Microplastics in soil affect the growth and physiological characteristics of Chinese fir and Phoebe bournei seedlings.

Pot experiments were conducted using Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and Phoebe bournei (Hemsl.) Yang) to investigate whether soil microplastics adversely affect the nurturing and renewal of plantations. Microplastics composed of polyethylene and polypropylene with a size of 48 µm were used. The treatments included a control group (without microplastics) and groups treated with microplastic concentrations of 1% and 2% (w/w). The effects of microplastics on the growth, photosynthetic pigments in leaves, antioxidant systems, and osmotic regulation substances of the seedlings were analysed by measuring the seedling height, ground-line diameter growth, chlorophyll (chlorophyll a, chlorophyll b, and total chlorophyll) contents, antioxidant enzyme (superoxide dismutase, peroxidase, catalase) activities, and malondialdehyde, soluble sugar, and soluble protein levels. The results indicated that treatment with 1% polyethylene microplastics increased the chlorophyll a, total chlorophyll, and soluble protein contents in the leaves of both types of seedlings while inhibiting superoxide dismutase and peroxidase activities in P. bournei seedlings. Treatment with 2% polyethylene or polypropylene microplastics suppressed the chlorophyll a, chlorophyll b, and total chlorophyll contents; superoxide dismutase, peroxidase, and catalase activities; and soluble sugar and soluble protein levels in the leaves of both types of seedlings, resulting in reduced growth in terms of height and ground-line diameter. The physiological effects of polyethylene microplastics were more evident than those of polypropylene at the same concentration. The results demonstrated that microplastics can affect photosynthesis, the antioxidant system, and osmotic regulation in Chinese fir and P. bournei seedlings, thereby inhibiting their normal growth and development. Exposure to 1% (w/w) microplastics triggered stress responses in seedlings, whereas 2% (w/w) microplastics impeded seedling growth.

Nutrient enrichment, propagule pressure, and herbivory interactively influence the competitive ability of an invasive alien macrophyte Myriophyllum aquaticum.

Introduction: Freshwater ecosystems are susceptible to invasion by alien macrophytes due to their connectivity and various plant dispersal vectors. These ecosystems often experience anthropogenic nutrient enrichment, favouring invasive species that efficiently exploit these resources. Propagule pressure (reflecting the quantity of introduced individuals) and habitat invasibility are key determinants of invasion success. Moreover, the enemy release hypothesis predicts that escape from natural enemies, such as herbivores, allows alien species to invest more resources to growth and reproduction rather than defense, enhancing their invasive potential. Yet, the combined impact of propagule pressure, herbivory, and nutrient enrichment on the competitive dynamics between invasive alien macrophytes and native macrophyte communities is not well understood due to a paucity of studies. Methods: We conducted a full factorial mesocosm experiment to explore the individual and combined effects of herbivory, nutrient levels, propagule pressure, and competition on the invasion success of the alien macrophyte Myriophyllum aquaticum into a native macrophyte community comprising Vallisneria natans, Hydrilla verticillata, and Myriophyllum spicatum. This setup included varying M. aquaticum densities (low vs. high, simulating low and high propagule pressures), two levels of herbivory by the native snail Lymnaea stagnalis (herbivory vs no-herbivory), and two nutrient conditions (low vs. high). Myriophyllum aquaticum was also grown separately at both densities without competition from native macrophytes. Results: The invasive alien macrophyte M. aquaticum produced the highest shoot and total biomass when simultaneously subjected to conditions of high-density intraspecific competition, no herbivory, and low-nutrient availability treatments. Moreover, a high propagule pressure of M. aquaticum significantly reduced the growth of the native macrophyte community in nutrient-rich conditions, but this effect was not observed in nutrient-poor conditions. Discussion: These findings indicate that M. aquaticum has adaptive traits enabling it to flourish in the absence of herbivory (supporting the enemy release hypothesis) and in challenging environments such as intense intraspecific competition and low nutrient availability. Additionally, the findings demonstrate that when present in large numbers, M. aquaticum can significantly inhibit the growth of native macrophyte communities, particularly in nutrient-rich environments. Consequently, reducing the propagule pressure of M. aquaticum could help control its spread and mitigate its ecological impact. Overall, these findings emphasize that the growth and impacts of invasive alien plants can vary across different habitat conditions and is shaped by the interplay of biotic and abiotic factors.

Nitrogen addition increases topsoil carbon stock in an alpine meadow of the Qinghai-Tibet Plateau.

Soil carbon (C) sequestration plays a critical role in mitigating climate change. Nitrogen (N) deposition greatly affects soil C dynamics by altering C input and output. However, how soil C stocks respond to various forms of N input is not well clear. This study aimed to explore the impact of N addition on soil C stock and to elucidate the underlying mechanisms in an alpine meadow on the eastern Qinghai-Tibet Plateau. The field experiment involved three N application rates and three N forms, using a non-N treatment as a control. After six years of N addition, the total C (TC) stocks in the topsoil (0-15 cm) were markedly increased by an average of 12.1 %, with a mean annual rate of 20.1 ‰, and no difference was found between the N forms. Irrespective of rate or form, N addition significantly increased the topsoil microbial biomass C (MBC) content, which was positively correlated with mineral-associated and particulate organic C content and was identified as the most important factor that affecting the topsoil TC. Meanwhile, N addition significantly increased the aboveground biomass in the years with moderate precipitation and relatively high temperature, which leads to higher C input into soils. Owing to decreased pH and/or activities of ß-1,4-glucosidase (ßG) and cellobiohydrolase (CBH) in the topsoil, organic matter decomposition was most likely inhibited by N addition, and this inhibiting effect varied under different N forms. Additionally, TC content in the topsoil and subsoil (15-30 cm) exhibited parabolic and positive linear relationship with the topsoil dissolved organic C (DOC) content, respectively, indicating that DOC leaching might be an important influencing factor for soil C accumulation. These findings improve our understanding of how N enrichment affects C cycles in alpine grassland ecosystems and suggest that soil C sequestration in alpine meadows probably increases with N deposition.

Soil bacterial community is more sensitive than fungal community to canopy nitrogen deposition and understory removal in a Chinese fir plantation.

Soil microorganisms are key regulators for plant growth and ecosystem health of forest ecosystem. Although previous research has demonstrated that soil microorganisms are greatly affected by understory nitrogen (N) addition, little is known about the effects of canopy N addition (CNA) and understory management on soil microorganisms in forests. In this study, we conducted a full designed field experiment with four treatments: CNA (25 kg N ha-1 year-1), understory removal (UR), canopy N addition, and understory removal (CNAUR) (25 kg N ha-1 year-1), and control in a Chinese fir plantation. High-throughput sequencing and qPCR techniques were used to determine the abundance, diversity, and composition of bacterial and fungal communities in three soil layers. Our results showed that CNA increased bacterial diversity in the 10-20 cm soil layer but decreased bacterial abundance in the 20-40 cm soil layer and fungal diversity in the 0-10 cm soil layer. UR increased bacterial abundance only in the 20-40 cm soil layer. CNA, not UR significantly altered the compositions of soil bacterial and fungal community compositions, especially in the 0-20 cm soil layer. CNA sharply reduced the relative abundance of copiotrophic taxa (i.e., taxa in the bacterial phylum Proteobacteria and the orders Eurotiales and Helotiales in the fungal phylum Ascomycota) but increased the relative abundance of oligotrophic taxa (i.e., in the bacterial phylum Verrucomicrobia). RDA analysis revealed that soil pH, DON, and DOC were the main factors associated with the variation in bacterial and fungal communities. Our findings suggest that short-term CNA changes both soil bacterial and fungal communities, with stronger responses in the surface and middle soil than in the deep soil layer, and that UR may enhance this effect on the soil bacterial abundance. This study improves our understanding of soil microorganisms in plantations managed with understory removal and that experience increases in N deposition.

Nitrogen-Induced Changes in Soil Environmental Factors Are More Important Than Nitrification and Denitrification Gene Abundance in Regulating N2O Emissions in Subtropical Forest Soils.

Subtropical regions are currently experiencing a dramatic increase in nitrogen (N) deposition; however, the contributions of nitrification and denitrification processes to soil N2O emissions and the underlying mechanisms under increasing N deposition remain unclear. Therefore, a 15N-tracing laboratory experiment with four N application rates (0, 12.5, 25, and 50 µg 15N g-1 soil) was conducted to investigate the response of nitrification- and denitrification-derived N2O to N additions in an evergreen broad-leaved forest (BF) and a Pinus forest (PF) in the Wuyi Mountains in southeastern China. Moreover, the abundance of functional genes related to nitrification (amoA), denitrification (nirK, nirS, and nosZ), and soil properties were measured to clarify the underlying mechanisms. Results showed that nitrification-derived N2O emissions were generally decreased with increasing N input. However, denitrification-derived N2O emissions were a non-linear response to N additions, with maximum N2O emissions at the middle N application rate. Denitrification-derived N2O was the dominant pathway of N2O production, accounting for 64 to 100% of the total N2O fluxes. Soil NH4 +-N content and pH were the predominant factors in regulating nitrification-derived N2O emissions in BF and PF, respectively. Soil pH and the nirS abundance contributed the most to the variations of denitrification-derived N2O emissions in BF and PF, respectively. Our results suggest that N application has the potential to increase the contribution of denitrification to N2O production in subtropical forest soils. Changes in soil chemical properties induced by N addition are more important than the abundance of nitrification and denitrification functional genes in regulating soil nitrification- and denitrification-derived N2O emissions.

How does Confucian culture affect technological innovation? Evidence from family enterprises in China.

Culture is one of the crucial elements of technological innovation. The existing studies hold that Confucian culture is conducive to the technological innovation of Chinese Listed Companies. However, Chinese family enterprises with relatively profound Confucianism encounter the bottleneck of weak innovation. This makes people wonder whether Confucian culture is conducive to the technological innovation of family enterprises. To solve this mystery, we investigated the effects of Chinese Confucianism on technological innovation in Chinese family enterprises. We found that family entrepreneur's entrepreneurship had worse innovation performance under the influence of Confucian culture. The results are robust to different measures of innovation and are still valid when controlling for the potential endogeneity between Confucian culture and technological innovation. This study provides a more fine-grained perspectives about Chinese innovation culture.

Changes in the stoichiometry of Castanopsis fargesii along an elevation gradient in a Chinese subtropical forest.

Elevation is important for determining the nutrient biogeochemical cycle in forest ecosystems. Changes in the ecological stoichiometry of nutrients along an elevation gradient can be used to predict how an element cycle responds in the midst of global climate change. We investigated changes in concentrations of and relationships between nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in the leaves and roots of the dominant tree species, Castanopsis fargesii, along an elevation gradient (from 500 to 1,000 m above mean sea level) in a subtropical natural forest in China. We analyzed correlations between C. fargesii's above-ground biomass and stoichiometry with environmental factors. We also analyzed the soil and plant stoichiometry of this C. fargesii population. Our results showed that leaf N decreased while leaf K and Ca increased at higher elevations. Meanwhile, leaf P showed no relationship with elevation. The leaf N:P indicated that C. fargesii was limited by N. Elevation gradients contributed 46.40% of the total variance of ecological stoichiometry when assessing environmental factors. Our research may provide a theoretical basis for the biogeochemical cycle along with better forest management and fertilization for this C. fargesii population.

Estimation of Soil Organic Carbon Storage in Palustrine Wetlands, China.

Wetlands regulate the balance of global organic carbon. Small changes in the carbon stocks of wetland ecosystem play a crucial role in the regional soil carbon cycle. However, an accurate estimation of carbon stocks is still be debated for China's wetlands ecosystem due to the limitation of data collection and methodology. Here, we investigate the soil organic carbon (SOC) storage in a 1-m depth in China's palustrine wetlands. A total of 1383 sample data were collected from palustrine wetlands in China. The data sources are divided into three parts, respectively, data collection from published literature, data from books, and actual measurement data of sample points. The results demonstrate that there is considerable SOC storage in China's palustrine wetlands (9.945 Pg C), primarily abundant in the northeast, northwest arid and semi-arid as well as Qinghai-Tibet Plateau regions. The SOC density in per unit area soil was higher in the wetland area of northeast, southwest and Qinghai-Tibet plateau. Within China terrestrial scale, the temperature and precipitation differences caused by latitude were the main environmental factors affecting the organic carbon content. Furthermore, except for the southeast and south wetland region, SOC content decreased with depth.

Effects of land use change from natural forest to plantation on C, N and natural abundance of 13C and 15N along a climate gradient in eastern China.

Soil C and N turnover rates and contents are strongly influenced by climates (e.g., mean annual temperature MAT, and mean annual precipitation MAP) as well as human activities. However, the effects of converting natural forests to intensively human-managed plantations on soil carbon (C), nitrogen (N) dynamics across various climatic zones are not well known. In this study, we evaluated C, N pool and natural abundances of δ13C and δ15N in forest floor layer and 1-meter depth mineral soils under natural forests (NF) and plantation forest (PF) at six sites in eastern China. Our results showed that forest floor had higher C contents and lower N contents in PF compared to NF, resulting in high forest floor C/N ratios and a decrease in the quality of organic materials in forest floor under plantations. In general, soil C, N contents and their isotope changed significantly in the forest floor and mineral soil after land use change (LUC). Soil δ13C was significantly enriched in forest floor after LUC while both δ13C and δ15N values were enriched in mineral soils. Linear and non-linear regressions were observed for MAP and MAT in soil C/N ratios and soil δ13C, in their changes with NF conversion to PF while soil δ15N values were positively correlated with MAT. Our findings implied that LUC alters soil C turnover and contents and MAP drive soil δ13C dynamic.

Recommended nitrogen fertilization enhances soil carbon sequestration in China's monsoonal temperate zone.

China consumes more than one-third of the world's nitrogen (N) fertilizer, and an increasing amount of N fertilizer has been applied over the past decades. Although N fertilization can increase the carbon sequestration potentials of cropland in China, the quantitative effects of different N fertilizer application levels on soil carbon changes have not been evaluated. Therefore, a 12-year cultivation experiment was conducted under three N fertilizer application levels (no N fertilizer input, the recommended N fertilizer input after soil testing, and the estimated additional fertilizer input) to estimate the effect of N addition on soil carbon changes in the root layer (0-80 cm) and non-root layer (80-200 cm) using a within-study meta-analysis method. The results showed significant declines in the soil inorganic carbon (SIC) in the root layers and significant growth in the SIC in the non-root layers under N fertilizer input. The soil organic carbon (SOC) in the root layers and the non-root layer significantly decreased under all the treatments. In addition, the recommended N fertilizer application level significantly increased the SOC and soil total carbon stocks compared with the future N fertilizer application level and no N input, while the future N fertilization significantly decreased the SIC and soil total carbon compared with no N input. The results suggest that N fertilization can rearrange the soil carbon distribution over the entire soil profile, and the recommended N fertilization rather than excess N input can increase the soil carbon stock, which suggests that the national soil testing program in China can improve the soil carbon sequestration potential.