Fuchen Shi

Heavy metal contamination and ecological risk in Spartina alterniflora marsh in intertidal sediments of Bohai Bay, China

To investigate the effects of Spartina alterniflora on heavy metals pollution of intertidal sediments, sediment cores of a S. alterniflora salt marsh and a mudflat in Bohai Bay, China were analyzed. The results showed that S. alterniflora caused higher total C and P, but lower bulk density and electrical conductivity. The levels of Cd, Cu and Pb were higher in S. alterniflora sediment. Both Cd and Zn were higher than the probable effect level at both sites, indicating their toxicological importance. The geo-accumulation and potential ecological risk indexes revealed higher metal contamination in S. alterniflora sediment. Multivariate analysis implied that anthropogenic activities altered mobility and bioavailability of heavy metals. The percentage of mobile heavy metals was higher in S. alterniflora sediment, indicating improvement of conversion from the immobilized fraction to the mobilized fraction. These findings indicate that S. alterniflora may facilitate accumulation of heavy metals and increase their bioavailability and mobility.

Effects of cadmium stress on growth, metal accumulation and organic acids of Spartina alterniflora Loisel.

A study quantifying the effects of exogenous cadmium (Cd) on growth, Cd bioaccumulation and organic acids of Spartina alterniflora was conducted. The experiment consisted of three levels of exogenous Cd 2+ concentrations: 0, 50, and 200 mg/kg. Total Cd and water-soluble Cd were determined. Plant height, tiller number, spike number, electrolyte leakage rate (ELR), free proline, malondialdehyde (MDA), soluble sugar and organic acids were also measured. The results showed that plant height, tiller number and spike number reduced with increasing Cd 2+ concentration. However, ELR, free proline, MDA, and soluble sugar were all promoted under Cd stress. Cd accumulated in inflorescences, leaves, stems, rhizomes and fine roots, and increased greatly with increasing Cd2+ concentration. Exogenous Cd 2+ significantly reduced the growth of inflorescences, leaves, stems and rhizomes, with Cd accumulations not more than 15.68 μg/g dry weight (DW), respectively. However, biomass of fine roots did not reduce significantly with increasing Cd 2+ concentration. Furthermore, Cd accumulation in fine roots reached to 390 μg/g DW under the treatment Cd200. Oxalic and citric acids were the two most abundant organic acids in S. alterniflora . Contents of oxalic acid in inflorescences, stems and fine roots were all positively related with Cd bioaccumulations indicating that oxalic acid might be related with Cd sequestration in fine roots and Cd transportation from underground to aboveground parts of S. alterniflora. Contents of citric acid in fine roots and ascorbic acid in rhizomes increased with increasing exogenous Cd 2+ concentration, suggesting that accumulation of citric acids in fine roots and ascorbic acid in rhizomes of S. alterniflora might also be related to its Cd bioaccumulation and detoxification. Key words : Spartina alterniflora , cadmium pollution, growth, organic acid, phytoremediation.

Seasonal changes in and relationship between soil microbial and microfaunal communities in a Tamarix chinensis community in the Yellow River Delta

The plant Tamarix chinensis is distributed along the coast of the Yellow River Delta in soils with high salinity. As the dominant local halophyte, it plays a unique role in modifying the local soil microenvironment. We investigated the effects of T. chinensis vegetative cover and the seasons on the soil microbe and microfauna communities in the Yellow River Delta. In April, June and October 2010, soil samples were taken from an estuary of the Yellow River. We measured microbiomass (using the soil chloroform fumigation extraction method), substrate induced respiration (SIR), and phospholipid fatty acids (PLFA). Microbe community structure and soil nematode species richness exhibited distinct seasonal variation. The levels of PLFAs, soil microbial biomass carbon (SMBC), microbial biomass nitrogen (SMBN) and SIR were lower in April than in October in T. chinensis sites. In June, there was a slight increase in the total abundance of PLFA and soil nematode diversity in T. chinensis sites. Stepwise regression analysis indicated that plant-feeding nematodes were a dominant factor for changes in soil microbial community composition, and soil moisture, soil organic carbon and fungalfeeding nematode capacity were secondary factors. The distinct seasonal changes in the soil microbe community composition were likely driven by changes in nematode trophic groups, soil moisture and soil organic carbon. Key words : Microbial biomass, phospholipid fatty acids (PLFA), community diversity, nematode.

Effects of long-term salinity on the growth of the halophyte Spartina alterniflora Loisel

The effects of salt stress on the growth of Spartina alterniflora were investigated by imposing seven levels of salt stress (0, 100, 200, 300, 400, 500, and 600 mM NaCl) on potted plants. The seedlings were grown in vermiculite in a greenhouse for six months. Optimal growth of S. alterniflora occurred at salinity levels of 100 and 200 mM NaCl. Seedlings grew less in freshwater conditions than in the 100 and 200 mM NaCl treatments. Higher levels of salinity (300 to 600 mM NaCl) caused a reduction in shoot number, height, biomass accumulation and leaf area. However, salt treatment resulted in only small changes in leaf water content. Although, chlorophyll concentrations were significantly higher at 100 and 200 mM NaCl than other salinity levels, photosynthetic rates were overall quite high regardless of treatment, ranging from 44.65 to 50.88 µmol m -2 S -1 of carbon gain. The results indicate that S.

Soil Microbial Community Structure Evolution along Halophyte Succession in Bohai Bay Wetland

It is urgent to recover Bohai Bay costal wetland ecosystem because of covering a large area of severe saline-alkali soil. To explore the relationship between halophyte herbaceous succession and microbial community structure, we chose four local communities which played an important role in improving soil microenvironment. We performed phospholipid fatty acid analysis, measured soil parameters, and evaluated shifts of microbial community structure. Results showed that microbial community structure changed significantly along succession and bacteria community was dominant. Total phospholipid fatty acid content increased in different successional stages but decreased with depth, with similar variations in bacterial and fungal biomass. Soil organic carbon and especially total nitrogen were positively correlated with microbial biomass. Colonization of pioneering salt-tolerant plants Suaeda glauca in saline-alkali bare land changed total soil microorganism content and composition. These results showed that belowground processes were strongly related with aboveground halophyte succession. Fungal/bacterial ratio, Gram-negative/Gram-positive bacteria ratio, total microbial biomass, and fungi and bacteria content could indicate the degree of succession stages in Bohai Bay wetland ecosystem. And also these findings demonstrated that microbial community biomass and composition evolved along with vegetation succession environmental variables.

Characteristics of Larch Forests in Daxingan Mountains, Northeast China

Daxingan Mountains are located in cold temperature region of northeast China, and are oriented from northeast to southwest direction. This area of China encompasses the southernmost distribution of continuous permafrost that extends from the Arctic region of Eurasia (see Fig. 1.1). The vegetation type is classified as deciduous conifer forest dominated by Larix gmelinii (Rupr.) Rupr. The major species accompanying L. gmelinii are Betula platyphylla Suk. and Populus davidiana Dode. These forests are extension of the larch forests of Central and Northeastern Siberia (Fukuda 1996; Kasischke and Stocks 2000). The climate in the region of Daxingan Mountains is more moderate than that of Northeastern Siberia. Therefore, the forest biomass and productivity are also higher than those of the Siberian counterpart. The climate differs among southern, middle, and northern regions within the Daxingan Mountains. It leads to regional-scale growth differences in the larch forests. For example, biomass and net primary productivity of L. gmelinii forests of ca. 30-year old in the southern region are 43.6 Mg ha−1 and 3.94 Mg ha−1 year−1 higher than those in the northern region (Zhou 1991; Shi 1999). The biomass and net primary productivity of L. gmelinii forests of ca. 50-year old in the middle region are 6 Mg ha−1 and 1.24 Mg ha−1 year−1 higher than those of the northern region.

Interspecific and Intersexual Differences in the Chemical Composition of Floral Scent in Glochidion Species (Phyllanthaceae) in South China

Plants of the Glochidion (Phyllanthaceae) genus are pollinated exclusively by host-specific Epicephala (Gracillariidae) moths. Floral scent has been thought to play key role in the obligate pollination mutualism between Glochidion plants and Epicephala moths, but few studies have been reported about chemical variation in floral volatiles of Glochidion species in China. Floral volatiles of male and female flowers of five Glochidion species in south China were collected by dynamic headspace absorption technique and then were chemically analyzed by using gas chromatography-mass spectrometry. A total of 69 compounds were identified from floral scents of five investigated species. Glochidion hirsutum and G. zeylanicum showed no qualitative differences in floral scent, whereas there were clear variations of floral scent among other species (G. eriocarpum, G. daltonii, and G. sphaerogynum) and also they distinctly differed from these two species. Male flowers emitted significantly more scent than female flowers. Glochidion plants exhibited qualitative and quantitative differences in floral scent between two sexes of flowers. The findings suggest that the volatile variation of floral scent among Glochidion species reflects adaptations to specific pollinators. Sexual dimorphism in floral scent has evolved to signal alternative rewards provided by each sex to Epicephala moths.

Effects of Exotic Cordgrass Spartina alterniflora on Soil Physical and Chemical Characteristics in the Haihe River Estuary, China

An exotic grass Spartina alterniflora was introduced in China almost 30 years ago, and since then it has become an urgent topic due to its invasiveness in the coastal zone of China. We investigated consequences of S. alterniflora invasion on inter-tidal ecosystem processes in Haihe River estuary salt marsh of Tianjin, China. Soil pH, salinity, buck density, soil organic C, total N, C/N, soil microbial biomass C (SMBC), and soil microbial biomass N (SMBN) were determined, respectively. Moreover, correlations between soil buck density, organic C, total N, C/N, SMBC, and SMBN were also measured. The results showed that soil pH, salinity, and buck density in Spartina salt marsh were significant lower than mudflat. However, soil organic C, total N, SMBC, and SMBN were significantly higher in Spartina salt marsh than mudflat. With the extension of sampling time, soil pH, salinity, organic C, total N, SMBC, and SMBN increased, except for soil buck density. Soil organic C and total N were positively related with SMBC and SMBN regardless of Spartina salt marsh or mudflat. Therefore, invasion of S. alterniflora improved soil physical and chemical properties in estuary salt marsh. Furthermore, it is necessary to take soil microorganism into account when evaluating effects of S. alterniflora on soil physical and chemical properties.

Comparative studies on the soil enzymic activities of two plant communities in the Yellow River delta

Soil enzyme plays an active role in the material recycling and energy flow of soil biochemical process. This article dealed with the month changes of catalase, dehydrogenase, phosphatase, urease, protease in Suaeda salsa and Aeluropus sinensis in the Yellow River Delta. Meanwhile, the relationship between the soil enzyme activities and physical-chemical factors was discussed by correlation analysis. The results showed: (1) Enzyme activities were significantly higher in the planted plots than that of plots unplanted. (2) Except soil catalase activities, the month variations of other four soil enzyme acticities in two communities were all maximal values in August. (3) The result from the correlation analysis showed that soil organi carbon and nitrate nitrogen were dominant factors, and soil salinity, available P and ammonium nitrogen were secondary for soil enzyme activities. These findings demonstrated that soil enzyme activities are influenced by different plant communities and environmental variables.

Population expansion of invasive plant Spartina alterniflora in the Tianjin coastal wetland, China

Since the introduction to Tianjin coastal area, Spartina alterniflora growed and adapted well to the local environment. According to the distribution patterns, we divided the S. alterniflora population into ‘patch’ and ‘blanket’. We investigated the spread process of the patch population. We also studied the seasonal dynamics of two types of S. alterniflora population, including the density, height, aboveground biomass and F/C value. The results showed that in the past growing season, the patch population expansion speed parallel to the shoreline (42∼92%) was larger than the speed vertical to the shoreline (39∼62%). The population density increased to 322.19 ramets·m⁻² (patch) and 763.33 ramets·m⁻² (blanket) at the end of the growing season. The aboveground biomass reached peak values at 2453.57 g·m⁻² for patch population and 5085.68 g·m⁻² for blanket population 170 days after returning green. The F/C value decreased through the growing season. The blanket population had higher density, more aboveground biomass and lower F/C value than the patch population. But there was no significant difference between the heights of the two patterns population.