Spectral Discrimination of the Invasive Plant Spartina alterniflora at Multiple Phenological Stages in a Saltmarsh Wetland

Spartina alterniflora has widely invaded the saltmarshes of the Yangtze River Estuary and brought negative effects to the ecosystem. Remote sensing technique has recently been used to monitor its distribution, but the similar morphology and canopy structure among S. alterniflora and its neighbor species make it difficult even with high-resolution images. Nevertheless, these species have divergence on phenological stages throughout the year, which cause distinguishing spectral characteristics among them and provide opportunities for discrimination. The field spectra of the S. alterniflora community as well as its major victims, native Phragmites australis and Scirpus mariqueter, were measured in 2009 and 2010 at multi-phenological stages in the Yangtze River Estuary, aiming to find the most appropriate periods for mapping S. alterniflora. Collected spectral data were analyzed separately for every stage firstly by re-sampling reflectance curves into continued 5-nm-wide hyper-spectral bands and then by re-sampling into broad multi-spectral bands – the same as the band ranges of the TM sensor, as well as calculating commonly used vegetation indices. The results showed that differences among saltmarsh communities’ spectral characteristics were affected by their phenological stages. The germination and early vegetative growth stage and the flowering stage were probably the best timings to identify S. alterniflora. Vegetation indices like NDVI, ANVI, VNVI, and RVI are likely to enhance spectral separability and also make it possible to discriminate S. alterniflora at its withering stage.     

Classification of rhizosphere components using visible–near infrared spectral images

To establish new techniques for automatic classification of rhizosphere components, we investigated the utility of visible (VIS) and near–infrared (NIR) spectral images of the rhizosphere under two soil moisture conditions (mean volumetric water content: 0.39 and 0.16 cm³ cm^?3). Spectral reflectance images of the belowground parts of hybrid poplar cuttings (Populus deltoides × P. euramericana, I45/51) grown in a rhizobox were recorded at 120 spectral bands ranging from 480 to 972 nm. We examined which wavelengths were suitable and the number of spectral bands needed to accurately classify live roots of four age classes, dead roots, leaf mold, and soil. VIS reflectance (<700 nm) of live roots first increased and then decreased with age, whereas NIR reflectance (≥700 nm) was stable in mature roots. The reflectance of dead roots was lower than that of mature roots in both the VIS and NIR spectral regions. VIS reflectance did not differ among dead roots, leaf mold, and soil, but the NIR reflectance was clearly lower in soil than in the other materials. The reflectance of leaf mold and soil increased mainly in the NIR spectral region with reducing soil moisture, but this increase did not affect the order of reflectance intensity among the rhizosphere components in general. Although the most suitable spectral bands statistically selected for classifying rhizosphere components differed somewhat between moist and dry conditions, the spectral bands 580–679 nm (VIS) and 848–894 nm (NIR) provided high reliability under both conditions. Classification accuracy was higher when using two to five VIS–NIR images (overall accuracy ≥87.8%) than three VIS images (red, green, and blue; accuracy <67.1%). The high accuracy with VIS–NIR was mainly due to successful separation of leaf mold and soil. Irrespective of soil moisture condition, the overall accuracy tended to be stable at 92–94% with use of four VIS–NIR images. The spectral bands effective in wet soil conditions could also be used for classification in dry conditions, with overall accuracies >86.9%. These results suggest that automatic image analysis using VIS–NIR images at four spectral bands, including red and NIR, allows for accurate classification of the growth stage or live/dead status of roots and distinguishes between leaf mold and soil.     

闽江河口湿地植物枯落物立枯和倒伏分解主要元素动态

采用分解袋法,对闽江河口湿地2种挺水植物——芦苇(Phragmites australis)和互花米草(Spartina alterniflora)花和叶枯落物的立枯和倒伏分解过程及C、N、P元素动态进行研究。结果表明:(1)立枯分解是2种湿地盐沼植物重要的分解阶段,干物质损失率在13.26%—31.89%之间。多项式模型能较好描述2种植物花和叶的枯落物分解残留率动态。(2)立枯分解阶段,芦苇花和叶的C含量主要为波动下降,互花米草较为稳定;倒伏阶段后期,2种植物都以升高为主。立枯分解阶段2种植物枯落物N含量略有下降,而倒伏阶段逐渐上升。分解过程中枯落物P含量的波动较大。(3)2种植物花和叶C、N的NAI值在分解过程中<100%。芦苇的花和叶中P的NAI值在立枯和倒伏分解阶段都经历了明显下降和升高的过程,而互花米草在立枯阶段变化不大,倒伏阶段下降较为明显。(4)与芦苇相比,互花米草的花和叶枯落物C库较高,N库较低,P库差异不大。     

Sulfur storage changed by exotic Spartina alterniflora in coastal saltmarshes of China

For the purpose of ecological engineering, Spartina alterniflora was introduced to China in 1979 and now covers about 112,000 ha of China's coastal lands. It was hypothesized that S. alterniflora could actively change the habitat environment, thus facilitating its competition over native species. In Yancheng Nature Reserve, sulfur storage of sediments and plant tissues was compared among marshes dominated by the exotic S. alterniflora and adjacent native Suaeda salsa and Phragmites australis and bare mudflat. Results showed that the S. alterniflora marsh contained the highest content of water-soluble, adsorbed, carbonate-occluded and total sulfur in the sediment. The sulfur levels were higher in the center than at the edges of the S. alterniflora marsh. Native marshes showed no significant difference in sediment sulfur levels. With greater biomass and higher tissue sulfur concentrations, plant sulfur storage of S. alterniflora vegetation was also larger than those of the native vegetations. Because higher concentrations of sulfur increase the competitive advantage of S. alterniflora over native halophytes, the results of the research showing that S. alterniflora increased marsh sulfur storage may shed light on the mechanism of expansion of monospecific vegetation in coastal China.     

Wide Dynamic Range Vegetation Index for remote quantification of biophysical characteristics of vegetation

The Normalized Difference Vegetation Index (NDVI) is widely used for monitoring, analyzing, and mapping temporal and spatial distributions of physiological and biophysical characteristics of vegetation. It is well documented that the NDVI approaches saturation asymptotically under conditions of moderate-to-high aboveground biomass. While reflectance in the red region (rho(red)) exhibits a nearly flat response once the leaf area index (LAI) exceeds 2, the near infrared (NIR) reflectance (PNIR) continue to respond significantly to changes in moderate-to-high vegetation density (LAI from 2 to 6) in crops. However, this higher sensitivity of the rho(NIR) has little effect on NDVI values once the rho(NIR) exceeds 30%. In this paper a simple modification of the NDVI was proposed. The Wide Dynamic Range Vegetation Index, WDRVI = (a * rho(NIR-rho(red))/(a * rho(NIR) + rho(red)), where the weighting coefficient a has a value of 0.1-0.2, increases correlation with vegetation fraction by linearizing the relationship for typical wheat, soybean, and maize canopies. The sensitivity of the WDRVI to moderate-to-high LAI (between 2 and 6) was at least three times greater than that of the NDVI. By enhancing the dynamic range while using the same bands as the NDVI, the WDRVI enables a more robust characterization of crop physiological and phenological characteristics. Although this index needs further evaluation, the linear relationship with vegetation fraction and much higher sensitivity to change in LAI will be especially valuable for precision agriculture and monitoring vegetation status under conditions of moderate-to-high density. It is anticipated that the new index will complement the NDVI and other vegetation indices that are based on the red and NIR spectral bands.     

Crustacean metamorphosis: an omics perspective

We quantified the independent impacts of flooding salinity, flooding depth, and flooding frequency on the native species, Phragmites australis and Scirpus mariqueter, and on the invasive species Spartina alterniflora in the Yangtze River Estuary, China. Total biomass of all three species decreased significantly with increasing salinity, but S. alterniflora was less severely affected than P. australis and S. mariqueter. Elevated flooding depth significantly decreased their live aboveground biomass of P. australis and S. mariqueter, while S. alterniflora still had high live aboveground biomass and total biomass even at the highest flooding depth. These findings indicated that S. alterniflora was more tolerant to experimental conditions than the two native species, and an unavoidable suggestion is the expansion of this non-native species in relation to the native counterparts in future scenarios of increased sea-level and saltwater intrusion. Even so, environmental stresses might lead to significant decreases in total biomass and live aboveground biomass of all three species, which would potentially weaken their ability to trap sediments and accumulate organic matter. However, the relatively high belowground-to-aboveground biomass ratio indicated phenotypic plasticity in response to stressful environmental conditions, which suggest that marsh species can adapt to sea-level rise and maintain marsh elevation.     

Exotic Spartina alterniflora invasion alters ecosystem–atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China

Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH₄ and N₂O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH₄ emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH₄ ha^?1 for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH₄ emissions by 57–505%. In contrast, negative N₂O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO₂ exchange during the growing season in S. alterniflora and P. australis marshes. Annual N₂O emissions were 0.24, 0.38, and 0.56 kg N₂O ha^?1 in open water, bare tidal flat and S. salsa marsh, respectively, compared with ‐0.51 kg N₂O ha^?1 for S. alterniflora marsh and ?0.25 kg N₂O ha^?1 for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha^?1 yr^?1 in the top 100 cm soil profile, a value that was 2.63‐ to 8.78‐fold higher than in native plant marshes. The estimated GWP was 1.78, ?0.60, ?4.09, and ?1.14 Mg CO₂eq ha^?1 yr^?1 in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to ?11.30 Mg CO₂eq ha^?1 yr^?1 in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH₄ emissions, it can efficiently mitigate increases in atmospheric CO₂ and N₂O along the coast of China.     

Use of Hyperspectral Imagery to Assess Cryptic Color Matching in Sargassum Associated Crabs

Mats of the pelagic macroalgae Sargassum represent a complex environment for the study of marine camouflage at the air-sea interface. Endemic organisms have convergently evolved similar colors and patterns, but quantitative assessments of camouflage strategies are lacking. Here, spectral camouflage of two crab species (Portunus sayi and Planes minutus) was assessed using hyperspectral imagery (HSI). Crabs matched Sargassum reflectance across blue and green wavelengths (400–550 nm) and diverged at longer wavelengths. Maximum discrepancy was observed in the far-red (i.e., 675 nm) where Chlorophyll a absorption occurred in Sargassum and not the crabs. In a quantum catch color model, both crabs showed effective color matching against blue/green sensitive dichromat fish, but were still discernible to tetrachromat bird predators that have visual sensitivity to far red wavelengths. The two species showed opposing trends in background matching with relation to body size. Variation in model parameters revealed that discrimination of crab and background was impacted by distance from the predator, and the ratio of cone cell types for bird predators. This is one of the first studies to detail background color matching in this unique, challenging ecosystem at the air-sea interface.     

黄土高原冬小麦田光谱特征变化及其与二氧化碳日收支的相关分析

根据光谱辐射仪对黄土高原冬小麦整个生育期光谱反射率的连续观测数据及CO₂通量观测数据,对冬小麦田光谱特征变化及其与CO₂日收支的相关性进行了分析.结果表明：冬小麦田不同波长光谱反射率和归一化植被指数（NDVI）呈现明显的日变化和季节变化.同一天内,反射率随太阳高度角的变化而变化,变化最大的波段（550 nm左右、700～1 050 nm）表现为峰.不同生育期同一时刻,可见光波段（350～670 nm）反射率变化不大,近红外波段（700～1 050 nm）出现较大差异,在出苗期、分蘖期和越冬期后红边位置向长波方向“红移”;越冬期前出现向短波方向“蓝移” 的现象;但成熟期“蓝移”现象不明显,表现为突变;其他生育时期没有观测到波谱位移.NDVI的日变化呈U型,13：00左右最低,16：00后出现较大波动,与抛物线有较好的拟合效果,小麦生长旺盛时期,对其地面遥感观测应选择在NDVI变化不大的13：00左右进行;整个冬小麦生长季11:00反射率及NDVI以播种后第140天为中心对称,NDVI的季节变化表现为M型,可用四次多项式拟合;在整个小麦生育期中NDVI与CO₂的日收支呈极显著负相关,但正午左右的相关性稍差.     

Spartina alterniflora invasions in the Yangtze River estuary,China: An overview of current status and ecosystem effects

The Yangtze River estuary is an important ecoregion. However, Spartina alterniflora, native to North America, was introduced to the estuary in the 1990s through both natural dispersal and humans and now it is a dominant species in the estuarine ecosystems, with its invasions leading to multiple consequences to the estuary. S. alterniflora had great competitive effects on native species, including Scirpus mariqueter and Phragmites australis, and could potentially exclude the natives locally. The presence of S. alterniflora had little influence on the total density of soil nematodes and macrobenthonic invertebrates, but significantly altered the structure of trophic functional groups of nematode and macrobenthonic invertebrate communities. The conversion of mudflats to Spartina meadows had significant effects on birds of Charadriidae and Scolopacidae, which might be attributable to the reduction of food resources and the physical alterations of habitats for shorebirds. S. alterniflora invasions increased the primary productivity of the invaded ecosystems, and altered carbon and nitrogen cycling processes. Our studies focused mainly on the effects of S. alterniflora invasions on the structure of native ecosystems; thus further studies are clearly needed to investigate how ecosystem functioning is affected by the modification of the structure of estuarine ecosystems by S. alterniflora invasions.     

Impacts of Spartina alterniflora invasion on the benthic communities of salt marshes in the Yangtze Estuary,China

As a species for ecological engineering, Spartina alterniflora was introduced to Chongming Dongtan in 1995, and over the last 10 years, this species has rapidly invaded large areas of the Chongming Dongtan nature reserve. In this study, use of a normalized biomass size-spectra (NBSS) approach was explored to evaluate the possible impacts of S. alterniflora invasion on the benthic communities along gradients of intertidal zones and the invasion history of S. alterniflora within the nature reserve. The results showed that the characteristics of macrobenthic communities and the variation in macrobenthic communities described by the first two CCA axes revealed clearly the gradients of elevation and invasion history of S. alterniflora. The differences in the macrobenthic assemblages between the Spartina alterniflara marshes and the native Phragmites australis marshes decreased with increasing of invasion history of S. alterniflara. The macrobenthic biomass showed a decreasing trend, while the meiobenthic biomass showed a reverse trend along the elevation gradient. The macrobenthic biomass of S. alterniflora marshes with longer invasion history was higher than that at recently invaded S. alterniflora marshes, while the meiobenthic biomass was lower. The slopes of NBSS for the sampling sites showed a trend of steeper slopes with decreasing of elevation and at the recently invaded S. alterniflora marshes than that at marshes with longer invasion history, while the differences between the native P. australis marshes and the S. alterniflora marshes with long invasion history tended to be diminished. The NBSS approach could thus be used more widely to detect possible impacts of S. alterniflara invasion on benthic assemblages. This study also indicated the potential for this approach to provide valuable insights into the ecosystem ecology of invasive species, which could be very important for wetland biodiversity conservation and resource management in the Yangtze River Estuary and other such impacted areas.     

Temporal and spatial impact of <Emphasis Type="Italic">Spartina alterniflora</Emphasis> invasion on methanogens community in Chongming Island,China

Methane production by methanogens in wetland is recognized as a significant contributor to global warming. Spartina alterniflora (S. alterniflora), which is an invasion plant in China’s wetland, was reported to have enormous effects on methane production. But studies on shifts in the methanogen community in response to S. alterniflora invasion at temporal and spatial scales in the initial invasion years are rare. Sediments derived from the invasive species S. alterniflora and the native species Phragmites australis (P. australis) in pairwise sites and an invasion chronosequence patch (4 years) were analyzed to investigate the abundance and community structure of methanogens using quantitative real-time PCR (qPCR) and Denaturing gradient gel electrophoresis (DGGE) cloning of the methyl-coenzyme M reductase A (mcrA) gene. For the pairwise sites, the abundance of methanogens in S. alterniflora soils was lower than that of P. australis soils. For the chronosequence patch, the abundance and diversity of methanogens was highest in the soil subjected to two years invasion, in which we detected some rare groups including Methanocellales and Methanococcales. These results indicated a priming effect at the initial invasion stages of S. alterniflora for microorganisms in the soil, which was also supported by the diverse root exudates. The shifts of methanogen communities after S. alterniflora invasion were due to changes in pH, salinity and sulfate. The results indicate that root exudates from S. alterniflora have a priming effect on methanogens in the initial years after invasion, and the predominate methylotrophic groups (Methanosarcinales) may adapt to the availability of diverse substrates and reflects the potential for high methane production after invasion by S. alterniflora.     

Determinants of annual–perennial plant zonation across a salt–fresh marsh interface: a multistage assessment

Vegetation zonation patterns in coastal marshes are hypothesized to be the result of both physical stress and competitive interactions. How these patterns may be driven by these factors at different life history stages remains poorly understood. We investigated the relative importance of species tolerance (response to physical stress) and competitive ability in determining the distributions of two dominant marsh species across a salt–fresh marsh interface in the Yellow River Estuary, China. There is a steep gradient in salinity across this interface and Suaeda salsa, an annual, dominates the saline side of the interface, while Phragmites australis, a perennial species, dominates the freshwater side. Using a series of field transplants, we examined the roles of physical stress and competition in mediating this zonation at different life history stages. Suaeda salsa performed well in its home zone, but seedling emergence, seedling survival, adult survival and adult growth were significantly suppressed by competition in the freshwater P. australis zone. Emergence, survival and growth of P. australis were inhibited in the saline S. salsa zone, regardless of neighbor treatments, but it performed well in its home zone. The magnitude of the competitive effect on the performance of S. salsa differed among the life history stages. Competition from P. australis had a much stronger effect on S. salsa seedling emergence and adult growth than on seedling survival and adult survival. Our results reveal that both physical stress and competition contributed to the observed zonation patterns in this marsh system. However, for S. salsa, the effect of competition varied with life-history stage. Insight into these ecological processes is critical to understanding how the zonation pattern in the marsh system is formed and maintained.     

盖度与冠层水深对沉水植物水盾草光谱特性的影响

遥感技术可应用于大尺度实时监测沉水植物的分布与生长状况。然而沉水植物的光谱特征受其冠层在水下深度的影响,从而影响湖泊和河流中沉水植物的遥感影像解译与信息提取。应用地物光谱仪,通过野外原位测定和室外控制试验,实测了沉水植物水盾草(Cabomba caroliniana)群落冠层在水下不同深度的反射光谱,分析了冠层水深对水盾草反射光谱的影响,并建立了基于光谱反射率和冠层水深的水盾草群落盖度反演模型。研究结果表明(1)不同盖度的水盾草群落光谱反射率的基本特征主要体现在绿光和近红外波段;(2)水盾草群落的光谱反射率与冠层水深基本呈负相关,相同盖度水盾草群落的光谱反射率随冠层水深的增加而减小,在近红外波段尤其明显;(3)水盾草群落冠层水深越小,其盖度与光谱反射率的相关性越强,且水盾草群落盖度越大,其光谱反射率与冠层水深的相关性越显著;(4)水盾草光谱反射率与盖度相关的最佳波段在692—898 nm,与冠层水深相关最佳的波段在710 nm和806 nm附近;(5)在710 nm和806 nm处建立的结合冠层水深的修正模型,无论是回归方程决定系数(R2),还是水盾草群落盖度的反演精度都明显高于仅用光谱反射率反演盖度的简单模型,因此可有效减除冠层水深对反演精度的影响。本研究的结果可为遥感监测沉水植物的分布和动态变化,以及沉水植物生物物理参量反演提供科学依据。     

Nondestructive estimation of anthocyanins and chlorophylls in anthocyanic leaves

The anthocyanin and chlorophyll contents in leaves provide valuable information about the physiological status of plants. Thus, there is a need for accurate, efficient, and practical methodologies to estimate these biochemical parameters of vegetation. In this study, we tested the performance and accuracy of several nondestructive, reflectance-based techniques for estimating anthocyanin and chlorophyll contents in leaves of four unrelated species, European hazel (Corylus avellana), Siberian dogwood (Cornus alba =Swida alba), Norway maple (Acer platanoides), and Virginia creeper (Parthenocissus quinquefolia), with widely variable pigment content and composition. An anthocyanin reflectance index, which uses reflectances in the green and red edge spectral bands, and a modified anthocyanin reflectance index, employing, in addition, the near-infrared (NIR) band, were able to accurately estimate leaf anthocyanin for all species taken together with no reparameterization of algorithms. Total chlorophyll content was accurately estimated by a red edge chlorophyll index that uses spectral bands in the red edge and the NIR. These approaches can be used to estimate anthocyanin and chlorophyll nondestructively and allow the development of simple handheld field instrumentation.     

Hyperspectral leaf signature as an added dimension for species discrimination: case study of four tropical mangroves

Hyperspectral leaf reflectance of a plant provides unique information that is characteristic of that plant. The present investigation is a preliminary attempt to assess whether spectra of leaves of mangrove species recorded under field conditions contain adequate spectral information for discerning mangroves at species rank. The paper highlights the hyperspectral characteristics of leaf surfaces of four prominent tropical mangrove species, viz., Avicennia alba, Avicennia marina, Rhizophora mucronata and Sonneratia caseolaris, found in the tidal forests of India. Hyperspectral observations were recorded using a field spectroradiometer, and pre-processed and averaged reflectance values of samples for three types of arrangements, viz., (1) randomly arranged leaves, (2) dorsal leaf surfaces and (3) ventral leaf surfaces of the species were statistically tested using one-way ANOVA to see whether the values significantly differed at every spectral location. All the four species were statistically different at all the spectral locations with majority of the bands exhibiting 99% confidence level. Finally, discriminant analysis was performed to identify the bands for maximum separability for the three types of arrangement of the leaves of the species taken separately and in different combinations. The optimal Wilks’ Lambda (L) were achieved with: six, three, eleven, six, five, thirteen and eleven wavelengths for discriminating random leaves of the four species, dorsal and ventral surfaces of A. alba, A. marina, R. mucronata, S. caseolaris, upper leaf surfaces of all the species, lower leaf surfaces, respectively. Factor analysis was used as an added tool to identify the wavelengths that were uncorrelated and contained maximum information in the combination of selected wavelengths. The results confirmed the unique spectral signatures of the four species, which could be explained in terms of leaf properties unique to the species. Cellular structure and pigmentation of the isolateral leaves of S. caseolaris are very different from the dorsiventral ones of the other three, which significantly changed the reflectance characteristics of the species.     

Evaluation of reflectance spectroscopy indices for estimation of chlorophyll content in leaves of a tropical tree species

The effectiveness of eight spectral reflectance indices for estimating chlorophyll (Chl) content in leaves of Eugenia uniflora L., a tropical tree species widely distributed throughout the world and a key species for ecosystem restoration projects, was evaluated. Spectral reflectance indices were tested using sun and shade leaves with a broad variation in leaf mass per area (LMA). Shortly after plants were exposed to chilling temperatures, there was a dramatic visible change in some sun leaves from green to red. Prior to testing Chl-related reflectance indices, the green and red leaves were separated according to the anthocyanin reflectance index (ARI). Slightly green to dark green leaves corresponded to an ARI value less than 0.11 (n = 107), whereas slightly red to red leaves corresponded to an ARI value greater than 0.11 (n = 35). To estimate leaf Chl, two simple reflectance indices (SR₆₈₀ and SR₇₀₅), two normalized difference indices (ND₆₈₀ and ND₇₀₅), two modified reflectance indices (mSR₇₀₅ and mND705), a modified Chl absorption ratio index (mCARI₇₀₅) and an index insensitive to the presence of anthocyanins (CI_re) were evaluated. Good estimates of leaf Chl content were obtained using the reflectance indices tested regardless of the presence of anthocyanins and changes in LMA. Based on the coefficients of determination (r ²) and the root mean square errors (RMS?_c) the best results were obtained with reflectance indices measured at wavelengths of 750 and 705 nm. Considering the performance of the models the best reflectance indices to estimate Chl contents in E. uniflora leaves with a broad variation in LMA and anthocyanin contents was SR₇₀₅ and mCARI₇₀₅.     

用MODIS遥感数据监测东亚飞蝗灾害——以河北省南大港为例

东亚飞蝗自20世纪80年代以来在我国再度猖獗危害。本文选择国家一类蝗区河北省南大港农场水库为实验区,以2002年东亚飞蝗（夏蝗）大发生为背景,测定了不同受害程度芦苇的光谱曲线,并用MODIS遥感数据分析蝗灾危害范围和程度。结果表明,健康芦苇（未受害）呈现出典型植被光谱的“峰和谷”特征;而受害芦苇,其红光区处反射率增加,且受害程度越重,增加愈显著,近红外区的反射率则显著降低,且受害程度越重,反射率愈低。比较多时相归一化植被指数（NDVI）受灾前后的变化,NDVI值增加表明未受蝗虫危害,而其下降则表明是受灾区域,结合地面数据,找出了不同危害程度的NDVI临界值;其次根据像元累计法,确定了不同受灾程度的面积。结果显示,NDVI小于0.2156和0.2389分别为严重受灾区和中等受灾区,其发生面积依次为168.74 hm²和337.48 hm²,判对率分别为72.97%和68.35%。MODIS遥感监测蝗灾发生面积（中等受灾及严重受灾）占实际发生面积的82.76%。研究结果为实时、快速、大面积监测蝗虫种群动态奠定了基础,并为合理 、经济地防治蝗灾提供了科学依据。     

Impacts of introduced Spartina alterniflora 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.     

Interactions between the grass shrimp <Emphasis Type="Italic">Palaemonetes pugio</Emphasis> and the salt marsh grasses <Emphasis Type="Italic">Phragmites australis</Emphasis> and <Emphasis Type="Italic">Spartina alterniflora</Emphasis>

The grass shrimp Palaemonetes pugio, a species common to Spartina alterniflora-dominated marshes, may be sensitive to the invasion of the common reed Phragmites australis in northeastern US salt marshes. We examined two questions: (1) Do grass shrimp have a preference for the native plant over the non-native plant? (2) Are grass shrimp more effective foragers on P. australis? We tested the first hypothesis by comparing the amount of time shrimp spend in physical contact with the plant types over a 1-h period. Shrimp were observed under different arrangements of vegetation to control for differences in conspicuous structural features. Additionally, the amount of time shrimp spent foraging on S. alterniflora and P. australis shoots was compared to determine if shrimp graze more often on S. alterniflora. Shrimp spent significantly more time in contact with S. alterniflora only when plant types were grouped at opposite ends of aquaria, but did not exhibit a foraging preference for this plant type. To address our second question, we investigated the effects of shrimp foraging on stem epifauna, an assemblage of semi-aquatic invertebrates associated with macrophyte shoots. Previous research showed that P. australis supports a lower density of stem-dwelling epifauna relative to S. alterniflora. We hypothesized that the primary grazer of this community, P. pugio, can forage on P. australis stems more effectively due to structural differences between the two plants, causing the lower abundance of epifauna through top-down effects. We exposed individual shoots inhabited by epifauna to shrimp and compared faunal densities on exposed shoots to densities on control shoots after 18 h. The reduction of epifauna by predation was proportional on the two plant types. Therefore, top-down effects can be ruled out as an explanation for the patchy distribution of epifauna observed in P. australis–S. alterniflora marshes.