Long-term changes of salt marsh communities by cattle grazing

Over a period of 9 years a grazing experiment was carried out in the mainland salt marsh of the Leybucht (Niedersachsen) with three stocking rates, namely, 0.5 ha^-1, 1 ha^-1, and 2 cattle ha^-1. These were also compared with an abandoned area. The results are based on sampling of the invertebrates in 1980, 1981, 1982, and 1988, and of the vegetation in 1980 and 1988. The rate of sedimentation is highest in the Puccinellia maritima-zone and decreases with the increase of stocking rates. The Elymus pycnanthus vegetation type becomes dominant in the higher salt marsh in the abandoned site. The canopy height decreases with increasing stocking rate, whereas a gradient in the structure of the vegetation develops with the lowest stocking rate. The population densities, the species-richness and the community diversity of invertebrates increases after the cessation of grazing. The high rate of sedimentation in the abandoned site promotes the immigration of species from higher salt marsh levels and adjacent grasslands, and eventually halotopophilous species and communities may disappear. On the other hand grazing reduces numerous species living both in or on upper parts of the vegetation or being sensitive to trampling by cattle. The community structure shows that the salt marsh ecosystem changed from a food web dominated by plant feeding animals to a food web dominated by animals foraging on detritus. The salt marsh management has to be differentiated into both ungrazed and lightly grazed areas (each 50%) or an overall grazing in large areas with less than 0.5 cattle ha^-1.     

Seasonal variation of fungal biomass in the sediment of a salt marsh in New Brunswick

In a marsh in New Brunswick, Canada, belowground biomass of Spartina alterniflora consistently exceeded aboveground biomass by a factor of approximately 9. Both values peaked in July. Redox potential of the sediment was negative at all levels tested (2, 6, and 11 cm below surface), and was negatively correlated with depth. Concentrations of ergosterol, a sterol typical of higher fungi, were negatively correlated with redox potential and were highest in roots and rhizomes in July and August, 1–3 cm below the surface. These maxima corresponded to a fungal content of approximately 0.6% per ash-free dry mass of Spartina material. Balsa wood panels buried in anaerobic salt marsh sediment were colonized by fungi within 12 weeks. Eight fungal species isolated from S. alterniflora roots did not grow in the absence of oxygen, but were able to grow downward into an anaerobic medium.Offprint requests to: F. Bärlocher.     

Seasonal patterns of CO2 and water vapor exchange of three salt marsh succulents

Summary Diurnal carbon dioxide exchange patterns of three salt marsh succulents, Borrichia frutescens, Batis maritima and Salicornia virginica, were determined on a seasonal basis in the marsh at Sapelo Island, Georgia. Year-round photosynthetic activity was observed in these species though winter rates of CO₂ exchange were reduced. Net primary productivity, estimated using gas exchange techniques, agreed with previously reported harvest data. The role of light and temperature in the control of seasonal photosynthetic changes was investigated. A similar variation in light utilization with season was found in all three species, while seasonal temperature acclimation was species dependent. Less than 20% of fixed CO₂ was lost through dark respiration in any of the species.Water use in the salt marsh succulents was found to be relatively inefficient. High rates of transpiration were observed both summer and winter in the succulents.The succulents were judged to be C₃ plants on the basis of several criteria.Contribution No. 391 from the University of Georgia Marine Institute     

Seasonal changes in fungal production and biomass on standing dead Scirpus lacustris litter in a northern prairie wetland

Decaying macrophytes are an important source of carbon and nutrients in fungal and bacterial communities of northern prairie wetlands. Dead macrophytes do not collapse into the water column immediately after death, and decomposition by fungi and bacteria begins while the plants are standing. The seasonal variations in fungal biomass and production on Scirpus lacustris stems, both above and below water, were measured to assess which environmental factors were dominant in affecting these variations in a typical prairie wetland. Fungal biomass and production were measured from early May to November, just prior to freeze-up. Fungal decomposition began and was greatest in the spring despite low water temperatures. The fungal production, as measured by the incorporation of [1-(14)C]acetate into ergosterol, ranged from 1.8 to 376 microg of C g of ash-free dry mass (AFDM)(-1) day(-1), and the biomass, as estimated by using ergosterol, ranged from nondetectable to 5.8 mg of C g of AFDM(-1). There was no significant difference in biomass or production between aerial and submerged portions of Scirpus stems. The water temperature was correlated with fungal production (r = 0.7, P < 0.005) for aerial stem pieces but not for submerged pieces. However, in laboratory experiments water temperature had a measurable effect on both biomass and production in submerged stem pieces. Changes in fungal biomass and productivity on freshly cut green Scirpus stems decaying in the water either exposed to natural solar radiation or protected from UV radiation were monitored over the summer. There was no significant difference in either fungal biomass (P = 0.76) or production (P = 0.96) between the two light treatments. The fungal biomass and rates of production were within the lower range of the values reported elsewhere, probably as a result of the colder climate and perhaps the lower lability of Scirpus stems compared to the labilities of the leaves and different macrophytes examined in other studies performed at lower latitudes.     

Seasonal changes in the microbial community of a salt marsh, measured by phospholipid fatty acid analysis

Microbial activity within the environment can have distinct geochemicaleffects, and so changes in a microbial community structure can result ingeochemical change. We examined seasonal changes in both the microbialcommunityand the geochemistry of an inter-tidal salt marsh in north-west England tocharacterise biogeochemical processes occurring at this site.Phospholipid fatty acid (PLFA) analysis of sediment samples collected atmonthly intervals was used to measure seasonal changes in microbial biomass andcommunity structure. The PLFA data were analysed using multivariate techniques(Ward's method and the Mahalanobis distance metric), and we show that the useofthe Mahalanobis distance metric improves the statistical analysis by providingdetailed information on the reasons samples cluster together and identifyingthedistinguishing features between the separate clusters. Five clusters of likesamples were defined, showing differences in the community structure over thecourse of a year.At all times, the microbial community was dominated by PLFA associated withaerobic bacteria, but this was most pronounced in summer (August). Theabundanceof branched fatty acids, a measure of the biomass of anaerobes, started toincrease later in the year than did those associated with aerobes and thefungalbiomarker 18:26 showed a brief late-summer peak.The salt marsh remained mildly oxic throughout the year despite the increase inmicrobial respiration, suggested by the large increases in the abundance ofPLFA, in the warmer months. The conditions therefore remained most favourablefor aerobic species throughout the year, explaining their continual dominanceatthis site. However, as the abundance of PLFA synthesised by anaerobesincreased,increases in dissolved Mn concentrations were observed, which we suggest weredue to anaerobic respiration of Mn(IV) to Mn(II). Overall, the geochemicalconditions were consistent with the microbial community structure and changeswithin it.     

Dynamics of bacterial and fungal communities on decaying salt marsh grass

Both bacteria and fungi play critical roles in decomposition processes in many natural environments, yet only rarely have they been studied as an integrated microbial community. Here we describe the bacterial and fungal assemblages associated with two decomposition stages of Spartina alterniflora detritus in a productive southeastern U.S. salt marsh. 16S rRNA genes and 18S-to-28S internal transcribed spacer (ITS) regions were used to target the bacterial and ascomycete fungal communities, respectively, based on DNA sequence analysis of isolates and environmental clones and by using community fingerprinting based on terminal restriction fragment length polymorphism (T-RFLP) analysis. Seven major bacterial taxa (six affiliated with the alpha-Proteobacteria and one with the Cytophagales) and four major fungal taxa were identified over five sample dates spanning 13 months. Fungal terminal restriction fragments (T-RFs) were informative at the species level; however, bacterial T-RFs frequently comprised a number of related genera. Amplicon abundances indicated that the salt marsh saprophyte communities have little-to-moderate variability spatially or with decomposition stage, but considerable variability temporally. However, the temporal variability could not be readily explained by either successional shifts or simple relationships with environmental factors. Significant correlations in abundance (both positive and negative) were found among dominant fungal and bacterial taxa that possibly indicate ecological interactions between decomposer organisms. Most associations involved one of four microbial taxa: two groups of bacteria affiliated with the alpha-Proteobacteria and two ascomycete fungi (Phaeosphaeria spartinicola and environmental isolate "4clt").     

Seasonal changes and vertical distribution of root standing biomass of graminoids and shrubs at a Siberian tundra site

Background &; aims

Elevated atmospheric CO₂ (eCO₂) can affect soil-plant systems via stimulating plant growth, rhizosphere activity and the decomposition of added (crop residues) or existing (priming) soil organic carbon (C). Increases in C inputs via root exudation, rhizodeposition and root turnover are likely to alter the decomposition of crop residues but will ultimately depend on the N content of the residues and the soil.

Methods

Two soil column experiments were conducted under ambient CO₂ (aCO₂, 390 ppm) and eCO₂ (700 ppm) in a glasshouse using dual-labelled (¹³C/¹⁵N) residues of wheat (Triticum aestivum cv. Yitpi) and field pea (Pisum sativum L. cv. PBA Twilight). The effects of eCO₂ and soil N status on wheat rhizosphere activity and residue decomposition and also N recovery from crop residues with different N status (C/N ratio 19.4–115.4) by different plant treatments (wheat, wheat + 25 mg N kg^?1 and field pea).

Results

Total belowground CO₂ efflux was enhanced under eCO₂ despite no increases in root biomass. Plants decreased residue decomposition, indicating a negative rhizosphere effect. For wheat, eCO₂ reduced the negative rhizosphere effect, resulting in greater rates of decomposition and recovery of N from field pea residues, but only when N fertiliser was added. For field pea, eCO₂ enhanced the negative rhizosphere effect resulting in lower decomposition rates and N recovery from field pea residue.

Conclusions

The effect of eCO₂ on N utilisation varied with the type of residue, enhancing N utilisation of wheat but repressing that of field pea residues, which in turn could alter the amount of N supplied to subsequent crops. Furthermore, reduced decomposition of residues under eCO₂ may slow the formation of new soil C and have implications for long-term soil fertility.

     

Nutrient changes in water flooding the high salt marsh

Summary Water samples were collected during inundation by the tides of the littoral Spartina patens vegetation. This grass is characterized by a more or less permanent inferior layer of dead grass which is thick and uniform enough to suggest a filtering system. Water analyses demonstrated clear variation with time in P, PO₄, and Mn; this variation corresponds with changes in the level of the water during high tide, as well as with the progressive inundation of the Spartina patens vegetation.

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Résumé Des échantillons d'eau ont été récoltés pendant l'inondation par la marée de la végétation littorale de Spartina patens. Cette graminée est caractérisée par une nappe plus ou moins permanente d'herbe morte suffisamment épaisse et uniforme pour suggérer un systéme de filtrage. Les analyses ont montré une variation nette dans le contenu de P, PO₄ et Mn, une variation qui correspond avec les changements dans le niveau d'eau pendant la marée haute, aussi avec l'inondation de la nappe d'herbe mentionnée.

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This work was carried out with the aid of funds from the National Science Foundation (Grant GB 568) and from the University of Wisconsin-Milwaukee Graduate School.

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Contribution No. 8 from the Center for Great Lakes Studies of the University of Wisconsin-Milwaukee.     

Root dynamics in a salt marsh over three consecutive years

The minirhizotron technique has been used to study root development in a salt marsh in the western part of the Nationalpark Niedersächsisches Wattenmeer during a three-year period. The objective of our study was to evaluate root depth distribution and seasonal changes in growth activities of natural plant root systems. Root number was counted at monthly intervals in the top soil layer (0–0.2 m) for every 2 cm soil depth. The number of roots was regarded as an easily detectable parameter reflecting root growth and decay.In general, highest rooting intensity was found in the soil's subsurface layer (0–0.08 m). The number of roots significantly decreased in deeper horizons of the soil. There was also a significant increase and decrease in the number of roots in the course of a year. The highest rooting intensity was found in late winter to early spring, which substantially decreased towards mid summer when the plants were in their reproductive phase. The data indicate that there is a clear seasonal pattern of root growth of salt marsh species.     

Co-development of wetland soils and benthic invertebrate communities following salt marsh creation

Wetlands Ecology and Management -     

Co-development of wetland soils and benthic invertebrate communities following salt marsh creation

The development of wetland soil characteristics andbenthic invertebrate communities were evaluated increated Spartina alterniflorasalt marshes inNorth Carolina ranging in age from 1 to 25 years-old.A combination of measurements from different-agecreated marshes as well as periodic measurements overtime on two marshes were used to (1) document rates ofwetland pedogenesis, especially soil organic matter,and, (2) explore relationships between soil andbenthic invertebrate community development. Soilmacro-organic matter (MOM, the living and dead rootand rhizome mat), organic C and N increased and bulkdensity decreased during the 25 years following marshestablishment. The most dramatic changes in bulkdensity, MOM, C and N occurred within the upper 10 cmof the soil with lesser changes below this depth.Created marshes were sinks for organic C (90–140g·m^-2·yr^-1) and N (7–11g·m^-2·yr^-1) but not for P (0–1g·m^-2·yr^-1). The density of benthicinvertebrates (>250 m) and subsurface-depositfeeding oligochaetes also increased over time oncreated salt marshes. Invertebrate and oligochaetedensity were strongly related to MOM content(r²= 0.83–0.87) and soil organic C(r²= 0.52–0.82) and N (r²= 0.62–0.84). Thesefindings suggest that, in created salt marshes,development of the benthic invertebrate community istied to marsh soil formation, especially accumulationof organic matter as MOM and soil. Field studies thatmanipulate the quantity and quality of soil organicmatter are needed to elucidate the relationshipbetween salt marsh pedogenesis and benthicinvertebrate community development.     

Seasonal dynamics and standing crops of biomass and nutrients in a subarctic tundra vegetation

Standing crops of biomass and nutrients were measured in Eriophorum vaginatum tussock tundra and on a north-facing slope, called the camp site, with similar species composition during the summer of 1976 at Eagle Creek, Alaska. These data were then compared to similar data collected at Meade River, Alaska in 1975. Four species are compared: Ledum palustre, Salix pulchra, Betula nana , and Eriophorum vaginatum . The density of aboveground individuals was greater at the tussock site than at the camp site. The total late season above- and belowground standing crop of organic matter and of biomass was greater at the camp site. The nitrogen and calcium contents of new leaves usually increased during the season while phosphorus and potassium contents decreased. Most of the nutrients were in the mosses and lichen compartments rather than in vascular plants.     

Production and standing crop patterns of giant cutgrass (Zizaniopsis miliacea) in a freshwater tidal marsh

Summary Growth cycles and production of aboveground and belowground giant cutgrass (Zizaniopsis miliacea (Michx.) Doell and Asch.) were studied in a freshwater tidal marsh along the lower Savannah River near Savannah, Georgia, USA. Minimum aboveground live standing crop (142 g/m²) occurred in March with a steady increase thereafter to an October maximum (1,039 g/m²) followed by a rapid decline. Giant cutgrass aboveground net primary production was approximately 1,530 g/m²/yr. Rhizomes (358 g/m²/yr) and roots (160 g/m²/yr) yielded an annual belowground production of 518 g/m²/yr. Total above and belowground annual net production was estimated at 2,048 g/m²/yr.Present Address: Institute of Ecology, University of Georgia, Athens, Georgia, 30602, USA     

Diversity, composition, and geographical distribution of microbial communities in California salt marsh sediments

The Pacific Estuarine Ecosystem Indicators Research Consortium seeks to develop bioindicators of toxicant-induced stress and bioavailability for wetland biota. Within this framework, the effects of environmental and pollutant variables on microbial communities were studied at different spatial scales over a 2-year period. Six salt marshes along the California coastline were characterized using phospholipid fatty acid (PLFA) analysis and terminal restriction fragment length polymorphism (TRFLP) analysis. Additionally, 27 metals, six currently used pesticides, total polychlorinated biphenyls and polycyclic aromatic hydrocarbons, chlordanes, nonachlors, dichlorodiphenyldichloroethane, and dichlorodiphenyldichloroethylene were analyzed. Sampling was performed over large (between salt marshes), medium (stations within a marsh), and small (different channel depths) spatial scales. Regression and ordination analysis suggested that the spatial variation in microbial communities exceeded the variation attributable to pollutants. PLFA analysis and TRFLP canonical correspondence analysis (CCA) explained 74 and 43% of the variation, respectively, and both methods attributed 34% of the variation to tidal cycles, marsh, year, and latitude. After accounting for spatial variation using partial CCA, we found that metals had a greater effect on microbial community composition than organic pollutants had. Organic carbon and nitrogen contents were positively correlated with PLFA biomass, whereas total metal concentrations were positively correlated with biomass and diversity. Higher concentrations of heavy metals were negatively correlated with branched PLFAs and positively correlated with methyl- and cyclo-substituted PLFAs. The strong relationships observed between pollutant concentrations and some of the microbial indicators indicated the potential for using microbial community analyses in assessments of the ecosystem health of salt marshes.     

Fungal biomass and decomposition in Spartina maritima leaves in the Mondego salt marsh (Portugal)

Spartina maritima (Curtis) Fernald is a dominant species in the Mondego salt marsh on the western coast of Portugal, and it plays a significant role in estuarine productivity. In this work, leaf litter production dynamics and fungal importance for leaf decomposition processes in Spartina maritima were studied. Leaf fall was highly seasonal, being significantly higher during dry months. It ranged from 42 g m^-2 in June to less than 6 g m^-2 during the winter. Fungal biomass, measured as ergosterol content, did not differ significantly between standing-decaying leaves and naturally detached leaves. Fungal biomass increased in wet months, with a maximum of 614 g g^-1 of ergosterol in January in standing-decaying leaves, and 1077 g g^-1 in December, in naturally detached leaves, decreasing greatly in summer. Seasonal pattern of fungal colonization was similar in leaves placed in litterbags on the marsh-sediment surface. However, ergosterol concentrations associated with standing-decaying and naturally detached leaves were always much higher than in litterbagged leaves, suggesting that fungal activity was more important before leaf fall. Dry mass of litterbagged leaves declined rapidly after 1 month (about 50%), mostly due to leaching of soluble organic compounds. After 13 months, Spartina leaves had lost 88% of their original dry weight. The decomposition rate constant (k) for Spartina maritima leaves was 0.151 month^-1.     

Proximate nutritive value changes during decomposition of salt marsh plants

Recognition of salt marsh plant detritus as a nutritious source of food for estuarine consumers prompted investigation of in situ decomposition and proximate nutritive values of three plants and their detritus namely: Spartina cynosuroides and Distichlis spicata (Gramineae) and Scirpus americanus (Cyperaceae) growing abundantly in Mississippi tidal marshes. During decomposition to particulate detritus, these plants retain 60–70% organic content and the caloric value either remains the same or increases slightly. Crude fiber, carbohydrate, and fat contents decline but protein shows 96–300% increase from dead plants to particulate detritus stage.