Ectomycorrhizal Trees Research Articles

Evidence that ericoid mycorrhizal shrubs can outcompete ectomycorrhizal trees for nitrogen in tannin‐rich litter

AbstractMycorrhizal associations of trees play a key role in ecosystem biogeochemistry, yet we know relatively little about the nutrient acquisition strategies of ericoid mycorrhizal (ErM) shrubs, despite their prevalence in forest understories. ErM shrubs tend to produce litter with high concentrations of polyphenols, which form decay‐resistant complexes with organic nitrogen (N). Some ErM fungi appear capable of producing a diverse suite of extracellular enzymes, but it is unclear whether this enables ErM shrubs to acquire the N from their own litter, and whether this ability is greater than that of ectomycorrhizal (EcM) trees, with which they commonly co‐occur. Here, we conducted two growth chamber experiments with 15N‐enriched root and leaf litters to determine whether EcM pine and ErM vaccinium differ in litter N acquisition from these sources. Grown individually, pine and vaccinium plants acquired 1 mg or 4% of the litter N after one year. Differences between pine and vaccinium in litter N acquisition were correlated with litter chemistry, where vaccinium acquired more N from litter with a high concentration of tannins and a high C:N, while pine acquired more N from litter with a high acid‐insoluble fraction. When plants were grown in pairs, the presence of a vaccinium neighbor reduced the biomass of both species by an average of 24%, but it only reduced litter N acquisition by pine (55%), demonstrating vaccinium's ability to compete with pine for litter N. Regardless of the competitive context, vaccinium allocated a greater percentage (76%) of its acquired litter N to aboveground biomass compared with pine (47%), suggesting vaccinium is more efficient at allocating this N to photosynthesis and growth. Our finding that EcM pine and ErM vaccinium have varying abilities to acquire N from these common litters suggests a degree of niche complementarity, which may facilitate the coexistence of these plants in forest ecosystems. However, our results also suggest that, at high densities, ErM vaccinium has the potential to suppress the growth and N acquisition of EcM pine. Distinct strategies of EcM trees and ErM shrubs for acquiring and using N have the potential to shape biogeochemical cycles of many forested ecosystems.

Plant–mycorrhizal associations may explain the latitudinal gradient of plant community assembly

Biogeographical variation in community assembly processes forms the basis of the latitudinal gradient of biodiversity by driving β‐diversity. Classical studies on community assembly predict environmental filtering affecting β‐diversity more strongly at higher latitudes, where productivity is lower and abiotic stress is stronger. Contrary to this prediction, recent evidence indicates that plant community composition at higher latitudes exhibits more spatially clustered distributions independently of background environments, suggesting the importance of spatial processes, such as priority effects. In this study, we propose a hypothesis that resolves this paradox by considering plant–soil feedback and biogeographic variations in the dominant mycorrhizal type: we predict that the increasing prevalence of ectomycorrhizal (EcM) trees with latitude contributes to the spatially clustered distribution of plants, as EcM trees tend to exhibit positive plant–soil feedback. We analyzed a large‐scale standardized dataset of Japanese forests covering a latitudinal gradient of >10° and found that 1) the proportion of EcM trees was higher at higher latitudes, and 2) EcM tree‐rich communities exhibited more spatially clustered distributions likely due to positive plant–soil feedback. Consequently, 3) tree species composition at higher latitudes was better explained by spatial variables suggesting the importance of priority effects. Consistent with the predictions of the plant–soil feedback theory, these patterns were more pronounced in understory than in canopy communities. Taken together, our results lend support to our hypothesis that biogeographic variation in tree community assembly patterns is defined by mycorrhizal types and plant–soil feedback, thereby resolving a paradox in the latitudinal gradient of plant community assembly. Our work highlights that plant mycorrhizal type underlies the determinants of β‐diversity which is a critical component of the latitudinal gradient of diversity.

Tree mycorrhizal type mediates the responses of foliar stoichiometry and tree growth to functionally dissimilar neighbours in a subtropical forest experiment

Abstract Plant nutrient stoichiometry is of critical importance to productivity and nutrient cycling in terrestrial ecosystems. The impacts of tree species diversity on productivity have been well studied at the stand level. However, it is unclear how neighbourhood interactions impact the foliar nutrient stoichiometry of trees at the neighbourhood scale and how plant mycorrhizal associations can mediate such effects. We randomly selected eight tree species from a large‐scale biodiversity experiment with mixtures up to 32 tree species in subtropical China to assess the effects of species richness, phylogenetic and trait dissimilarities and competition on the foliar nutrient stoichiometry of focal trees associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. We further investigated whether neighbourhood diversity can alter focal tree growth by regulating C:N:P stoichiometry. Neighbourhood species richness had no significant impact on the foliar C:N, N:P or C:P for both AM and EM trees. Increased neighbourhood phylogenetic dissimilarity significantly decreased the foliar N:P and C:P of AM trees but did not affect those of EM tree species. Foliar C:N, N:P and C:P of AM trees decreased with increasing neighbour trait (specific leaf area, root diameter, wood density dissimilarity, total trait) dissimilarities, while those of EM trees increased or remained unchanged. The increase of the neighbourhood competition index resulted in an increase in the foliar C:N of AM tree species but not EM tree species. The structural equation model analysis revealed that the increase of neighbourhood phylogenetic dissimilarity and functional trait dissimilarity indirectly enhanced tree growth of AM trees by decreasing foliar C:N. Conversely, the increase of neighbourhood‐specific root length and wood density dissimilarity indirectly reduced the growth of EM trees by increasing foliar N:P. Synthesis. Our results indicate that neighbourhood trait dissimilarity regulated tree foliar stoichiometry and growth performance, but the effects depended on the mycorrhizal type of trees. Our findings highlight the importance of tree mycorrhizal associations for better understanding the relationship between plant diversity and ecosystem functions. Read the free Plain Language Summary for this article on the Journal blog.

Ectomycorrhizal trees enhanced water-holding capacity in forest ecosystems in northeastern China

Ectomycorrhizal trees enhanced water-holding capacity in forest ecosystems in northeastern China

Soil Horizons Harbor Differing Fungal Communities

In the present study, the mycobiomes of two soils with different ecological conditions located in Benin (West Africa) were investigated by environmental sequencing (Illumina MiSeq) of the ITS2-region of ribosomal DNA to gain information about the influence of pedological stratification on fungal diversity. For each soil depth and horizon, fungal diversity and community composition were analyzed as well as the potential impact of site characteristics, like vegetation, on these traits. The retrieved sequences revealed in all their replicates high similarities between fungal communities of samples from the same site and soil horizon, but differed within one site in their horizons. It was possible to assign a saprotrophic, symbiotrophic, or parasitic lifestyle to 24% of the recorded fungal mOTUs. Plant parasites were found in all samples in similar proportions. The presence of ectomycorrhizal fungi in one site could be linked to the presence of ectomycorrhizal trees. Overall, it was observed that fungal diversity decreased with increasing depth if only one horizon was present, whereas a deeper horizon present at one site contained communities with a distinct composition regarding the taxonomical affiliations and lifestyles of the fungi found compared to the upper layer. Hence, soil horizonation seems to drive differences in the composition of fungal communities, and should be regarded with more attention when analyzing soil mycobiomes.

Plant–soil feedback is dependent on tree mycorrhizal types and tree species richness in a subtropical forest

Plant-soil feedback (PSF) is an important driver of plant species coexistence and diversity maintenance. However, it remains unclear how changes in PSF due to decline in tree species richness influence the performance of arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) tree species. A PSF experiment was established with eight target tree species (four AM and four EcM tree species) based on a subtropical forest Biodiversity-Ecosystem Functioning Experimental in China (BEF-China) platform, where soil inocula were collected beneath the canopy of target tree species individuals growing in monoculture and eight tree-species mixture plots. We hypothesized that the negative PSF strength of AM tree species would be stronger in monocultures than that in eight tree-species mixtures, resulting in better performance in highly diverse plant communities, whereas EcM tree species would benefit less from tree species richness. However, the results showed consistent PSFs of AM tree species regardless of tree species richness. In contrast, EcM tree species experienced a change from positive in monocultures to negative PSF in eight tree-species mixtures, influencing the performance of EcM tree seedlings. With high concern of the cascading effects of tree species richness on PSFs via modulating soil fungal communities, we revealed that the alterations in EcM fungal abundance, putatively pathogenic fungal diversity, and fungal co-occurrence network complexity mirrored those of PSF associated with EcM tree species, showing the changes from positive in monocultures to negative feedback in eight tree-species mixtures. Our findings highlight the differential PSFs exhibited by AM and EcM tree species in response to tree species richness, and provide insight into the potential role of fungal functional guilds and co-occurrence network complexity in shaping the PSFs of them.

Arbuscular mycorrhizal and ectomycorrhizal plants together shape seedling diversity in a subtropical forest

IntroductionBurgeoning mycorrhizal research has focused on identifying the various diverse mycorrhizal strategies of forest communities. Mounting evidence suggests that mycorrhizae play important roles in regulating forest community structure and composition. However, research into the manifestation of this influence in the seedling stage is lacking, especially in small-scale plots.MethodsOur research utilized structural equation models parameterized using data from a subtropical monsoon broad-leaved evergreen forest situated in Yunnan Province, China.ResultsWe noted that seedlings included plants that utilized both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. More seedling plots with the relatively higher species diversity were the product of the mixed mycorrhizal strategy, meaning the coexistence of AM and EM seedlings in a small-scale plot rather than the dominance of one type of strategies. These mixed communities were primarily found on slopes and mountain ridges. The abundance of AM or EM trees indirectly affected seedling diversity by influencing the abundance of different mycorrhizal seedlings. In this case, the diversity of the mixed mycorrhizal community was also restricted by the level of leaf thickness in the community, followed by abiotic factors such as elevation, convexity, soil pH and soil available phosphorus.DiscussionThe effect of leaf thickness on mycorrhizal seedling abundance reflected the importance of water conditions in shaping seedling communities. The effect of convexity on seedling diversity also reflected the limitation of seedling communities by the distribution of humidity and heat conditions during topographic change. The results suggested that it is crucial to preserve seedling diversity via the mixed mycorrhizal strategy of communities in the subtropical forest.

Tropical tree ectomycorrhiza are distributed independently of soil nutrients.

Mycorrhizae, a form of plant-fungal symbioses, mediate vegetation impacts on ecosystem functioning. Climatic effects on decomposition and soil quality are suggested to drive mycorrhizal distributions, with arbuscular mycorrhizal plants prevailing in low-latitude/high-soil-quality areas and ectomycorrhizal (EcM) plants in high-latitude/low-soil-quality areas. However, these generalizations, based on coarse-resolution data, obscure finer-scale variations and result in high uncertainties in the predicted distributions of mycorrhizal types and their drivers. Using data from 31 lowland tropical forests, both at a coarse scale (mean-plot-level data) and fine scale (20 × 20 metres from a subset of 16 sites), we demonstrate that the distribution and abundance of EcM-associated trees are independent of soil quality. Resource exchange differences among mycorrhizal partners, stemming from diverse evolutionary origins of mycorrhizal fungi, may decouple soil fertility from the advantage provided by mycorrhizal associations. Additionally, distinct historical biogeographies and diversification patterns have led to differences in forest composition and nutrient-acquisition strategies across three major tropical regions. Notably, Africa and Asia's lowland tropical forests have abundant EcM trees, whereas they are relatively scarce in lowland neotropical forests. A greater understanding of the functional biology of mycorrhizal symbiosis is required, especially in the lowland tropics, to overcome biases from assuming similarity to temperate and boreal regions.

Soil microbial community response to ectomycorrhizal dominance in diverse neotropical montane forests

Ectomycorrhizal (EM) associations can promote the dominance of tree species in otherwise diverse tropical forests. These EM associations between trees and their fungal mutualists have important consequences for soil organic matter cycling, yet the influence of these EM-associated effects on surrounding microbial communities is not well known, particularly in neotropical forests. We examined fungal and prokaryotic community composition in surface soil samples from mixed arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) stands as well as stands dominated by EM-associated Oreomunnea mexicana (Juglandaceae) in four watersheds differing in soil fertility in the Fortuna Forest Reserve, Panama. We hypothesized that EM-dominated stands would support distinct microbial community assemblages relative to the mixed AM-EM stands due to differences in carbon and nitrogen cycling associated with the dominance of EM trees. We expected that this microbiome selection in EM-dominated stands would lead to lower overall microbial community diversity and turnover, with tighter correspondence between general fungal and prokaryotic communities. We measured fungal and prokaryotic community composition via high-throughput Illumina sequencing of the ITS2 (fungi) and 16S rRNA (prokaryotic) gene regions. We analyzed differences in alpha and beta diversity between forest stands associated with different mycorrhizal types, as well as the relative abundance of fungal functional groups and various microbial taxa. We found that fungal and prokaryotic community composition differed based on stand mycorrhizal type. There was lower prokaryotic diversity and lower relative abundance of fungal saprotrophs and pathogens in EM-dominated than AM-EM mixed stands. However, contrary to our prediction, there was lower homogeneity for fungal communities in EM-dominated stands compared to mixed AM-EM stands. Overall, we demonstrate that EM-dominated tropical forest stands have distinct soil microbiomes relative to surrounding diverse forests, suggesting that EM fungi may filter microbial functional groups in ways that could potentially influence plant performance or ecosystem function.

Tree mycorrhizal associations determine how biodiversity, large trees, and environmental factors drive aboveground carbon stock in temperate forests

Biodiversity, large trees, and environmental conditions such as climate and soil have important effects on forest carbon stocks. However, recent studies in temperate forests suggest that the relative importance of these factors depends on tree mycorrhizal associations, whereby large-tree effects may be driven by ectomycorrhizal (EM) trees, diversity effects may be driven by arbuscular mycorrhizal (AM) trees, and environment effects may depend on differential climate and soil preferences of AM and EM trees. To test this hypothesis, we used forest-inventory data consisting of over 80,000 trees from 631 temperate-forest plots (30 m ​× ​30 ​m) across Northeast China to examine how biodiversity (species diversity and ecological uniqueness), large trees (top 1% of tree diameters), and environmental factors (climate and soil nutrients) differently regulate aboveground carbon stocks of AM trees, EM trees, and AM and EM trees combined (i.e. total aboveground carbon stock). We found that large trees had a positive effect on both AM and EM tree carbon stocks. However, biodiversity and environmental factors had opposite effects on AM vs. EM tree carbon stocks. Specifically, the two components of biodiversity had positive effects on AM tree carbon stocks, but negative effects on EM tree carbon stocks. Environmental heterogeneity (mean annual temperature and soil nutrients) also exhibited contrasting effects on AM and EM tree carbon stocks. Consequently, for the total carbon stock, the positive large-tree effect far surpasses the diversity and environment effect. This is mainly because when integrating AM and EM tree carbon stock into total carbon stock, the opposite diversity-effect (also environment-effect) on AM vs. EM tree carbon stock counteracts each other while the consistent positive large-tree effect on AM and EM tree carbon stock is amplified. In summary, this study emphasized a mycorrhizal viewpoint to better understand the determinants of overarching aboveground carbon profile across regional forests.

High Species Diversity but Low Specificity to Ectomycorrhizal Tree Partners Exhibited by Native Truffle Species (Tuber spp., Pezizales) in Poland, Central Europe

Truffles represent one of the most expensive edible fungi. About two-thirds of all known truffle records originate from Europe. Historically, the Mediterranean region in Southern Europe is associated with truffle cultivation and it is widely regarded as a center of truffle distribution in Europe. On the contrary, little is known about truffles in the central and northern regions of Europe. Here, native truffle species in Poland, their symbiotic ectomycorrhizal (ECM) tree partners, and their continental-scale distribution were studied. Altogether, 16 truffle species were identified based on the sequences of the Internal Transcribed Spacer (ITS) rDNA, a barcode region for fungi. Truffle species were associated with deciduous tree species of Fagales (Fagaceae, Betulaceae, Juglandaceae), Malvales (Malvaceae), Malpighiales (Salicaceae), and coniferous trees of Pinales (Pinaceae). Fagales trees constituted 70% of ECM associations formed by truffle species. Three genera of the order Fagales, Quercus, Fagus, and Corylus formed 50% of all ECM associations. Coniferous trees of Pinales formed 16% of associations. Two other orders of deciduous trees, Malvales and Malpighiales, together formed 14% of ECM associations. All but three identified truffle species exhibited low specificity to their ECM tree partners. Two-thirds of truffle species formed ECM symbiosis with both coniferous and deciduous tree species, but the share of coniferous tree partners was considerably lower than that of deciduous trees, reaching up to 30% for T. anniae, T. puberulum, and T. borchii (clade/puberulum). All the identified truffles were noted in both Central Europe and the Mediterranean region. Among them, about 80% of truffle species were widely distributed across the continent and represented by similar or higher numbers of records in Northern Europe, i.e., above the 48th parallel north, than in Southern Europe. This study showed higher taxa richness of native truffle species in Poland, but low specificity to their ECM tree partners. However, further studies on the regional-scale distribution of truffles in Poland are needed to improve the knowledge of the patterns of truffle distribution in forest ecosystems and the potential productivity of edible truffle species with high economic value.

Tree mycorrhizal type regulates leaf and needle microbial communities, affects microbial assembly and co-occurrence network patterns, and influences litter decomposition rates in temperate forest

BackgroundTree mycorrhizal types (arbuscular mycorrhizal fungi and ectomycorrhizal fungi) alter nutrient use traits and leaf physicochemical properties and, thus, affect leaf litter decomposition. However, little is known about how different tree mycorrhizal species affect the microbial diversity, community composition, function, and community assembly processes that govern leaf litter-dwelling microbes during leaf litter decomposition. MethodsIn this study, we investigated the microbial diversity, community dynamics, and community assembly processes of nine temperate tree species using high-resolution molecular technique (Illumina sequencing), including broadleaved arbuscular mycorrhizal, broadleaved ectomycorrhizal, and coniferous ectomycorrhizal tree types, during leaf litter decomposition.Results and discussionThe leaves and needles of different tree mycorrhizal types significantly affected the microbial richness and community composition during leaf litter decomposition. Leaf litter mass loss was related to higher sequence reads of a few bacterial functional groups, particularly N-fixing bacteria. Furthermore, a link between bacterial and fungal community composition and hydrolytic and/or oxidative enzyme activity was found. The microbial communities in the leaf litter of different tree mycorrhizal types were governed by different proportions of determinism and stochasticity, which changed throughout litter decomposition. Specifically, determinism (mainly variable selection) controlling bacterial community composition increased over time. In contrast, stochasticity (mainly ecological drift) increasingly governed fungal community composition. Finally, the co-occurrence network analysis showed greater competition between bacteria and fungi in the early stages of litter decomposition and revealed a contrasting pattern between mycorrhizal types.ConclusionOverall, we conclude that tree mycorrhizal types influence leaf litter quality, which affects microbial richness and community composition, and thus, leaf litter decomposition.

Ectomycorrhizal trees rely on nitrogen resorption less than arbuscular mycorrhizal trees globally.

Nitrogen (N) resorption is an important pathway of N conservation, contributing to an importantproportion of plant N requirement. However, whether the ratio of N resorption to N requirementmaybe affected by environmental factors, mycorrhizal types or atmospheric CO2 concentration remains unclear. Here, we conducted a meta-analysis on the impacts of environmental factors and mycorrhizal types on this ratio. We found this ratio in ectomycorrhizal (EM) trees decreased with mean annual precipitation, mean annual temperature, soil total N content and atmospheric CO2 concentration and was significantly lower than that in arbuscular mycorrhizal (AM) trees. An in situ 15 N tracing experiment further confirmed that AM trees have a stronger reliance on N resorption than EM trees. Our study suggests that AM and EM trees potentially have different strategies for alleviation of progressive N limitation, highlighting the necessity of incorporating plant mycorrhizal types into Earth System Models.

Long-term nitrogen fertilization impacts plant-microbial interactions differently in arbuscular and ectomycorrhizal trees

Long-term nitrogen fertilization impacts plant-microbial interactions differently in arbuscular and ectomycorrhizal trees

Mycorrhizal feedbacks influence global forest structure and diversity

One mechanism proposed to explain high species diversity in tropical systems is strong negative conspecific density dependence (CDD), which reduces recruitment of juveniles in proximity to conspecific adult plants. Although evidence shows that plant-specific soil pathogens can drive negative CDD, trees also form key mutualisms with mycorrhizal fungi, which may counteract these effects. Across 43 large-scale forest plots worldwide, we tested whether ectomycorrhizal tree species exhibit weaker negative CDD than arbuscular mycorrhizal tree species. We further tested for conmycorrhizal density dependence (CMDD) to test for benefit from shared mutualists. We found that the strength of CDD varies systematically with mycorrhizal type, with ectomycorrhizal tree species exhibiting higher sapling densities with increasing adult densities than arbuscular mycorrhizal tree species. Moreover, we found evidence of positive CMDD for tree species of both mycorrhizal types. Collectively, these findings indicate that mycorrhizal interactions likely play a foundational role in global forest diversity patterns and structure.

Long-term field translocation differentially affects arbuscular mycorrhizal and ectomycorrhizal trees in a sub-tropical forest

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) trees are commonly represented in tropical forests, but their response to warming is generally not known. We conducted a long-term (9-year) field experiment in subtropical China by translocating AM tree species (Machilus breviflora and Schima superba) and EcM tree species (Syzygium rehderianum and Castanopsis hystrix) from a cooler high-elevation site (300 m) to a 1 °C warmer low-elevation site (30 m). Here, we report leaf chemical and physiological data from the last three years (Years 7–9) of the translocation experiment. Translocation to warmer site induced higher air (Tair) and soil (Tsoil) temperatures, but lower soil volumetric water content (SVWC). Translocation treatment significantly increased the light-saturated photosynthetic rate (Asat) for AM trees due to higher stomatal conductance (gs) and Rubisco carboxylation capacity (Vcmax), generating increased growth in AM trees. Translocation treatment reduced the maximum efficiency of photosynthetic quantum yield (Fv/Fm) and growth in EcM trees. Translocation treatment increased leaf turgor loss point (TLP) in AM trees, but reduced TLP in EcM trees. Translocation treatment increased foliar nitrogen (N) concentrations and phosphorus (P) concentrations for AM trees. In EcM trees, stable foliar N and P concentrations were related to higher N and P resorption efficiencies. Translocation treatment was more beneficial for the growth of AM trees than EcM trees, while EcM trees were more tolerant of soil water deficit. Differential responses to these co-occurring climate drivers may alter the composition of tree functional groups and ecosystem function in tropical forests in response to future warmer and drier climate conditions.

Simulated nitrogen deposition alters the ectomycorrhizal fungal community structure in northern Korean pine plantations

Northern temperate forests are sensitive to nitrogen deposition. Korean pines are the zonal dominant vegetation in these forest ecosystems and a typical obligate ectomycorrhizal (ECM) tree. However, the impact of varying nitrogen additions on the ectomycorrhizal fungal (ECMF) community structure in Korean pine plantations remains unclear. In this experiment, nitrogen deposition was simulated (CK = 0 kg N ha−1 yr−1, LN = 20 kg N ha−1 yr−1, MN = 40 kg N ha−1 yr−1, HN = 80 kg N ha−1 yr−1), and soil biochemical indicators, ECMF community composition, and diversity were measured. The results showed that high nitrogen addition led to increased ECMF colonization, decreased ECMF community diversity and richness, and altered the occurrence of biomarkers. The MN treatment significantly increased the Simpson index compared to the LN treatment (P < 0.05), with Amphinema sp, Tuber sp, and Tylospora asterophora identified as biomarkers in the CK, LN, and HN treatments, respectively. The HN treatment significantly reduced the Chao1 index (P < 0.05), with Inocybe quietiodor, Tarzetta catinus, Inocybe giacomi, and Russula viscida serving as biomarkers in the CK, LN, MN, and HN treatments, respectively. Nitrogen addition led to decreased soil pH and available phosphorus content, increased ammonium nitrogen content, and affected ectomycorrhiza colonization by altering the soil ECMF community structure. Among these factors, ammonium nitrogen was the most influential in changing the ECMF community structure. This research offers valuable data to help predict changes in ECMF community structure in Korean pine plantations as nitrogen additions increase.

Proximity to an old-growth forest edge and ectomycorrhizal tree islands enhance ectomycorrhizal fungal colonization of Betula lenta L. (black birch) seedlings in secondary forest soils

Proximity to an old-growth forest edge and ectomycorrhizal tree islands enhance ectomycorrhizal fungal colonization of Betula lenta L. (black birch) seedlings in secondary forest soils

Phosphorus Addition Reduces Seedling Growth and Survival for the Arbuscular Mycorrhizal Tree Cinnamomum camphora (Lauraceae) and Ectomycorrhizal Tree Castanopsis sclerophylla (Fagaceae) in Fragmented Forests in Eastern China.

Global changes in nutrient deposition rates and habitat fragmentation are likely to have profound effects on plant communities, particularly in the nutrient-limited systems of the tropics and subtropics. However, it remains unclear how increased phosphorus (P) supply affects seedling growth in P-deficient subtropical fragmented forests. To explore this, we applied P to 11 islands in a subtropical Chinese archipelago and examined the results in combination with a contemporary greenhouse experiment to test the influence of P addition on seedling growth and survival. We measured the growth (i.e., base area) and mortality rate of seedlings for one arbuscular mycorrhizal (AM) and one ectomycorrhizal (EcM) tree species separately and calculated their relative growth rate and mortality when compared with P addition and control treatment on each island. We also measured three functional traits and the biomass of seedlings in the greenhouse experiment. Results showed that P addition significantly increased the mortality of AM and EcM seedlings and reduced the growth rate of EcM seedlings. The relative growth rate of AM seedlings, but not EcM seedlings, significantly decreased as the island area decreased, suggesting that P addition could promote the relative growth rate of AM seedlings on larger islands. The greenhouse experiment showed that P addition could reduce the specific root length of AM and EcM seedlings and reduce the aboveground and total biomass of seedlings, indicating that P addition may affect the resource acquisition of seedlings, thereby affecting their survival and growth. Our study reveals the synergistic influence of habitat fragmentation and P deposition, which may affect the regeneration of forest communities and biodiversity maintenance in fragmented habitats.

Proportion of mycorrhiza-associated trees mediates community assemblages of soil fungi but not of bacteria

Recent studies have shown that mycorrhizal trees can greatly influence soil microbial communities, which in turn play important roles in the function offorest ecosystems. However, there is lack of understanding how the composition of trees with different mycorrhizal types affects soil microbial communities. Here, we collected 1606 soil samples from a 25-ha subtropical forest plot to investigate how the proportion of arbuscular mycorrhizal (AM) versus ectomycorrhizal (EcM) trees mediated soil microbial assemblages. Results showed the alpha diversities of both soil fungal and bacterial communities were significantly positively correlated with the ratio of AM/EcM trees. The AM/EcM tree ratio was important to the fungal community assembly, whereas soil pH was key to the bacterial communities. The increase in the AM/EcM tree ratio decreased the importance of stochastic forces in assembling fungal communities, while it had no significant effect on the bacterial communities. The differential importance of the AM/EcM tree ratio to fungal and bacterial communities highlights the role of mycorrhiza-associated tree composition in regulating soil microbial communities. This finding suggests that forests with different AM/EcM tree ratios would have different soil microbial communities, potentially leading to differences in soil nutrient cycling and in return different tree diversity and forest productivity.