Quantifying the characteristics of particulate matters captured by urban plants using an automatic approach

It is widely accepted that urban plant leaves can capture airborne particles. Previous studies on the particle capture capacity of plant leaves have mostly focused on particle mass and/or size distribution. Fewer studies, however, have examined the particle density, and the size and shape characteristics of particles, which may have important implications for evaluating the particle capture efficiency of plants, and identifying the particle sources. In addition, the role of different vegetation types is as yet unclear. Here, we chose three species of different vegetation types, and firstly applied an object-based classification approach to automatically identify the particles from scanning electron microscope（SEM）micrographs. We then quantified the particle capture efficiency, and the major sources of particles were identified. We found（1） Rosa xanthina Lindl（shrub species） had greater retention efficiency than Broussonetia papyrifera（broadleaf species） and Pinus bungeana Zucc.（coniferous species）, in terms of particle number and particle area cover.（2） 97.9% of the identified particles had diameter ≤10 μm, and 67.1% of them had diameter ≤2.5 μm. 89.8% of the particles had smooth boundaries, with 23.4% of them being nearly spherical.（3） 32.4%–74.1% of the particles were generated from bare soil and construction activities, and 15.5%–23.0% were mainly from vehicle exhaust and cooking fumes.

High rodent abundance increases seed removal but decreases scatter-hoarding and seedling recruitment along an elevational gradient

The distributions of small rodents in mountainous environments across different elevations can provide important information regarding the effects of climate change on the dispersal of plant species.However,few studies of oak forest ecosystems have compared the elevational patterns of sympatric rodent diversity,seed dispersal,seed bank,and seedling abundance.Thus,we tested the differences in the seed disperser composition and abundance,seed dispersal,seed bank abundance,and seedling recruitment for Quercus wutaishanica along 10 elevation levels in the Taihang Mountains,China.Our results provide strong evidence that complex asymmetric seed dispersal and seedling regeneration exist along an elevational gradient.The abundance of rodents had a significant negative correlation with the elevation and the seed removal rates peaked and then declined with increasing elevation.The seed removal rates were higher at middle and lower elevations than higher elevations but acorns were predated by 5 species of seed predators at middle and lower elevations,and thus,there was a lower likelihood of recruitment compared with those dropped beneath mother oaks at higher elevations.More importantly,the number of individual seeds in the seed bank and seedlings increased with the elevation,although dispersal services were reduced at sites lacking rodents.As conditional mutualists,the rodents could possibly act as antagonistic seed predators rather than mutualistic seed dispersers at low and middle elevations,thereby resulting in the asymmetric pattern of rodent and seedling abundance with increasing elevation to affect the community assembly and ecosystem functions on a large spatial scale.

The effect of land use structure on the distribution of soil nutrients in the hilly area of the Loess Plateau,China

The irrational land use is one of the main reasons for the soil erosion and nutrient loss in the loess hilly area of China. In this project, 4 types of typical land use structure of sustain ment for about 15 years in the loess hill slope are selected to study the effect of land use structure on the distribution of soil nutrients. From hill bottom to hill top, the patterns of land use types are:, grassland-slope farmland-forest, slope farmland-grassland-forest, terrace-grassland-forest and slope farmland-forest-grassland. By measuring the contents of the total N, total P, available N, available P and organic matter of soils, the results show that the land use structure types of slope farmland-grassland-forest and terrace-grassland-forest have a better capacity to maintain the soil nutrients.

Contrasting elevational diversity patterns for soil bacteria between two ecosystems divided by the treeline

Above- and below-ground organisms are closely linked, but how elevational distribution pattern of soil microbes shifting across the treeline still remains unknown. Sampling of 140 plots with transect, we herein investigated soil bacterial distribution pattern from a temperate forest up to a subalpine meadow along an elevational gradient using Illumina sequencing. Our results revealed distinct elevational patterns of bacterial diversity above and below the treeline in responding to changes in soil conditions:a hollow elevational pattern in the forest(correlated with soil temperature, pH, and C:N ratio) and a significantly decreasing pattern in the meadow(correlated with soil pH, and available phosphorus). The bacterial community structure was also distinct between the forest and meadow, relating to soil pH in the forest and soil temperature in the meadow. Soil bacteria did not follow the distribution pattern of herb diversity, but bacterial community structure could be predicted by herb community composition. These results suggest that plant communities have an important influence on soil characteristics, and thus change the elevational distribution of soil bacteria. Our findings are useful for future assessments of climate change impacts on microbial community.

Effects of plant coverage on shrub fertile islands in the Upper Minjiang River Valley

The patchy distribution of vegetation in dry land results in well-documented "fertile islands". However, the response of shrub fertile islands to plant recovery and the underlying mechanisms, such as the linkage plant and soil properties, remain unknown.We sampled soils from areas with three different plant coverages(25%, 45%, and 75%) and three of their adjacent inter-plants to investigate soil physicochemical and microbial properties in the upper Minjiang River arid valley. The results showed that these factors were influenced by the persistence of plants that contrasted with the inter-plant interspaces. We found fertile islands in under-plant soil that were enhanced with increasing plant coverage, from 25% to 45% and 75%; however, there were no significant differences between 45% and 75% plant coverage apart from the soil clay content and the fungi to bacteria ratio. The soil microbial communities in under-plant soil were strongly influenced by the total soil carbon(TC), soil organic carbon(SOC),and available nitrogen(AN), whereas the microbial communities in inter-plant soil were primarily constrained by the AN and available phosphorous(AP). Moreover, the inter-plant soil properties, including gravimetric soil water content, pH, electrical conductivity(EC), and soil C:N ratio, were also strongly influenced by adjacent vegetation, which suggested that fertile islands may be beneficial for plant recovery in this region.

Spatial heterogeneity of urban soils:the case of the Beijing metropolitan region,China

Introduction:Urban soils are large pools of carbon,nitrogen,and other elements,supporting plant growth,sustaining biogeochemical cycles,and serving as the foundation for maintaining ecosystem function and services of urban green spaces(UGS).Quantifying urban soil properties is essential for assessing urban ecosystem services and detecting pollution.Characterizing spatial heterogeneity of urban soil properties,which may change with land use or urbanization,is crucial for understanding urban ecosystem functions.Methods:We collected 466 soil composite samples across the Beijing metropolitan region and then analyzed the heterogeneity of soil properties in UGS of Beijing metropolitan region by ANOVA along the urbanization gradient spanning different land uses.Results:Our results show that soil properties vary considerably among land-use types and along the urban-rural gradient.Soil moisture content,soil organic carbon(SOC),available phosphorus,available potassium,total nitrogen(TN),the ratio of SOC:TN(C/N),Pb,and Cu increased notably from suburbs to the urban core,while soil pH,bulk density,TN,Cr,Ni,and Mn were not significantly different across urbanization levels.Most soil properties,except soil TN,Cu,Cr,Ni,exhibited significant differences between different land uses.The highest levels of soil nutrients and heavy metals were found in roadsides and residential areas among all the land uses.Conclusions:The spatial heterogeneity of urban soils in the Beijing metropolitan region is mainly attributable to the different land uses.Soil nutrient content has increased in UGS due to fertilization and pollution.Contamination of urban soils by heavy metals is due largely to traffic emissions and pollution by industrial and household wastes.Although human activities tend to augment urban soil nutrient pools to maximize certain ecosystem services,they may inadvertently compromise these and other services by increasing pollution.Knowledge of urban soil spatial heterogeneity in UGS is indispensable for improving urban ecosystem management.

Effects of road dust on the growth characteristics of Sophora japonica L.seedlings

Road dust is one of the most common pollutants and causes a series of negative effects on plant physiology. Dust＇s impacts on plants can be regarded as a combination of load,composition and grain size impacts on plants; however, there is a lack of integrated dust effect studies involving these three aspects. In our study, Sophora japonica seedlings were artificially dusted with road dust collected from the road surface of Beijing so that we could study the impacts of this dust on nitrogen/carbon allocation, biomass allocation and photosynthetic pigments from the three aspects of composition, load and grain size. The results showed that the growth characteristics of S. japonica seedlings were mostly influenced by dust composition and load. Leaf N, root–shoot ratio and chlorophyll a/b were significantly affected by dust composition and load; leaf C/N, shoot biomass, total chlorophyll and carotenoid were significantly affected by dust load; stem N and stem C/N were significantly affected by dust composition; while the dust grain size alone did not affect any of the growth characteristics. Road dust did influence the growth characteristics more extensively than loam. Therefore, a higher dust load could increase the differences between road dust and loam treatments. The elements in dust are well correlated to the shoot N, shoot C/N, and root–shoot ratio of S. japonica seedlings. This knowledge could benefit the management of urban green spaces.