Amount and characteristics of microplastic and organic matter in wind-blown sediment at different heights within the aeolian sand saltation layer.

Soils of croplands especially where plastic film mulch is commonly applied, are normally contaminated by Microplastics (MPs). Microplastics can threaten air quality, food and water health, as well as human health by wind erosion processes. In this research, we investigated MPs collected in four wind erosion events at sampling heights between 0 and 60 cm in typical semiarid farmlands in northern China that employ plastic film mulch. Height distribution and enrichment heights of the MPs were measured. The results revealed that the average amounts of MPs for 0-20 cm, 20-40 cm and 40-60 cm sampling heights were 868.71 ± 249.21, 799.87 ± 271.25, 1102.54 ± 317.44 particles kg-1. The average enrichment ratios of MPs for the different heights were 0.89 ± 0.54, 0.85 ± 0.56, 1.15 ± 0.73. Height distribution of MPs was combined affected by shape (fiber and non-fiber) and size of MPs, wind speed and soil aggregate stability. The amount of fibers approximately <4 mm in size and non-fibers <2 mm in size increased with sampling height, while both shapes of larger MPs than these two sizes was almost independent of the sampling height. Enrichment ratios of microfibers were positively related to wind speed but negatively related to soil aggregate stability at each sampling height. The results revealed that although MPs have similar density to organic matter (OM), the MPs' amount and enrichment were independent of height but the OM content and enrichment ratios increased with height. These results suggested that more attention should be paid to the exploration of the influence of higher sampling heights (>60 cm) on the distribution of MPs in the future and the MPs characteristics for different sampling heights require carefully parameterization in detailed models of atmospheric MPs transport by wind erosion.

Wind erosion induced low-density microplastics migration at landscape scale in a semi-arid region of northern China.

Microplastics (MPs) have been extensively investigated in terrestrial environments, while the occurrence and movement of MPs at the landscape scale in semi-arid regions with serious wind erosion are less well studied. Here, we sampled film mulching farmland and downwind nearby grassland surface soils in a semi-arid region of northern China to explore the distribution of MPs at different downwind distances and the potential environmental risk to the local landscapes. The results revealed that the MP abundances presented a decreasing trend with increasing downwind distance (Mann-Kendall test, P < 0.01). The MP size distributions at different distances showed similar sigmoid trends described by logistic models. MP fiber size (500-2000 µm) abundance in the farmland was higher than that of the grassland. By contrast, MP non-fiber size (<1000 µm) abundance of farmlands was less than that of the grassland. The abundances of fibers larger than 500 µm and non-fibers larger than 1000 µm in size decreased exponentially with increasing downwind distance. The size of transported MPs at the landscape scale was larger than that of long-distance dispersal. The migration of MPs from farmlands can pose a potential threat to the downwind landscape, leading the downwind grassland to be a potential MP emission source. This study presents the first insights into the MPs distribution among different downwind distances at the landscape scale. Future research is required to deploy aeolian sediment sampling devices and establish the connection between the field data and the MP emission models.

Regional Potential Wind Erosion Simulation Using Different Models in the Agro-Pastoral Ecotone of Northern China.

Wind erosion is crucial for assessing regional ecosystem services and sustainable development. The Agro-Pastoral Ecotone of northern China (APEC) is a typical region undergoing wind erosion and soil degradation. In this study, the National Wind Erosion Survey Model of China, the Integrated Wind Erosion Modeling System, and the regional versions of the Revised Wind Erosion Equation and Wind Erosion Prediction System were used to evaluate the regional potential wind erosion of the APEC during 2000 and 2012. The results showed that the potential wind erosion predicted by National Wind Erosion Survey Model of China (NWESMC), Revised Wind Erosion Equation (RWEQ), Wind Erosion Prediction System (WEPS), and Integrated Wind Erosion Modeling System (IWEMS) were significantly related to the observed wind erosion collected from published literature, but the observed data were generally smaller than the predicted values. The average potential wind erosions were 12.58, 25.87, 52.63, and 58.72 t hm-2 a-1 for NWESMC, RWEQ, WEPS, and IWEMS, respectively, while the spatial pattern and temporal trend of annual potential wind erosion were similar for different wind erosion models. Wind speed, soil moisture, and vegetation coverage were the dominant factors affecting regional wind erosion estimation. These results highlight that it is necessary to comprehensively calibrate and validate the selected wind erosion models. A long-term standard wind erosion monitoring network is urgently required. This study can serve as a useful reference for improving wind erosion models.

Beneficial effects of warming on temperate tree carbon storage depend on precipitation and mycorrhizal types.

Despite evidence from multiple observation data sets and numerical model simulations that interactions between biotic and abiotic factors control tree carbon (C) storage in the Northern Hemisphere, it remains unclear whether the effect of one factor will be altered by other factors. Here, we used forest inventory data consisting of more than 500,000 trees from 1910 plots to explore the relative importance of these drivers of plant C storage in northeast China. We found that tree C storage was significantly positively associated with mean annual temperature (MAT). After controlling for the role of mean annual precipitation (MAP), directionality in the tree C storage-MAT relationship reversed, indicating that the direction of MAT affecting tree C storage depends on MAP. Accounting for the effects of tree-fungal symbioses on plant resistance to drought and warming, we found that warming increased AM tree C storage even after controlling the role of MAP, but decreased EcM tree C storage after controlling the role of MAP. Our analysis also shows that species richness, especially the relative richness of AM tree species, had a significantly positive relationship with all types of tree C storage. Our findings have implications for improving temperate forest C sink and afforestation strategies: the increasing richness of AM trees has the potential to enhance the tree C sink and reduce the sensitivity of warming-induced tree growth benefits to changes in precipitation.

Plastic mulch film induced soil microplastic enrichment and its impact on wind-blown sand and dust.

Microplastics (MPs) pollution is being increasingly recognized as a global concern in all environments. Wind-blown sand and dust contaminated by MPs are an important pathway of MPs transport across different environments, which can result in on-site and off-site potential MP pollution. Here, we designed field experiments to detect MPs in surface soil and wind-blown sand and dust in farmlands with and without film mulch in a semi-arid region of northern China. This study provides the first insights into MPs enrichment in wind-blown sand and dust deposited by natural storms. The results reveal that fibers, fragments, and films constitute the major types of MPs in farmland soil and wind-blown sand and dust. The MPs abundances of 1-3 mm, <1 mm, and 3-5 mm items kg-1 successively decrease. The enrichment of MPs in wind-blown dust is one to two orders of magnitude higher than that in wind-blown sand. For the farmlands with (without) film mulch, the MPs enrichment ratios ranged from 0.22 (0.29) to 1.35 (2.26) in the wind-blown sand and that varied from 1.79 (1.01) to 16.6 (25.79) in the wind-blown dust. Fibers are preferentially transported by wind erosion compared to fragments and films. Soil aggregating processes, wind speed, and MPs shape may influence enrichment in wind-blown sand and dust. Film mulch debris and the application of manure may be the primary sources of MPs in farmland soils. This study further highlights the importance of the transport of airborne MPs from surface soil into the atmosphere. Future research is required to establish the quantitative relationships between the MPs shape, wind speed, and surface soil properties and the MPs enrichment in wind-blown sand and dust.

Comment on "Impacts of species richness on productivity in a large-scale subtropical forest experiment".

Huang et al (Reports, 5 October 2018, p. 80) report significant increases in forest productivity from monocultures to multispecies mixtures in subtropical China. However, their estimated productivity decrease due to a 10% tree species loss seems high. We propose that including species richness distribution of the study forests would provide more meaningful estimates of forest-scale responses.

[Characteristics of soil seed banks in logging gaps of forests at different succession stages in Changbai Mountains].

An investigation was made on the soil seed banks in the logging gaps of Populus davidiana--Betula platyphylla secondary forest, secondary broad-leaved forest, and broad-leaved Korean pine mixed forest at their different succession stages in Changbai Mountains. Among the test forests, secondary broad-leaved forest had the highest individual density (652 ind x m(-2)) in its soil seed bank. With the succession of forest community, the diversity and uniformity of soil seed bank increased, but the dominance decreased. The seed density of climax species such as Pinus koraiensis, Abies nephrolepis, and Acer mono increased, whereas that of Maackia amurensis and Fraxinus mandshurica decreased. Moreover, the similarity in species composition between soil seed bank and the seedlings within logging gaps became higher. The individual density and similarity between soil seed bank and the seedlings in non-logging gaps were similar to those in logging gaps. All of these indicated that soil seed bank provided rich seed resources for forest recovery and succession, and the influence of soil seed bank on seedlings regeneration increased with the succession.

[Biodiversity of tree species, their populations' spatial distribution pattern and interspecific association in mixed deciduous broadleaved forest in Changbai Mountains].

Based on the data collected from the sampling plot with an area of 1 hm2 at the Experimental and Management Bureau of Jiaohe in Jilin Province, this paper analyzed and researched the community structure, biological diversity, spatial distribution pattern and interspecific association between tree species populations in a mixed deciduous broadleaved forest. The results indicated that there was no obvious dominant order among tree species populations, and the indices of tree species diversity such as Shannon-Wiener index (H'), Pielou evenness index (E) and Simpson ecological dominant index (D) were all low. Shrub and herb species diversity indices were also not high. The spatial distribution pattern of five dominant tree species all presented aggregative. Based on 2 x 2 contigency table, the interspecific associations of 15 tree species in the community were examined by means of chi2-test, together with the association coefficient (AC). The results showed that there were 14 species pairs in 15 species showing significantly negative association. The proportion of species pairs showing negative association was much more than that of showing positive association. It could be deduced that the community was instable and at the stage of autogenic succession from soft deciduous broadleaved forest to hard deciduous broadleaved forest, and then, the Korean pine broadleaved forest.