Arbuscular mycorrhizal fungal propagules in a salt marsh

The tolerance of indigenous arbuscular mycorrhizal fungi (AMF) to stressful soil conditions and the relative contribution of spores of these fungi to plant colonization were examined in a Portuguese salt marsh. Glomus geosporum is dominant in this salt marsh. Using tetrazolium as a vital stain, a high proportion of field-collected spores were found to be metabolically active at all sampling dates. Spore germination tests showed that salt marsh spores were not affected by increasing levels of salinity, in contrast to two non-marsh spore isolates, and had a significantly higher ability to germinate under increased levels of salinity (20) than in the absence of or at low salinity (10). Germination of salt marsh spores was not affected by soil water levels above field capacity, in contrast to one of the two non-marsh spore isolates. For the evaluation of infectivity, a bioassay was established with undisturbed soil cores (containing all types of AM fungal propagules) and soil cores containing only spores as AM fungal propagules. Different types of propagules were able to initiate and to expand the root colonization of a native plant species, but spores were slower than mycelium and/or root fragments in colonizing host roots. The AM fungal adaptation shown by this study may explain the maintenance of AMF in salt marshes.     

Plant regeneration from embryogenic suspension cultures of dune reed

Embryogenic callus, derived from mature seeds of dune reed (Phragmites communisTrinius) was used to establish suspension culture. Green shoot-forming type and albino shoot-forming type embryogenic callus of dune reed were selected carefully by the difference of shape and color of callus growing under light and mechanically dispersed before suspending in liquid MS medium supplemented with 1.0 mg l^–12,4-D. They were subcultured every 5 days to remove mucilaginous material in the early culture stage. Both fine albino and green shoot-forming cell suspension lines of dune reed were composed of rapidly growing small cell aggregates that were densely cytoplasmic and potentially embryogenic. Globular somatic embryos were continuously produced in each liquid medium containing 1.0 mg l^–1 2,4-D. The cell aggregates in fine albino cell suspension line (size below 300 m) were smaller than that of green shoot-forming cell suspension line (size between 300 and 800 m). Following transfer to a differentiation medium, both suspension cultures formed regenerating plants with normal roots and albinotic or green shoots, respectively.     

Tolerance and bioaccumulation of copper in Phragmites australis and Zea mays

The effects of copper on the growth, tolerance indices, mineral composition (N, P, K, Fe, Zn and Mn) and metal uptake of reed (Phragmites australis [Cav. Trin. ex Steudel]) and maize (Zea mays L.) were investigated in hydroponic experiments at copper concentrations ranging from 0.5 to 157 M Cu. A reduction in root length was shown to be a good indicator of copper toxicity, concentrations of 15.7 and 78.7 M Cu inhibiting root growth in maize and reed, respectively. The reed was significantly more tolerant of copper than maize and at 7.85 M Cu (external concentration), reed can be described as a Cu tolerant plant, and maize as a Cu non-tolerant species. As a result of Cu toxicity, the concentrations of macronutrients N, P and K decreased in both shoot and root of maize, while the concentrations were hardly affected in reed tissues. Fe concentration increased in shoots and roots of maize and in roots of reed with increasing Cu treatments, leading to highly significant (p<0.01) linear relationships between tissue Fe and Cu concentrations. The bioconcentration factor (BCF) of Cu was higher in roots than in shoots of both plant species, ranging from 612 to 1592 in reed for the Cu treatments tested. In the roots of maize, BCF of Cu increased from 349 to 1931 when increasing Cu in nutrient solution from 7.85 M to 78.5 M. Therefore, reed could be useful in wastewater treatments for the removal of Cu. However, the use of reed in phytoextraction of Cu from contaminated soils is limited by the low accumulation rate in shoots and although reed can be more efficient than maize for Cu phytoextraction, harvesting the full biomass, including roots, may be required.     

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.     

A geostatistical analysis of small-scale spatial variability in bacterial abundance and community structure in salt marsh creek bank sediments

Small-scale variations in bacterial abundance and community structure were examined in salt marsh sediments from Virginia's eastern shore. Samples were collected at 5 cm intervals (horizontally) along a 50 cm elevation gradient, over a 215 cm horizontal transect. For each sample, bacterial abundance was determined using acridine orange direct counts and community structure was analyzed using randomly amplified polymorphic DNA fingerprinting of whole-community DNA extracts. A geostatistical analysis was used to determine the degree of spatial autocorrelation among the samples, for each variable and each direction (horizontal and vertical). The proportion of variance in bacterial abundance that could be accounted for by the spatial model was quite high (vertical: 60%, horizontal: 73%); significant autocorrelation was found among samples separated by 25 cm in the vertical direction and up to 115 cm horizontally. In contrast, most of the variability in community structure was not accounted for by simply considering the spatial separation of samples (vertical: 11%, horizontal: 22%), and must reflect variability from other parameters (e.g., variation at other spatial scales, experimental error, or environmental heterogeneity). Microbial community patch size based upon overall similarity in community structure varied between 17 cm (vertical) and 35 cm (horizontal). Overall, variability due to horizontal position (distance from the creek bank) was much smaller than that due to vertical position (elevation) for both community properties assayed. This suggests that processes more correlated with elevation (e.g., drainage and redox potential) vary at a smaller scale (therefore producing smaller patch sizes) than processes controlled by distance from the creek bank.     

Estimating root lifespan of two grasses at contrasting elevation in a salt marsh by applying vitality staining on roots from in-growth cores

Contrasting soil conditions caused by different inundation frequenciesrequire different root growth strategies along the elevational gradient ofcoastal salt marshes. The objective of this study was to examine (1) if rootlifespan was shorter in Elymus pycnanthus, a relativelyfast-growing competitive species dominating high marshes, than inSpartina anglica, a relatively slow-growingstress-tolerating species dominating low marshes, and (2) if the species withlonger lifespan had higher tissue density (g cm^–3) and lowerspecific root length (m g^–1) than the species with shorterlifespan. Root production and mortality rates were established by samplingrootsin in-growth cores, and using triphenyltetrazolium chloride (TTC) staining todistinguish vital from dead roots. Root lifespan was estimated by dividing theliving root biomass (Elymus: 36 gm^–2, Spartina: 100 gm^–2) by root production (Elymus:0.28 g day^–1 m^–2,Spartina: 0.25 g day^–1m^–2) or root mortality rates(Elymus: 0.42–0.53 g day^–1m^–2). Spartina did not exhibitsubstantial mortality. Despite the present method only yielding rough estimatesof average root lifespan, it is evident that root longevity is much shorter inElymus than in Spartina. Rootlifespanranged between 10–19 weeks for Elymus but was closeto 1 year in Spartina, indicating thatElymus replaces it's roots continuously throughout thegrowing season, whereas Spartina maintains its roots overthe growing season. Fine roots of Elymus had slightlylowertissue density (0.094) than those of Spartina (0.139),whereas coarse roots of Elymus andSpartina had similar tissue density (0.100 gcm^–3). Fine roots of Elymus andSpartina had similar specific root length (195 mg^–1). However, coarse roots ofElymus (50 m g^–1) had higherspecific root length than those of Spartina (20 mg^–1) due to having smaller root diameter(Elymus: 548 m,Spartina: 961 m). We conclude thatpresentobservations on Elymus and Spartinasupport our first hypothesis that the competitive species fromthehigh marsh had short-lived roots compared to the'stress-tolerating'species from the low marsh. However, our result provide only weak support forthe existence of a positive correlation between root longevity and tissuedensity and a negative correlation between root longevity and specific rootlength.     

Temporal dynamics of three culturable γ-Proteobacteria taxa in salt marsh sediments

Temporal dynamics of three marine -Proteobacteria taxa withculturable members were followed in sediment communities in southeastern USsaltmarshes using a whole-genome hybridization approach. Labeled DNA from threebacterial isolates was used to probe sediment community DNA from two saltmarshes on Sapelo Island, GA at multiple time points over a three-year period.The relative abundance of the three isolates (and their close relatives)accounted for up to 28% of the total sediment community DNA. Hybridizationsignals for the taxon represented by isolate SIGA28M (with a 16S rRNA sequencesimilarity of 97% to Vibrio proteolyticus) showedsignificant temporal variation in both marshes, varying from 1% to 28% over thethree-year period. The taxa represented by isolates SIGA172a and SIGA198 (16SrRNA sequence similarities of 90% and 92% to Shewanellafrigidimarina and Vibrio nigripulchritudo,respectively) accounted for less than 6% of the sediment community at any timepoint. The variation in relative abundance of these three groups did not appearto follow clear seasonal trends, and could not be readily correlated withenvironmental variables.     

Significance of rooting depth in mire plants: Evidence from natural <Superscript>15</Superscript>N abundance

Variation in stable nitrogen isotope ratios (¹⁵N) was assessed for plants comprising two wetland communities, a bog-fen system and a flood plain, in central Japan. ¹⁵N of 12 species from the bog-fen system and six species from the flood plain were remarkably variable, ranging from –5.9 to +1.1 and from +3.1 to +8.7, respectively. Phragmites australis exhibited the highest ¹⁵N value at both sites. Rooting depth also differed greatly with plant species, ranging from 5cm to over 200cm in the bog-fen system. There was a tendency for plants having deeper root systems to exhibit higher ¹⁵N values; plant ¹⁵N was positively associated with rooting depth. Moreover, an increasing gradient of peat ¹⁵N was found along with depth. This evidence, together with the fact that inorganic nitrogen was depleted under a deep-rooted Phragmites australis stand, strongly suggests that deep-rooted plants actually absorb nitrogen from the deep peat layer. Thus, we successfully demonstrated the diverse traits of nitrogen nutrition among mire plants using stable isotope analysis. The ecological significance of deep rooting in mire plants is that it enables those plants to monopolize nutrients in deep substratum layers. This advantage should compensate for any consequential structural and/or physiological costs. Good evidence of the benefits of deep rooting is provided by the fact that Phragmites australis dominates as a tall mire grass.     

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.     

Age and growth,reproduction and diet of a sublittoral population of the rock goby Gobius paganellus (Teleostei,Gobiidae)

Colonisation of extremely acidic waters (pH 3) by aquatic angiosperms occurs widely, but is poorly documented. Unlike acid rain affected and other naturally acidic aquatic ecosystems, waters with pH 3 usually have a high conductivity, with high concentrations of SO₄ ^2- and often high concentrations of Fe³⁺, other heavy metal ions and Al³⁺. Where Fe³⁺ concentration is high, as in many mine waters, it provides a strong buffering system. In such waters, the biogeochemical Fe cycle exerts over water chemistry and the availability of nutrients and carbon for organisms. Biological activity is limited by low concentrations of phosphorus and inorganic carbon (DIC), which in this pH range is essentially all in the form of dissolved CO₂. A number of angiosperms grow in such waters including Phragmites australis, Typha spp. and Juncus bulbosus, though the last is the only one reported to grow totally submerged in waters with pH 3 . J. bulbosus occurs in many lignite mining lakes in Lusatia (north eastern Germany) with pH 3. The characteristics and possible survival strategies for this and other species are discussed.