Scirpus Mariqueter Research Articles

Development of microsatellites for Scirpus mariqueter Wang et Tang (Cyperaceae) and cross‐species amplification in Scirpus planiculmis F. Schmidt

We report eight microsatellite markers developed for Scirpus mariqueter Wang et Tang using 5'-anchored PCR. They were tested using 30 S. mariqueter individuals. The observed and expected heterozygosity levels ranged from 0.0690 to 0.8426 and from 0.0678 to 0.5249, respectively. Cross-amplification was carried out in a congener, S. planiculmis F. Schmidt. All these markers will be very helpful in population genetics study of S. mariqueter and S. planiculmis.

Influences of the macrophyte (Scirpus mariqueter) on phosphorous geochemical properties in the intertidal marsh of the Yangtze Estuary

The role of the marsh plant (Scirpus mariqueter) in phosphorus (P) biogeochemical cycling was investigated in the present study. The marsh plant had a significant influence on P adsorption, benthic fluxes and P speciation in the intertidal system. The adsorption capacities of P were significantly higher in the rhizosphere sediments (54.38–77.12 mg kg−1) than in the bare sediments (43.91–54.81 mg kg−1). Lower half saturation concentration constants also appeared in the rhizosphere sediments. Similar adsorption kinetic patterns were found for the bare and vegetated habitats, which showed an initial fast P adsorption reaction, followed by a slow adsorption process. However, compared with the unvegetated sediments, the relatively higher adsorption rate appeared in the rhizosphere sediments during the fast adsorption stage. Also, soluble inorganic P was effluxed into the overlying water in the unvegetated habitat. In contrast, soluble inorganic P was transported from the overlying water into the vegetated sediments during the growth season of S. mariqueter. The comparative analysis of P speciation in both bare and vegetated habitats revealed that S. mariqueter could enhance the accumulation of Fe‐bound P, authigenic P and organic P in the rhizosphere sediments. The important role of S. mariqueter in P removal and storage has significant implications for the conservation and management of the Yangtze estuarine and intertidal marsh.

Ecophysiological characteristics of invasive Spartina alterniflora and native species in salt marshes of Yangtze River estuary, China

Biological invasions represent one of the significant components of global change. A comparative study of invaders and co-occurring natives is a useful approach to gaining insights into the invasiveness of exotic plants. Spartina alterniflora, a C 4 grass, is a widespread invader in the coastal wetlands in China and other regions of the world. We conducted a comparative study of S. alterniflora and native C 3 species, Phragmites australis and Scirpus mariqueter, in terms of their gas exchange and efficiencies in resource utilization. We tested the hypothesis that S. alterniflora has growth-related ecophysiological advantages over the natives in its non-native range, which result in its rapid growth and enhance its invasiveness. Photosynthesis, leaf area index (LAI), specific leaf area (SLA), and the efficiency of resource use (light, water, and nitrogen) were examined monthly for eight months in 2004. Overall, S. alterniflora had greater LAI, higher maximal net photosynthetic rate ( A max), and longer growing season than those of the native species. On average, the efficiencies of S. alterniflora in light, water, and nitrogen utilization were respectively 10.1%, 26.1%, and 33.1% higher than those of P. australis, and respectively 70.3%, 53.5%, 28.3% higher than those of S. mariqueter. However, SLA of S. alterniflora was significantly lower than those of P. australis and S. mariqueter. Although there was no general pattern in the relationship between invasiveness and plant photosynthetic types, in this study, most of the ecophysiological characteristics that gave S. alterniflora a competitive advantage in the Yangtze River estuary were associated with photosynthetic pathways. Our results offer a greater understanding of the relationship between invasiveness and plant photosynthetic type. Our results also indicate that LAI and the length of the photosynthetic season, which vary with habitats, are also important in invasion success.

Analyzing the habitat suitability for migratory birds at the Chongming Dongtan Nature Reserve in Shanghai, China

The Dongtan Nature Reserve, one of the largest nature reserves in East Asia, is located in the mouth of the Yangtze Estuary and is an important habitat for migratory birds. The Dongtan wetlands were listed in the Chinese Protected Wetlands in 1992, and were designated as internationally important under the Ramsar Wetlands Convention in 2001 and as a national nature reserve in 2005. By their very nature and location, the estuarine and coastal habitats are dynamic and their biodiversity conservation and management relies on up-to-date spatial information. By establishing qualitative and quantitative relationships between bird populations and key habitat factors such as elevation, land cover type, tidal creek density and macrophytobenthos biomass, we developed an object-oriented image approach, in conjunction with Geographical Information Systems and the data from current field surveys, to analyze and assess the habitat suitability for the main types of birds, namely Anatidae, Charadriidae, Ardeidae and Laridae, at the reserve. The results from this study showed that about 40% of the total area of the Dongtan Reserve contained suitable habitats for these four bird families. The Scirpus mariqueter zone, mudflat zone, and tidal creeks were the most important habitats for these birds. This study indicated the potential of this approach for objective and effective evaluation of the species habitat suitability in a dynamic estuarine and coastal area. The implications of the results as a tool for biodiversity conservation, wetland conservation, and ecosystem management are discussed.

Assessing the effects of short-term Spartina alterniflora invasion on labile and recalcitrant C and N pools by means of soil fractionation and stable C and N isotopes

An exotic grass Spartina alterniflora was intentionally introduced to Jiuduansha wetlands in Yangtze River estuary in 1997, and since then it had rapidly replaced native plant Scirpus mariqueter that used to dominate the estuarine salt marshes. We investigated consequences of S. alterniflora invasion to soil labile and recalcitrant C and N compared to the native S. mariqueter using soil fractionation and stable C and N isotopes. Results showed that S. alterniflora increased soil labile carbon (LC), recalcitrant carbon (RC), and soil recalcitrant nitrogen (RN) contents significantly ( P < 0.05) in the upper soil layers (0–60 cm) compared to the S. mariqueter soil. Soil labile nitrogen (LN) in the S. alterniflora soil, however, remained lower than that in the S. mariqueter soil ( P < 0.01), except for the surface soil layer (0–20 cm). The LC accounted for, on average, 36–38% of soil organic matter (SOM) in both communities, while labile N accounted for 32% of SOM in S. alterniflora soil and 48% in S. mariqueter soil. The δ 13C values in S. alterniflora soil showed that S. alterniflora contributed on average 8.6% and 3.3% to the LC and RC pools, respectively, within the 0–100-cm soil layer. The greatest labile C contribution derived from S. alterniflora was found at the 40-cm soil whereas the proportion of recalcitrant C originating from S. alterniflora showed a decreasing trend with soil depth. These changes appeared to be associated with vertical distributions of roots and rhizodeposition. We also found that the δ 15N values of SOM were more enriched in S. alterniflora soil compared to S. mariqueter soil, suggesting that greater SOM input by S. alterniflora residues would stimulate microbial activity rates that could lead to increased N turnover rates in S. alterniflora soil.

Litter pool sizes, decomposition, and nitrogen dynamics in Spartina alterniflora-invaded and native coastal marshlands of the Yangtze Estuary

Past studies have focused primarily on the effects of invasive plants on litter decomposition at soil surfaces. In natural ecosystems, however, considerable amounts of litter may be at aerial and belowground positions. This study was designed to examine the effects of Spartina alterniflora invasion on the pool sizes and decomposition of aerial, surficial, and belowground litter in coastal marshlands, the Yangtze Estuary, which were originally occupied by two native species, Scirpus mariqueter and Phragmites australis. We collected aerial and surficial litter of the three species once a month and belowground litter once every 2 months. We used the litterbag method to quantify litter decomposition at the aerial, surficial and belowground positions for the three species. Yearly averaged litter mass in the Spartina stands was 1.99 kg m(-2); this was 250 and 22.8% higher than that in the Scirpus (0.57 kg m(-2)) and Phragmites (1.62 kg m(-2)) stands, respectively. The litter in the Spartina stands was primarily distributed in the air (45%) and belowground (48%), while Scirpus and Phragmites litter was mainly allocated to belowground positions (85 and 59%, respectively). The averaged decomposition rates of aerial, surficial, and belowground litter were 0.82, 1.83, and 1.27 year(-1) for Spartina, respectively; these were 52, 62 and 69% of those for Scirpus litter at corresponding positions and 158, 144 and 78% of those for Phragmites litter, respectively. The differences in decomposition rates between Spartina and the two native species were largely due to differences in litter quality among the three species, particularly for the belowground litter. The absolute amount of nitrogen increased during the decomposition of Spartina stem, sheath and root litter, while the amount of nitrogen in Scirpus and Phragmites litter declined during decomposition for all tissue types. Our results suggest that Spartina invasion altered the carbon and nitrogen cycling in the coastal marshlands of China.

Tidal marshes as energy sources for commercially important nektonic organisms: stable isotope analysis

Tidal marshes provide nursery habitats for many commercial nektonic species; thus, determining trophic linkages between tidal marshes and aquatic consumers is important for sustain- ing fishery production in estuarine ecosystems. We examined stable isotopes (δ 13 C, δ 15 N) in 4 com- mercial nekton species (Chelon haematocheilus, Synechogobius ommaturus, Lateolabrax maculatus and Exopalaemon carinicauda) in the tidal marshes of the Yangtze River estuary, China. We esti- mated the frequency and range of potential contribution (0 to 100%) from different food sources (benthic microalgae, suspended particulate organic matter, the invasive C4 plant Spartina alterniflora and native C3 plants Phragmites australis and Scirpus mariqueter) to the nektonic consumers, and then pooled the contributions for primary producers with similar isotope values (giving 3 groups: microalgae, invasive C4 plant and native C3 plants). Marsh vascular plants and microalgae were at the base of the food web supporting these nektonic species. For C. haematocheilus and S. ommatu- rus, vascular plants constituted a larger fraction of their carbon source than microalgae. S. alterniflora contributed more than 50% of their total organic carbon and was more important than the native C3 plants. For L. maculatus and E. carinicauda, intermediate δ 13 C values precluded definitive assign- ment of a major carbon source. We have shown that tidal marshes provide important food sources for some dominant estuarine nektonic species, and that the exotic plant S. alterniflora has been incorpo- rated into aquatic food webs of the Yangtze River estuary.

Invasion of Spartina alterniflora Enhanced Ecosystem Carbon and Nitrogen Stocks in the Yangtze Estuary, China

Whether plant invasion increases ecosystem carbon (C) stocks is controversial largely due to the lack of knowledge about differences in ecophysiological properties between invasive and native species. We conducted a field experiment in which we measured ecophysiological properties to explore the response of the ecosystem C stocks to the invasion of Spartina alterniflora (Spartina) in wetlands dominated by native Scirpus mariqueter (Scirpus) and Phragmites australis (Phragmites) in the Yangtze Estuary, China. We measured growing season length, leaf area index (LAI), net photosynthetic rate (Pn), root biomass, net primary production (NPP), litter quality and litter decomposition, plant and soil C and nitrogen (N) stocks in ecosystems dominated by the three species. Our results showed that Spartina had a longer growing season, higher LAI, higher Pn, and greater root biomass than Scirpus and Phragmites. Net primary production (NPP) was 2.16 kg C m−2 y−1 in Spartina ecosystems, which was, on average, 1.44 and 0.47 kg C m−2 y−1 greater than that in Scirpus and Phragmites ecosystems, respectively. The litter decomposition rate, particularly the belowground decomposition rate, was lower for Spartina than Scirpus and Phragmites due to the lower litter quality of Spartina. The ecosystem C stock (20.94 kg m−2) for Spartina was greater than that for Scirpus (17.07 kg m−2), Phragmites (19.51 kg m−2) and the mudflats (15.12 kg m−2). Additionally, Spartina ecosystems had a significantly greater N stock (698.8 g m−2) than Scirpus (597.1 g m−2), Phragmites ecosystems (578.2 g m−2) and the mudflats (375.1 g m−2). Our results suggest that Spartina invasion altered ecophysiological processes, resulted in changes in NPP and litter decomposition, and ultimately led to enhanced ecosystem C and N stocks in the invaded ecosystems in comparison to the ecosystems with native species.

Characterization of Bacterial Community Structure and Diversity in Rhizosphere Soils of Three Plants in Rapidly Changing Salt Marshes Using 16S rDNA

The structure and diversity of the bacterial communities in rhizosphere soils of native Phragmites australis and Scirpus mariqueter and alien Spartina alterniflora in the Yangtze River Estuary were investigated by constructing 16S ribosomal DNA (rDNA) clone libraries. The bacterial diversity was quantified by placing the clones into operational taxonomic unit (OTU) groups at the level of sequence similarity of > 97%. Phylogenetic analysis of the resulting 398 clone sequences indicated a high diversity of bacteria in the rhizosphere soils of these plants. The members of Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria of the phylum Proteobacteria were the most abundant in rhizobacteria. Chao 1 nonparametric diversity estimator coupled with the reciprocal of Simpson's index (1/D) was applied to sequence data obtained from each library to evaluate total sequence diversity and quantitatively compare the level of dominance. The results showed that Phragmites, Scirpus, and Spartina rhizosphere soils contained 200, 668, and 382 OTUs, respectively. The bacterial communities in the Spartina and Phragmites rhizosphere soils displayed species dominance revealed by 1/D, whereas the bacterial community in Scirpus rhizosphere soil had uniform distributions of species abundance. Overall, analysis of 16S rDNA clone libraries from the rhizosphere soils indicates that the changes in bacterial composition may occur concomitantly with the shift of species composition in plant communities.

Landward changes of soil enzyme activities in a tidal flat wetland of the Yangtze River Estuary and correlations with physico-chemical factors

The landward changes of soil enzyme activities and physico-chemical properties of the surface sediment in Chongming Dongtan of the Yangtze River Estuary, were studied. Along the elevation gradient or succession series, the contents of total phosphorus ( TP), total nitrogen ( TN) and organic matter ( OM) in the sediment increased, but the average grain size ( AGS) of the sediment and the content of the dissolved inorganic phosphorus ( DIP) decreased. The activity of alkaline phosphatase increased gradually along the elevation gradient, and was positively correlated with the values of TP, TN and OM ( P<0.05), but negatively to AGS and DIP ( P<0.05). It was correlated with a mechanism of substrate inductivity and product inhibition. Catalase activity had the similar trend of gradual increase along the elevation gradient, enhancing the fertility of the soil and the oxidative process of OM in the sediment. Along the succession series, from the tidal flat to the bulrush ( Scirpus mariqueter) zone, and then to the reed ( Phragmites australis) zone, the activity of sucrase only changed insignificantly, but there was a higher activity in the bulrush zone than in other zones. The activity of proteinase decreased from the tidal flat to the reed zone, and the activity was negatively correlated with OM and TN ( P<0.05), but positively with DIP ( P<0.05). Through the succession zones a decrease in the number of diatoms resulted in a decline in the concentration of protein, which influenced the proteinase activity, suggesting that the proteinase in the sediment was produced by diatoms.

Effects of Spartina alterniflora invasion on benthic nematode communities in the Yangtze Estuary

Invasions of exotic plant species in estuaries have occurred worldwide, and may pro- foundly affect native biodiversity and estuarine ecosystem functioning. To assess the effect of plant invasions on benthic meiofauna, we compared the nematode communities in marshes dominated, respectively, by invasive Spartina alterniflora and native Scirpus mariqueter and Phragmites australis at 3 local sites over 2 seasons in the Yangtze River estuary, PR China. S. alterniflora stands had gen- erally lower nematode trophic diversity than the stands of the 2 native plants, suggesting that the exotic plant led to a simplified benthic food web. The relative abundance of bacterial-feeding nema- todes tended to increase in S. alterniflora marshes compared to P. australis marshes. The increased bacterial-feeding nematodes in S. alterniflora stands are likely to reflect the altered decomposition processes, rates and pathways, which may, in turn, modify belowground nutrient cycling of the estu- arine ecosystems. The dissimilarity in nematode community structure between S. alterniflora and S. mariqueter marshes was smaller than that between S. alterniflora and P. australis marshes, and the dissimilarity between Spartina-invaded and native marshes was even smaller than between the 2 native plant marshes. It is suggested that the detection of the ecological consequences of plant inva- sions depends on which native plant species is considered. Site effects were generally detected in the comparison of sediment properties and nematodes among 3 plant marshes. Sediment water content, electrical conductivity, bacterial biomass and litter biomass were identified as the most important factors in the shaping of the nematode communities.

Summer-time denitrification and nitrous oxide exchange in the intertidal zone of the Yangtze Estuary

Sediment denitrification rates and nitrous oxide (N 2O) exchange fluxes in the Yangtze estuary intertidal zone (mudflats and salt marshes) were measured in summer-time using an acetylene inhibition technique and an in situ static closed chamber method. N 2O natural production rates ranged between 0.10 μmol N m −2 h −1 and 8.50 μmol N m −2 h −1, and the denitrification rates ranged from 18.71 μmol N m −2 h −1 to 35.87 μmol N m −2 h −1. The N 2O natural production rates in overlying water were low, with intertidal sediment being the source of overlying water N 2O during the submerged period. Data analysis indicated that most sediment N 2O was not derived from denitrification, but from several other nitrogen-cycling processes. During the low tide, the middle tidal marsh was the source of atmosphere N 2O (exchange fluxes changed between −11.03 μmol N m −2 h −1 and 13.17 μmol N m −2 h −1). 5 cm and 10 cm depth ground temperatures were significant factors controlling the emission flux. At the low tidal flat, N 2O emission flux rates ranged from −5.75 μmol N m −2 h −1 to 0.49 μmol N m −2 h −1 at the sediment-atmosphere interface. Overall, the middle tidal marsh was the source of atmospheric N 2O, while the low tidal flat was a sink for atmospheric N 2O. Plants of the intertidal zone ( Scirpus mariqueter and benthic algae) were significant factors controlling N 2O exchange flux. Photosynthesis of intertidal zone plants inhibited the emission of N 2O and induced consumption, while plant respiration may enhance N 2O emission from the intertidal zone. N 2O emission and consumption at the intertidal zone-atmosphere interface correlated positively with the emission and consumption of CO 2.

Uptake and distribution of N, P and heavy metals in three dominant salt marsh macrophytes from Yangtze River estuary, China

We examined the variation in aboveground biomass accumulation and tissue concentrations of nitrogen (N), phosphorus (P), copper (Cu), zinc (Zn) and lead (Pb) in Phragmites australis (common reed), Spartina alterniflora (salt cordgrass), and Scirpus mariqueter throughout the growing season (April-October 2005), in order to determine the differences in net element accumulation and distribution between the three salt marsh macrophytes in the Yangtze River estuary, China. The aboveground biomass was significantly greater in the plots of S. alterniflora than in the plots of P. australis and S. mariqueter throughout the growing season (P<0.05). In August, the peak aboveground biomass was 1246+/-89 gDW/m(2), 2759+/-250 gDW/m(2) and 548+/-54 gDW/m(2) for P. australis, S. alterniflora and S. mariqueter, respectively. The concentrations of nutrients and heavy metals in plant tissues showed similar seasonal patterns. There was a steady decline in element concentrations of the aboveground tissues from April to October. Relative element concentrations in aboveground tissues were at a peak during the spring sampling intervals with minimum levels during the fall. But the concentrations of total nitrogen and total phosphorus in the belowground tissues were relatively constant throughout growing season. Generally, trace metal concentrations in the aboveground tissues of S. mariqueter was the highest throughout the growing season, and the metal concentrations of S. alterniflora tissues (aboveground and belowground) were greater than those of P. australis. Furthermore, the aboveground pools of nutrients and metals were consistently greater for S. alterniflora than for P. australis and S. mariqueter, which suggested that the rapid replacement of native P. australis and S. mariqueter with invasive S. alterniflora would significantly improve the magnitude of nutrient cycling and bioavailability of trace metals in the salt marsh and maybe transport more toxic metals into the water column and the detrital food web in the estuary.

Impacts of introduced Spartinaalterniflora along an elevation gradient at the Jiuduansha Shoals in the Yangtze Estuary, suburban Shanghai, China

Although much research has focused upon the negative impacts of invasive Spartina alterniflora upon salt marshes dominated by other Spartina spp., little is known about its impacts upon native Scirpus mariqueter marshes. In 1997, S. alterniflora was introduced to the Jiuduansha Shoals, Yangtze Estuary, China, to accelerate the formation of marsh habitat via accretionary processes, with the larger goal of drawing waterfowl away from wetlands near the Pudong International Airport, Shanghai, China. In 2000, a nature reserve was established on the Jiuduansha Shoals, making the impact upon the native S. mariqueter community a high priority for research. Our objective was to quantify the impacts of introduced S. alterniflora and Phragmites australis to the native S. mariqueter-dominated community at this site in four elevation zones, as compared with a nearby natural shoal. We found that species diversity was greater in the lower elevations with the engineering, through elimination of the natural dominance of S. mariqueter. We also found that diversity was lessened in the higher elevations, due to rapid growth and exclusion by the planted S. alterniflora in conjunction with the native P. australis. Moreover, we found that the growth of the native S. mariqueter was stimulated when S. alterniflora was planted nearby. It is quite likely that the net effect of these ecological processes will be to accelerate further accretion, leading to an eventual replacement of the S. mariqueter-dominated community in the long-term. Future management approaches should focus upon harvesting, grazing, and perimeter-ditching the S. alterniflora to avoid this situation.

Short-term C 4 plant Spartina alterniflora invasions change the soil carbon in C 3 plant-dominated tidal wetlands on a growing estuarine Island

Spartina alterniflora is an invasive C 4 perennial grass, native to North America, and has spread rapidly along the east coast of China since its introduction in 1979. Since its intentional introduction to the Jiuduansha Island in the Yangtze River estuary, Spartina alterniflora community has become one of the dominant vegetation types. We investigated the soil carbon in the Spartina alterniflora community and compared it with that of the native C 3 Scirpus mariqueter community by measuring total soil carbon (TC), soil organic carbon (SOC), total soil nitrogen (TN), and the stable carbon isotope composition ( δ 13C) of various fractions. TC and SOC were significantly higher in Spartina alterniflora in the top 60 cm of soil. However, there was no significant difference in soil inorganic carbon (IC) between the two communities. Stable carbon isotopic analysis suggests that the fraction of SOC pool contributed by Spartina alterniflora varied from 0.90% to 10.64% at a soil depth of 0–100 cm with a greater percentage between 20 and 40 cm deep soils. The δ 13C decreased with increasing soil depth in both communities, but the difference in δ 13C among layers of the top 60 cm soil was significant ( p < 0.05 ), while that for the deeper soil layers (>60 cm) was not detected statistically. The changes in δ 13C with depth appeared to be associated with the small contribution of residues from Spartina alterniflora at greater soil depth that was directly related to the vertical root distribution of the species.

Wintering bird communities in newly‐formed wetland in the Yangtze River estuary

AbstractWe compared wintering bird communities and their habitats among three shoals at Jiuduansha, a newly‐formed wetland in the Yangtze River estuary. The highest species richness and diversity were recorded in Shangsha, which is the highest shoal, and the highest abundance and lowest species diversity were recorded in Xiasha, which is the lowest shoal. Shangsha had the largest abundance of perching birds whereas Xiasha was the most abundant in waterbirds. Bird assemblages showed different associations with the different habitat types—perching birds were favored by reed (Phragmites australis) communities, shallow water foragers and dabbling ducks preferred sea‐bulrush (Scirpus mariqueter) communities, and moist‐soil foragers and gulls showed a preference for bare intertidal zones. All bird assemblages, however, avoided the smooth cordgrass (Spartina alterniflora) communities, which are dominated by an alien invasive plant. The composition of avian communities was related to habitat types at the three shoals. Our results suggest that the newly‐formed tidelands can provide suitable habitats for waterbirds and that the lower tidelands can attract more waterfowl than the higher tidelands. Because the shoal with low species diversity could have exclusive bird species, conservation efforts should not concentrate only on the area with high species diversity. The estuarine wetlands should be considered as a whole when conservation strategies are designed. The alien invasive plant should, moreover, be effectively controlled, to provide suitable habitats for birds.

Multi-seasonal spectral characteristics analysis of coastal salt marsh vegetation in Shanghai, China

Remote sensing technology has become the primary tool for ecological research on a large scale. The spectral characteristics of the salt marsh vegetation canopy, including four main communities, Phragmites australis community, Spartina alterniflora community, Scirpus mariqueter community and Carex scabrifolia community, were measured in the seasons of spring, summer and autumn by a ground FieldSpec™ Pro JR spectroradiometer, at the Chongming Dongtan Nature Reserve in Shanghai. The spectral data were converted to the reflectance curves, and their first derivative curves between 350 nm and 1000 nm were calculated. The differences in the reflectance and first derivative curves were then analyzed, with particular attention paid to the characteristics in the bands of visible, “green peak”, “red edge” and near infrared. The results from this study showed that the different salt marsh communities had different and rather unique spectral characteristics during the three seasons studied. The near-ground spectral reflectance varied with the growing season, community type and its phenology. The discrimination ability, in terms of variations in the spectral reflectance, among the four major salt marsh communities was highest in autumn. It is proposed that a realistic strategy for classifying the salt marsh vegetation could be adopted by integrating and analyzing their remotely sensed images of multi-seasons. The implications of the results from this study in terms of serving as a tool for monitoring and mapping the distribution pattern and dynamics of salt marsh vegetation on the eastern coast of China are discussed.

IDENTIFICATION OF THE SPECTRAL CHARACTERISTICS OF SALTMARSH VEGETATION USING INDIRECT ORDINATION: A CASE STUDY FROM CHONGMING DONGTAN, SHANGHAI

Remote sensing is a major source of spatial information of the attributes of the earth's surface, and remote sensing technology has become a primary tool for vegetation classification at large scales. The relationship between vegetation and their spectral characteristics is key for interpreting remote sensing images. This study related characteristics of saltmarsh vegetation at the intertidal zone of Chongming Dongtan Nature Reserve, Shanghai, to patterns of their spectral reflectance. Paired measurements of saltmarsh community and spectral characteristics were carried out along three transects covering the major variations in vegetation and environment within the study area. The spectral characteristics were measured by a ground FieldSpec Pro JR spectroradiometer and the spectral data were converted to simulate the 10 bands of Compact Airborne Spectrographic Imager (CASI) bandset. The spectral data sets were then ordinated using Principal Component Analysis (PCA), an indirect ordination technique. The eigenvalue of the first PCA axis was 19.9, which represented 98.5% of the variation in the spectral data. A sequence of bare mudflat, Scirpus mariqueter community, Spartina alterniflora community and Phragmites australis community changed along the first ordination axis showed a strong correspondence with variation in the bands six to ten, i.e. the simulated CASI wavebands covering the 736 to 870 nm wavelengths. A significant relationship between the first axis PCA scores for the spectral data of quadrats and their percentage community cover and height also was identified. The second axis accounted for only 1.4% of the variation in the spectral data and it proved impossible to demonstrate any close link between any specific plant community type and a distinct set of spectral characteristics because of its low representation of the variation in the spectral data. Our study has demonstrated that the variation in the spectral data of saltmarsh vegetation at Chongming Dongtan Nature Reserve can be identified using the indirect ordination technique of PCA and then applying correlation and regression analyses to explain the relationships between the variation in the spectral data with the vegetation and ecological data. Our results indicate that PCA is of value for identifying relationships between community types and the spectral data of CASI bandsets for saltmarsh vegetation. This could provide an effective and practical approach for classification of saltmarsh vegetation at large scales and for monitoring spatio_temporally dynamic patterns of saltmarshes at Chongming Dongtan Nature Reserve. Further work is required in order to test these conclusions. The method has been evaluated for a single season with a limited sample of saltmarsh plant communities, and the application of PCA and spectral data of CASI bandsets to other saltmarsh vegetation as well as multi_seasonal spectral data are necessary to determine whether similar patterns emerge and whether the approach has more general applicability in terms of characterizing remote sensing/spectral imagery and community types in saltmarsh vegetation.

Effect of Scirpus mariqueter Vegetation on Salt Marsh Benthic Macrofaunal Community of the Changjiang Estuary

Benthic macrofaunal community structure was related to vegetation and sediment properties along a low to high marsh elevational gradient in Scirpus mariqueter marsh on the eastern coast of Chongming Island in the Changjiang estuary, China. Multivariate analysis indicated that there were significant differences in macrofaunal community structure between the marsh zones sampled. There were positive relationships between attributes of salt marsh vegetation and macrofaunal community. The main factors explaining macrofaunal community structure along the habitat gradient were shoot height and below-ground plant biomass. In the Scirpus mariqueter marsh studied, above-ground and below-ground plant structure formed a complex habitat, adding structural heterogeneity to the surface sedimentary environment. Habitat heterogeneity is important for supporting diverse macrofaunal assemblages.

Some growth characteristics and relative competitive ability of invasive Spartina alterniflora and native Scirpus mariqueter

Some growth characteristics and relative competitive ability of invasive Spartina alterniflora and native Scirpus mariqueter