Guangmei Wang

Biodiversity conservation in a fast-growing metropolitan area in China: a case study of plant diversity in Beijing

As the capital of China, Beijing has experienced extensive urbanization in the past two decades. To explore the effect of urbanization on plant diversity, we investigated the vascular plant diversity of the whole Beijing Municipality in three different functional (urban, suburban and exurban) regions. For its geo-diversity, Beijing has a rather abundant vascular plant diversity (2,276 species), including 207 species of conservation concern such as endemic, threatened and protected species. The exurban region had not only the highest species diversity (1,998 species), but also the most species of conservation concern (194 species). Urban region possessed the maximum alien species in terms of both absolute number and proportional representation, while the suburban region had the least species diversity (1,026 species). Some problems, such as wetland shrink and biological invasions, were common in the whole Beijing Municipality. However, primary threats to biodiversity differed in the three functional regions. The urban and suburban regions mainly suffered from habitat loss and fragmentation due to urban sprawl, while the exurban region faced serious ecosystem degradation from increasing disturbance from both local and urban people. Based on our investigation, we put forward conservation strategies for the three regions: improving the structure and ecological function of green spaces in urban region, preserving as much remnant natural habitats in the suburban region, and restricting the rural tourism and establishing a biosphere reserve in the exurban region. In addition, improving public education and orientating that more to social aspects of conservation practice is strongly recommended.

Effects of episodic flooding on the net ecosystem CO2 exchange of a supratidal wetland in the Yellow River Delta

Episodic flooding due to intense rainfall events is characteristic in many wetlands, which may modify wetland-atmosphere exchange of CO2. However, the degree to which episodic flooding affects net ecosystem CO2 exchange (NEE) is poorly documented in supratidal wetlands of coastal zone, where rainfall-driven episodic flooding often occurs. To address this issue, the ecosystem CO2 fluxes were continuously measured using the eddy covariance technique for 4 years (2010-2013) in a supratidal wetland in the Yellow River Delta. Our results showed that over the growing season, the daily average uptake in the supratidal wetland was -1.4, -1.3, -1.0, and -1.3 g Cm-2 d(-1) for 2010, 2011, 2012, and 2013, respectively. On the annual scale, the supratidal wetland functioned as a strong sink for atmospheric CO2, with the annual NEE of -223, -164, and -247 g Cm-2 yr(-1) for 2011, 2012, and 2013, respectively. The mean diurnal pattern of NEE exhibited a smaller range of variation before episodic flooding than after it. Episodic flooding reduced the average daytime net CO2 uptake and the maximum rates of photosynthesis. In addition, flooding clearly suppressed the nighttime CO2 release from the wetland but increased its temperature sensitivity. Therefore, effects of episodic flooding on the direction and magnitude of NEE should be considered when predicting the ecosystem responses to future climate change in supratidal wetlands.

Bacterial community structure and function shift along a successional series of tidal flats in the Yellow River Delta

Coastal ecosystems play significant ecological and economic roles but are threatened and facing decline. Microbes drive various biogeochemical processes in coastal ecosystems. Tidal flats are critical components of coastal ecosystems; however, the structure and function of microbial communities in tidal flats are poorly understood. Here we investigated the seasonal variations of bacterial communities along a tidal flat series (subtidal, intertidal and supratidal flats) and the factors affecting the variations. Bacterial community composition and diversity were analyzed over four seasons by 16S rRNA genes using the Ion Torrent PGM platform. Bacterial community composition differed significantly along the tidal flat series. Bacterial phylogenetic diversity increased while phylogenetic turnover decreased from subtidal to supratidal flats. Moreover, the bacterial community structure differed seasonally. Canonical correspondence analysis identified salinity as a major environmental factor structuring the microbial community in the sediment along the successional series. Meanwhile, temperature and nitrite concentration were major drivers of seasonal microbial changes. Despite major compositional shifts, nitrogen, methane and energy metabolisms predicted by PICRUSt were inhibited in the winter. Taken together, this study indicates that bacterial community structure changed along the successional tidal flat series and provides new insights on the characteristics of bacterial communities in coastal ecosystems.

Changes of Soil Particle Size Distribution in Tidal Flats in the Yellow River Delta

Background The tidal flat is one of the important components of coastal wetland systems in the Yellow River Delta (YRD). It can stabilize shorelines and protect coastal biodiversity. The erosion risk in tidal flats in coastal wetlands was seldom been studied. Characterizing changes of soil particle size distribution (PSD) is an important way to quantity soil erosion in tidal flats. Method/Principal findings Based on the fractal scale theory and network analysis, we determined the fractal characterizations (singular fractal dimension and multifractal dimension) soil PSD in a successional series of tidal flats in a coastal wetland in the YRD in eastern China. The results showed that the major soil texture was from silt loam to sandy loam. The values of fractal dimensions, ranging from 2.35 to 2.55, decreased from the low tidal flat to the high tidal flat. We also found that the percent of particles with size ranging between 0.4 and 126 μm was related with fractal dimensions. Tide played a great effort on soil PSD than vegetation by increasing soil organic matter (SOM) content and salinity in the coastal wetland in the YRD. Conclusions/Significance Tidal flats in coastal wetlands in the YRD, especially low tidal flats, are facing the risk of soil erosion. This study will be essential to provide a firm basis for the coast erosion control and assessment, as well as wetland ecosystem restoration.

Wet and dry atmospheric depositions of inorganic nitrogen during plant growing season in the coastal zone of Yellow River Delta.

The ecological problems caused by dry and wet deposition of atmospheric nitrogen have been widespread concern in the world. In this study, wet and dry atmospheric depositions were monitored in plant growing season in the coastal zone of the Yellow River Delta (YRD) using automatic sampling equipment. The results showed that SO4 2− and Na+ were the predominant anion and cation, respectively, in both wet and dry atmospheric depositions. The total atmospheric nitrogen deposition was ~2264.24 mg m−2, in which dry atmospheric nitrogen deposition was about 32.02%. The highest values of dry and wet atmospheric nitrogen deposition appeared in May and August, respectively. In the studied area, NO3 −–N was the main nitrogen form in dry deposition, while the predominant nitrogen in wet atmospheric deposition was NH4 +–N with ~56.51% of total wet atmospheric nitrogen deposition. The average monthly attribution rate of atmospheric deposition of NO3 −–N and NH4 +–N was ~31.38% and ~20.50% for the contents of NO3 −–N and NH4 +–N in 0–10 cm soil layer, respectively, suggested that the atmospheric nitrogen was one of main sources for soil nitrogen in coastal zone of the YRD.

Distribution of carbon, nitrogen and phosphorus in coastal wetland soil related land use in the Modern Yellow River Delta

The delivery and distribution of nutrients in coastal wetland ecosystems is much related to the land use. The spatial variations of TOC, TN, NH4+-N, NO3−-N and TP and associated soil salinity with depth in 9 kinds land uses in coastal zone of the modern Yellow River Delta (YRD) was evaluated based on monitoring data in field from 2009 to 2015. The results showed that the average contents of soil TOC, TN, NO3−-N, NH4+-N and TP were 4.21 ± 2.40 g kg−1, 375.91 ± 213.44, 5.36 ± 9.59 and 7.20 ± 5.58 and 591.27 ± 91.16 mg kg−1, respectively. The high N and C contents were found in cropland in southern part and low values in natural wetland, while TP was relatively stable both in profiles and in different land uses. The land use, land formation age and salinity were important factors influencing distributions of TOC and N. Higher contents of TOC and N were observed in older formation age lands in whole study region, while the opposite regulation were found in new-born natural wetland, indicating that the anthropogenic activities could greatly alter the original distribution regulations of nutrients in coastal natural wetlands by changing the regional land use.

Ecological Effects of Roads on the Plant Diversity of Coastal Wetland in the Yellow River Delta

The 26 sample sites in 7 study plots adjacent to asphalt road and earth road in coastal wetland in the Yellow River Delta were selected to quantify plant diversity using quadrat sampling method in plant bloom phase of July and August 2012. The indice of β T and Jaccards coefficient were applied to evaluate the species diversity. The results showed that the plant diversities and alien plants were high in the range of 0–20 m to the road verge. There were more exotics and halophytes in plots of asphalt roadside than that of earth roadside. However, proportion of halophytes in habitats of asphalt roadsides was lower than that of earth roadside. By comparing β-diversity, there were more common species in the asphalt roadsides than that in the earth roadsides. The similarity of plant communities in studied plots of asphalt roadsides and earth roadsides increased with increasing the distance to road verge. The effect range of roads for plant diversity in study region was about 20 m to road verge. Our results indicate that the construction and maintenance of roads in wetland could increase the plant species diversities of communities and risk of alien species invasion.

Effects of Age and Stand Density of Mother Trees on Early Pinus thunbergii Seedling Establishment in the Coastal Zone, China

Effects of age and stand density of mother tree on seed germination, seedling biomass allocation, and seedling growth of Pinus thunbergii were studied. The results showed that age of mother tree did not have significant influences on seed germination, but it was significant on seedling biomass allocation and growth. Seedlings from the minimum and maximum age of mother tree had higher leaf mass ratio and lower root mass ratio than from the middle age of mother tree. Moreover, they also had higher relative height growth rate and slenderness, which were related to their biomass allocation. Stand density of mother tree mainly demonstrated significant effects on seed germination and seedling growth. Seed from higher stand density of mother tree did not decrease germination rate, but had higher mean germination time, indicating that it delayed germination process. Seedlings of higher stand density of mother tree showed higher relative height growth rate and slenderness. These traits of offspring from higher stand density of mother tree were similar to its mother, indicating significant environmental maternal effects. So, mother tree identity of maternal age and environments had important effects on natural regeneration of the coastal P. thunbergii forest.

Seasonal Variations of C: N: P Stoichiometry and Their Trade-Offs in Different Organs of Suaeda salsa in Coastal Wetland of Yellow River Delta, China

Variations of plant C: N: P stoichiometry could be affected by both some environmental fluctuations and plant physiological processes. However, the trade-off mechanism between them and their influencial factors were not understood completely. In this study, C, N, P contents and their stoichiometry of S. salsa’s plant organs (leaves, stems, and roots), together with their environmental factors including salinity, pH, soil N and soil P, were examined in the intertidal and supratidal habitats of coastal wetlands during the different sampling times (May, July, September, November). The results showed that both plant organ and sampling times affected C, N, and P and stoichiometry of S. salsa in the intertidal and supratidal habitats, however, their influencial conditions and mechanisms were different. In the intertidal habitat, the different slopes of C-P and N-P within interspecific organs suggested that plant P, C:P and N:P of S. salsa were modulated by P concentrations that allocated in the specific organs. However, the slopes of C-N were found to be not significant within interspecific organs, but during the sampling times. These differences of plant N and C:N were related with the physiological demand for N in the specific life history stage. In the supratidal habitat, no significant differences were found in the slopes of C-N, C-P, and N-P within interspecific organs. However, different slopes of C-N among the sampling times also indicated a self-regulation strategy for plant N and C:N of S. salsa in different ontogenetic stages. In contrast to the intertidal habitat, seasonal variations of P, C:P and N:P ratios within interspecific organs reflected the soil P characteristics in the supratidal habitat. Our results showed that the stoichiometric constraint strategy of plant S. salsa in this region was strongly correlated with the local soil nutrient conditions.

Challenge of weed risk assessment (WRA) for ecological restoration in China: The case of Rhus typhina L. and the new officially released weed risk assessment system

China has conducted many ecological restoration projects to alleviate environmental degradation, with numerous alien species having good adaptability widely used for fast effect. However, unsuitable plant selection may bring negative impacts and even cause biological invasion. Weed risk assessment (WRA) is therefore indispensable, yet it is often contentious especially concerning those species that has been widely utilized before weedy attributes were noted. In this paper, we take Rhus typhina L. as an example to illustrate how scientific researches and social factors can influence the evaluation of alien species and cause challenge to WRA. The evaluation of this species is not only a pure scientific issue but also influenced by many factors such as the introduction history, current utilization status in afforestation, and divergent underlying values varying through persons and sectors. These factors determined the kind of data to be assessed, which lead to different evaluations, therefore, causing challenge to its WRA. We further examined newly officially released WRA system in China from the invasion biology viewpoint, arguing that it had some major flaws in design and validation and need much improvement. Considering the human dimension and biological characters together, we suggest that the “black list” and “green list” approaches with rigorous expert assessment should be adopted simultaneously in alien species management in China.