Lignocellulolysis by ascomycetes (fungi) of a saltmarsh grass (smooth cordgrass)

1994

Microb Ecol

Although they are very unlikely to play large direct roles in water-column microbial loops, eukaryotic mycelial decomposers (the mycelial true fungi, eumycotes, and zoosporic "fungi," oomycotes) have the potential to be important secondary producers in decaying plant material in shallow aquatic systems. Their secondary productivity may lead to important exchanges of material with microbial loops: output of ascospores, conidia, zoosporic flagellates, leaked lysates, and particles of decayed plants containing mycelium; input of dissolved organics and inorganic nutrients. Development of methods for ecological study of the aquatic mycelial eukaryotic decomposers has not advanced as rapidly as that for the prokaryotes of microbial loops, probably because (1) there are fewer aquatic microbial ecologists with mycological training and inclination than with prokaryotic leanings; and (2) the mycelial decomposers are difficult to work with, because they produce their mycelial mass virtually entirely within opaque solid substrates. Direct microscopic methods have emerged as prime tools for the measurement of prokaryotic mass, whereas an index-chemical assay (ergosterol) is currently the most efficient way to measure the mass of eumycotes. For measuring productivity of prokaryotes of microbial loops, microbial ecologists may choose from several (>10) published and field-tested methods, involving direct microscopy or monitoring of radiotracers. Extensive reviews of distribution and dynamics of aquatic bacterial mass and productivity have appeared. For measuring productivity of eukaryotic mycelial decomposers, one has only two published methods from which to choose, a direct-microscopic and a radiotracer method, neither of which has had adequate field testing. We are, furthermore, much less well equipped to obtain mass and productivity information for the poorly known mycelial oomycotes than we are for the eumycotes. Application of productivity techniques and nucleic-acid technology, may within the next decade allow knowledge of ecology of aquatic eukaryotic mycelial decomposers to advance to levels approaching that for the prokaryotes of microbial loops.

Section: Introductionmentioning

confidence: 99%

Ecomethodology for organoosmotrophs: Prokaryotic unicellular versus eukaryotic mycelial

1994

Microb Ecol

“…The two most prevalent and virtually omnipresent species are Phaeosphaeria spartinicola and Mycosphaerella sp. strain 2 (17), both of which are involved in lysis of lignocellulosic components of the blades (2,26,28). Additional species that are typical but less prevalent members of the community (occurring in Ͻ40% of blades examined) include Phaeosphaeria halima, environmental isolate "4clt" (an ascomycetous species that does not yet have a formal taxonomic description; see reference 4), and Buergenerula spartinae (4,25).…”

mentioning

confidence: 99%

Dynamics of Bacterial and Fungal Communities on Decaying Salt Marsh Grass

Buchan

Butler

et al. 2003

Appl Environ Microbiol

102

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 ␣-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 ␣-Proteobacteria and two ascomycete fungi (Phaeosphaeria spartinicola and environmental isolate "4clt").Southeastern U.S. coastal salt marshes are among the most productive ecosystems known (24, 31) and provide a model environment for investigating detritus-based ecosystems and their decomposer communities. In these systems, both fungi and bacteria are recognized as key components of the decomposer community (1, 26), providing primary links in the remineralization and transformation of decaying vascular plant material.In the few studies that have considered the activity of salt marsh bacterial and fungal saprophytes simultaneously, interactions between fungi and bacteria have been hypothesized to be based on temporal resource partitioning (29). According to this view, fungal colonization of senescing salt marsh cord grass (Spartina alterniflora) mediates the initial transformation of organic matter through extracellular enzyme activity and physical disruption (24, 26). In the fungus-dominated stage, Spartina undergoes loss of up to 60% of the original organic mass (26). As decomposition proceeds, the blades gradually collapse onto the marsh sediment and are reduced to smaller pieces with larger surface areas. Bacterial standing crop gradually increases, and bacteria assume a more prominent position in the latter stages of the decomposition process (1,29).This view of temporally...

“…This conclusion has been reached by using transmission electron microscopy and direct epifluorescence microscopy and by the dynamics of a fungal index sterol, ergosterol (37,44,47). Most monitoring of the fungal mass dynamics in standing decaying smooth cordgrass (Spartina alterniflora), a major salt marsh grass of the western Atlantic Ocean (4,10,11,29), has been performed in Georgia salt marshes (40), although the range of smooth cordgrass extends north into Canada and south into Florida (30,31).…”

mentioning

confidence: 99%

Autumnal Biomass and Potential Productivity of Salt Marsh Fungi from 29° to 43° North Latitude along the United States Atlantic Coast

Blum

Crawford

et al. 2000

Appl Environ Microbiol

It has been established that substantial amounts of fungal mass accumulate in standing decaying smooth cordgrass (Spartina alterniflora) marshes in the southeastern United States (e.g., in standing decaying leaf blades with a total fungal organic mass that accounts for about 20% of the decay system organic mass), but it has been hypothesized that in marshes farther north this is not true. We obtained samples of autumnal standing decaying smooth cordgrass from sites in Florida to Maine over a 3-year period. The variation in latitude could not explain any of the variation in the living fungal standing crop (as determined by ergosterol content) or in the instantaneous rates of fungal growth (as determined by acetate incorporation into ergosterol at a standard temperature, 20°C), which led to the conclusion that the potential levels of fungal production per unit of naturally decaying grass are not different in northern and southern marshes. Twenty-one percent of the variation in the size of the living fungal standing crop could be explained by variation in the C/N ratio (the higher the C/N ratio the smaller the fungal crop), but the C/P ratio was not related to the size of the fungal crop. Instantaneous rates of fungal growth were negatively related to the size of the living fungal crop (r ‫؍‬ ؊0.35), but these rates were not correlated with C/nutrient ratios. The same two predominant species of ascomycetes (one Phaeosphaeria species and one Mycosphaerella species) were found ejecting ascospores from standing decaying smooth cordgrass blades at all of the sites examined from Florida to Maine.