Independent roles of ectomycorrhizal and saprotrophic communities in soil organic matter decomposition

The relative roles of ectomycorrhizal (ECM) and saprotrophic communities in controlling the decomposition of soil organic matter remain unclear. We tested the hypothesis that ECM community structure and activity influences the breakdown of nutrient-rich biopolymers in soils, while saprotrophic communities primarily regulate the breakdown of carbon-rich biopolymers. To test this hypothesis, we used high-throughput techniques to measure ECM and saprotrophic community structure, soil resource availability, and extracellular enzyme activity in whole soils and on ECM root tips in a coastal pine forest. We found that ECM and saprotroph richness did not show spatial structure and did not co-vary with any soil resource. However, species richness of ECM fungi explained variation in the activity of enzymes targeting recalcitrant N sources (protease and peroxidase) in bulk soil. Activity of carbohydrate- and organic P- targeting enzymes (e.g. cellobiohydrolase, β-glucosidase, α-glucosidase, hemicellulases, N-acetyl-glucosaminidase, and acid phosphatase) was correlated with saprotroph community structure and soil resource abundance (total soil C, N, and moisture), both of which varied along the soil profile. These observations suggest independent roles of ECM fungi and saprotrophic fungi in the cycling of N-rich, C-rich, and P-rich molecules through soil organic matter. Enzymatic activity on ECM root tips taken from the same soil cores used for bulk enzyme analysis did not correlate with the activity of any enzyme measured in the bulk soil, suggesting that ECM contributions to larger-scale soil C and nutrient cycling may occur primarily via extramatrical hyphae outside the rhizosphere.     

Physical extent,frequency, and intensity of phosphatase activity varies on soil profiles across a Douglas-fir chronosequence

In forest soils, the availability of phosphate is largely dependent on phosphatase activity. We used soil imprinting to compare in situ activity and fine-scale distribution of phosphatase on soil profiles located across forest chronosequences of four age classes young (5–6 yrs), canopy closure (24–30 yrs), stem exclusion (61–71 yrs), and older (90–103 yrs) of mixed Douglas-fir/paper birch stands regenerated after fire or clearcutting in southern interior British Columbia, Canada. Chromatography paper treated with a mixture of substrate and colorimetric reagent was applied directly to vertical soil surfaces, accessed through root windows. Stands older than 61 years had both the highest level of in situ phosphatase activity and larger, more intense regions of activity. Bray-extractable phosphorus was negatively related to imprintable phosphatase activity. We compared the changes in phosphatase activity with differences in the ectomycorrhizal fungal (EMF) community that had been documented previously in the same stands. Of 84 ectomycorrhizal fungi found on roots in at least two of the stand-age classes, eight taxa were positively correlated and one taxon (Rhizopogon vinicolor/vesiculosus) negatively correlated with high phosphatase activity. The frequency of three taxa appeared to be positively correlated with larger areas of activity on the soil profiles. By using an imprinting approach, this study was able to demonstrate, for the first time, that in situ phosphatase activity and physical attributes of that activity (i.e., number, size, and relative rates of each area of activity) were related to concentrations of soil nutrients and with the frequency of individual ectomycorrhizal fungi.     

Relationship between soil enzyme activities, nutrient cycling and soil fungal communities in a northern hardwood forest

Soil fungi are highly diverse and act as the primary agents of nutrient cycling in forests. These fungal communities are often dominated by mycorrhizal fungi that form mutually beneficial relationships with plant roots and some mycorrhizal fungi produce extracellular and cell-bound enzymes that catalyze the hydrolysis of nitrogen (N)- and phosphorus (P)- containing compounds in soil organic matter. Here we investigated whether the community structure of different types of mycorrhizal fungi (arbuscular and ectomycorrhizal fungi) is correlated with soil chemistry and enzyme activity in a northern hardwood forest and whether these correlations change over the growing season. We quantified these relationships in an experimental paired plot study where white-tailed deer (access or excluded 4.5 yrs) treatment was crossed with garlic mustard (presence or removal 1 yr). We collected soil samples early and late in the growing season and analyzed them for soil chemistry, extracellular enzyme activity and molecular analysis of both arbuscular mycorrhizal (AM) and ectomycorrhizal/saprotrophic fungal communities using terminal restriction fragment length polymorphism (TRFLP). AM fungal communities did not change seasonally but were positively correlated with the activities of urease and leucine aminopeptidase (LAP), enzymes involved in N cycling. The density of garlic mustard was correlated with the presence of specific AM fungal species, while deer exclusion or access had no effect on either fungal community after 4.5 yrs. Ectomycorrhizal/saprotrophic fungal communities changed seasonally and were positively correlated with most soil enzymes, including enzymes involved in carbon (C), N and P cycling, but only during late summer sampling. Our results suggest that fine scale temporal and spatial changes in soil fungal communities may affect soil nutrient and carbon cycling. Although AM fungi are not generally considered capable of producing extracellular enzymes, the correlation between some AM taxa and the activity of N acquisition enzymes suggests that these fungi may play a role in forest understory N cycling.     

Control of soil phosphatase activities at millimeter scales in a mixed paper birch – Douglas-fir forest: The importance of carbon and nitrogen

Organic P can serve as an important source of P for plants and microbes when mineralized by extracellular phosphatases. Substrate induction, end-product repression and/or resource limitation regulate activities of phosphatase in bulk soils. Yet, factors controlling enzyme activities in fine-scale microsites may differ from those observed at larger scales. Understanding such differences is needed to improve estimates of global models of biogeochemical cycling. Imprinting of soil profiles using cellulose sheets infused with chromogenic substrates allows study of extracellular enzymes at mm scales under naturally occurring soil temperatures, with minimal disturbance to soil microbial communities. In this study, we used a soil imprinting approach to investigate soil chemical characteristics associated with mm-scale regions of high in situ phosphatase activities in a mixed paper birch – Douglas-fir forest in the southern interior of British Columbia. In addition, we tested whether the addition of simple (ammonium chloride plus sodium acetate) and complex (cellulose, collagen, chitin) forms of carbon (C) and/or nitrogen (N) to 1 cm² microplots on soil profiles influenced in situ phosphatase activity. In unamended microplots, percent C was 30% higher on average (P = 0.05) and percent N was about 15% higher (P = 0.05) in high-phosphatase microsites. Extractable P did not differ between high and low-phosphatase microsites, regardless of the form of P measured. Within the first 24 h, no difference in imprintable phosphatase was observed between C and N addition treatments, but after 72 h, microplots receiving any substrate containing N had higher phosphatase activities than those receiving only water (P < 0.001). The results from both of our studies support a role for resource limitation in regulating phosphatase activities at this site because either (i) P became limiting in microsites with higher amounts of C and N, and/or (ii) microsites with higher C and N were the ones where these nutrients were in sufficient supply to allow microbes to excrete extracellular enzymes. We conclude that phosphatase excretion occurs in C + N-enriched soil microsites, but that any such phosphatase-active microsites located beyond the rhizosphere are unlikely to supply P to roots because of the low diffusion rates of orthophosphate.     

Woodland trees modulate soil resources and conserve fungal diversity in fragmented landscapes

Resource islands around woody plants are thought to define the structure and function of many semiarid and arid ecosystems, but their role in patterning of soil microbial communities remains largely unexamined in dry environments. This study examined soil resource distribution and associated fungal communities in two Allocasuarina luehmannii (buloke) remnants of semiarid north-western Victoria, Australia. These savannah-like woodlands are listed as endangered due to extensive clearing for agriculture. We used the DNA-based profiling technique T-RFLP and ordination-based statistical methods to compare fungal community compositions in surface soils from two remnants (located 1.6 km apart) and three sampling positions (beneath individual buloke canopies; grassy inter-canopy areas; and adjoining cleared paddocks). Resource island formation beneath buloke trees was clearly evident in soil physicochemical properties (e.g. threefold concentrations of total carbon and nitrogen in canopy versus non-canopy soils). This heterogeneity of resources was moderately correlated with soil fungal community compositions, which were distinct for each sampling position. We argue that fungal composition patterns reflected multiple roles of fungi in dryland ecosystems, namely: responses of saprotrophic fungi to tree organic matter inputs; specificity of ectomycorrhizal fungi to tree rooting zones; and fungal involvement in biological soil crusts that variably covered non-canopy soils. Our data did not indicate that buloke canopy areas were particular hotspots of soil fungal diversity, but that they increased landscape-level diversity by supporting a distinct suite of fungi. In addition, we provide evidence of phylogenetic differentiation of soil fungal communities between our two remnants, which adds to growing evidence of fungal genetic structure at localised scales. These findings highlight the importance of remnant trees in conserving both soil resources and microbial genetic diversity. In addition, evidence of differentiation of soil fungal phylogenetics between nearby but isolated remnants suggests that conserving soil fungal diversity requires conservation of host habitats over their entire (remaining) range, and indicates previously unseen consequences of tree loss from extensively cleared landscapes.     

Temporal and functional pattern of secreted enzyme activities in an ectomycorrhizal community

The ectomycorrhizal community of an oak forest has been monitored monthly throughout fifteen months. Eight enzymatic activities secreted by the ectomycorrhizal root tips and involved in the mobilization of nutrients from soil organic matter have been measured using microplate assays, resulting in potential activity patterns of individual fungal species. Both the species structure of the community and the specific activity level of each individual species changed with the season and soil horizon. This versatility may be an adaptative response of the ectomycorrhizal fungal community to a highly variable environment. The results also suggest that some ectomycorrhizal fungi behave as occasional saprobes and contribute to the decomposition of soil organic matter and nutrient cycling together with true saprotrophic fungi.     

Responses of oribatid mites to tree girdling and nutrient addition in boreal coniferous forests

Tree girdling has been experimentally used to stop the allocation of carbohydrates from the canopy to tree roots and their associated ectomycorrhizal (EM) mycelia. We used three already established girdling experiments in northern Sweden, one in a Pinus sylvestris stand and two in Picea abies stands, to determine the effect of tree girdling on soil-living oribatid mites. These mites often feed on fungal hyphae, but it is not known to what extent they feed on EM or saprotrophic fungi. We hypothesised that a presumed decline in EM fungi after girdling would strongly reduce EM-feeding specialists and, correspondingly, reduce total abundance and species richness of oribatids in girdled plots. Tree girdling resulted in a significant decline in total abundance of oribatid mites in the two spruce stands, which was assumed to be linked to the decline in EM fungi, but not in the pine stand. Species richness decreased in girdled plots in one of the spruce forests. The decline in total abundance in girdled spruce stands was primarily dependent on a significant and consistent population decrease in Oppiella nova, which was the most abundant oribatid mite in the ungirdled spruce plots. Its abundance after girdling was only 8–18% of that in ungirdled spruce plots. In the pine stand, O. nova had much lower abundance than in the spruce stands, and despite a tendency to decline in number after girdling also in the pine stand, it had a minor effect on total abundance. These results suggest that O. nova may be dependent on EM fungi in spruce forest soils, whereas the dependence on EM fungi in pine forest soils is less evident.     

Clonal and seasonal shifts in communities of saprotrophic microfungi and soil enzyme activities in the mycorrhizosphere of Salix spp.

The species‐specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient‐releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. × dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. × dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. × dasyclados than under S. viminalis. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid‐phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline‐phosphatase activities did not show clone‐specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindrocarpon destructans, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid‐ and alkaline‐phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil‐enzyme activities of the P and S cycles under different willow clones.     

Influence of repeated prescribed burning on incorporation of C from cellulose by forest soil fungi as determined by RNA stable isotope probing

Repeated prescribed burning is frequently used as a forest management tool and can influence soil microbial diversity and activity. Soil fungi play key roles in carbon and nutrient cycling processes and soil fungal community structure has been shown to alter with increasing burning frequency. Such changes are accompanied by changes to soil carbon and nitrogen pools, however, we know little regarding how repeated prescribed burning alters functional diversity in soil fungal communities. We amended soil with ¹³C-cellulose and used RNA stable isotope probing to investigate the effect of biennial repeated prescribed burning over a 34-year period on cellulolytic soil fungi. Results indicated that repeated burning altered fungal community structure. Moreover, fungal community structure and diversity in ¹²C and ¹³C fractions from the unburned soil were not significantly different from each other, while those from the biennial burned soils differed from each other. The data indicate that fewer active fungi in the biennially burned soil incorporated ¹³C from the labelled cellulose and that repeated prescribed burning had a significant impact on the diversity of an important functional group of soil fungi (cellulolytic fungi) that are key drivers of forest soil decomposition and carbon cycling processes.     

Distinctive fungal and bacterial communities are associated with mats formed by ectomycorrhizal fungi

The distinct rhizomorphic mats formed by ectomycorrhizal Piloderma fungi are common features of the organic soil horizons of coniferous forests of the Pacific Northwest. These mats have been found to cover 25-40% of the forest floor in some Douglas-fir stands, and are associated with physical and biochemical properties that distinguish them from the surrounding non-mat soils. In this study, we examined the fungal and bacterial communities associated with Piloderma mat and non-mat soils. Each mat and non-mat area was repeatedly sampled at four times throughout the year. Characterization of the mat activity and community was achieved using a combination of N-acetylglucosaminidase (NAGase) enzyme assays, and molecular analysis of fungal and bacterial communities using T-RFLP profiles, clone libraries, and quantitative PCR. Piloderma mats had consistently greater NAGase activity across all dates, although the magnitude of the difference varied by season. Furthermore, we found distinct fungal and bacterial communities associated with the Piloderma mats, yet the size of the microbial populations differed little between the mat and non-mat soils. Significant temporal variation was seen in the NAGase activity and in the sizes of the fungal and bacterial populations, but the community composition remained stable through time. Our results demonstrate the presence of two distinct microbial communities occupying the forest floor of Douglas-fir stands, whose populations and activities fluctuate seasonally but with little change in composition, which appears to be related to the physiochemical nature of mat and non-mat habitats.     

Differential response of ectomycorrhizal and saprotrophic fungal mycelium from coniferous forest soils to selected monoterpenes

The mycelia of saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter of some tree species.Monoterpenes are mycotoxic and could potentially affect fungi that are exposed to them in the litter layers. In order to investigate whether monoterpenes typical of coniferous litters could influence fungal communities, we analysed the monoterpene content of freshly fallen needles of Pinus sylvestris, Picea abies and Picea sitchensis. The most abundant monoterpenes were found to be α-pinene, β-pinene and 3-carene. We evaluated the effects of these three monoterpene vapours on the biomass production of 23 SP isolates and 16 ECM isolates. Overall, 75% of ECM isolates and 26% of SP isolates were significantly inhibited by at least one of the monoterpene treatments and both intra- and inter-specific variations in response were observed.Monoterpene concentrations are highest in surface litters. The differential effects on fungal taxa may influence the spatial and temporal distribution of fungal community composition, indirectly affecting decomposition and nutrient cycling, the fundamental ecosystem processes in which fungi have a key role in coniferous forest soils.     

Soil fungal and prokaryotic community structure exhibits differential short-term responses to timber harvest in the Pacific Northwest

Conventional clear-cut timber harvest is a widespread industrial practice across the Pacific Northwest;however,information regarding how these practices impact soil microbial community structure at the regional scale is limited.With evidence of consistent and substantial impact of harvest on soil microbial functional profiles across the region(despite a range of environmental conditions),the objective of this study was to determine the extent to which harvest also influences the structure of prokaryotic and fungal soil microbial communities,and how generalized these trends are throughout the geographic region.Paired soil samples were collected one year before and after harvest across nine second-growth Douglas-fir forests in the Pacific Northwest.Total community DNA was extracted from the soils,and high-throughput targeted gene sequencing of the 16 S r RNA gene for prokaryotes and the internal transcribed spacer(ITS)gene for fungi was performed.Alpha diversity was consistently and significantly higher after harvest;it was moderately so for fungal communities(+14.6%),but only marginally so for prokaryotic communities(+2.0%).Similarly,on average,a greater proportion of the variation in the community structure of fungi(20.1%)at each site was associated with forest harvest compared to that of prokaryotes(13.2%).Overall,the greatest influence of timber harvest on soil microbial communities appeared to be a relative depletion of ectomycorrhizal fungi,with a concomitant enrichment of saprotrophic fungi.Understanding the short-term responses of soil microbial communities across the region,particularly those of tree root-associated symbionts,may aid our understanding of the role soil microbial communities play in ecological succession.     

Can the extent of degradation of soil fungal mycelium during soil incubation be used to estimate ectomycorrhizal biomass in soil?

The extent of degradation of the fungal biomass in forest soil during laboratory incubation was investigated as a measure of ectomycorrhizal (EM) biomass. The method simulates the disappearance of fungal mycelium after root trenching, where the EM fungi, deprived of its energy source (the tree), will start to die off. Incubating a forest humus soil at 25 °C resulted in a decrease in the relative proportion (mol%) of the phospholipid fatty acid 18:2ω6,9 (a fungal marker molecule) within 3-6 months, indicating that fungal biomass was disappearing. Incubation at 5 °C resulted in essentially no change in the amount of 18:2ω6,9. The measurement of ergosterol, another fungal marker molecule, gave similar results. Incubation of different forest soils (pine, spruce and spruce/oak), and assuming that the disappearance of fungal biomass during this period of time was entirely due to EM fungi, resulted in an estimation of EM biomass of between 47 and 84% of the total fungal biomass in these soils. The humus layer had more EM biomass than deeper mineral layers.     

Temporal and seasonal change in microbial community structure of an undisturbed,disturbed, and carbon-amended pasture soil

Disturbance and change to C inputs can alter microbial community structure and impact ecosystem function. Particularly in temperate regions, seasonal change also has an effect on microbial communities both directly through climate and indirectly through plant function. The temporal change in microbial communities of an undisturbed pasture, disturbed pasture (similar to a single tillage event) and pasture soil amended with two forms of particulate carbon were monitored over eight consecutive seasons after grass was reestablished. The soil microbial community was assessed by a DNA fingerprinting technique (terminal restriction fragment length polymorphism, TRFLP) of bacterial, fungal and archaeal communities, and also from phospholipid fatty acid (PLFA) analysis. The single disturbance had a significant effect on fungal microbial community structure (by TRFLP) and significantly decreased the fungal:bacterial ratio. Though the change was relatively small, it persisted throughout the sampling period. Nitrate was also higher on the disturbed treatment providing evidence for the theory that changes to fungal:bacterial ratios can alter nutrient cycling and retention. Fungal communities were the most altered by the C amendments, and while bacteria were also affected by the C amendments, seasonal change was a greater cause of variation. Correlation to soil and climatic variables explained more of the total variability for PLFA (78% for all treatments) than bacterial (50%), fungal (35%) and archaeal (14%) restriction fragments. Most climate and soil variables explained significant variation for seasonal patterns in the multivariate community structures but measurements of soil moisture were important for all communities while pH was relatively more important for bacteria, temperature for fungi, and soil C:N ratio for archaea. Autumn was particularly distinct from other seasons for bacteria (less so for the fungal community) and although there was seasonal change in pH suggesting pasture management was a factor, the significant correlation of other soil characteristics suggests that plant physiological changes (most probably root exudates) also played a significant role. The large change in the saprotrophic fungal community due to the particulate C addition but minor seasonal change would tend to suggest that the fungal community may be more responsive to changes in litter inputs rather than root exudates while the reverse is true for bacteria.     

Ectomycorrhizal community and extracellular enzyme activity following simulated atmospheric N deposition

Ectomycorrhizal (EM) fungi are abundant in temperate and boreal ecosystems and are understood to be an important means whereby plants can fulfill their nutrition requirements. The extent of the EM fungal involvement in accessing organic sources of N, however, remains unknown. Some EM fungi have been found to produce lignolytic and proteolytic enzymes which are necessary to depolymerize organic substrates, but this ability varies by species. Both EM fungal communities and the activities of lignolytic and proteolytic enzymes may be sensitive to changes in inorganic N availability such as through increased atmospheric deposition. Our objectives were to simulate an ecologically relevant increase in atmospheric N deposition in areas currently receiving very little exogenous N and examine changes in EM community composition, lignin degrading enzyme activity, and soil protein depolymerization. We found a distinct shift in the EM community composition following simulated atmospheric N deposition. Likewise, we found a significant decrease in the activity of lignin degrading enzymes, which could have important implications on ecosystem N and C cycling. Contrary to our hypotheses, proteolysis increased following N addition. The fact that lignolytic and proteolytic enzymes exhibit opposite responses is counterintuitive and suggests much is yet to be learned about how N addition affects global C storage by affecting the decomposition of organic matter. Our data suggest small increases in atmospheric N deposition could produce significant changes in communities of EM fungi and N and C cycles.     

Invertebrate grazing determines enzyme production by basidiomycete fungi

Extracellular enzymes produced by heterotrophic microorganisms in the soil are responsible for the decomposition of organic compounds. Basidiomycete fungi are the primary decomposer agents in temperate wooded ecosystems and contribute extensively to extracellular enzyme activity and nutrient mineralisation within soils. Growth and development of basidiomycete mycelia is influenced by soil-dwelling invertebrate grazers with potential implications for fungal activity and ecosystem functioning. The impacts of four invertebrate taxa belonging to Isopoda, Myriapoda, Collembola and Nematoda on the production of eight hydrolytic enzymes by four saprotrophic basidiomycetes (Phanerochaete velutina, Resinicium bicolor and two strains of Hypholoma fasciculare) were compared in a factorial microcosm study. Grazing generally increased enzyme production but invertebrates had species-specific impacts on enzyme activity. The magnitude of grazing influenced enzyme activity; macrofauna (woodlice and millipedes) induced the greatest responses. Enzymatic responses varied markedly between fungi. Grazing enhanced enzyme activity in the exploitative mycelial networks of P. velutina and H. fasciculare, while the opposite effects were observed in the explorative R. bicolor networks. The impacts of soil fauna on nutrient mineralisation depend on fungal community composition. β-glucosidase, cellobiohydrolase, N-acetylglucosaminidase, acid phosphatase and phosphodiesterase activities were affected most frequently by grazing and invertebrate activity, and thus had direct consequences for carbon, nitrogen and phosphorous cycling. The results indicate that invertebrate diversity and community composition may influence the spatial distribution and activity of extracellular enzymes with direct implications for nutrient mineralisation and trunover in woodland soils.     

Using lipid analysis and hyphal length to quantify AM and saprotrophic fungal abundance along a soil chronosequence

We evaluate the use of signature fatty acids and direct hyphal counts as tools to detect and quantify arbuscular mycorrhizal (AM) and saprotrophic fungal (SF) biomass in three Hawaiian soils along a natural soil fertility gradient. Phospholipids16:1ω5c and 18:2ω6,9c were used as an index of AM and saprotrophic fungal biomass, respectively. Both phospholipid analysis and hyphal length indicated that the biomass of AMF was greatest at the highest fertility site, and lowest where phosphorus limits plant growth. Saprotrophic fungal biomass did not vary. Hyphal length counts appeared to under-estimate SF abundance, while the phospholipid AMF:SF ratio was in line with expectations. This study indicates that phospholipids may be a valuable and reliable tool for studying the abundance, distribution, and interactions between AM and saprotrophic fungi in soil.     

Spatial distribution of fungal communities in a coastal grassland soil

In grasslands, saprotrophic fungi, including basidiomycetes, are major decomposers of dead organic matter, although spatial distributions of their mycelial assemblages are little described. The aim of this study was to characterise the scale and distribution of saprotrophic fungal communities in a coastal grassland soil using terminal restriction fragment length polymorphism (T-RFLP).Soil fungi were sampled at Point Reyes, California, USA, by taking forty-five 26 mm diam. cores in a spatially defined manner. Within each sampled core, complete core sections at 1-2 cm and 14-15 cm depths were removed and sub-sampled for DNA extraction and amplification using the primer pairs ITS1F-FAM/ITS4 (general fungi) or ITS1F-FAM/ITS4B (basidiomycete-specific).Nonmetric Multidimensional Scaling showed that general fungal communities could be clearly separated by depth, although basidiomycete communities could not. There were no strong patterns of community similarity or dissimilarity for general or basidiomycete fungal communities at horizontal geographical distances from 25 cm to 96 m in the upper horizon. These results show considerable vertical, but little horizontal, variability in fungal community structure in a semi-natural grassland at the spatial scales measured here.     

Population responses of oribatids and enchytraeids to ectomycorrhizal and saprotrophic fungi in plant-soil microcosms

The oribatid mites Oppiella nova, Tectocepheus velatus and Nothrus silvestris and the enchytraeid worm Cognettia sphagnetorum are four common animal species in boreal forest soils. According to the literature, they respond differently to clear-cutting of forest stands. O. nova responds with population decreases, T. velatus and N. silvestris with small changes and C. sphagnetorum with population increases. We hypothesised that the presence/absence of ectomycorrhizal (EM) fungi is a major factor in explaining these reactions. The population responses of these soil animals to inoculation of five species of EM fungi growing in symbiosis with their host tree (Pinus sylvestris L.) and one saprotrophic fungus, Hypholoma capnoides, growing on wood were tested in pot microcosms with artificial soil (peat and vermiculite) for 70-84 days. Additionally, plants without inoculation of EM fungi, plants growing in forest soil (FS) and plant-free peat and vermiculite (PV) were included. O. nova increased significantly in abundance in the treatments with the EM fungi Suillus variegatus and Paxillus involutus, but not in the other treatments. T. velatus increased significantly in abundance in FS, but declined in most of the other treatments, and N. silvestris showed a similar, albeit not significant, response. C. sphagnetorum did not increase in abundance in any of the treatments with EM fungi but increased its abundance four times in both FS and PV. The results show that the fungivore O. nova preferentially feeds on certain EM fungi, especially S. variegatus, whereas the EM fungus Piloderma fallax and the saprotrophic H. capnoides are not preferred. In contrast, C. sphagnetorum is restricted in its population growth by the EM fungi studied, and this dominant microbi-detritivore is clearly favoured by the absence of EM fungi.     

Low importance for a fungal based food web in arable soils under mineral and organic fertilization indicated by Collembola grazers

We investigated the Collembola community at an arable field where mineral and organic fertilizers have been applied at low and high rates for 27 years. As food resources for Collembola, the soil microbial community was analyzed using phospholipid fatty acids (PLFAs). A special focus was put on AM fungi, which were estimated by the marker 16:1ω5 in PLFA (viable hyphae) and neutral lipid fatty acid (NLFA – storage fat in spores) fractions. Additionally, whole cellular lipids in crop plant tissues and manure were assessed. Greater Collembola species richness occurred in plots where mineral fertilizer was added. In contrast, soil microbial biomass including AM fungal hyphae increased with addition of organic fertilizer, while the amount of AM fungal spores and biomass of saprotrophic fungi were not affected by fertilizer type. The lipid pattern in wheat roots was altered by fertilizer type, application rate and their interaction, indicating different rhizosphere communities. In sum, the availability and composition of food resources for Collembola changed considerably due to farm management practice. The major diet of three dominant Collembola species, Isotoma viridis, Willemia anophthalma and Polyacanthella schäffer was determined by lipid profiling. Multivariate analysis demonstrated species specific lipid patterns, suggesting greater importance of species than management practice on the diet choice. Nevertheless, feeding strategy was affected by fertilizer type and availability of resources, as trophic biomarker fatty acids indicated feeding on wheat roots (and to some extent saprotrophic fungi) with mineral and a shift to soil organic matter (litter, detritus) with organic fertilization. Although AM fungi dominated the soil fungal community, the AMF marker 16:1ω5 was not detected in Collembola lipids, indicating that these were not consumed. The very low amount of saprotrophic fungi in the soil and the fact that Collembola as major fungal grazers did not feed on AM fungi indicates that the fungal energy channel in the investigated arable field is of little importance to the faunal food web.