Structure and function of microbial communities in the rhizosphere of Scots pine after tree-felling

We evaluated changes occurring in the rhizosphere microbial communities of Scots pine (Pinus sylvestris L.) due to tree-felling and decrease of the photosynthetic C flow into the soil under field conditions over one growing season. Samples were taken from tree rhizospheres, freshly felled stump rhizospheres and bulk soil. We used culture dependent (CFU counts, community level physiological profiles, CLPPs) and independent methods (fluorogenic MUF-substrates, PLFA pattern and PCR-DGGE) to monitor the microbial communities in soil samples. The numbers of cultivable bacteria and amounts of phosphatase activity in the rhizosphere of trees were significantly higher compared with those in the bulk soil. The organic C consuming community measured by CLPP was stimulated directly after the tree-felling in stump rhizospheres; utilization of the disintegration components of cellulose, hemicellulose and chitin increased. Furthermore, bacterial and fungal biomass as well as chitin decomposers (CFU) increased in the stump rhizosphere. After 11 weeks of tree-felling the stump rhizosphere soluble PO₄-P and NH₄-N as well as amounts of total C and N began to resemble the concentrations measured in the bulk soil. However, the stump rhizosphere community structure detected by PLFA and PCR-DGGE still resembled that of the tree rhizosphere.     

Decreases in soil moisture and organic matter quality suppress microbial decomposition following a boreal forest fire

Climate warming is projected to increase the frequency and severity of wildfires in boreal forests, and increased wildfire activity may alter the large soil carbon (C) stocks in boreal forests. Changes in boreal soil C stocks that result from increased wildfire activity will be regulated in part by the response of microbial decomposition to fire, but post-fire changes in microbial decomposition are poorly understood. Here, we investigate the response of microbial decomposition to a boreal forest fire in interior Alaska and test the mechanisms that control post-fire changes in microbial decomposition. We used a reciprocal transplant between a recently burned boreal forest stand and a late successional boreal forest stand to test how post-fire changes in abiotic conditions, soil organic matter (SOM) composition, and soil microbial communities influence microbial decomposition. We found that SOM decomposing at the burned site lost 30.9% less mass over two years than SOM decomposing at the unburned site, indicating that post-fire changes in abiotic conditions suppress microbial decomposition. Our results suggest that moisture availability is one abiotic factor that constrains microbial decomposition in recently burned forests. In addition, we observed that burned SOM decomposed more slowly than unburned SOM, but the exact nature of SOM changes in the recently burned stand are unclear. Finally, we found no evidence that post-fire changes in soil microbial community composition significantly affect decomposition. Taken together, our study has demonstrated that boreal forest fires can suppress microbial decomposition due to post-fire changes in abiotic factors and the composition of SOM. Models that predict the consequences of increased wildfires for C storage in boreal forests may increase their predictive power by incorporating the observed negative response of microbial decomposition to boreal wildfires.     

Influence of single trees on spatial and temporal patterns of belowground properties in native pine forest

Linkages between forest dynamics and ecosystem processes are poorly understood and this limits our ability to adequately estimate future changes in forest ecosystems due to human-induced global change. In particular at the single tree level, our understanding of temporal and spatial changes of belowground properties during forest succession is limited. Thus, our aim was to test whether we find a spatial and temporal gradient in nutrient availability and an associated shift in microbial community structure with increasing distance and age of single trees. We found that inorganic nitrogen was less available below the crown of single trees, while soluble organic carbon (DOC) was much more abundant, in particular in the inner zone of influence, i.e. close to the stem. The fungal:bacterial PLFA ratio was greater while microbial biomass carbon (MicC) was lower below the tree crown, indicating a strong influence of trees on spatial patterns of microbial biomass and community structure. Moreover, the positive correlation between MicC and total extractable N, and the negative correlation between fungal:bacterial biomass and δ¹⁵N, suggested that the microbial biomass was N limited below the tree crown and as a consequence nutrient cycling was presumably decelerated compared to open conditions. We also found a temporal pattern of increasing surface soil C and N content with increasing tree age (up to 250 years), underlining the significant role of single trees in creating spatial and temporal heterogeneity in forests.     

Moisture effects on microbial communities in boreal forest floors are stand-dependent

Landscape level factors such as overstory canopy composition can have a profound effect on the ecology of microbial communities in boreal forest floors. However, factors influencing community composition at the microsite scale are still poorly described and understood. Here we explored moisture effects on microbial communities in forest floor derived from undisturbed trembling aspen and white spruce stands, two of the dominant trees in the boreal forest of western Canada. Forest floor samples were incubated in a laboratory experiment for a period of one month under a moisture regime ranging from moist to dry (field capacity, 60% of field capacity and wilting point). As in previous studies we found that the origin of the forest floor material had a strong effect on the microbial community. Additionally, we found that moisture manipulation did not alter the microbial communities of the white spruce forest floor. On the other hand, the moisture had a profound effect on the aspen forest floor, and resulted in structurally and functionally distinct microbial communities. This different response to moisture could be linked to the adaptation of microbial groups to the physical environment inherent to the aspen and spruce forest floors and provides an avenue to further work into microbial mediated biogeochemical processes in the boreal forest.     

Functional diversity of microbial communities in the mixed boreal plain forest of central Canada

This study was designed to examine whether or not specific tree species (Picea glauca, Picea mariana, Pinus banksiana, Populus tremuloides), their post-fire stand age, or their position in a successional pathway had any significant effect on the functional diversity of associated soil microbial communities in a typical mixed boreal forest ecosystem (Duck Mountain Provincial Forest, Manitoba, Canada). Multivariate analyses designed to identify significant biotic and/or abiotic variables associated with patterns of organic substrate utilization (assessed using the BIOLOG™ System) revealed the overall similarity in substrate utilization by the soil microbial communities. The five clusters identified differed mainly by their substrate-utilization value rather than by specific substrate utilization. Variability in community functional diversity was not strongly associated to tree species or post-fire stand age; however, redundancy analysis indicated a stronger association between substrate utilization and successional pathway and soil pH. For example, microbial communities associated with the relatively high pH soils of the P. tremuloides-P. glauca successional pathway, exhibited a greater degree of substrate utilization than those associated with the P. banksiana-P. mariana successional pathway and more acidic soils. Differences in functional diversity specific to tree species were not observed and this may have reflected the mixed nature of the forest stands and of their heterogeneous forest floor. In a densely treed, mixed boreal forest ecosystem, great overlap in tree and understory species occur making it difficult to assign a definitive microbial community to any particular tree species. The presence of P. tremuloides in all stand types and post fire stand ages has probably contributed to the large amount of overlap in utilization profiles among soil samples.     

Effects of tree identity dominate over tree diversity on the soil microbial community structure

This study investigated the possible effects of tree species diversity and identity on the soil microbial community in a species-rich temperate broad-leaved forest. For the first time, we separated the effects of tree identity and tree species diversity on the link between above and belowground communities in a near-natural forest. We established 100 tree clusters consisting of each three tree individuals represented by beech (Fagus sylvatica L.), ash (Fraxinus excelsior L.), hornbeam (Carpinus betulus L.), maple (Acer pseudoplatanus L.), or lime (Tilia spec.) at two different sites in the Hainich National Park (Thuringia, Germany). The tree clusters included one, two or three species forming a diversity gradient. We investigated the microbial community structure, using phospholipid fatty acid (PLFA) profiles, in mineral soil samples (0–10 cm) collected in the centre of each cluster.The lowest total PLFA amounts were found in the pure beech clusters (79.0 ± 23.5 nmol g⁻¹ soil dw), the highest PLFA amounts existed in the pure ash clusters (287.3 ± 211.3 nmol g⁻¹ soil dw). Using principle components analyses (PCA) and redundancy analyses (RDA), we found only for the variables ‘relative proportion of beech trees’ and ‘living lime fine root tips associated with ectomycorrhiza’ a significant effect on the PLFA composition. The microbial community structure was mainly determined by abiotic environmental parameters such as soil pH or clay content. The different species richness levels in the clusters did not significantly differ in their total PLFA amounts and their PLFA composition. We observed a tendency that the PLFA profiles of the microbial communities in more tree species-rich clusters were less influenced by individual PLFAs (more homogenous) than those from species-poor clusters.We concluded that tree species identity and site conditions were more important factors determining the soil microbial community structure than tree species diversity per se.     

Composition of lipophilic compounds and carbohydrates in the accumulated plant litter and soil organic matter in boreal forests

Carbohydrates and lipophilic compounds constitute an important component of litter and soil organic matter in boreal forests, but are still poorly identified. We characterized needle litter and coarse tree litter (cones, seeds, bark and twigs) from coniferous trees (Pinus sylvestris L. and Picea abies Karst.), and moss litter (Pleurozium schreberi, Hylocomnium speldens), fermentation (F) and humus (H) layers in four boreal forest sites in Finland using a combination of sequential fractionation (non‐polar extractions, NPE; water‐soluble extractions, WSE; acid‐soluble fraction, AS) and detailed analyses on the soluble fractions using GC‐MS. Comparisons among the different layers of the soil organic horizon were used to assess which lipophilic compounds and carbohydrates increased in the F and H layers in proportion to their relative abundance in the litter layer and thus might have a large potential to accumulate in soil organic matter. Both concentrations and relative proportions of different compounds varied among the soil layers. Several of the fatty acids (FAs) found in the litter samples were absent in the F and the H layers. Needle and coarse tree litter contained a wide range of di‐ and triterpenes, but in the F and H layers oxidized forms of dehydroabietic acid and sterols were abundant. The large proportion of dehydroabietic acid in the lipophilic fraction in the H layer suggests that it may be poorly degradable by soil microorganisms, probably because of its anti‐microbial function in trees. The composition of the acid‐soluble fraction indicated that the proportion of cellulose in relation to hemicelluloses increased from the litter layer to the F and H layers. Put together, changes in the relative proportions of organic compounds in soluble fractions indicate that selective preservation of compounds, litter input by plant roots and microbial synthesis of compounds all contribute to the accumulation of aliphatic compounds in the H layer of boreal forests.     

Forest floor microbial communities in relation to stand composition and timber harvesting in northern Alberta

With the growing interest in silvicultural techniques that more closely emulate natural disturbance regimes, there is a need to better understand how partial harvesting affects the soil microbial community in stands with varying ecological characteristics, e.g., tree species composition. Four and a half and 5.5 years post-harvest, we used phospholipid fatty acid (PLFA) and substrate-induced respiration (SIR) analyses to compare the microbial biomass and microbial community structure of forest floors from stands dominated by white spruce (Picea glauca; SPRUCE) or by trembling aspen (Populus tremuloides; ASPEN) and from mixed-species (MIXED) stands in northern Alberta, Canada, that had been clearcut, partial-cut with 20% retention, partial-cut with 50% retention or left uncut (controls). PLFA and SIR analyses revealed that ASPEN forest floors supported a larger microbial biomass with a very different community structure than MIXED or SPRUCE forest floors. The microbial community structure of these soils appeared to be strongly affected by the presence of white spruce and the composition of the understory vegetation. There were no effects of timber harvesting detected within or across stand types on any of the variables measured, with the exception of the PLFA 16:1ω5, which was relatively more abundant in the clearcuts and 50% retention treatments than in the uncut controls, perhaps in response to an increased forest floor pH and grass cover in the disturbed areas. The resilience to timber harvesting of the forest floors from these stands may be the result of efforts to minimize soil disturbance during harvesting and to allow vegetation to regenerate naturally. From the perspective of the forest floor microbial community, partial harvesting does not appear to have any benefit over clearcut harvesting at these boreal forest sites.     

Multiple effects of reindeer grazing on the soil processes in nutrient-poor northern boreal forests

Reindeer grazing has a great influence on the ground vegetation of nutrient-poor northern boreal forests dominated by Cladonia lichens in Fennoscandia. Grazing may influence the soil processes in these systems either by influencing the quality of plant litter, or by indirect effects through the soil microclimate. In order to investigate the mechanisms underlying the effects of reindeer on boreal forest soils, we analyzed litter decomposition, soil and microbial C and N, microbial community composition, and soil organic matter quality in three forest sites with old reindeer exclosures adjacent to grazed areas. There was no effect of grazing on soil C/N ratio, inorganic N concentrations, microbial biomass C, microbial community structure analyzed by phospholipid fatty acid (PLFA) analysis, and organic matter quality analyzed by sequential fractionation, in the soil organic layer. However, microbial N was enhanced by grazing at some of the sampling dates and was negatively correlated with soil moisture, which indicates that increased microbial N could be a stress response to drought. The effect of grazing on litter decomposition varied among the decomposition stages: during the first 1.5 months, the litter C loss was significantly higher in the grazed than the ungrazed areas, but the difference rapidly levelled out and, after one year, the accumulated litter C loss was higher in the ungrazed than the grazed areas. Litter N loss was, however, higher in the grazed areas. Our study demonstrates that herbivores may influence soil processes through several mechanisms at the same time, and to a varying extent in the different stages of decomposition.     

Changes of the functional diversity of soil microbial community during the colonization of abandoned grassland by a forest

The impact of secondary succession of grassland communities towards a Norway spruce forest on soil microbial community was studied on a belt transect established in the Pol’ana Mts., Central Europe. Data on understory vegetation, light availability, soil properties and microbial activity were collected on 147 plots distributed over regular grid. Moreover, distributions of functional groups of microorganisms were assessed using BIOLOG analysis on a subset of 27 plots. Mantel partial correlations between microbial community indicators and environmental variables showed that microbial activity generally decreased with increasing tree density and size, whereas it increased with increasing radiation at the soil surface, soil temperature, and cover and diversity of understory vegetation. Functional richness and diversity of microorganisms were positively correlated with solar radiation, but also with plant species richness and diversity. Abundance of several functional groups correlated closely with succession-related variables. Redundance analysis of microbial data provided slightly different outcomes. Forward selection yielded only two environmental variables significantly influencing the composition of the microbial community: tree influence potential and organic carbon content. Abundances of several functional microbial groups correlated with tree influence, documenting that microbial community changes are at least partially driven by the colonization of grassland by trees. Nevertheless, the relative importance of abiotic environment change and plant community succession on microbial community dynamics remains unresolved.     

Edge effects and trampling in boreal urban forest fragments – impacts on the soil microbial community

Fragmentation of forest ecosystems increases the proportion of edge habitat and is accompanied by a change in plant species composition. The recreational use of urban forests leads to decreased vegetation cover and the formation of paths, and thus, to fragmentation at small scales. We studied the impacts of forest and path edge effects on the soil microbial community structure (by using the phospholipid fatty acid (PLFA) method) and microbial activity (measured as basal respiration) in 34 mesic boreal urban forest fragments in Finland. We sampled the humus layer 1) from the forest edge into the interior (0–80 m), and 2) at different distances from paths. Microbial community structure was only slightly affected by the forest edge but differences were found between distances of 0–10 m and over 50 m from the edge. These changes correlated with changes in soil pH. Although changes in the microbial community structure were not pronounced, microbial biomass and activity were 30–45% lower at the first 20 m into the forest fragments, due to a low moisture content of the humus near the edge. The decreased microbial activity detected at forest edges implies decreased litter decomposition rates, and thus, a change in ecosystem nutrient cycling. The microbial community structure differed between paths and surrounding areas and correlated with changes in soil pH. Paths also supported approximately 25–30% higher microbial biomass with a transition zone of at least 1 m from the path edge. Path associated disturbances (mainly alterations in vegetation and soil pH) were reflected in the soil microbial community structure up to 1.5 m from the paths.     

Changes in soil microbial community structure following the abandonment of agricultural terraces in mountainous areas of Eastern Spain

In Eastern Spain, almond trees have been cultivated in terraced orchards for centuries, forming an integral part of the Mediterranean forest scene. In the last decades, orchards have been abandoned due to changes in society. This study investigates effects of changes in land use from forest to agricultural land and the posterior land abandonment on soil microbial community, and the influence of soil physico-chemical properties on the microbial community composition (assessed as abundances of phospholipids fatty acids, PLFA). For this purpose, three land uses (forest, agricultural and abandoned agricultural) at four locations in SE Spain were selected. Multivariate analysis showed a substantial level of differentiation in microbial community structure according to land use. The microbial communities of forest soils were highly associated with soil organic matter content. However, we have not found any physical or chemical soil property capable of explaining the differences between agricultural and abandoned agricultural soils. Thus, it was suggested that the cessation of the perturbation caused by agriculture and shifts in vegetation may have led to changes in the microbial community structure. PLFAs indicative of fungi and ratio of fungal to bacterial PLFAs were higher in abandoned agricultural soils, whereas the relative abundance of bacteria was higher in agricultural soils. Actinomycetes were generally lower in abandoned agricultural soils, while the proportions of vesicular–arbuscular mycorrhyzal fungi were, as a general trend, higher in agricultural and abandoned agricultural soils than in forests. Total microbial biomass and richness increased as agricultural < abandoned agricultural < forest soils.     

Soil moisture is the major factor influencing microbial community structure and enzyme activities across seven biogeoclimatic zones in western Canada

Although soil microorganisms play a central role in the soil processes that determine nutrient availability and productivity of forest ecosystems, we are only beginning to understand how microbial communities are shaped by environmental factors and how the structure and function of soil microbial communities in turn influence rates of key soil processes. Here we compare the structure and function of soil microbial communities in seven mature, undisturbed forest types across a range of regional climates in British Columbia and Alberta, and examine the variation in community composition within forest types. We collected the forest floor fermentation (F) and humus (H) layers and upper 10 cm of mineral soil at 3 sites in each of seven forest types (corresponding to seven Biogeoclimatic zones) in both spring and summer. Phospholipid fatty acid analysis was used to investigate the structure of soil microbial communities and total soil microbial biomass; potential activities of extra-cellular enzymes indicated the functional potential of the soil microbial community in each layer at each site.Multivariate analysis indicated that both structure and enzyme activities of soil microbial communities differed among the forest types, and significantly separated along the regional climate gradient, despite high local variation. Soil moisture and organic matter contents were most closely related to microbial community characteristics. Forests in the Ponderosa Pine and Mountain Hemlock zones were distinct from other forests and from each other when comparing potential enzyme activities and had the most extreme moisture and temperature values. Forest floors from the hot and dry Ponderosa Pine forests were associated with enzymes characteristic of water-stress and high concentrations of phenols and other recalcitrant compounds. The wet and cold Mountain Hemlock forests were associated with low enzyme activity.An influence of tree species was apparent at the three sites within the Coastal Western Hemlock zone; high bacterial:fungal biomass ratios were found under western redcedar (Thuja plicata) which also had high pH and base-cation levels, and under Douglas-fir (Pseudotsuga menziesii), which had high N availability. Potential activities enzymes differed among soil layers: potential activities of phenol oxidase and peroxidase were highest in mineral soil, whereas phosphatase, betaglucosidase, NAGase, sulfatase, xylosidase and cellobiohydrolase were highest in the forest floors.     

Tree species-mediated spatial patchiness of the composition of microbial community and physicochemical properties in the topsoils of a tropical montane forest

To evaluate the importance of plant-soil feedbacks in forest ecosystems, it is fundamental to understand the spatial range within which plant species control soil physicochemical and microbial properties. We investigated the spatial pattern of soil properties associated with canopy trees in a tropical montane forest on Mt. Kianbalu, Borneo. We analyzed soil physicochemical properties and microbial communities (biomarker lipid abundance) as a function of soil depth and distance from the tree trunk of a conifer (Dacrydium gracilis) or a broadleaf tree (Lithocarpus clementianus). The concentration of condensed tannins and fungi-to-bacteria were higher beneath Dacrydium than beneath Lithocarpus. Furthermore, carbon-degrading enzyme activities were lower beneath Dacrydium. These effects of the tree species were more distinct on soil properties beneath the tree crown than on those outside the tree crown. These effects appeared to be largely due to differences in litter chemistry, and the distinct set of soil properties formed corresponding to the above canopy crown. In conclusion, the species-rich forest on the tropical mountain contains spatially distinct units of soil properties associated with canopy trees, and this spatial pattern can influence ecosystem dynamics in the forest through plant-soil feedback effects.     

The effects of clear‐felling subalpine coniferous forests on soil physical and chemical properties in the eastern Tibetan Plateau

Establishing soil quality changes following clear‐felling is important for guiding the sustainable management of forests. In this study we identified changes after 4, 5, 10 and 17 yr in soil physical and chemical properties from clear‐felling in the eastern Tibetan Plateau. These properties were also compared with those of soil from an adjacent primary forest. The results show that: (i) bulk density at 0–20 and 20–40 cm soil layer continuously increased; (ii) soil C and total N in the 0–20 cm soil layer continuously declined following clear‐felling; and (iii) available soil nutrients and exchangeable cations were significantly influenced by clear‐felling. Almost all soil properties showed deteriorating trends within a short time from clear‐felling and subsequent seasonal grazing by cattle. Therefore, improved management is imperative for sustaining soil quality and maintaining the long‐term nutrient balance in clear‐cut stands. The cessation of anthropogenic activities such as grazing should be the main strategy for soil restoration in clear‐felled areas.     

The match between microbial community structure and soil properties is modulated by land use types and sample origin within an integrated agroecosystem

It is of global concern to adopt measures to mitigate land degradation caused by agricultural production systems. One of the strategies proposed is to replace degraded pastures with agrosilvopastoral systems which integrate three different land-use types: crop production, livestock pasture and forestry plantation (denoted iCLF). However, little is known about the differences between iCLF and other land use types in terms of soil microbial community structure. Distance matrices based on individual soil chemical properties and individual soil microbial variables were correlated by Procrustes analysis and these relationships yielded vectors of residuals depicting these correlations (matches). These vectors were used as univariate response variables in an ANOVA framework in order to investigate how the match sizes (the strength of correlation/covariance) between individual soil chemical properties and individual soil microbial variables vary across land use types (levels: iCLF; degradated pasture; improved pasture; and a native cerrado fragment) and also across sample origin within iCLF (levels: soil samples under more influence of the exotic tree forest stand; soil samples under influence of the pasture; samples within the transition between the forest stand and the pasture). We were able to obtain insights into the fact that the land use distinction can be driven by more than just individual soil chemical and microbial variables. The integration of crop, livestock and forestry promoted a dominance of fungi in this low fertility and low pH environment. P availability and the composite variable exchangeable base cations (Ca⁺², Mg⁺², K⁺) were the soil properties whose strengths of correlation (match sizes) with individual microbial variables were the most affected by land use type and sampling origin within iCLF. While the strength of the correlation between soil microbial structure variables and P availability was typically land use type dependent, the response of the microbial structure to exchangeable base cations was mainly affected by the sample origin within iCLF. Finally our results point towards the conclusion that increases in the heterogeneity of vegetation within integrated crop, pasture and forestry systems are an important driver of microbial community response to environmental changes, and may be one means by which to increase the sustainability of tropical agroecosystems.     

Timber harvesting alters soil carbon mineralization and microbial community structure in coniferous forests

Timber harvesting influences both above and belowground ecosystem nutrient dynamics. Impact of timber harvesting on soil organic matter (SOM) mineralization and microbial community structure was evaluated in two coniferous forest species, ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta). Management of ponderosa pine forests, particularly even-aged stand practices, increased the loss of CO₂-C and hence reduced SOM storage potential. Changes in soil microbial community structure were more pronounced in ponderosa pine uneven-aged and heavy harvest stands and in lodgepole pine even-aged stand as compared to their respective unmanaged stands. Harvesting of trees had a negative impact on SOM mineralization and soil microbial community structure in both coniferous forests, potentially reducing coniferous forest C storage potential.     

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.     

The influence of different types of urban land use on soil microbial biomass and functional diversity in Beijing,China

Soil microbes in urban ecosystems are affected by a variety of abiotic and biotic factors resulting from changes in land use. However, the influence of different types of land use on soil microbial properties and soil quality in urban areas remains largely unknown. Here, by comparing five types of land use: natural forest, park, agriculture, street green and roadside trees, we examined the effects of different land uses on soil microbial biomass and microbial functional diversity in Beijing, China. We found that soil properties varied with land uses in urban environments. Compared to natural forest, soil nutrients under the other four types of urban land use were markedly depleted, and accumulation of Cu, Zn, Pb and Cd was apparent. Importantly, under these four types of land use, there was less microbial biomass, but it had greater functional diversity, particularly in the roadside‐tree soils. Furthermore, there were significant correlations between the microbial characteristics and physicochemical properties, such as organic matter, total nitrogen and total phosphorus (P < 0.05), suggesting that lack of nutrients was the major reason for the decrease in microbial biomass. In addition, the larger C/N ratio, Ni concentration and pool of organic matter together with a higher pH contributed to the increase in microbial functional diversity in urban soils. We concluded that different land uses have indirect effects on soil microbial biomass and microbial community functional diversity through their influence on soil physicochemical properties, especially nutrient availability and heavy metal content.     

Effects of land use on the level, variation and spatial structure of soil enzyme activities and bacterial communities

The aim of this study was to evaluate the long-term influence of contrasting rural land use types on the level, plot-scale variation and horizontal spatial structure of decomposition activities and the bacterial community in soil. Experimental data were collected in the southern boreal zone from topsoil layers of adjacent spruce forest, unmanaged meadow (former field) and organically cultivated field that all shared the same soil origin. The forest soil was sampled separately for the organic and mineral layers. A geostatistical design comprising 50 sampling points per plot area of 10 × 10 m² was used. The measured microbiological characteristics included eight different hydrolytic soil enzyme activities involved in C, P and S cycles, bacterial 16S rDNA length heterogeneity profiles (LH-PCR) and total DNA yield as a relative estimate of microbial biomass.Effects of land use were pronounced on both the bacterial community structure and soil enzyme activities. Soil organic matter (SOM) content predicted well the major differences in soil enzyme activities and microbial biomass. Highest enzyme activities were generally found in the forest organic soil whereas the underlying mineral soil showed significantly lower activities with a pattern similar to those of the other mineral soils, especially the cultivated field. Bacterial LH-PCR fingerprints were distinct but at the same time remarkably similar between field and meadow soils whereas the forest organic layer differed clearly from the mineral soils. Within-plot variation of soil microbiological characteristics was best explained by the variation of SOM. Relative standard deviations of soil microbiological characteristics typically decreased in the order: forest organic layer ≈ forest mineral layer > meadow > field. However, bacterial fingerprints showed lowest variation within the meadow. Most of the microbiological variables studied showed no or only weak spatial structure at the scale sampled.