With the continuation of industrialization and urbanization, acid rain (AR) has aroused extensive concern because of its potential negative effects on ecosystems. However, analysis of the current status and development trends in AR research area has seldom been systematically studied. Therefore, we motivated to conduct a bibliometric analysis of AR publications (1900–2018) using HistCite and CiteSpace software programs. Compared to traditional reviews by experts, this study offers an alternative method to quantitatively analyze and visualize the development of AR field at a large time scale. The results indicated that the overall concern of AR research studies had increased from 1900 to 2018. The most productive country was the United States, while the institution with the most publications was Chinese Academy of Sciences. “Environmental Sciences” was the most popular subject category, Water, Air, and Soil Pollution was the dominant journal, and C.T. Driscoll was the most prominent author in AR field. There were three hotspots in the field of AR, including analyzing AR status and its control policies in Europe, the United States, and China in the past few decades, investigating the ecological consequences of AR on plant histological, physiological, and biochemical traits, as well as surface water and soil properties, and the model application for quantitatively assessing AR and its effects on terrestrial and aquatic ecosystems at regional scale. Further, “behavior”, “phosphorus”, “fractionation”, “soil acidification”, “corrosion”, “performance”, “recovery”, “rainwater”, “trace element”, and “surface water” have been emerging active topics in recent years. This study can help new researchers to find out the most relevant subject categories, countries, institutions, journals, authors, and articles, and identify research trends and frontiers in the field of AR.

Soil acidification is a global environmental issue that decreases soil functions, and it has been significantly accelerated by anthropogenic activities in recent decades. Soils can resist acidification upon receiving acid inputs due to the resistance or/and resilience capacity of soils, which is termed the acid buffering capacity of soils, and it is often indicated by the soil pH buffering capacity (pHBC). An increasing number of studies have been conducted to quantify soil pHBC at various sites, but to date, integration of global data is lacking; therefore, the variations in large-scale soil pHBC and the factors that influence these variations are still unclear. In this study, we collected previously published data on soil pHBC to analyze its variations on a large scale, as well as investigate the underlying factors influencing these variations. The results showed that soil pHBC varied substantially from site to site, with a mean of 51.07 ± 50.11 mmol kg⁻¹ pH⁻¹. Soil texture and pH, separately or collectively, explained a considerable proportion of the total variation of global soil pHBC. It is well-established that a series of processes contribute to the soil acid buffering capacity in different pH ranges, and the global data analyses showed that pH 5.5 could be a key threshold value; different buffering systems may be active at pH > 5.5 and pH < 5.5. Moreover, tropical soils were more acid-sensitive than temperate and subtropical soils, and forest soils had significantly lower soil pHBCs than grassland and cropland soils. This could be attributed in part to the different soil properties, such as soil texture or pH, among the different climatic zones and ecosystems.

Acid rain (AR), as a global environmental threat, has profoundly adverse effects on natural soil ecosystems. Microorganisms involved in the nitrogen (N) cycle regulate the global N balance and climate stabilization, but little is known whether and how AR influences the structure and complexity of these microbial communities. Herein, we conducted an intact soil core experiment by manipulating the acidity of simulated rain (pH 7.5 (control, CK) vs. pH 4.0 (AR)) in subtropical agricultural soil, to reveal the differences in the structure and complexity of soil nitrifying and denitrifying microbiota using Illumina amplicon sequencing of functional genes (amoA, nirS, and nosZ). Networks of ammonia-oxidizing archaea (AOA) and nirS-carrying denitrifiers in AR treatment were less complex with fewer nodes and lower connectivity, while network of nosZ-carrying denitrifiers in AR treatment had higher complexity and connectivity relative to CK. Supporting this, AR reduced the abundance of keystone taxa in networks of AOA and nirS-carrying denitrifiers, but increased the abundance of keystone taxa in nosZ-carrying denitrifiers network. However, AR did not alter the community structure of AOA, ammonia-oxidizing bacteria (AOB), nirS-, and nosZ-carrying denitrifiers. Moreover, AR did not change soil N₂O emissions during the experimental period. AOB community structure significantly correlated with content of soil available phosphorus (P), while the community structures of nirS- and nosZ-carrying denitrifiers both correlated with soil pH and available P content. Soil N₂O emission was mainly driven by the nirS-carrying denitrifiers. Our results present new perspective on the impacts of AR on soil N-cycle microbial network complexity and keystone taxa in the context of global changes.

The earthworm, as a soil engineer, plays highly important roles in the soil ecosystem for shaping soil structure, promoting soil fertility, regulating microbial community composition and activities and decomposing soil pollutants. However, the research progresses on this important soil fauna have rarely been reviewed so far. Therefore, we conducted a bibliometric analysis of the literature published during 1900–2022, which was collected from the Web of Science Core Collection (WoS). The results showed that three periods (1900–1990, 1991–2005 and 2006–2022) could be identified in terms of the intensity of publications on the topic, and the number of publications kept increasing since 2006. The United States produced the highest publication record at the country scale, whereas Chinese Academy of Sciences was the most productive institution. Chinese institutions and authors played an active and prominent role during 2018–2022. Soil Biology & Biochemistry was the most popular journal for the topic-related research. In these publications, Professor Lavelle P was the most influential author. Based on a citation network of the top 50 cited papers, four hotspots were identified, i.e., the ecological effects of earthworms, the impact of agricultural activities on earthworms, earthworm ecotoxicology and earthworm invasion. Moreover, “impact”, “biodiversity”, “oxidative stress”, “diversity”, “response”, “Eisenia fetida” and “exposure” were the emerging and active topics in recent years. This study can help us to better understand the relevant subject categories, journals, countries, institutions, authors and articles and identify the research hotspots and emerging trends in the field of soil earthworm research.

Microplastic (MP) pollution has raised global concerns, and biodegradable plastics have been recommended to replace conventional ones. The “plastisphere” has been considered a hotspot for the interactions among organisms and environments, but the differences in the properties of soil microbial communities in the plastisphere of conventional and biodegradable MPs remain unclear. This in situ experiment was conducted to compare the diversity and structure of the bacterial community in the plastisphere of conventional MPs (polyethylene [PE]) and biodegradable MPs (polylactic acid [PLA]) in vegetable fields, orchards, paddy fields, and woodlands. It was discovered that the bacterial α-diversity within the plastisphere was significantly lower than that in the soil across all land use. Significant differences between plastic types were only found in the vegetable field. Regarding the community composition, the relative abundances of Actinobacteriota (43.2%) and Proteobacteria (70.9%) in the plastisphere were found to exceed those in the soil, while the relative abundances of Acidobacteriota (45.5%) and Chloroflexi (27.8%) in the soil were significantly higher. The complexity of the microbial network within the plastisphere was lower than that of the soil. Compared with the soil, the proportion of dispersal limitation in the PLA plastisphere significantly decreased, with the greatest reduction observed in the vegetable field treatment, where it dropped from 57.72% to 3.81%. These findings indicate that different land use types have a greater impact on bacterial community diversity and structure than plastics themselves, and that biodegradable MPs may pose a greater challenge to the ecological function and health of soil ecosystems than conventional MPs.

Long-term continuous cropping in cotton fields of Southern Xinjiang has limited crop productivity. To investigate how subsoiling depth regulates ecosystem-level water partitioning and thereby enhances water productivity mechanisms, a two-year field experiment was conducted in a mulched drip irrigation cotton field in Southern Xinjiang. Using a non-subsoiled field in the current season (CT) as the control, three subsoiling depths were established: subsoiling at 30 cm (ST1), 40 cm (ST2), and 50 cm (ST3). Changes in evapotranspiration partitioning and water use efficiency were analyzed. The results showed that subsoiling enhanced the utilization of deep soil water. Compared with CT, the ST2 and ST3 treatments significantly reduced soil water storage in the 0–60 cm layer during the flower opening to boll-setting stages, while soil water consumption increased by 26.4 mm and 28.8 mm, respectively. We demonstrate that subsoiling depth exerts a predominant control on the partitioning of evapotranspiration. Increasing subsoiling depth systematically shifted water loss from non-productive soil evaporation to productive plant transpiration, with the ST2 and ST3 treatments decreasing seasonal soil evaporation by 24.1% and 25.1%, respectively, and increasing plant transpiration by 21.9% and 22.8%, and lowering the Es/ET (where Es is soil evaporation and ET is evapotranspiration) ratio by 22.1% and 27.1%. However, this maximal physiological water-saving did not yield the optimal agronomic return. We established a non-linear relationship in which the ST2 treatment uniquely achieved the maximum seed cotton yield, WUE (water use efficiency), and IWUE (irrigation water use efficiency) (increasing by up to 34.4%, 17.2%, and 23.4%, respectively). This optimal depth better balances water resource allocation and reproductive growth. We conclude that under sandy loam soil conditions in typical mulched drip-irrigated cotton areas of Southern Xinjiang, implementing an optimal subsoiling depth (40 cm) can engineer a more resilient soil–plant–water continuum, providing a feasible pathway toward enhancing water and crop production sustainability.