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Nitrogen (N) deposition-induced soil acidification has become a global problem. However, the response patterns of soil acidification to N addition and the underlying mechanisms remain far from clear. Here, we conducted a meta-analysis of 106 studies to reveal global patterns of soil acidification in responses to N addition. We found that N addition significantly reduced soil pH by 0.26 on average globally. However, the responses of soil pH varied with ecosystem types, N addition rate, N fertilization forms, and experimental durations. Soil pH decreased most in grassland, whereas boreal forest was not observed a decrease to N addition in soil acidification. Soil pH decreased linearly with N addition rates. Addition of urea and NH4NO3 contributed more to soil acidification than NH4-form fertilizer. When experimental duration was longer than 20 years, N addition effects on soil acidification diminished. Environmental factors such as initial soil pH, soil carbon and nitrogen content, precipitation, and temperature all influenced the responses of soil pH. Base cations of Ca2+, Mg2+ and K+ were critical important in buffering against N-induced soil acidification at the early stage. However, N addition has shifted global soils into the Al3+ buffering phase. Overall, this study indicates that acidification in global soils is very sensitive to N deposition, which is greatly modified by biotic and abiotic factors. Global soils are now at a buffering transition from base cations (Ca2+, Mg2+ and K+) to non-base cations (Mn2+ and Al3+). This calls our attention to care about the limitation of base cations and the toxic impact of non-base cations for terrestrial ecosystems with N deposition.

Soil has the nature of acidity and alkalinity, mostly indicated by soil pH that could greatly affect soil ecological processes and functions. With exogenous inputs of acidic materials (such as acid rain), soils may more or less resist to maintain their pH levels within specific thresholds by various buffering processes. It has been well established that soil properties such as cation exchange capacity (CEC), soil organic matter (SOM), and clay content play important roles in mitigating the effects of acid inputs, but the factors varied across soils. This microcosm experiment was conducted to investigate changes in the soil pH and quantitatively estimate the critical pH threshold of simulated acid rain for three highly weathered soils (red soil, lateritic red soil, and latosol) that are typical soil types widely distributed across the world’s subtropical and tropical climatic zones, as well as important influential factors, after continuously adding different levels of simulated acid rain on the surface of soil cores. The results showed that the change in the soil pH was not significantly different among the three soils, although it was exponentially related to soil CEC and clay content. Resultantly, the latosol that had high soil CEC and clay content was more resistant to simulated acid rain, especially when relatively weak simulated acid rain treatments were applied. The lateritic red soil that contained the lowest soil CEC and clay content showed the greatest decline in the soil pH under the strongest simulated acid rain treatment of pH being 2.5. Furthermore, we estimated the critical pH threshold of simulated acid rain for the three soils and observed that it was considerably different among the soils. Surprisingly, the pH threshold of simulated acid rain was also positively related to the soil CEC and clay content, therefore making the highest pH threshold in the latosol. Our results imply that soil CEC and clay content may play critical roles in the soil acid-buffering processes from two aspects; it could not only contribute to the soil acid-buffering capacity, but also affect the threshold of acidity of acid rain below which abrupt soil acidification may occur.

The treatment of damaged enamel surfaces involves modification of the enamel surface with artificial materials or the development of a pseudo-enamel, with research focusing on bioactive and biomimetic materials. In this study, a bioactive auto-polymerizing resin (APR) was developed by adding surface-pre-reacted glass ionomer (S-PRG) fillers of different quantities to APR. Its bioactive effects were evaluated via pH neutralization, ion release, and inhibition of enamel demineralization studies. The pH and fluoride ion release were measured using ion-specific electrodes, revealing that the APR disk with the S-PRG filler immediately neutralized the lactic acid solution (pH 4.0) through ion release. Inductively coupled plasma atomic emission spectrometry revealed that the Sr ion release peaked on the first day, with the other ions following the order F > B > Si > Al > Na, exhibiting a weekly decrease in the same order. Scanning electron microscopy was used to examine the enamel block morphology of the disks after 7 d of incubation, revealing enamel demineralization in disks without the S-PRG filler, whereas no demineralization occurred in disks with the S-PRG filler. APR containing the S-PRG filler demonstrated acid buffering suppressed enamel demineralization and bioactive properties.

Changes in soil exchangeable cations relative to soil acidification are less studied particularly under long-term cash crop plantation. This study investigated soil acidification in an Ali-Periudic Argosols after 10-year (2002–2012) long-term continuous tobacco plantation. Soils were respectively sampled at 1933 and 2143 sites in 2002 and 2012 (also 647 tobacco plants), from seven tobacco plantation counties in the Chongqing Municipal City, southwest China. After 10-year continuous tobacco plantation, a substantial acidification was evidenced by an average decrease of 0.20 soil pH unit with a substantial increase of soil sites toward the acidic status, especially those pH ranging from 4.5 to 5.5, whereas 1.93 kmol H⁺ production ha⁻¹ year⁻¹ was mostly derived from nitrogen (N) fertilizer input and plant N uptake output. After 1 decade, an average decrease of 27.6 % total exchangeable base cations or of 0.20 pH unit occurred in all seven tobacco plantation counties. Meanwhile, for one unit pH decrease, 40.3 and 28.3 mmol base cations kg⁻¹ soil were consumed in 2002 and 2012, respectively. Furthermore, the aboveground tobacco biomass harvest removed 339.23 kg base cations ha⁻¹ year⁻¹ from soil, which was 7.57 times higher than the anions removal, leading to a 12.52 kmol H⁺ production ha⁻¹ year⁻¹ as the main reason inducing soil acidification. Overall, our results showed that long-term tobacco plantation not only stimulated soil acidification but also decreased soil acid-buffering capacity, resulting in negative effects on sustainable soil uses. On the other hand, our results addressed the importance of a continuous monitoring of soil pH changes in tobacco plantation sites, which would enhance our understanding of soil fertility of health in this region.

We aimed to evaluate the properties of a novel tissue conditioner containing a surface pre-reacted glass-ionomer (S-PRG) nanofiller. Tissue conditioners containing 0 (control), 2.5, 5, 10, 20, or 30 wt% S-PRG nanofiller or 10 or 20 wt% S-PRG microfiller were prepared. The S-PRG nanofillers and microfillers were observed using scanning electron microscopy. The ion release, acid buffering capacity, detail reproduction, consistency, Shore A0 hardness, surface roughness, and Candida albicans adhesion of the tissue conditioners were examined. The results indicated that the nanofiller particles were smaller and more homogeneous in size than the microfiller particles. In addition, Al, B, F, and Sr ions eluted from S-PRG were generally found to decrease after 1 day. Acid neutralization was confirmed in a concentration-dependent manner. The mechanical properties of tissue conditioners containing S-PRG nanofiller were clinically acceptable according to ISO standard 10139-1:2018, although the surface roughness increased with increasing filler content. Conditioners with 5–30 wt% nanofiller had a sublethal effect on C. albicans and reduced fungal adhesion in vitro. In summary, tissue conditioner containing at least 5 wt% S-PRG nanofiller can reduce C. albicans adhesion and has potential as an alternative soft lining material.

BackgroundGlobally increasing atmospheric nitrogen (N) deposition has altered soil phosphorus (P) transformations and availability, and thereby influenced structure and function of terrestrial ecosystems. Edaphic characteristics and chemical form of deposited N could be important factors determining impacts of N deposition on soil P transformations, yet the underlying mechanisms remain largely unknown. Objectives of this study were to examine how mineral-N and amino N differently affect P fractions, and identify key soil properties determining N addition impacts on soil P transformations. Considering that amino N is an important component of deposited N and forest soils vary greatly in different regions, the results of present study can guide the management of forests across different soils under ongoing N deposition scenarios.MethodsWe conducted a 60-day laboratory experiment to investigate the effects of N addition (NH4NO3 and glycine) on soil P fractions and related biochemical properties in four representative forest soils (brown, yellow brown, aeolian sandy, and red soils) in China. Glycine and NH4NO3 were separately added at three rates (5, 10 and 20 g N m–2 yr–1).ResultsFirstly, the percent changes in organic P fractions with N addition were significantly greater than changes in inorganic P fractions across all soils. Secondly, the percent changes in P fractions with glycine and NH4NO3 additions were significantly correlated across all soils and treatments. However, glycine addition had significantly greater impacts on organic P fractions than NH4NO3 addition in the aeolian sandy and red soils with low organic carbon content. Thirdly, P fractions responded differently to N addition among the four soils. N-induced changes in microbial biomass and phosphatase activities, pH, exchangeable Ca2+ and Mg2+ contributed differently to the changes in P fractions with N addition in the four soils.ConclusionsThe different responses of P fractions to N addition in the four soils were mainly generated by the differences in extent of microbial N limitation, acid buffering capacity, and cation exchange capacity among the soils. The different impacts of mineral and amino N on soil P fractions can be ascribed to their divergent effects on soil pH, microbial biomass and activities.

Declining rainfall and extraction of groundwater increase the vulnerability of wetland sediments to ignition and combustion. This study investigated the existence of a unique hydrochemical porewater signal associated with organic-rich sulfidic sediments that have been overheated, dried, cracked, and burnt, by the passage of fire. Porewater was collected from wetland sediments with recent fire histories, as well as a wetland that had not suffered any type of burn in recent times (i.e. 5+ years). The results show that fire brought about elevated base cation concentrations in addition to substantial increase in oxidation of sulfidic wetland sediments, the generation of acidic porewaters, and the concomitant mobilisation of metal species. These changes were episodic in nature, varying with seasonal fluctuations of groundwater and sediment hydration and saturation, and persistent for at least several years. The seasonally episodic nature of acid generation following fire leads to the depletion of the acid-neutralising capacity of the sediments (potentially faster than would otherwise have occurred as a result of drought-induced acidification events alone) and ultimately exhausts the buffering capacity of the sediments.

The opportunistic pathogenic bacterium C. sakazakii poses a significant infection risk to infants through contaminated powdered infant formulae (PIFs) when proper hygiene and temperature control are neglected during reconstitution. This study aimed to investigate whether the acid-buffering capacity (ABC) of commercially available PIFs enriched with the probiotic strain Bifidobacterium animalis subsp. lactis (BB-12®) could influence the growth of C. sakazakii. Two PIFs differing in their ABC were reconstituted (RIF), inoculated, and incubated in monoculture and co-culture at 22 °C and 37 °C for 24 h. After 24 h of incubation at 22 °C, regardless of the ABC type of PIF, the population of C. sakazakii in the monoculture was approx. 1.4 log cycles higher than the inoculum, while, in the co-culture, the C. sakazakii count was approx. 0.34 log cycles lower. In contrast, at 37 °C during the 24 h co-culture in the lower ABC infant formula, C. sakazakii was <10 CFU/mL. In all co-culture samples, the pH was significantly lower (p < 0.05) in the PIF with the lower ABC. An analysis of the weak organic acids at 12 and 24 h of incubation revealed that the antimicrobial activity is significantly affected by the final pH value, the type of the weak organic acids, and their ionic–non-ionic ratio, which is formed through the common ion effect.

Cetaceans (dolphins and whales) are born into the aquatic environment and are immediately challenged by the demands of hypoxia and exercise. This should promote rapid development of the muscle biochemistry that supports diving, but previous research on two odontocete (toothed whales and dolphins) species showed protracted postnatal development for myoglobin content and buffering capacity. A minimum of 1 and 1.5 years were required for Fraser’s ( Lagenodelphis hosei ) and bottlenose ( Tursiops truncatus ) dolphins to obtain mature myoglobin contents, respectively; this corresponded to their lengthy 2 and 2.5-year calving intervals (a proxy for the dependency period of cetacean calves). To further examine the correlation between the durations for muscle maturation and maternal dependency, we measured myoglobin content and buffering capacity in the main locomotor muscle ( longissimus dorsi ) of harbor porpoises ( Phocoena phocoena ), a species with a comparatively short calving interval (1.5 years). We found that at birth, porpoises had 51 and 69 % of adult levels for myoglobin and buffering capacity, respectively, demonstrating greater muscle maturity at birth than that found previously for neonatal bottlenose dolphins (10 and 65 %, respectively). Porpoises achieved adult levels for myoglobin and buffering capacity by 9–10 months and 2–3 years postpartum, respectively. This muscle maturation occurred at an earlier age than that found previously for the dolphin species. These results support the observation that variability in the duration for muscular development is associated with disparate life history patterns across odontocetes, suggesting that the pace of muscle maturation is not solely influenced by exposure to hypoxia and exercise. Though the mechanism that drives this variability remains unknown, nonetheless, these results highlight the importance of documenting the species-specific physiological development that limits diving capabilities and ultimately defines habitat utilization patterns across age classes.