Within population genetic differentiation in traits affecting clonal growth: Festuca rubra in a mountain grassland

Festuca rubra , a clonal grass of mountain grasslands, possesses a considerable variability in traits related to spatial spreading (rhizome production, length and branching; tussock architecture). Since these traits highly influence the success of the species in a spatially heterogeneous system of grasslands, a combined field and growth chamber approach was adopted to determine the within-population variation in these parameters. Clones were sampled in a mountain grassland (The Krkono?e Mts., Czech Republic); the environment (mean neighbour density) of individual clones varied highly. Before the clones were collected, shoot demography and tussock architecture within these clones were recorded in the field for four seasons. Their clone identity was determined using DNA RAPD. Vegetatively propagated plants from these clones were cultivated in a common garden experiment to demonstrate variation in tussock growth and architecture. Their response to change in red/far red light ratio was determined in the growth chamber. Highly significant variation among clones was found in almost all parameters. In the common garden, the clones differed in tussock growth (mean tillering rate), architecture (mean shoot angle, mean tussock density) and proportion of flowering shoots. In the growth chamber, both the aboveground parameters and parameters of the rhizome system were strongly affected by red/far red ratio; among-clone variation was also almost always significant. The genotype × environment interaction was significant for tillering rate and rhizome architecture. The structure of the rhizome system (which is the major component of clonal spread in space) is a complex result of several components whose inter-clone variations differ: (i) genetically determined mean rhizome system size, (ii) overall plasticity in rhizome system size (with no significant genetic variation in plasticity), and (iii) genetically determined plasticity in rhizome architecture. Because of the variation in plasticity in rhizome architecture, some c lones seemed to possess the ability to exploit a favourable habitat patch by producing short branches when there; whereas the remaining clones appeared to possess only a simple escape mechanism from unfavourable patches. Environmental variation in the light levels in the studied grassland is fine grained; horizontal growth rates of F. rubra are sufficient to make genets experience different patches in their lifetime. The high variation in both genotype means and plasticities is likely to be due to selection early in genet life in an environment which is heterogeneous at a fine scale.     

Clone-specific response of Festuca rubra to natural variation in biomass and species composition of neighbours

A long-term implant experiment with four clones of Festuca rubra was performed to identify fine-scale spatial variation in a competitive environment within a grassland sward of natural composition and density variation. Total above-ground biomass and shoot counts of all species were recorded in 10×10 cm neighbourhoods of each implant, and their effect on the growth response of the implant was tested. Two types of response were recorded: (1) shoot sizes and vertical shoot growth dynamics, and (2) horizontal space encroachment by means of new shoot natality, mortality and their mode of formation (intravaginal or extravaginal). The vertical growth of individual shoots showed the strongest response to neighbourhood composition; it responded to the overall aboveground biomass of the neighbours, but not to their species composition. The responses in parameters of horizontal growth of individuals (natality, mortality, proportion of extravaginal shoots) were much weaker and not consistent over the observation period; however, both total biomass of the neighbours and species composition affected the response of the target plants.
The overall response was rather weak in spite of a tenfold variation in neighbouring density and a thirtyfold variation in neighbouring biomass. This indicates that the response to this variation is rather flat under field conditions, either due to high overall values of density or due to interactions with below-ground processes. Consequently, though the plant is capable of remarkable plastic responses in both vertical growth and morphogenetic change, under field conditions this capacity for plastic response is expressed only to a limited degree.     

The dynamics of the bacterial population associated with a salt marsh

The distribution and temporal fluctuations in the density of bacteria in the water covering a high-salinity marsh were investigated employing epifluorescence microscopy for quantification as well as by transmission and scanning electron microscopy. The observed densities ranged from about 1 to 19 × 10⁶ bacteria/ml during the course of the study. High-marsh sampling sites had an average population level of 7.8 × 10⁶ bacteria/ml which was more than double the mean density recovered from large creeks near the mouth of the marsh system. Bacteria associated with seston varied tidally and seasonally, whereas the population of free planktonic bacteria varied only seasonally. Very small fluorescing bodies were commonly observed during epifluorescent observation of samples. These small bodies were observed at densities two orders of magnitude higher than easily recognized bacteria. In a salt marsh, the relative density of epibacteria was influenced by short-term tidal effects, and the population of planktobacteria was apparently controlled by long-term seasonal phenomena.     

Changes to spotted turtle (Clemmys guttata) habitat selection in response to a salt marsh restoration

Wetlands Ecology and Management - Development of coastal New England has led to the replacement of up to 37% of salt marshes with degraded freshwater wetlands, primarily through tidal restrictions....     

Root response to above-ground light quality – Differences between rhizomatous and non-rhizomatous clones of Festuca rubra

Root response to reduced red/far red ratio above ground was studied in an experiment with 12 vegetatively propagated clones of Festuca rubra, a rhizomatous grass species. A new method suitable for describing the node position within rhizome systems was developed. It uses a combination of developmental and functional directions of ordering, adopting methods of topology. At each node the root structure was defined as consisting of three root types: unbranched, long branched and fine branched. Root system size was expressed as the number and length of roots of these individual types. Rhizomatous and non-rhizomatous clones of Festuca rubra differed in the size and structure of their root systems and in the response to lowered red/far red light ratio. This response was caused more by the behaviour of the rhizomes than of the roots alone. In rhizomatous clones, the largest differences in root system structure were between the mother-nodes and the nodes on the rhizomes. The size of the root system also depended on the node position. Response to the red/far red ratio was clone specific only in some of the root parameters, especially in traits of unbranched roots at young nodes. The role of the three root morphotypes in the plant's ontogeny, nutrient uptake and ability to cope with environmental heterogeneity both above- and below ground, is discussed.     

Germination and early establishment of lower salt-marsh species in grazed and mown salt marsh

Abstract. Lower salt-marsh species occur more in the grazed than in the mown sites of a salt marsh in Schiermonnikoog in the Netherlands. This was demonstrated by a sowing experiment which determined which characteristic of the stand structure, height of the canopy or percentage of bare soil, is responsible for this difference. The total number of seedlings which emerged was negatively related to the height of the canopy and positively to the percentage of bare soil. The survival of seedlings of Suaeda maritima and Plantago maritima could be explained by the height of the canopy and for the latter species also by the percentage of bare soil. The survival of Aster tripolium and Plantago maritima was higher in grazed than in mown sites. Since the amount of bare soil was higher than seemed necessary for germination and survival, it was concluded that the taller canopy was responsible for the absence of lower salt-marsh species in the mown sites.     

Modeling productivity of a salt marsh

A model of primary productivity in a salt marsh is developed and compared to a regression analysis study of data showing dependence of growth on growing season, mean tidal height, and average monthly temperatures for several grass species.     

Saturnospora ahearnii,a new salt marsh yeast from Louisiana

Saturnospora ahearnii, a new, nonhyphal saturn-spored yeast, is described. The type strain (NRRL Y-7555, CBS 6121) of this species was isolated from the rhizosphere of marsh grass in Louisiana. Comparisons of nuclear DNA complementarity showedS. ahearnii to be closely related toS. saitoi, a species presently known only from Japan.     

Marine fungi from Mira river salt marsh in Portugal

The occurrence of fungi in the Mira salt marsh, Portugal was investigated for 12 months. Baits of Spartina maritima stems were exposed to permanent or temporary submersion at the upper and lower limits of the intertidal zone. The baits were observed for fruit bodies and spores directly and after incubation in moist chambers. Twenty six marine species were identified (17 Ascomycota, two Basidiomycota and seven mitosporic fungi). Twenty four are new records for Portugal. Nia globospora Barata and Basílio was published as a new species. Species were characterized with respect to frequency of occurrence, colonization capability and substrate succession. The diversity and similarity indexes of the fungi under different conditions were determined.     

Carbon metabolism in model microbial systems from a temperate salt marsh.

The metabolism of a saltwater leachate of 14C-labeled Spartina alterniflora was examined in laboratory systems using mixed, salt marsh microbial communities and, by addition of appropriate antibiotics, communities with bacteria or eukaryotes inhibited. Label uptake was more rapid in the systems with bacteria alone and with the mixed microbial community than with fungi alone. Mineralization of the added label was more extensive in the mixed and bacterial systems, whereas the fungi appear more efficient at converting the label into particulate biomass. Particulate biomass production efficiencies ranged from a high of 0.82 for the fungal system to 0.21 in the mixed community, with the bacterial system giving an intermediate value of 0.54. The presence of protozoa and microcrustaceans in the mixed system appears to account for an increase in the mineralization of the label assimilated. Additional experiments with whole labeled Spartina, a leachate from Spartina, and Spartina after leaching revealed that the seawater-soluble portions of the plants were attacked most rapidly by the microbial community.     

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.     

Reduced atmospheric CO2 inhibits nitrogen mobilization in Festuca rubra

In defoliated grasses, where photosynthesis is reduced due to removal of leaf material, it is well established that remobilization of nitrogen occurs from both older remaining leaves and roots towards the younger growing leaves. In contrast, little is known about the movement of nitrogen within intact grass plants experiencing prolonged inhibition of photosynthesis. We tested the following hypotheses in Festuca rubra L. ssp. rubra cv. Boreal: that both reduction of the atmospheric CO2 concentration and defoliation (1) induce mobilization of nitrogen from roots and older leaves towards growing leaves and (2) elicit similar directional change in the abundance of proteins in roots and older leaves relevant to the process of nitrogen mobilization including, glutamine synthetase (GS), EC 6.3.1.2; papain, EC 3.4.22.2; chymopapain, EC 3.4.22.6; ribulose bisphosphate carboxylase/oxygenase (Rubisco), EC 4.1.1.39; and the light harvesting complex of photosystem II (LHCPII). After growth at ambient atmospheric CO2 concentration, plants of F. rubra were subject to atmospheres containing either ambient (350 micro l l-1) or deplete (< 20 micro l l-1) CO2. Concurrently, plants were either left intact or defoliated on one occasion. Steady state 15N labelling coupled with a series of destructive harvests over a 7-day period enabled changes in the nitrogen dynamics of the plants to be established. Proteins pertinent to the process of nitrogen mobilization were quantified by immunoblotting. Irrespective of defoliation, plants in ambient CO2 mobilized nitrogen from older to growing leaves. This mobilization was inhibited by deplete CO2. Greater concentration of Rubisco and reduced chymopapain abundance in older remaining leaves of intact plants, in deplete compared with ambient CO2, suggested the inhibition of mobilization was due to inhibition of protein degradation, rather than to the export of degradation products. Both deplete CO2 and defoliation induced nitrogen mobilization from roots to growing leaves. In plants at ambient CO2, defoliation did not affect nitrogen uptake or its allocation. Therefore in F. rubra nitrogen mobilization can occur independently of any downregulation of nitrogen uptake. This suggests either different signal compounds may act to downregulate uptake and upregulate mobilization, or if one particular signalling compound is used its concentration threshold differs for induction of mobilization and downregulation of uptake. The abundance of the cysteine proteases papain and chymopapain was low in roots suggesting that they were not involved in protein degradation in this tissue.     

Ecotypic differentiation within Festuca rubra L. occurring in a heterogeneous coastal environment

In order to study the genetic differentiation between Festuca rubra L. individuals growing in a heterogeneous environment, indices of salt tolerance, mean relative growth rates and the numbers of tillers formed by plants grown in a Hoagland solution, were determined. It was found that plants from salt marsh sites have a high index of salt tolerance, a high mean relative growth rate and numerous tillers; plants from coastal sand dunes are less tolerant, grow slowly and form few tillers; plants from the inland polder sites are rather salt sensitive, fast growing and form a high number of tillers. The heritability of the mean relative growth rate and the tiller number appeared to differ from zero. Apparently, these characters have been under recent selection and thus give a picture of the adaptations of individual plants to the different environments encountered. An indication of gene flow has been found, although the effect of gene flow seems to be small in the face of the force of selection. It was concluded that the distinction of three ecotypes within the species F. rubra is insufficient to describe the differentiation found. Considering the differences observed, it seems more reasonable to speak of ecotypic variation.     

Defoliation alters the relative contributions of recent and non-recent assimilate to root exudation from Festuca rubra

The deposition of organic compounds from plant roots is a key determinant of rhizosphere microbial activity and community structure. Consequently, C-flow from roots to soil is an important process in coupling plant and microbial productivity, via impacts on microbial nutrient cycling in soil. Experimentally, isotopic tracers (¹³C or ¹⁴C) are used to track C inputs to soil and microbial communities. However, in many such studies the relationship between labelled C-flows and total C-flows are not established, limiting the interpretative value of the results. In this study, we applied steady-state near natural abundance ¹³CO₂ labelling to determine the impact of partial defoliation of Festuca rubra on root exudation. This approach in axenic culture facilitated determination of the contribution of pre- and post-defoliation assimilates both to root C-flow and plant tissues. The results demonstrated that total root exudation was increased in the two days following defoliation. This was concurrent with reduced net CO₂ assimilation and reduced allocation of post-defoliation assimilates below-ground and to active root meristems. Through determination of the δ¹³C of root exudates, it was established that the source of the increased root exudation was pre-defoliation assimilate. However, this response was transient, with reduced deposition of pre- and post-defoliation assimilates from roots during the period 2–4 d following defoliation. The results highlight the limitations of pulse-labelling approaches as a means of quantifying impacts of treatments on root exudation, particularly where the treatment is likely to affect plant C-partitioning or the balance between deposition to, and re-mobilization from, C-storage pools.     

Cadmium- and mercury-resistant Bacillus strains from a salt marsh and from Boston Harbor

Bacteria resistant to cadmium or mercury or both were isolated from the Great Sippewissett Marsh (Cape Cod, Mass.) and from Boston Harbor. Many of these metal-resistant isolates were gram-positive aerobic sporeformers, although not necessarily isolated as spores. Although several of the isolated strains bore plasmids, cadmium and mercury resistances appeared to be, for the most part, chromosomally encoded. DNA sequence homology of the gram-positive cadmium- and mercury-resistant isolates was not demonstrable with metal resistance genes from plasmids of either gram-positive (pI258) or gram-negative (pDB7) origin. Cadmium resistance of all the marsh isolates tested resulted from reduced Cd2+ transport. On the other hand, three cadmium-resistant harbor isolates displayed considerable influx but no efflux of Cd2+. Hg-resistant strains detoxified mercury by transforming Hg2+ to volatile Hg0 via mercuric reductase.