Ectomycorrhizal fungal exoenzyme activity differs on spruce seedlings planted in forests versus clearcuts

Key message

Ectomycorrhizal (ECM) fungal community structure and potential exoenzymatic activity change after clearcut harvesting, but functional complementarity and redundancy among those ECM fungal species remaining support growth of regenerating seedlings.

Abstract

Ectomycorrhizal (ECM) fungal community composition is altered by forest harvesting, but it is not clear if this shift in structure influences ECM fungal physiological function at the community level. In this study, we characterized activities of extracellular enzymes in the ectomycorrhizospheres of Picea engelmannii seedlings grown in forest and clearcut plots. These exoenzymes are critical for the breakdown of large organic molecules, from which nutrients are subsequently absorbed and translocated by ECM fungi to host plants. We found that ectomycorrhizae on seedlings planted in forests had different exoenzyme activity profiles than those on seedlings planted in clearcuts. Specifically, the activities of glucuronidase, laccase, and acid phosphatase were higher on forest seedlings (P ≤ 0.006). These differences may have been partly driven by soil properties. Total carbon, total nitrogen (N), extractable phosphorus, extractable ammonium-N, and mineralizable N were higher, while pH was lower in forest plots (P ≤ 0.01). However, we also found that enzyme activity only shifted where community composition also changed. Functional complementarity can be inferred within ECM fungal communities in both forests and clearcuts because ectomycorrhizae formed by different species in the same environment had distinct enzyme profiles (P < 0.0001). However, ectomycorrhizae of Thelephora terrestris exhibited high levels of N- and P-mobilizing exoenzyme activities. Seedling biomass did not differ between forest and clearcut environments, so the high abundance of T. terrestris ectomycorrhizae in the clearcuts may have sustained nutrient acquisition by clearcut seedlings even in soils with lower N and P and with reduced ECM fungal species richness.

     

Weak vertical canopy gradients of photosynthetic capacities and stomatal responses in a fertile Norway spruce stand

Wildfire severity in forests is projected to increase with warming and drying conditions associated with climate change. Our objective was to determine the impact of wildfire and clearcutting severity on the ectomycorrhizal fungal (EMF) community of Douglas-fir seedlings in the dry forests of interior British Columbia, Canada. We located our study within and surrounding the area of the McLure fire (August 2003). We hypothesized that disturbance would affect EMF community assembly due to reductions in fungal inoculum. Five treatments representing a range of disturbance severities were compared: high severity burn, low severity burn, screefed clearcut (manual removal of forest floor), clearcut, and undisturbed forest. EMF communities in the undisturbed forest were more complex than those in all disturbance treatments. However, aspects of community assembly varied with disturbance type, where the burn treatments had the simplest communities. After 4 months, regenerating seedlings in the burn treatments had the lowest colonization, but seedlings in all treatments were fully colonized within 1 year. EMF communities were similar among the four disturbance types, largely due to dominance of Wilcoxina throughout the study period. However, forest floor retention influenced community assembly as the EMF in the clearcut treatment, where forest floor was retained, had levels of diversity and richness comparable to the undisturbed forest. Overall, the results suggest that increasing forest floor disturbance can alter EMF community assembly in the first year of regeneration. A correlation between poorly colonized seedlings and seedling productivity also suggests a role for productivity in influencing community assembly.     

Dynamic changes in nursery and indigenous mycorrhiza ofPinus sylvestris seedlings planted out in forest and clearcuts

The community of indigenous mycorrhizal fungi on planted-out nursery seedlings of Scots pine (Pinus sylvestris L.) was surveyed for two years at two sites in Sweden. Factors studied were the effect of forests versus clearcuts on these communities, age of clearcut, planting-out in early summer versus autumn, age of planted-out seedlings and time of soil scarification. Analyses of variance and detrended correspondence analysis showed that the relative magnitude of the effects of these factors upon the composition of the ectomycorrhizal community on seedlings planted out was site > time of outplanting > forest/clearcut > age of clearcut > time of soil scarification. In general, clear-cutting had a minor effect, both qualitatively and quantitatively. Nineteen different mycorrhizal types were recorded. After two seasons, seedlings hosted an average of 1.8 indigenous mycorrhizal types and 0.95 nursery mycorrhizal types comprising 35% and 65% of the mycorrhizal roots, respectively.Piloderma croceum colonized seedlings significantly more frequently in forests than in clearcuts, whereas the reverse was found forCenococcum geophilum, and two other mycorrhizal types. However, there is a general agreement between mature coniferous forests and clearcuts as regards both the inoculum potential of dominant fungi adapted to early colonization, and the composition of these fungal species. The fungal adaptations to forests obviously resemble those conditions occurring at clearcuts.     

The effect of forest soil and community composition on ectomycorrhizal colonization and seedling growth

Plant–soil feedbacks have been observed in many forest communities, but the role of the mycorrhizal community in perpetuating feedback loops is still poorly understood. Mycorrhizal community composition is closely linked to soil properties and host plant composition, which highlights their potential importance in plant–soil–fungus loops. Eastern hemlock (hemlock; Tsuga canadensis) seedlings were grown in soil bioassays in growth chambers and transplanted under closed forest canopy to examine the effect of hardwood and hemlock forest soil on seedling growth, survival, and ectomycorrhizal fungi (EMF) colonization. Seedlings propagated in hemlock forest soil had greater height growth compared with sterile control soil and achieved greater mycorrhizal colonization than seedlings grown in hardwood forest soils after 9 months in a growth chamber. Outplanted seedlings grown in hemlock communities achieved significantly greater increment growth than those seedlings grown in hardwood communities (mean height difference (95% CI)?=?0.39 cm (0.14–0.63 cm)), although final survival and EMF colonization was similar between forest types. EMF diversity (Shannon-Wiener index (SE)?=?1.88 (0.28) and 1.23 (0.44) for hardwood and hemlock, respectively) and community assemblage (Jaccard index (SE)?=?19.0% (4%)) differed between the two forest communities. EMF community assemblage was associated with both the forest type (i.e. plant community/microsite effects) and initial soil type (i.e. soil characteristics/resistant inoculum). The results support previously observed positive feedbacks between conspecifics under hemlock forest communities and provides evidence for the role of the EMF community within this feedback loop. Alternatively, the reduced growth of hemlocks under hardwoods may be attributed to the different EMF community associated with that forest.     

Unstable microhabitats (merocenoses) as specific habitats of Uropodina mites (Acari: Mesostigmata)

Unstable microhabitats (merocenoses)—such as decayed wood, ant hills, bird and mammal nests—constitute an important component of forest (and non-forest) environments. These microhabitats are often inhabited by specific communities of invertebrates and their presence increases the total biodiversity. The primary objective of the present study was to compare communities of Uropodina (Acari: Mesostigmata) inhabiting soil and unstable microhabitats in order to explore the specificity of these communities and their importance in such ecosystems. Uropodine communities inhabiting merocenoses are often predominated by one or two species, which constitute more than 50 % of the entire community. Many species occur commonly in particular merocenoses, but are absent or rare in soil and litter, for example, Allodinychus flagelliger, Metagynella carpatica, Oplitis alophora, and Phaulodiaspis borealis. The biology of Uropodina inhabiting unstable microhabitats is modified by the adaptations required for living in such habitats. Mites associated with merocenoses developed special dispersal mechanisms, such as phoresy, which enable them to migrate from disappearing environments. Communities of Uropodina in soil and litter predominately consisted of species which reproduce parthenogenetically (thelytoky), whereas in merocenoses bisexual species prevail.     

Establishment of ectomycorrhizal fungal community on isolated Nothofagus cunninghamii seedlings regenerating on dead wood in Australian wet temperate forests: does fruit-body type matter?

Decaying wood provides an important habitat for animals and forms a seed bed for many shade-intolerant, small-seeded plants, particularly Nothofagus. Using morphotyping and rDNA sequence analysis, we compared the ectomycorrhizal fungal community of isolated N. cunninghamii seedlings regenerating in decayed wood against that of mature tree roots in the forest floor soil. The /cortinarius, /russula-lactarius, and /laccaria were the most species-rich and abundant lineages in forest floor soil in Australian sites at Yarra, Victoria and Warra, Tasmania. On root tips of seedlings in dead wood, a subset of the forest floor taxa were prevalent among them species of /laccaria, /tomentella-thelephora, and /descolea, but other forest floor dominants were rare. Statistical analyses suggested that the fungal community differs between forest floor soil and dead wood at the level of both species and phylogenetic lineage. The fungal species colonizing isolated seedlings on decayed wood in austral forests were taxonomically dissimilar to the species dominating in similar habitats in Europe. We conclude that formation of a resupinate fruit body type on the underside of decayed wood is not necessarily related to preferential root colonization in decayed wood. Rather, biogeographic factors as well as differential dispersal and competitive abilities of fungal taxa are likely to play a key role in structuring the ectomycorrhizal fungal community on isolated seedlings in decaying wood.     

Importance of high quality early-successional habitats in managed forest landscapes to rare beetle species

Species adapted to early-successional forest habitats are in managed landscapes largely confined to clearcuts. To improve habitat quality on clearcuts, green tree and dead wood retention is widely applied in forestry; however, its effects on rare early-successional species have rarely been shown. We repeatedly surveyed two red-listed beetle species (Upis ceramboides and Platysoma minus) on clearcuts in a managed boreal forest landscape. We found that U. ceramboides decreased its occupancy over time while P. minus increased, indicating that red-listed species vary in their ability to successfully utilise managed habitats. We found no effect of connectivity on probability of occurrence, colonisation or extinction per clearcut. Trees retained alive improved habitat quality of clearcuts, since both species were more frequent in dead wood of such trees, in comparison to logging residues. We suggest that retention can be improved by protecting and creating dead wood as intact trees during harvesting. Rare specialist species require habitat of high quality, and consequently it is impossible to meet the requirements of these species on every clearcut. To preserve all early-successional species at a regional scale, we recommend focusing retention of green trees and dead wood to one or a few trees species on each clearcut and in each landscape.     

Ectomycorrhizal fungal succession coincides with shifts in organic nitrogen availability and canopy closure in post-wildfire jack pine forests

Successional changes in belowground ectomycorrhizal fungal (EMF) communities have been observed with increasing forest stand age; however, mechanisms behind this change remain unclear. It has been hypothesized that declines of inorganic nitrogen (N) and increases of organic N influence changes in EMF taxa over forest development. In a post-wildfire chronosequence of six jack pine (Pinus banksiana) stands ranging in age from 5 to 56 years, we investigated EMF community composition and compared shifts in taxa with detailed soluble inorganic and organic N data. Taxa were identified by internal transcribed spacer rDNA sequencing, and changes in community composition evaluated with non-metric multi-dimensional scaling (NMDS). Dissimilarities in the community data were tested for correlations with N variables. We observed a successional shift along NMDS axis 1 from such taxa as Suillus brevipes and Thelephora terrestris in sites age 5 and 11 to species of Cortinarius and Russula, among others, in the four older sites. This change was positively correlated with soluble organic N (SON) (r ² = 0.902, P = 0.033) and free amino-acid N (r ² = 0.945, P = 0.021), but not inorganic N. Overall, our results show a successional shift of EMF communities occurring between stand initiation and canopy closure without a change in species of the dominant plant–host, and associated with SON and free amino-acid N in soil. It is uncertain whether EMF taxa are responding to these organic N forms directly, affecting their availability, or are ultimately responding to changes in other site variables, such as belowground productivity.     

Plant and soil properties determine microbial community structure of shared Pinus-Vaccinium rhizospheres in petroleum hydrocarbon contaminated forest soils

Rhizosphere communities are critical to plant and ecosystem function, yet our understanding of the role of disturbance in structuring these communities is limited. We tested the hypothesis that soil contamination with petroleum hydrocarbons (PHCs) alters spatial patterns of ecto- (ECM) and ericoid (ERM) mycorrhizal fungal and root-associated bacterial community structure in the shared rhizosphere of pine (Pinus contorta var. latifolia) and lingonberry (Vaccinium vitis-idaea) in reconstructed sub-boreal forest soils. Pine seeds and lingonberry cuttings were planted into containers with an organic (mor humus, FH or coarse woody debris, CWD) layer overlying sandy mineral horizons (Ae and Bf) of forest soils collected from field sites in central British Columbia, Canada. After 4 months, 219 mg cm^-2 crude oil was applied to the soil surface of half of the systems; systems were sampled 1 or 16 weeks later. Composition, relative abundance and vertical distribution of pine ECMs were assessed using light microscopy; community profiles were generated using LH-PCR of ribosomal DNA. Multivariate analysis revealed that plant and soil factors were more important determinants of community composition than was crude oil treatment. Fungal communities differed between pine and lingonberry roots; ECM communities were structured by soil layer whereas ERM communities varied between FH and CWD soil systems. Bacterial communities varied between plants and soil layers, indicating properties of ECM and ERM rhizospheres and the soil environment influence bacterial niche differentiation. This integration of mycorrhizal and bacterial community analysis contributes to a greater understanding of forest soil sustainability in forest ecosystems potentially contaminated with PHCs.     

Ecology of Compounding Disturbances: The Effects of Prescribed Burning After Clearcutting

Disturbance regimes in much of the boreal forest have shifted from wildfire to clearcutting over the last century, resulting in concerns for biodiversity. Because the boreal forest has evolved under a natural fire regimes, we hypothesized that application of prescribed burning (PB) after clearcutting would result in plant communities more similar to wildfire than clearcut only. However, because clearcutting + PB involves multiple disturbances in a short interval, we proposed an alternate hypothesis that clearcutting + PB would result in a species composition and trait assemblage that differ from those that develop after a single wildfire or clearcutting event. We determined species composition, diversity, and trait composition of 17 clearcut, 17 clearcut + PB, and 15 wildfire sites of jack pine (Pinus banksiana) dominated forests in northwestern Ontario, Canada 15–37 years after disturbance. Contrary to our primary hypothesis we found that clearcut + PB formed communities different from wildfire and clearcut, the latter two being similar. Clearcut + PB harbored more early successional species associated with seed banking, wind dispersal, deciduous foliage, and alien origin than wildfire or clearcut sites, which showed no specific trait associations. Taxonomic and trait analysis of clearcut + PB sites exhibited effects of compound disturbances, as observed after short-interval fires, supporting our alternate hypothesis. We concluded that PB after clearcutting formed plant communities significantly different from those developed either after clearcutting or wildfire alone. We attribute this community divergence to the compounding effects associated with the addition of prescribed fire to these previously disturbed forests.     

Edge effects of three anthropogenic disturbances on spider communities in Alberta’s boreal forest

Increasing fragmentation of forests worldwide by timber and industrial development makes it important to understand the edge effects of common anthropogenic disturbances on forest fauna. We collected ground-active spiders along transects across the edge of logging clearcuts, gravel roads and gas pipelines in the boreal forest of Alberta, sampling on the disturbance (10?m from forest edge), and 10, 45, and 200?m into the forest. We asked whether the three disturbances were associated with edge effects on spider communities, and whether the extent of their associated edge effects were equivalent. The spider community at the edges of clearcuts was distinct from interior and on-disturbance communities 10?m into the forest from the clearcut edge, showing an edge effect of between 10 and 45?m from clearcut edges, while no edge effects were apparent at road and pipeline edges. Edge effects therefore differ at linear and non-linear openings in the boreal forest, which suggests that small linear openings may be associated with minimal edge effects compared to large polygonal forest openings. This result has important consequences for forest management, where clearcuts and other non-linear openings are likely to cause edge effects on spider communities that are between 10 and 45?m in their extent. The small size of clearcuts as practiced in the public forests of Canada, and their dense and broad application across the landscape, makes this edge effect of broad spatial significance in protecting biodiversity in managed landscapes.     

阿拉斯加东南部温带雨林加氏(鼠平)和肯氏鹿鼠密度与微生境利用的相关性

为了验证对阿拉斯加东南部温带雨林中有关栖息地关系的预测,我们于1999年和2000年8-9月以及1999年和2000年4-5月研究了亚历山大群岛加氏(Clethrionomys gapperi)和肯氏鹿鼠(Peromyscus keeni)种群。我们测量了26个植被和结构特征以检验林隙老龄生长林、多时代老龄生长林、采伐前壮龄(23岁)生长林和泥炭混交针叶林的丰富度与微栖息地利用的相关性。微栖息地利用随季节和栖息地而变化,但加氏与林下落叶灌木覆盖度的正相关最显著。肯氏鹿鼠利用的微环境的林地有较少的苔藓,但是林隙与抓获加氏的概率有直接关系。两种鼠在两个季节的密度与林下腐朽的倒木直接相关。春季的肯氏鹿鼠密度说明加氏密度变化的62%,说明肯氏鹿鼠密度变化的89%。我们的结果印证了早期对阿拉斯加东南部肯氏鹿鼠在各种栖息地尤其早期的演替林中兴旺时的研究;但偏离了西部地貌中肯氏鹿鼠种群在晚期演替针叶林中达到最高密度的普遍结论。与北美西北部其它地区的种群不同,加氏能持久生活在上层被砍伐的雨林板块中。泥炭针叶混交林对两种鼠的繁殖种群几乎没有贡献,因而不可能减轻对多产的老龄生长雨林大规模皆伐所造成的影响。     

Comparison of Bacterial and Fungal Communities Between Natural and Planted Pine Forests in Subtropical China

To improve our understanding of the changes in bacterial and fungal diversity in natural pine and planted forests in subtropical region of China, we examined bacterial and fungal communities from a native and a nearby planted pine forest of the Mt. Lushan by constructing clone libraries of 16S and 18S rRNA genes. For bacterial communities, Proteobacteria and Acidobacteria were dominant bacterial taxa in both two types of forest soils. The Shannon–Wiener diversity index, rarefaction curve analysis, and LibShuff analysis suggest that these two forests contained similar diversity of bacterial communities. Low soil acidity (pH ≈ 4) of our study forests might be one of the most important selection factors determining growth of acidophilic Acidobacteria and Proteobacteria. However, the natural forest harbored greater level of fungal diversity than the planted forest according to the Shannon–Wiener diversity index and rarefaction curve analysis. Basidiomycota and Ascomycota were dominant fungal taxa in the soils of natural and planted forests, respectively. Our results suggest that fungal community was more sensitive than the bacterial community in characterizing the differences in plant cover impacts on the microbial flora in the natural and planted forests. The natural and planted forests may function differently due to the differences in soil fungal diversity and relative abundance.     

Quercus rubra-associated ectomycorrhizal fungal communities of disturbed urban sites and mature forests

The presence and quality of the belowground mycorrhizal fungal community could greatly influence plant community structure and host species response. This study tests whether mycorrhizal fungal communities in areas highly impacted by anthropogenic disturbance and urbanization are less species rich or exhibit lower host root colonization rates when compared to those of less disturbed systems. Using a soil bioassay, we sampled the ectomycorrhizal fungal (EMF) communities associating with Quercus rubra (northern red oak) seedlings in soil collected from seven sites: two mature forest reference sites and five urban sites of varying levels of disturbance. Morphological and polymerase chain reaction–restriction fragment length polymorphism analyses of fungi colonizing root tips revealed that colonization rates and fungal species richness were significantly lower on root systems of seedlings grown in disturbed site soils. Analysis of similarity showed that EMF community composition was not significantly different among several urban site soils but did differ significantly between mature forest sites and all but one urban site. We identified a suite of fungal species that occurred across several urban sites. Lack of a diverse community of belowground mutualists could be a constraint on urban plant community development, especially of late-successional woodlands. Analysis of urban EMF communities can add to our understanding of urban plant community structure and should be addressed during ecological assessment before pragmatic decisions to restore habitats are framed.     

Effects of forest dieback on wood decay,saproxylic communities,and spruce seedling regeneration on coarse woody debris

Picea is one of the most dominant conifer genera in the Northern Hemisphere and includes species which require coarse woody debris (CWD) as a seedbed for regeneration. To understand the future of forest distribution under global climate change, it is important to investigate regeneration mechanisms in Picea forests on the borders of its distribution. In the present study, we evaluated the biotic factors affecting the establishment of Picea jezoensis var. hondoensis seedlings on CWD in one of its southernmost populations in central Japan, where there is dieback of Picea forest. Amplicon sequencing of the fungal ITS1 region of rDNA obtained from wood samples showed that forest dieback increased the frequency of brown rot fungi in CWD. The frequency of brown-rotted wood, in which wood holocellulose is decayed, increased with dieback intensity. The domination of brown-rotted wood in dieback forests was negatively associated with bryophyte cover which was positively associated with Picea seedling density. Forest dieback itself also had other strong negative effects on bryophytes. Thus, linkages between dead wood and spruce seedlings via bryophytes had collapsed after the dieback event, which may partly be a reason that the spruce forest shifted to and is staying as open grassland.     

Mycetophilidae (Diptera), an insect group vulnerable to forestry practices? A comparison of clearcut,managed and semi-natural spruce forests in southern Norway

The mycetophilid fauna and environmental variables were studied at 15 sites within a spruce forest in southern Norway. There were five replications of each of the following categories: semi-natural forests, clearcuts, and managed forests (clearcut 70–120 years ago). Clearcutting seems to induce a long lasting effect on the Mycetophilidae fauna. The semi-natural forests were more speciesrich and contained more potentially rare species than the two other categories. Even though managed forests and clearcuts differed in faunal composition, their species richness was not significantly different. Continuity is probably a main factor for maintaining the diversity of Mycetophilidae species. Lumping the 15 sites together, the number of species was strongly correlated with the (temporal) continuity of tree cover and substrates, which may reflect an increased diversity of fungal habitats both in dead wood and on the ground. The degree of continuity was recognized by means of indicator species of fungi, lichen and vascular plants. The amount of dead wood was correlated with the species diversity, but was probably dependent on the continuity factor, since clearcuts with much dead wood had relatively fewer species.Important elements in a strategy for conservation of the diversity of mycetophilid species seem to be: (i) to identify and protect the remnant patches of forests with long continuity, (ii) as far as possible, to practice timber harvesting in earlier clearcut forests instead of semi-natural forests.     

Site identity and moss species as determinants of soil microbial community structure in Norway spruce forests across three vegetation zones

Soil microbial community structure was investigated by PLFA-analysis in four spruce forests in Norway. The maximum latitudinal distance between the sites was approximately 350 km. Bilberry Vaccinium myrtillus dominated the forest floor vegetation in the study sites, which were selected because of the vegetation type. Soil samples were taken from all four sites under close to 100% homogeneous ground cover of each of two feathermoss species, i.e. Hylocomium splendens or Pleurozium schreberi, respectively. These mosses are ubiquitous in the boreal forest and constitute an abundant component of the forest floor vegetation over vast areas. Since there are no studies on how these mosses affect soil microbial community structure, our first aim was to investigate the effect of moss species on soil microbial communities. Our second aim was to investigate whether microbial communities differ among geographically separated forest sites with similar vegetation across vegetation zones. Soil microbial community structure differed between the study sites, although they appeared similar in terms of vegetation and abiotic soil conditions. Study site was the most important predictor of the variation in the PLFAs, more important than moss species, although there was a tendency for separation of microbial community structure between the two moss species.     

Physiological differences in Rhododendron calophytum seedlings regenerated in mineral soil or on fallen dead wood of different decaying stages

Regeneration substrates may differ in water and nutrient availability, and that may lead to differences in physiological traits among seedlings. This assumption was tested by investigating the effects of different regeneration substrates (fallen dead wood and soil) on physiological traits in seedlings of Rhododendron calophytum Franch. in a subalpine conifer forest, southwest China. The seedlings were divided into three groups according to their regeneration substrates: moderately decayed dead wood (DW_m); severely decayed dead wood (DW_s) and soil (S). The results showed that there were significant differences in leaf mass per area (LMA), photosynthetic capacity, non-structural carbohydrate composition (NSC), leaf phosphorus (P) concentration, carbon isotope composition (δ¹³C) and ultrastructural morphology, not only between the seedlings regenerated in soil and on dead wood, but also between the seedlings regenerated on dead wood of different decaying stages. Overall, the photosynthetic capacity of the seedlings increased in the order of DW_m <?S < DW_s, and the long-term water use efficiency (WUE) of the seedlings increased in the order of DW_m < DW_s < S. Different nutrient and water availability in the substrates might be responsible for these differences. We suggest that severely decomposed fallen dead wood is the most suitable substrate for the regeneration of R. calophytum.     

Temporal dynamics of ectomycorrhizal fungal communities in Shorea siamensis forest fragments

Investigating the dynamics of ectomycorrhizal fungal (EMF) communities in seasonally dry tropical forests is essential for sustainable management and for understanding the resilience of this forest type in future climate change scenarios. EMF communities in secondary forest fragments with Shorea siamensis as a single host tree species in central Thailand were sampled seasonally for 2.5 y. Ten EMF taxa were identified from ectomycorrhizal morphotypes, with/tomentella-thelephora and/russula-lactarius as the dominant taxa. Seasonal differences in EMF diversity were not detected; the dominant morphotypes were present in both seasons and their abundance varied. Most EMF taxa exhibited wide environmental ranges and only a few taxa were correlated with soil moisture. Seasonal dynamics of ectomycorrhizal colonization was likely influenced by climatic factors and the phenology of host species. Together, these results suggested that climatic variation may have a long-term and subtle influence on the composition of ectomycorrhizal communities.     

人工与天然云杉林土壤真菌群落多样性及菌群网络关系特征

土壤真菌群落多样性和菌群关系是维持生态系统的多样性及稳定性的关键。本文以粗枝云杉人工林和天然林为研究对象,利用高通量测序技术和生物信息学分析方法,研究了云杉根际和非根际土壤真菌群落组成、多样性及菌群网络关系。结果表明: 从群落组成上看,人工林中相对丰度最高的科是丝盖伞科,而天然林中是蜡壳耳科,两处林型下占比最高的属均为丝盖伞属。群落的β多样性在两处林型的根际、非根际下存在显著差异。环境变量与真菌类群的相对丰度和α多样性相关关系不显著,而草本覆盖度、土壤含水率、总有机碳和植被丰富度是群落β多样性的主要影响因素。网络分析显示,天然林土壤真菌菌群之间以负相关关系为主,表明天然林土壤中菌群之间主要存在竞争作用。比较两处林型下的根际、非根际土壤真菌菌群关系发现,非根际区域菌群之间负相关性均较高,表明非根际土壤中菌群的种间竞争作用可能要强于根际土壤。结合差异丰度分析,两处林型下根际和非根际之间存在显著差异的物种中仅有蜡壳耳科为真菌网络中共有的关键菌群,表明人工林和天然林土壤真菌群落结构中差异种群的变化可能对其群落稳定性影响较小。