Estimation of primary production using five different methods in a Spartina alterniflora salt marsh

The aboveground production of Spartina alterniflora in a salt marsh in Barataria Bay, Louisiana, USA was estimated using five different harvest methods: peak standing crop (PSC), Milner-Hughes, Smalley, Wiegert-Evans, and Lomnicki et al., and a non-destructive method based on measurement of stem density and longevity. Annual production estimates were 831 ± 41, 831 ± 62, 1231 ± 252, 1873 ± 147 and 1437 ± 96 g dry wt m^–2 for each method, respectively. The average longevity of individually tagged young shoots was 5.2 ± 0.2 months, equivalent to an annual turnover rate of 2.3 crops per year. Among the five methods, Wiegert-Evans and Lomnicki et al. were considered more accurate than the other three because they corrected for mortality losses between sampling times. The Lomnicki et al. method was preferred over the Wiegert-Evans method because of its greater simplicity.     

Estimation of forest-stand net primary productivity using fraction phytomass distribution model

Methods for assessing the primary productivity of the forest stands between various tree species in different environmental conditions are considered. Methods for the primary productivity assessment using data on the phytomass fractions and stand wood stock have been proposed. It is shown that the Zipf-Pareto equation of the relationship between the phytomass of some tree fractions in the stand can be used for a primary productivity estimation of the stock volume. A model analogous to R. Solow’s macroeconomic model has been proposed to describe the processes of the phytomass growth in the forest stand.     

Latitudinal trends in Spartina alterniflora productivity and the response of coastal marshes to global change

Marshes worldwide are actively degrading in response to increased sea level rise rates and reduced sediment delivery, though the growth rate of vegetation plays a critical role in determining their stability. We have compiled 56 measurements of aboveground annual productivity for Spartina alterniflora , the dominant macrophyte in North American coastal wetlands. Our compilation indicates a significant latitudinal gradient in productivity, which we interpret to be determined primarily by temperature and/or the length of growing season. Simple linear regression yields a 27 g m⁻² yr⁻¹ increase in productivity with an increase of mean annual temperature by 1 °C. If temperatures warm 2–4 °C over the next century, then marsh productivity may increase by 10–40%, though physiological research suggests that increases in the north could potentially be offset by some decreases in the south. This increase in productivity is roughly equivalent to estimates of marsh lost due to future sea level change. If a warming-induced stimulation of vegetation growth will enhance vertical accretion and limit erosion, then the combined effects of global change may be to increase the total productivity and ecosystem services of tidal wetlands, at least in northern latitudes.     

Seasonal patterns of daily net photosynthesis,transpiration and net primary productivity of Juncus roemerianus and Spartina alterniflora in a Georgia salt marsh

Summary Studies of the seasonal CO₂ and water vapor exchange patterns of Juncus roemerianus and Spartina alterniflora were conducted in an undisturbed marsh community on Sapelo Island, Georgia. Daily patterns of net photosynthesis, transpiration, leaf diffusive conductance and water-use efficiency in response to ambient conditions were monitored on intact, in situ plants. Net primary productivity was calculated from the daytime CO₂ fixation totals, nighttime CO₂ loss, leaf standing stock and aboveground to belowground biomass ratios for each plant type.The tall form of S. alterniflora had higher rates of photosynthesis and higher water-use efficiency values which, in conjunction with low respiratory losses and large leaf standing crop, results in high values of net primary productivity. The environmental factors in the marsh which permit these physiological responses occur in less than 10% of the marsh. Overall, the physiological capabilities of the short form of S. alterniflora were reduced in comparison to the tall form, but the combination of environmental factors which determine the physiological responses of this form occur in a much greater portion of the marsh, and the short form of S. alterniflora dominates the Sapelo Island marshes.The response patterns of the C₃ species, J. roemerianus, differed somewhat from the height forms of S. alterniflora. A large, seasonally constant leaf standing crop coupled with moderate rates of photosynthesis resulted in a net primary productivity value which was between the tall and short height forms of S. alterniflora. However, as with the tall S. alterniflora, the environmental conditions under which this high productivity and high water loss rate can be sustained are restricted to specific regions of the environmental gradient in the marsh.Contribution No. 435 from the University of Georgia Marine Institute     

互花米草群落功率最大化倾向

植物新种进入新区域后,通过扰动或搅局,改变生态系统的结构,形成有特色的自组 织生态系统,趋向新条件下的功率最大化.本文应用能值分析的方法,分别对苏北互花米草 生态系统和光滩生态系统进行能值分析和系统评估.结果表明：互花米草生态系统每年能值 产出比光滩生态系统高1.52E+18 sej.能值密度是光滩的4.72倍,基础能值产出率约为光滩生态系统的5倍.互花米草生态系统能更有效地利用能量,增加系统内部的 能值贮存,实现系统内部的功率最大化.互花米草入侵某区域滩涂后,通过自组织促使整个互花米草生态系统趋于功率最大化,充分发挥生态服务功能,但由于其繁殖扩散过快,导致种群爆发,产生了一系列负面效应,如抑制本土物种、侵占航道、危害贝类养殖等.     

The relative importance of sexual and asexual reproduction in the spread of Spartina alterniflora using a spatially explicit individual-based model

This study investigates a spatially explicit, individual-based model for simulating the spread of invasive smooth cordgrass (Spartina alterniflora) in Yancheng coastal wetlands from 1995 to 2010. The model, which considers the landscape heterogeneity and changes detected by remote sensing, also reveals the relative importance of sexual and asexual reproduction in the spread by global sensitivity analysis. The model was verified as suitable for simulating the range expansion of S. alterniflora. The results show that: (1) although seedling recruitment is low, it significantly contributes to the range expansion of S. alterniflora. Removing sexual propagation greatly reduces the expansion rate. Rapid expansion requires both sexual and asexual reproduction; (2) in the global sensitivity analysis, the most significant affecters of S. alterniflora invasion were seed dispersal distance, adult survival rate and asexual recruitment survival rate. Sexual propagation contributes much more significantly to quick range expansion than asexual reproduction, but asexual reproduction is the main source of recruitment. Invasion control strategies should target a single reproduction mode. Here, limiting the germination and dispersal of seeds is suggested as a realistic strategy for controlling and managing invasion by this species.     

Effects of seasonality and environmental gradients on Spartina alterniflora allometry and primary production

Predictions of how salt marsh primary production and carbon storage will respond to environmental change can be improved through detailed datasets documenting responses to real‐world environmental variation. To address a shortage of detailed studies of natural variation, we examined drivers of Spartina alterniflora stem allometry and productivity in seven marshes across three regions in southern Louisiana. Live‐stem allometry varied spatially and seasonally, generally with short stems weighing more (and tall stems weighing less) in the summer and fall, differences that persist even after correcting for flowering. Strong predictive relationships exist between allometry parameters representing emergent stem mass and mass accumulation rates, suggesting that S. alterniflora populations navigate a trade‐off between larger mass at emergence and faster rates of biomass accumulation. Aboveground production and belowground production were calculated using five and four approaches, respectively. End‐of‐season aboveground biomass was a poor proxy for increment‐based production measures. Aboveground production (Smalley) ranged from 390 to 3,350 g m^?2 year^?1 across all marshes and years. Belowground production (max–min) was on average three times higher than aboveground; total production ranged from 1,400 to 8,500 g m^?2 year^?1. Above‐ and belowground production were both positively correlated with dissolved nutrient concentrations and negatively correlated to salinity. Synthesis: Interannual variation in water quality is sufficient to drive above‐ and belowground productivity. The positive relationship between nutrients and belowground production indicates that inputs of nutrients and freshwater may increase salt marsh carbon storage and ecosystem resilience to sea level rise.     

互花米草生物质能利用潜力

作为外来种,互花米草(Spartina alterniflora)对入侵地的生态系统产生了较强的干扰,但同时高生物量的互花米草也是一种潜在的生物质能源.发展生物质能是充分利用互花米草资源并控制其恶性扩张的较为有效和实用的途径,具有生态和经济双重效益.本文总结了互花米草生物质能的利用潜力,其表现为时间与空间上的生物量资源优势、高效的光合作用机制与高生产力、高贮能、较高的碳水化合物、蛋白质和脂肪储量以及不占用耕地等;同时介绍了互花米草生物质能开发利用现状,并指出互花米草生物质能的开发与利用有着光明的前景.     

沼泽湿地互花米草植物体传输与排放甲烷特征

于各测定月的小潮日,使用悬管装置采集气样并结合气相色谱测定,对闽江河口互花米草（Spartina alterniflora）沼泽湿地互花米草植株的甲烷传输量及其主要释放部位进行了研究,另又采用静态箱法-气相色谱法测定了互花米草沼泽湿地甲烷的排放通量,以此分析互花米草植物体甲烷传输对互花米草沼泽湿地甲烷排放通量的贡献率,最后测定了互花米草植株髓腔内的甲烷浓度。结果表明,不同生长阶段的互花米草植株甲烷传输量明显不同,快速生长阶段的互花米草植株甲烷传输量最高;互花米草植株甲烷传输对互花米草沼泽湿地甲烷排放通量的贡献率介于9%-94%之间;互花米草植物体传输甲烷的主要释放部位是距地面0-20cm处,该部位对植物甲烷传输量的贡献率为50%（平均值）;髓腔内的甲烷浓度远高于大气中的甲烷浓度,且自下而上呈递减趋势。     

Gas Transport in the Marsh Grass, Spartina alterniflora

Spartina plants have continuous gas spaces from the leaves tothe tips of the roots. Oxygen values in the roots are as lowas 3 per cent and increase toward the stem. Carbon dioxide valuesare highest in the rhizome and decrease up the stem and towardthe root tips. Oxygen and carbon dioxide moved through the plantsat equal rates for equal gradients, and these rates agree withmeasurements made on plants in the marsh. Calculated oxygenand carbon dioxide fluxes for the observed gradients in theobserved gas spaces agreed with measured fluxes. We concludethat gases move in and out of Spartina roots by diffusion throughuninterrupted gas spaces within the plant.     

Genotypic diversity enhances invasive ability of Spartina alterniflora

Although genetic diversity is very important for alien species, which have to cope with new environments, little is known about the role that genetic diversity plays in their invasive success. In this study, we set up a manipulation experiment including three levels of genotypic diversity to test whether genotypic diversity can enhance the invasive ability of alien species, in our case the invasive Spartina alterniflora in China, and to infer the underlying mechanisms. There was no significant relationship between genotypic diversity and parameters of performance in the first year; however, from the summer of the second year onwards, genotypic diversity enhanced four of the six parameters of performance. After two growing seasons, there were significant positive relationships between genotypic diversity and maximum spread distance, patch size, shoot number per patch, and aboveground biomass. Moreover, abundance of the native dominant species Scirpus mariqueter was marginally significantly decreased with genotypic diversity of S. alterniflora, suggesting that enhanced invasive ability of S. alterniflora may have depressed the growth of the native species. There was no significant difference in most measures of performance among six genotypes, but we observed a transgressive over performance in four measures in multiple‐genotype patches. At the end of the experiment, there were significant nonadditive effects of genotypic diversity according to Monte Carlo permutations, in six‐genotype, but not three‐genotype plots. Our results indicated that both additive and nonadditive effects played roles in the positive relationship between genetic diversity and invasion success, and nonadditive effects were stronger as duration increased.     

外来入侵种互花米草防治研究进展

互花米草在其原产地具有保滩护堤、促淤造陆等生态功能,但在被引入其他地区后,常给当地生态系统带来诸多负面影响,因此,互花米草常被视为入侵种,对互花米草的入侵性以及防控方面的研究成为一大热点.本研究从物理防治、化学防治、生物防治、生物替代防治、综合防治和防控策略6个方面综述了互花米草防治的最新研究进展,对各类措施的理论基础、技术方案、防治效果和环境影响等方面进行了分析,指出了现有防治技术的不足,并提出生态风险分区防控等建议.     

Populations of Anaerobic Phototrophic Bacteria in a Spartina alterniflora Salt Marsh

Habitat-simulating media were used with the Hungate anaerobic roll tube technique to enumerate culturable anaerobic photosynthetic bacteria in sediment, tidal waters, and Spartina alterniflora plant samples collected from the salt marsh at Sapelo Island, Ga. No phototrophs were detected in samples of creekside (low marsh) sediment or in tidal waters in creekside regions. In the high marsh region, 90% of anaerobic phototrophic bacteria occurred in the top 5 mm of sediment and none were detected below 6 mm. There was a seasonal variation, with maximal populations occurring in summer and fall (mean, 4.4 × 10⁵ phototrophs g of dry sediment⁻¹) and minimal numbers occurring in winter (mean, 3.9 × 10³ phototrophs g of dry sediment⁻¹). During winter and late spring, phototrophs had a patchy distribution over the high marsh sediment surface. In contrast, during late summer they had a random uniform distribution. Tidal water collected over high marsh sediment contained an average of 8.7 × 10² phototrophs ml⁻¹, with no significant seasonal variation. Anaerobic phototrophic bacteria were also cultured from the lower stem tissue of S. alterniflora growing in both the high (4.3 × 10⁴ phototrophs g of dry tissue⁻¹) and creekside (4.9 × 10⁴ phototrophs g of dry tissue⁻¹) marsh regions. Chromatium buderi, Chromatium vinosum, Thiospirillum sanguineum, Rhodospirillum molischianum, and Chlorobium phaeobacteroides were the predominant anaerobic phototrophic species cultured from high marsh sediment. The two Chromatium species were dominant.     

Ecological control and integral utilization of Spartina alterniflora

Spartina alterniflora Loisel (S. alterniflora) is native to the Atlantic and Gulf Coasts of North America and was introduced to China in 1979. Over the years, S. alterniflora played an important role in protecting coastal banks, accelerating sediment deposition, improving local economies, and alleviating natural disasters. As an exotic species, S. alterniflora has a very strong capability of propagation, which has caused some negative effects, such as occupying ecological niches of some seashells and blocking harbors by fast sediment deposition. As a result, ecological control of S. alterniflora in some areas has drawn wide attention from biologists and ecologists in China and abroad. For this paper, we studied the technology of topography and hydrology modification to substitute S. alterniflora with P. asutralis and reported our results in a project applying this technology. Furthermore, we studied various ways to make use of biomass of S. alterniflora and found that such ways were a good alternative to ecological control of S. alterniflora.     

三种类型互花米草抗盐生态型的分化

从美国引种成功的三种类型互花米草在不同NaCl浓度的盐渍生境中,叶细胞膜透性、渗透调节物(主要是K+、Na+)和氨基酸的变化以及光合作用、呼吸作用的变化都存在明显的差异,这是由于长期不同生境的选择和互花米草的基因型适应所造成的生态型分化的结果。按抗盐性分：G型抗性最强、F型最弱、N型居中。     

A comparison of the seed dormancy characteristics of Spartina patens and Spartina alterniflora (Poaceae)

Seed dormancy characteristics of Spartina alterniflora were delineated previously by Plyler and Carrick (American Journal of Botany, vol. 80, pp. 752–756, 1993). This study was undertaken in order to determine whether or not the dormancy characteristics of S. patens are similar. As in the previous study, the site of a dormancy mechanism was determined by assessing the germinability of surgically altered dormant seeds. Likewise, the effects of three growth-regulating substances (abscisic acid, fusicoccin, and gibberellic acid), prechilling, and light were studied by assessing the germinability of appropriately treated dormant seeds. Surgical injury to the endosperm, and to a lesser extent the scutellum, produced significant germination in S. patens, whereas only injury to the scutellum produced germination in S. alterniflora. Exogenously applied abscisic acid was highly effective in maintaining dormancy in injured seeds of both species. Gibberellic acid and fusicoccin were ineffective in promoting germination in S. patens, but fusicoccin was highly effective in breaking dormancy in 5. alterniflora. Prechilling was effective in breaking dormancy in S. patens but not in S. alterniflora. In S. patens, treatments that broke dormancy were only successful when seeds were exposed to light during the germination period. It is concluded that the dissimilarities in the dormancy mechanisms may be manifestations of the different environmental adaptations these closely related species display.     

Analysis of a diverse assemblage of diazotrophic bacteria from Spartina alterniflora using DGGE and clone library screening

Methods to assess the diversity of the diazotroph assemblage in the rhizosphere of the salt marsh cordgrass, Spartina alterniflora were examined. The effectiveness of nifH PCR-denaturing gradient gel electrophoresis (DGGE) was compared to that of nifH clone library analysis. Seventeen DGGE gel bands were sequenced and yielded 58 nonidentical nifH sequences from a total of 67 sequences determined. A clone library constructed using the GC-clamp nifH primers that were employed in the PCR-DGGE (designated the GC-Library) yielded 83 nonidentical sequences from a total of 257 nifH sequences. A second library constructed using an alternate set of nifH primers (N-Library) yielded 83 nonidentical sequences from a total of 138 nifH sequences. Rarefaction curves for the libraries did not reach saturation, although the GC-Library curve was substantially dampened and appeared to be closer to saturation than the N-Library curve. Phylogenetic analyses showed that DGGE gel band sequencing recovered nifH sequences that were frequently sampled in the GC-Library, as well as sequences that were infrequently sampled, and provided a species composition assessment that was robust, efficient, and relatively inexpensive to obtain. Further, the DGGE method permits a large number of samples to be examined for differences in banding patterns, after which bands of interest can be sampled for sequence determination.     

On the Relationship Between Sea Level and Spartina alterniflora Production

A positive relationship between interannual sea level and plant growth is thought to stabilize many coastal landforms responding to accelerating rates of sea level rise. Numerical models of delta growth, tidal channel network evolution, and ecosystem resilience incorporate a hump-shaped relationship between inundation and plant primary production, where vegetation growth increases with sea level up to an optimum water depth or inundation frequency. In contrast, we use decade-long measurements of Spartina alterniflora biomass in seven coastal Virginia (USA) marshes to demonstrate that interannual sea level is rarely a primary determinant of vegetation growth. Although we find tepid support for a hump-shaped relationship between aboveground production and inundation when marshes of different elevation are considered, our results suggest that marshes high in the intertidal zone and low in relief are unresponsive to sea level fluctuations. We suggest existing models are unable to capture the behavior of wetlands in these portions of the landscape, and may underestimate their vulnerability to sea level rise because sea level rise will not be accompanied by enhanced plant growth and resultant sediment accumulation.     

刈割与水位调节集成技术控制互花米草(Spartina alterniflora)

治理和控制外来物种互花米草（Spartina alterniflora）对维护崇明东滩自然保护区生物多样性具有重要的意义和必要性。研究在上海崇明东滩鸟类国家级自然保护区建立的受损滩涂湿地生态修复示范样地中开展“刈割与水位调节集成技术”治理互花米草的物理控制实验,以期寻求有效治理互花米草的控制技术。示范研究结果表明,单一的水位调节方法虽然可以降低互花米草群落的密度和叶面积指数（LAI）,但至水淹处理100d后,处理样区内互花米草的生长和生物量已与对照区无显著差异。单一的水位调节方法不能达到有效快速控制互花米草的效果。通过在互花米草生长关键期（7月的扬花期）刈割＋水位调节集成技术处理后,互花米草地上部分无再新生现象,至当年10月份（生长季末期）,样区内互花米草的地上部分和地下部分已完全死亡并开始腐烂,达到了有效控制互花米草的效果。因此,应用刈割＋水位调节集成技术治理互花米草,必须选择关键季节刈割互花米草地上部分,同时配合一定水位的持续淹水（约3个月）,才能有效发挥其迅速有效治理互花米草的效果。扬花期刈割＋水位调节集成技术可为沿海地区大范围防治互花米草扩散提供有效途径。