The mechanisms regulating community composition and local dominance of trees in species-rich forests are poorly resolved, but the importance of interactions with soil microbes is increasingly ...acknowledged. Here, we show that tree seedlings that interact via root-associated fungal hyphae with soils beneath neighbouring adult trees grow faster and have greater survival than seedlings that are isolated from external fungal mycelia, but these effects are observed for species possessing ectomycorrhizas (ECM) and not arbuscular mycorrhizal (AM) fungi. Moreover, survival of naturally-regenerating AM seedlings over ten years is negatively related to the density of surrounding conspecific plants, while survival of ECM tree seedlings displays positive density dependence over this interval, and AM seedling roots contain greater abundance of pathogenic fungi than roots of ECM seedlings. Our findings show that neighbourhood interactions mediated by beneficial and pathogenic soil fungi regulate plant demography and community structure in hyperdiverse forests.
Ecology Letters (2011)
Observational evidence increasingly suggests that the Janzen–Connell effect extends beyond the species boundary. However, this has not been confirmed experimentally. Herein, we ...present both observational and experimental evidence for a phylogenetic Janzen–Connell effect. In a subtropical forest in Guangdong province, China, we observed that co‐occurring tree species are less phylogenetically related than expected. The inhibition effects of neighbouring trees on seedling survival decreased with increasing phylogenetic distance between them. In a shade‐house experiment, we studied seedling survival of eight species on soil collected close to Castanopsis fissa relative to their survival on soil close to their own adult trees, and found that this relative survival rate increased with phylogenetic distance from C. fissa. This phylogenetic signal disappeared when seedlings were planted in fungicide‐treated soil. Our results clearly support negative effects of phylogenetically similar neighbouring trees on seedling survival and suggest that these effects are caused by associated host‐specific fungal pathogens.
In plant communities, some mechanisms maintain differences in species’ abundances, while other mechanisms promote coexistence. Asymmetry in conspecific negative density dependence (CNDD) and/or ...habitat preference is hypothesized to shape relative species abundance, whereas community compensatory trends (CCTs) induced by community-level CNDD and heterospecific facilitation are hypothesized to promote coexistence. We use survey data from three 1-ha permanent dynamic plots in a subtropical forest over the course of a decade to find out which of these processes are important and at which life-history stages (the seedling, sapling, and juvenile stages) they exert their effects. CNDD was not related to abundance in any of the life-history stages. Suitable habitats positively influenced plant abundance at all tested life stages, but especially so for juveniles. Community-level CNDD of seedling neighbors was detected at the seedling stage, while heterospecific facilitation was detected across all tested life-history stages. A CCT in seedling survival was detected, but there was no evidence for such trends across the other life-history stages. Altogether, our results suggest that habitat specificity increases the rarity of species, whereas a CCT at the seedling stage, which is likely to be induced by CNDD and heterospecific facilitation, enables such species to maintain their populations.
The structure of a plant community in terms of functional traits can strongly affect community productivity. Two components may contribute to this, community‐wide trait means (mass‐ratio hypothesis) ...or community‐wide trait variations (diversity hypothesis) across species and individuals. We compared the explanatory power of the two hypotheses for explaining biomass variation among individuals and communities as measures of productivity. We set up experimental communities of tree seedlings that ranged in species richness from 1 to 8. We measured above‐ and belowground biomass, leaf area, specific leaf area and height of all individuals separately after 16 months of growth and calculated species‐level values by averaging across all individuals of each species grown in monoculture. Using species‐ and individual‐level trait data, we calculated community‐ (CWM) and neighbourhood‐weighted mean (NWM) values to assess the mass‐ratio hypothesis and community functional dissimilarity (FD) and average trait dissimilarity of target individuals to neighbours (ATD), i.e. trait variations, to assess the diversity hypothesis. CWMs explained much more variation in community biomass than did species richness or FD, supporting the mass‐ratio hypothesis. The explanatory power of CWMs increased when calculated with individual‐level data, demonstrating positive effects of trait adjustments of individuals in response to species richness, i.e. plasticity in the broad sense. FD calculated with individual‐level data also increased community biomass, lending some support to the diversity hypothesis. The effects of trait means and variations on community biomass were related to effects of trait means and variations on the biomass of individuals. Overall, our results suggest that trait means rather than trait variations may drive community biomass productivity at the earliest stage of forest development.
Introduction
As a crucial factor in determining ecosystem functioning, interaction between plants and soil-borne fungal pathogens deserves considerable attention. However, little attention has been ...paid into the determinants of root-associated fungal pathogens in subtropical seedlings, especially the influence of different mycorrhizal plants.
Methods
Using high-throughput sequencing techniques, we analyzed the root-associated fungal pathogen community for 19 subtropical forest species, including 10 ectomycorrhizal plants and 9 arbuscular mycorrhizal plants. We identified the roles of different factors in determining the root-associated fungal pathogen community. Further, we identified the community assembly process at species and mycorrhizal level and managed to reveal the drivers underlying the community assembly.
Results
We found that plant species identity, plant habitat, and plant mycorrhizal type accounted for the variations in fungal pathogen community composition, with species identity and mycorrhizal type showing dominant effects. The relative importance of different community assembly processes, mainly, homogeneous selection and drift, varied with plant species identity. Interestingly, functional traits associated with acquisitive resource-use strategy tended to promote the relative importance of homogeneous selection, while traits associated with conservative resource-use strategy showed converse effect. Drift showed the opposite relationships with functional traits compared with homogeneous selection. Notably, the relative importance of different community assembly processes was not structured by plant phylogeny. Drift was stronger in the pathogen community for ectomycorrhizal plants with more conservative traits, suggesting the predominant role of stochastic gain and loss in the community assembly.
Discussion
Our work demonstrates the determinants of root-associated fungal pathogens, addressing the important roles of plant species identity and plant mycorrhizal type. Furthermore, we explored the community assembly mechanisms of root-associated pathogens and stressed the determinant roles of functional traits, especially leaf phosphorus content (LP), root nitrogen content (RN) and root tissue density (RTD), at species and mycorrhizal type levels, offering new perspectives on the microbial dynamics underlying ecosystem functioning.
Island ecosystems often have a disproportionate number of endemic species and unique and fragile functional characteristics. However, few examples of this type of ecosystem have been reported.
We ...conducted a comprehensive field study on Neilingding Island, southern China. The leaf samples of 79 subtropical forest tree species were obtained and their functional traits were studied in the dry and wet seasons to explain the relationships between plant functional traits and soil nutrients.
We found a greater availability of soil moisture content (SMC) and nutrients in the wet season than in the dry season. The values of wet season soil available phosphorus (5.97 mg·kg
), SMC (17.67%), and soil available potassium (SAK, 266.96 mg·kg
) were significantly higher than those of the dry season. The leaf dry matter content, specific leaf weight, leaf density, leaf total carbon, leaf total nitrogen, leaf total calcium, and the N/P and C/P ratios of leaves were all significantly higher in the dry season than in the wet season, being 18.06%, 12.90%, 12.00%, 0.17%, 3.41%, 9.02%, 26.80%, and 24.14% higher, respectively. In contrast, the leaf area (51.01 cm
), specific leaf area (152.76 cm
·g
), leaf water content (0.59%), leaf total nitrogen (1.31%), leaf total phosphorus (0.14%), and leaf total magnesium (0.33%) were much lower in the dry season than in the wet one. There were significant pairwise correlations between leaf functional traits, but the number and strength of correlations were significantly different in the dry and wet seasons. The SAK, soil total phosphorus (STP), and pH impacted plant leaf functional traits in the dry season, whereas in the wet season, they were affected by SAK, STP, pH, and NO
(nitrate).
Both soil nutrients and water availability varied seasonally and could cause variation in a number of leaf traits.
Phosphorus (P) is one of the most limiting elements for efficient plant growth and regeneration, coexisting plants are found to be able to partition soil P components through different types of ...mycorrhizal symbiosis. However, previous evidences were mostly based on artificial addition of different forms of P chemicals, there is still a lack of observational and experimental verifications on how tree species respond to soil P heterogeneity in natural soils. Herein, we conducted a field survey to investigate how spatial distribution of tree species with different types of mycorrhizal associations are related with soil P compositions. We found that arbuscular mycorrhizal (AM) trees tend to distribute in soils rich in inorganic P, while ectomycorrhizal (ECM) trees distribute in habitats with low inorganic P. We further established a shade-house experiment to evaluate how P availability of field soils affects seedling performance of AM and ECM trees. Biomass of AM seedlings was highest when grew in soil with the medium level of inorganic P, while ECM seedlings grown best in soil with the lowest inorganic P level. Seedling survival and mycorrhizal colonisation rates decreased, while specific root length and specific area of seedling roots increased, with increasing inorganic P concentrations. Using field soil with natural composition of P-forms and spatial heterogeneity, our findings confirmed the hypothesis that AM trees prefer inorganic P while ECM trees are able to utilise organic P in a more realistic setting, which regulated spatial distributions and promoted coexistence of subtropical tree species at local scale.
•Ectomycorrhizal trees tend to distribute in soils with low inorganic P.•Arbuscular mycorrhizal trees prefer habitats with inorganic P-rich soil.•Seedlings of ectomycorrhizal trees grow best in field soil with lowest inorganic P.•Coexisting trees partition soil P through different types of mycorrhizal symbioses.
Soilborne pathogens can contribute to diversity maintenance in tree communities through the Janzen-Connell effect, whereby the pathogenic reduction of seedling performance attenuates with distance ...from conspecifics. By contrast, arbuscular mycorrhizal fungi (AMF) have been reported to promote seedling performance; however, it is unknown whether this is also distance dependent. Here, we investigate the distance dependence of seedling performance in the presence of both pathogens and AMF. In a subtropical forest in south China, we conducted a four-year field census of four species with relatively large phylogenetic distances and found no distance-dependent mortality for newly germinated seedlings. By experimentally separating the effects of AMF and pathogens on seedling performance of six subtropical tree species in a shade house, we found that soil pathogens significantly inhibited seedling survival and growth while AMF largely promoted seedling growth, and these effects were host specific and declined with increasing conspecific distance. Together, our field and experimental results suggest that AMF can neutralize the negative effect of pathogens and that the Janzen-Connell effect may play a less prominent role in explaining diversity of nondominant tree species than previously thought.
•Faster decomposition of litter from trees with arbuscular mycorrhizal (AM) fungi than ectomycorrhizal (ECM) fungi.•Higher litter decay rate associated with more saprotrophic fungi in soils around AM ...trees.•Greater activity of extracellular enzymes in soils around AM trees than soils around ECM trees.
Leaf litter decomposition is a fundamental process involved in soil carbon and nitrogen dynamics. Observational and experimental evidence suggests that leaf litter from arbuscular mycorrhizal (AM) tree species has a faster decomposition rate than leaf litter from ectomycorrhizal (ECM) tree species. This could be due to the diversity and activity of decomposer microorganisms, but remains to be confirmed in subtropical forests. In this study, we compared the effects of fungi and bacteria on decomposition rates of litter from AM and ECM subtropical trees. In the field, we conducted a fungal hyphal exclusion experiment beneath AM and ECM trees. We also used fungicides and bactericides to distinguish the contribution of bacteria and fungi to litter decomposition in a shade-house experiment. Fungi were responsible more leaf litter decay in soil around AM trees than in soil around ECM trees. When fungi were excluded, AM and ECM litters with similar chemical properties decomposed at the same rate, but the AM litters decayed more quickly when saprotrophic fungi were present. Soil around AM trees had more abundance of saprotrophic fungi and greater N-acetylglucosaminidase and acid phosphatase activities than soil around ECM trees. We conclude that the higher leaf litter decomposition rates under AM trees were due to the saprotrophic fungi in the soil microbial community.
Sea-level rise has been threatening the terrestrial ecosystem functioning of coastal islands, of which the most important component is carbon (C) cycling. However, metagenomic and metabolomic ...evidence documenting salt intrusion effects on molecular biological processes of C cycling are still lacking. Here, we investigated microbial communities, metagenomic taxonomy and function, and metabolomic profiles in the marine-terrestrial transition zone of low- and high-tide, and low- and high-land areas based on distances of 0 m, 50 m, 100 m, and 200 m, respectively, to the water-land junction of Neilingding Island. Our results showed that soil salinity (EC) was the dominant driver controlling bacterial abundance and community composition and metagenomic taxonomy and function. The metabolomic profiling at the low-tide site was significantly different from that of other sites. The low-tide site had greater abundance of Proteobacteria and Bacteroidetes (1.6–3.7 fold), especially Gammaproteobacteria, but lower abundance (62–83%) of Acidobacteria and Chloroflexi, compared with other three sites. The metagenomic functional genes related to carbohydrate metabolism decreased at the low-tide site by 15.2%, including the metabolism of aminosugars, di- and oligo-saccharides, glycoside hydrolases, and monosaccharides, leading to significant decreases in 21 soil metabolites, such as monosaccharide (l-gulose), disaccharide (sucrose and turanose), and oligosaccharides (stachyose and maltotetraose). Our study demonstrates that elevated salinity due to sea-level rise may suppress C-cycling genes and their metabolites, therefore having negative impacts on microbial metabolism of organic matter.
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•Effects of elevated salinity on microbial community, C-cycling genes, and their metabolites were assessed.•Soil salinity was the primary factor affecting microbial community and C functions.•Salinity increased Proteobacteria and Bacteroidetes, decreased Acidobacteria and Chloroflexi.•Salinity decreased the abundance of functional genes of carbohydrate metabolisms, and microbial metabolites.
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