than recalcitrant C (i.e. tannin) (+29.1%). Synthesis. Soil acidification reduced fungal diversity and stimulated SOC decomposition in an alkaline grassland. Given that pH decline can also accelerate soil inorganic C dissolution and carbonate‐derived CO2 release, these results highlight that soil acidification can exacerbate C loss in the alkaline soils over the long term. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]