Influence of Mycorrhizal Inoculation, Inundation Period, Salinity, and Phosphorus Availability on the Growth of Two Salt Marsh Grasses, Spartina alterniflora Lois. and Spartina cynosuroides (L.) Roth., in Nursery Systems

Restoration of salt marsh ecosystems is an important concern in the eastern United States to mitigate damage caused by industrial development. Little attention has been directed to the mycorrhizal influence on plantings of salt marsh species to stabilize estuarine sediments and establish cover. In our study, seedlings of two salt marsh grasses, Spartina alterniflora and Spartina cynosuroides, were grown in soil with a commercial, mixed species inoculum of arbuscular mycorrhizal fungi. Plants were grown in experimental “ebb and flow” boxes, simulating three levels of tidal inundation, to which two levels of applied phosphorus (P) and two levels of salinity were imposed. After 2.5 months, S. alterniflora was poorly colonized by arbuscular mycorrhizae, developing only fungal hyphae and no arbuscules, but S. cynosuroides became moderately colonized. Mycorrhizal inoculation marginally improved growth and P and nitrogen (N) content of both plant species at low levels of P supply but significantly increased tillering in both plant species. This factor could be beneficial in enhancing ground cover during restoration procedures. Greater P availability increased the mycorrhizal status of S. cynosuroides and improved P nutrition of both plant species, despite a reduction in the root‐to‐shoot ratio. Increasing salinity reduced mycorrhizal colonization of S. alterniflora but not of S. cynosuroides. Growth and nutrient content of S. alterniflora was improved at higher levels of salinity, but only increased nutrient content in S. cynosuroides. Increased duration of tidal inundation decreased plant growth in both species, but tissue P and N concentrations were highest with the longest time of inundation in both species.     

EFFECTS OF SULFIDE ON THE GROWTH OF THREE SALT MARSH HALOPHYTES OF THE SOUTHEASTERN UNITED STATES

A hydroponic culture experiment was performed to ascertain whether sediment soluble sulfide at in situ concentrations plays a role in the determination of height forms of Spartina alterniflora in salt marshes of the United States. Additional experiments were conducted for both Spartina cynosuroides and Borrichia frutescens to determine if sulfide also influences the overall distribution of these species in the marsh. In situ soluble sulfide concentrations ranged from 0.02 mm in creek bank sites up to 3.0 mm in the inner marsh. In culture treatments, both plant height and biomass production of S. alterniflora were inhibited at a sulfide concentration as low as 1.0 mm , strongly suggesting a role for sulfide in the determination of height forms in the marsh. Production of S. cynosuroides was inhibited at high sulfide concentrations. However, over a range of concentrations similar to in situ values, no significant reduction in growth was observed, indicating sulfide was not a primary determinant of growth in stands of S. cynosuroides on Sapelo Island, Georgia. A sulfide concentration of 0.5 mm inhibited production in B. frutescens. In situ sulfide concentrations as high as 0.5 mm were found only in mixed stands of Juncus roemerianus and B. frutescens.     

Development and interspecific transferability of genic microsatellite markers in Spartina spp. with different genome size

Flow cytometry analysis showed variation of nuclear DNA content among different species of Spartina. Spartina alterniflora had the biggest genome (1763.9 Mbp) and S. cynosuroides had the smallest genome (756.35 Mbp), whereas the genomes of S. patens (969.36 Mbp) and S. spartinae (979.78 Mbp) were comparable. Mining simple sequence repeats (SSR) from 1227 expressed sequence tags (EST) generated from salt stressed S. alterniflora showed an abundance of di- and tri-nucleotide repeats. Of 100 ESSR (EST-derived SSR) loci with five or more repeats, 81 loci were successfully amplified in eight S. alterniflora genotypes and 15 (22.2%) ESSR markers were polymorphic. Eleven of the 15 polymorphic ESSRs showed amplification across six different species of Spartina while 100% cross transferability was observed with at least one species of Spartina. The average number of alleles per marker was 3.9 and 5.8 within S. alterniflora and among Spartina species, respectively. The ESSR markers discriminated different members within and between species of Spartina genus.     

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.     

Sensitivity of US Gulf of Mexico coastal marsh vegetation to crude oil: Comparison of greenhouse and field responses

Greenhouse and field studies were conducted to evaluate the effect of crude oil on selected US Gulf of Mexico coastal marsh species. Species showed different levels of sensitivity to oiling between greenhouse and field conditions. In greenhouse studies, two crude oils were used: South Louisiana crude oil (SLC) and Arabian Medium crude oil (AMC). The majority of Spartina patens plants died within one month following oiling with little or no recovery after three months. Panicum hemitomon and Spartina alterniflora were also adversely affected by oiling under greenhouse conditions but to a lesser extent than S. patens. The SLC or AMC oiling led to biomass reductions in S. alterniflora and S. patens. The dry biomass was not affected by oiling in P. hemitomon, Sagittaria lancifolia, Typha latifolia, and Scirpus olneyi. Results showed that S. patens plants were more sensitive to SLC as compared to AMC oil. Gross CO₂-C fixation data collected in the greenhouse indicated no differences in recovery among species across oiling treatments for S. lancifolia, S. olneyi, and T. latifolia. Field studies with S. alterniflora, S. patens and S. lancifolia demonstrated initial sensitivity of these species to oiling, and recovery following oiling with SLC. Our data also showed that caution must be employed whenever results from greenhouse studies are extrapolated to predict oil impact on vegetation under field conditions. Development of any sensitivity index of plant responses to oiling should not be based on greenhouse experiments only. Field evaluations should be included which best depict plant responses to oiling. Thus, restoration measures of US Gulf of Mexico coastal marshes following oiling should rely primarily on field studies. The field research suggests that the US Gulf of Mexico coastal marsh vegetation are likely to recover from oil spills naturally without the need for remediation procedures.     

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.     

A comparative study of above-ground productivity of dominant U.S. Gulf Coast marsh species

Above-ground productivity of dominant freshwater, brackish, and salt-marsh species from the U.S. Gulf Coast was evaluated using both gas exchange techniques and harvest methods. Both techniques showed significant differences in productivity among the study species which represent major components of their respective communities. Estimates of net aerial primary productivity using the harvest method yielded 3683 g dw (dry weight) m^?2yr^?1 for Spartina alterniflora (tall), 2008 g dw m^?2yr^?1 for S. alterniflora (short), 3677 g dw m^?yr^?1 for S. patens and 1641 g dwm^?yr^?1 for Panicum hemitomon. Carbon balance estimated from gas exchange calculation yielded values approximately equivalent to a biomass accumulation of 6024 g dw m^?2yr^?1 for S. alterniflora (tall), 3047 g dw m^?yr^?1 for S. alterniflora (short), 5702 g dw m^?yr^?1 for S. patens, and 2912 g dm^?yr^?1 for P. hemitomon. The net aerial primary production was estimated to be approximately 61% of total productivity in S. alterniflora (tall-form) and 66%o of total productivity in short-form, 64% in S. patens and 56%) in P. hemitomon. The assimilation data also indicated that Spartina alterniflora and S. patens continue carbon fixation throughout the year while assimilation in Panicum hemitomon is absent due to lack of live leaves during the winter. Various aspects of harvest and gas exchange techniques are discussed.     

Lignocellulosic structural changes of Spartina alterniflora after anaerobic mono- and co-digestion

Lignocellulosic structural changes of Spartina alterniflora after anaerobic digestion were investigated by Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry (XRD), and scanning electron microscopy (SEM). Batch experiments for anaerobic mono-digestion of S. alterniflora and co-digestion with potato at S. alterniflora to potato (SA:P) of 4:1 and 6:1 (based on volatile solids [VS]) were performed at 35 ± 1 °C at initial VS of 6%. FTIR spectroscopy study showed that the ratio of lignin to carbohydrate peak area for digested S. alterniflora was more than twice that for the undigested one, and the ratio of lignin to hemicellulosic peak area of samples from co-digestion was approximately twice that from mono-digestion, indicating co-digestion improved hemicellulosic degradation of S. alterniflora. This should attribute to the concentration increase of volatile fatty acids with a peak of about 11 g Ae l^?1 for co-digestion compared with 5 g Ae l^?1 for mono-digestion. XRD analysis indicated that anaerobic digestion decreased the crystallinity of S. alterniflora by 6.1–8.6%, but the degree of crystallinity decrease for co-digestion was slightly different from that of mono-digestion. SEM observation showed that physical structural destruction of S. alterniflora caused by co-digestion was similar to that caused by mono-digestion, and the degradation of S. alterniflora stem occurred mainly in vascular bundle tissue, whereas the degradation of parenchyma cells was not obvious.     

植被类型对盐沼湿地空气生境节肢动物功能群的影响

2007年4-11月,在长江口崇明东滩盐沼湿地的芦苇带、海三棱藨草带和互花米草带设置固定样地,每月小潮期对空气生境的节肢动物进行了扫网取样调查。在此基础上,分析研究了盐沼湿地空气生境节肢动物功能群特征以及植被类型的影响,特别是对互花米草的生态效应进行了进一步讨论。调查期间共获得节肢动物标本3778头,分属2纲11目37科49种。根据不同种类的营养特征将其划分为植食性、捕食寄生性和腐食性三大功能群。其中,植食性功能群的种类、数量最为丰富,涉及1纲6目19科25种,物种数占总数的51.0%,个体数占总数的86.2%;捕食寄生性功能群次之,涉及2纲7目15科21种,物种数占总数的42.9%,个体数占总数的7.8%;腐食性功能群种类、数量最少,涉及1纲1目3科3种,物种数占总数的6.1%,个体数占总数的6.0%。不同植被带捕食寄生性功能群与植食性功能群均具有一定的"天敌跟随"特征,但主要表现在物种数上,而在个体数上的对应关系并不明显。不同植被带功能群的组成、多样性及月际变化特征存在一定差异,但是植被类型对功能群的影响并不显著。与已有研究结果不同,研究中外来种互花米草对空气生境的节肢动物并未表现出显著的负面影响,相应节肢动物功能群的物种数、个体数、多样性、月际变化等特征与其他植被带并没有显著差异。就植食性功能群而言,尽管互花米草带植食性功能群的个体数明显低于其它植被带,但是物种数并没有减少,相应的作用机理还有待进一步研究。     

Differences in macrobenthic faunal communities in mangrove wetland habitats (Zhanjiang,China) invaded and non-invaded by exotic cordgrass <Emphasis Type="Italic">Spartina alterniflora</Emphasis>

Mangroves are essential for maintaining local biodiversity and human well-being, and mangrove structure and functioning depend on the macrobenthos. Although exotic cordgrass, Spartina alterniflora, is an increasing threat to the mangrove wetlands (including the associated unvegetated shoals) of China, its effects on the macrobenthic fauna in such wetlands is poorly understood. The macrobenthic faunal communities were compared in (1) an Avicennia marina monoculture vs. an S. alterniflora-invaded A. marina stand (a mixture of A. marina and S. alterniflora) and in (2) an unvegetated shoal vs. an S. alterniflora-invaded shoal that had rapidly become an S. alterniflora monoculture in Zhanjiang, China. S. alterniflora invasion significantly increased plant density regardless of invaded habitat but significantly increased the contents of total carbon, organic matter, and total sulfur in the sediment only in the unvegetated shoal. The presence of S. alterniflora had little influence on indices of the macrobenthic faunal community in the A. marina monoculture, but significantly decreased the density and biomass of macrobenthic faunal community in the unvegetated shoal. These results indicate that the effects of S. alterniflora on the macrobenthic faunal community depend on which type of mangrove habitat is invaded. The composition of the macrobenthic faunal community was more similar between the invaded and non-invaded A. marina stand than between the invaded and non-invaded unvegetated shoal. Overall, the differences in the macrobenthic faunal community between invaded and non-invaded habitats were associated with increases in the sediment organic matter content and plant density.     

Development and interspecific transferability of genic microsatellite markers in Spartina spp. with different genome size

Flow cytometry analysis showed variation of nuclear DNA content among different species of Spartina. Spartina alterniflora had the biggest genome (1763.9 Mbp) and S. cynosuroides had the smallest genome (756.35 Mbp), whereas the genomes of S. patens (969.36 Mbp) and S. spartinae (979.78 Mbp) were comparable. Mining simple sequence repeats (SSR) from 1227 expressed sequence tags (EST) generated from salt stressed S. alterniflora showed an abundance of di- and tri-nucleotide repeats. Of 100 ESSR (EST-derived SSR) loci with five or more repeats, 81 loci were successfully amplified in eight S. alterniflora genotypes and 15 (22.2%) ESSR markers were polymorphic. Eleven of the 15 polymorphic ESSRs showed amplification across six different species of Spartina while 100% cross transferability was observed with at least one species of Spartina. The average number of alleles per marker was 3.9 and 5.8 within S. alterniflora and among Spartina species, respectively. The ESSR markers discriminated different members within and between species of Spartina genus.     

THE EFFECT OF AERATION ON THE GROWTH OF SPARTINA ALTERNIFLORA LOISEL.

A greenhouse experiment was designed to investigate the correlations between waterlogging and aeration, and associated changes in pH, redox potentials and sulfide concentrations, on the growth of Spartina alterniflora Loisel. Elemental concentrations of the aerial and root material were determined and used for correlations with growth response. Redox potentials adjusted to pH 7 (Eh 7) ranged from −184 mv to 5 mv and were highly correlated (r) with aerial and root dry weight biomass (.97 and .97, respectively) and plant height (1.0). The range of soil pH at the conclusion of the study was 6.07 to 6.74 and was negatively correlated with aerial and root dry weight biomass. Sulfide concentrations ranged from 10–² to 10–⁷ m and vorrelations with aerial and root dry weights and height were −.85, −.85 and −.87, respectively. High negative correlations were found between sodium and sulfur concentrations and S. alterniflora growth. Positive correlations between potassium, phosphorus, manganese, zinc, copper, iron and growth response were also observed. Correlations of elemental concentrations of the plants with redox potentials and/or pH suggest that these two physical variables may be responsible in part for the regulation of 5. alterniflora growth in nature by regulating availability of nutritional elements.     

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.     

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。     

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.     

人工管理和自然驱动下盐城海滨湿地互花米草沼泽演变及空间差异

将盐城国家级自然保护区核心区划分为人工管理区和自然湿地区两种模式,根据2000年、2006年、2011年3个时相的ETM+影像,运用RS、GIS技术和景观生态学方法,分析不同驱动力下互花米草沼泽景观变化的差异.结果表明:(1)人工管理区,2000-2011年,互花米草沼泽面积由272hm2增加到781hm2;平均分维数呈下降的趋势,聚合度指数呈上升的趋势,表明互花米草沼泽在空间上趋于聚集,在形状上趋于规则;从互花米草沼泽增长速率看,2000-2011年,呈现先快后慢的特征.在景观空间演变上,互花米草沼泽的平均宽度从598.679m增加到1719.002m,表现出向海陆两个方向扩张的特征.(2)自然湿地区,2000-2011年互花米草沼泽面积由2023hm2增加到3974hm2;平均分维数和聚合度指数呈先上升后下降的趋势;米草沼泽增长稳定,年增长约160-180 hm2/a,单位长度岸线年增长面积约为15 hm2· km-1·a-1左右;比较发现,自然湿地区互花米草沼泽的增长速度高于人工管理区的增长速度.在景观空间演变上,互花米草沼泽平均宽度从1625.586m增加到3193.317m,2000-2006年表现出向海洋单方向扩张的特征,2006-2011年表现出向海陆两个方向扩张的性质.(3)在自然条件下互花米草沼泽扩张受到气候、地貌过程、水文过程、植被类型及种间竞争的影响,表现出明显的带状特征.在人工管理下,通过建设拦水堤坝等,阻止了潮汐作用下海水的扩散能力,生态过程发生改变,致使生态系统类型向淡水湿地方向演变,抑制了互花米草沼泽的扩张,表现出一定的镶嵌格局.     

Seasonal variation in CH4 emission and its 13C-isotopic signature from Spartina alterniflora and Scirpus mariqueter soils in an estuarine wetland

Although invasions by non-native species represent a major threat to biodiversity and ecosystem functioning, little attention has been paid to the potential impacts of these invasions on methane (CH₄) emission and its ¹³C-CH₄-isotope signature in salt marshes. An invasive perennial C₄ grass Spartina alterniflora has spread rapidly along the east coast of China since its introduction from North America in 1979. Since its intentional introduction to the Jiuduansha Island in the Yangtze River estuary in 1997, S. alterniflora monocultures have become the dominant component of the Jiuduansha’s vegetation, where monocultures of the native plant Scirpus mariqueter (a C₃ grass) used to dominate the vegetation for more than 30 years. We investigated seasonal variation in soil CH₄ emission and its ¹³C-CH₄-isotope signature from S. alterniflora and S. mariqueter marshes. The results obtained here show that S. alterniflora invasion increased soil CH₄ emissions compared to native S. mariqueter, possibly resulting from great belowground biomass of S. alterniflora, which might have affected soil microenvironments and /or CH₄ production pathways. CH₄ emissions from soils in both marshes followed similar seasonal patterns in CH₄ emissions that increased significantly from April to August and then decreased from August to October. CH₄ emissions were positively correlated with soil temperature, but negatively correlated with soil moisture for both S. alterniflora and S. mariqueter soils (p?<?0.05). The δ¹³C values of CH₄ from S. alterniflora, and S. mariqueter soils ranged from -39.0‰ to -45.0‰, and -37.3‰ to -45.7‰, respectively, with the lowest δ¹³C values occurring in August in both marshes. Although the leaves, roots and soil organic matter of S. alterniflora had significantly higher δ¹³C values than those of S. mariqueter, S. alterniflora invasion did not significantly change the ¹³C- isotopic signature of soil emitted CH₄ (p?>?0.05). Generally, the CH₄ emissions from both invasive S. alterniflora and native S. mariqueter soils in the salt marshes of Jiuduansha Island were very low (0.01–0.26 mg m^-2 h^-1), suggesting that S. alterniflora invasion along the east coast of China may not be a significant potential source of atmospheric CH₄.     

Using sediment alginate amendment as a tool in the restoration of Spartina alterniflora marsh

Growth and survival of transplanted vegetation for salt marsh restoration can be greatly affected by edaphic conditions. We investigated the potential for an organic carbon sediment amendment, alginate, to enhance establishment and growth of Spartina alterniflora transplants, as well as colonization by macroinvertebrates commonly associated with S. alterniflora (Uca sp. and Littoraria irrorata). Plots were established in a bare mud area previously inhabited by S. alterniflora, and transplant rhizospheres were either treated with alginate or left unamended as controls. Growth of transplanted S. alterniflora and colonization by Uca sp. and L. irrorata were evaluated over portions of three growing seasons. Within the first month post-transplantation, a nonsignificant trend toward greater live stem density emerged, but disappeared completely by week ten. Both Uca sp. and L. irrorata densities were significantly greater in the alginate treatment compared to the control only during the first ten weeks post-transplantation. However, the initial organic content of the sediment in the transplant area was more than twice that in the adjacent natural marsh. Therefore, our findings suggest that a threshold level of sediment organic matter above which alginate addition does not confer an advantage on transplanted S. alterniflora may exist, and the conditions under which amendments are most beneficial to transplanted S. alterniflora should be determined.     

UNDERGROUND BIOMASS PROFILES AND PRODUCTIVITY IN ATLANTIC COASTAL MARSHES

An underground biomass profile and productivity study involved year-long sampling programs in 18 stands of salt marsh plants in Georgia, Delaware, and Maine. As the result of the monthly or bimonthly marsh coring program three types of underground biomass profiles were found. In the first, the concentration of macro-organic matter (MOM) was uniform with depth; the notable example of this type was creekbank Spartina alterniflora in the southern part of the coast. A second type had a high MOM concentration at the surface which decreased with depth. This, the most common type of profile, was exemplified by Spartina patens, S. alterniflora from the high marsh along the southern coast (Georgia), and creekbank S. alterniflora from the northern part of its range (Maine). The third type of profile was seen where a large rhizome mat developed 15–20 cm below the surface. Spartina cynosuroides and Phragmites communis were typical examples of this type of profile, resulting in a low biomass at the surface, a higher biomass somewhat below the surface, and a low concentration at depth. The annual maxima and minima of MOM biomass were used to calculate annual increments, which can be considered minimum annual production values. These productivity values ranged from a low of 80 g C/m² for creekhead S. alterniflora in Maine to a high of 1690 g C/m² for Juncus gerardi in Maine. The mean for all plant stands was 650 g C/m². Since the average carbon content of the MOM was 35.3%, this corresponds to 1850 g dry weight/m² per year. As a measure of the relative activity of the total pool of macro-organic material in the soil, turnover times were calculated by dividing the total macro-organic matter by the annual increments. Within the MOM pool there are several components with turnover times varying from days to years. The turnover time for the entire pool ranged from 18 months in two Georgia salt marsh plant stands to 224 months for one in Maine. In the two instances where values for a species could be compared between Maine and Georgia, the turnover time was shorter at the more southerly site. These results can probably be attributed to slower microbial decay rates in the cooler climate. In Georgia and Maine where the turnover values for a species were determined for two elevations, the time was shorter at the lower elevation.