Lithological constraints on resource economies shape the mycorrhizal composition of a Bornean rain forest

Divergent altitudinal patterns of arbuscular and ectomycorrhizal fungal communities in a mid-subtropical mountain ecosystem

Arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF) form ubiquitous symbiotic relationships with plants through co-evolutionary processes, providing multiple benefits for plant growth, productivity, health, and stress mitigation. Mountain ecosystem multifunctionality is significantly influenced by mycorrhizal responses to climate change, highlighting the importance of understanding the complex interactions between these fungi and environmental variables. In this study, we investigated five vegetation zones across an altitudinal gradient (675-2157 m a.s.l.) in Wuyi Mountain, one of the most well-preserved mid-subtropical mountain ecosystems in eastern China. Using high-throughput sequencing, we examined the altitudinal distribution patterns, community assembly mechanisms, and network interactions of soil AMF and EMF. Our analyses demonstrated significant altitudinal variations in the composition and diversity of mycorrhizal fungal communities. AMF richness peaked in the subalpine dwarf forest at intermediate elevations, whereas EMF richness was highest in the low-altitude evergreen broad-leaved forest, showing a marked decrease in the alpine meadow ecosystem. β-diversity decomposition revealed that species turnover constituted the primary mechanism of community differentiation for both fungal types, explaining >56% of the observed variation. Stochastic processes dominated community assembly, with the relative importance of dispersal limitation and drift showing distinct altitudinal patterns. Network analysis indicated that AMF networks reached maximum complexity in evergreen broad-leaved forests, while EMF networks showed similar complexity levels in coniferous forests. Among the examined factors, soil properties emerged as the predominant driver of altitudinal variations in ecosystem multifunctionality, followed by AMF communities and climatic variables. These findings provide critical insights into the ecological functions and environmental adaptations of mycorrhizal fungi, advancing our understanding of their responses to environmental changes in mountain ecosystems and informing evidence-based conservation strategies.

Testing the ectomycorrhizal-dominance hypothesis for ecosystem multifunctionality in a subtropical mountain forest

Mycorrhizal associations are key mutualisms that shape the structure of forest communities and multiple ecosystem functions. However, we lack a framework for predicting the varying dominance of distinct mycorrhizal associations in an integrated proxy of multifunctionality across ecosystems. Here, we used the datasets containing diversity of mycorrhizal associations and 18 ecosystem processes related to supporting, provisioning, and regulating services to examine how the dominance of ectomycorrhiza (EcM) associations affects ecosystem multifunctionality in subtropical mountain forests in Southwest China. Meanwhile, we synthesized the prevalence of EcM-dominant effects on ecosystem functioning in forest biomes. Our results demonstrated that elevation significantly modified the distributions of EcM trees and fungal dominance, which in turn influenced multiple functions simultaneously. Multifunctionality increased with increasing proportion of EcM associations, supporting the ectomycorrhizal-dominance hypothesis. Meanwhile, we observed that the impacts of EcM dominance on individual ecosystem functions exhibited different relationships among forest biomes. Our findings highlight the importance of ectomycorrhizal dominance in regulating multifunctionality in subtropical forests. However, this ectomycorrhizal feedback in shaping ecosystem functions cannot necessarily be generalized across forests. Therefore, we argue that the predictions for ecosystem multifunctionality in response to the shifts of mycorrhizal composition could vary across space and time.

Arbuscular Mycorrhizal Fungi Diversity in Sophora japonica Rhizosphere at Different Altitudes and Lithologies

Arbuscular mycorrhizal fungi play a key role in mediating soil-plant relationships within karst ecosystems. Sophora japonica, a medicinal plant with anti-inflammatory and antitumor properties, is widely cultivated in karst areas of Guangxi, China. We considered limestone, dolomite, and sandstone at altitudes ranging from 100 to 800 m and employed Illumina sequencing to evaluate AMF diversity and identify the factors driving S. japonica rhizosphere AMF community changes. We showed that the increase in altitude increased S. japonica AMF colonization and the Shannon index. The colonization of limestone plots was higher than that of other lithology. In total, 3,096,236 sequences and 5767 OTUs were identified in S. japonica rhizosphere soil. Among these, 270 OTUs were defined at the genus level and divided into 7 genera and 35 species. Moreover, available nitrogen, soil organic matter, and available calcium content had a coupling effect and positive influence on AMF colonization and Shannon and Chao1 indices. Conversely, available phosphorus, available potassium, and available magnesium negatively affected AMF Shannon and Chao1 indices. Lithology, altitude, pH, and available phosphorus are important factors that affect the dynamics of AMF in the S. japonica rhizosphere.

Toward a coordinated understanding of hydro-biogeochemical root functions in tropical forests for application in vegetation models

Tropical forest root characteristics and resource acquisition strategies are underrepresented in vegetation and global models, hampering the prediction of forest-climate feedbacks for these carbon-rich ecosystems. Lowland tropical forests often have globally unique combinations of high taxonomic and functional biodiversity, rainfall seasonality, and strongly weathered infertile soils, giving rise to distinct patterns in root traits and functions compared with higher latitude ecosystems. We provide a roadmap for integrating recent advances in our understanding of tropical forest belowground function into vegetation models, focusing on water and nutrient acquisition. We offer comparisons of recent advances in empirical and model understanding of root characteristics that represent important functional processes in tropical forests. We focus on: (1) fine-root strategies for soil resource exploration, (2) coupling and trade-offs in fine-root water vs nutrient acquisition, and (3) aboveground-belowground linkages in plant resource acquisition and use. We suggest avenues for representing these extremely diverse plant communities in computationally manageable and ecologically meaningful groups in models for linked aboveground-belowground hydro-nutrient functions. Tropical forests are undergoing warming, shifting rainfall regimes, and exacerbation of soil nutrient scarcity caused by elevated atmospheric CO2. The accurate model representation of tropical forest functions is crucial for understanding the interactions of this biome with the climate.

Lithology and niche habitat have significant effect on arbuscular mycorrhizal fungal abundance and their interspecific interactions

The chemical properties of bedrock play a crucial role in shaping the communities of soil and root-associated arbuscular mycorrhizal fungi (AMF). We investigate AMF community composition and diversity in bulk soil, rhizosphere soil, and roots in karst and non-karst forests. Chemical properties of bedrock of the calcium oxide (CaO) and ratio of calcium oxide and magnesium oxide (Ca/Mg), soil pH, and exchangeable Ca2+ were higher in karst carbonate rocks compared to non-karst clastic rocks. Conversely, bedrock phosphorus content (P-rock), silicon dioxide (SiO2) content, and tree diversity exhibited an opposing trend. AMF abundance was higher in non-karst clastic rocks than in karst carbonate rocks. Stronger interspecific interactions among AMF taxa occurred in the bulk soil and rhizosphere soil of non-karst clastic rocks compared to karst carbonate rocks. AMF abundance and diversity were higher in rhizosphere soil and roots, attributed to increasing nutrient availability when compared to the bulk soil. A more complex network within AMF taxa was observed in rhizosphere soil and roots compared to bulk soil due to an increase in AMF abundance and diversity in rhizosphere soil and roots. Comparing non-karst clastic rocks, karst carbonate rocks increased soil nitrogen (N) and P levels, which can be attributed to the elevated content of soil Ca2+ and Mg2+ content, facilitated by the high CaO content and Ca/Mg ratio in the bedrock of karst forests. However, the thicker soil layer exhibited higher soil nutrient storage, resulting in greater tree diversity in non-karst forests. These findings suggest that high tree richness may increase root biomass and secretion of root exudates in non-karst regions, thereby enhancing the abundance of AMF and their interspecies interactions. Consequently, the diverse bedrock properties that drive variations in soil properties, nutrients, and plant diversity can impact AMF communities, ultimately promoting plant growth and contributing to vegetation recovery.

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.

Impacts of Lithology and Slope Position on Arbuscular Mycorrhizal Fungi Communities in a Karst Forest Soil

The influence of lithology and slope position on arbuscular mycorrhizal fungi (AMF) communities has been explored in various ecosystems, but there is a limited understanding of these mechanisms in karst regions. This study focused on typical karst hills with contrasting lithologies, specifically dolomite and limestone. Additionally, three slope positions (upper, middle, and lower) were investigated within each hill in karst forest ecosystems. Total phosphorus (TP) content in the soil was higher in dolomite compared to limestone. Conversely, exchangeable calcium (Ca) was lower in dolomite than in limestone. Notably, the lithology, rather than the slope position, exerted a significant impact on AMF diversity and abundance and the presence of specific AMF taxa. Dolomite exhibited greater AMF richness and a higher Shannon index in comparison to limestone when not accounting for slope position. The AMF community composition differed between dolomite and limestone. For instance, without considering slope position, the relative abundance of Acaulospora, Diversispora, and Paraglomus was higher in dolomite than in limestone, while the relative abundance of Claroideoglomus displayed an opposing trend. Furthermore, a more complex interaction among AMF taxa was observed in dolomite as compared to limestone, as evidenced by an increase in the number of nodes and edges in the co-occurrence networks within the dolomite. The genera Glomus, Claroideoglomus, and Diversispora exhibited a higher number of links with each other and with other AMF taxa. The study identified TP and Ca as the primary factors determining variations in AMF diversity between dolomite and limestone. Consequently, it is imperative to consider the underlying lithology and soil conditions when addressing the restoration of degraded karst hilly areas.

Root-associated fungal communities are influenced more by soils than by plant-host root traits in a Chinese tropical forest

Forest fungal communities are shaped by the interactions between host tree root systems and the associated soil conditions. We investigated how the soil environment, root morphological traits, and root chemistry influence root-inhabiting fungal communities in three tropical forest sites of varying successional status in Xishuangbanna, China. For 150 trees of 66 species, we measured root morphology and tissue chemistry. Tree species identity was confirmed by sequencing rbcL, and root-associated fungal (RAF) communities were determined using high-throughput ITS2 sequencing. Using distance-based redundancy analysis and hierarchical variation partitioning, we quantified the relative importance of two soil variables (site average total phosphorus and available phosphorus), four root traits (dry matter content, tissue density, specific tip abundance, and forks), and three root tissue elemental concentrations (nitrogen, calcium, and manganese) on RAF community dissimilarity. The root and soil environment collectively explained 23% of RAF compositional variation. Soil phosphorus explained 76% of that variation. Twenty fungal taxa differentiated RAF communities among the three sites. Soil phosphorus most strongly affects RAF assemblages in this tropical forest. Variation in root calcium and manganese concentrations and root morphology among tree hosts, principally an architectural trade-off between dense, highly branched vs less-dense, herringbone-type root systems, are important secondary determinants.

Dynamic Energy Budget models: fertile ground for understanding resource allocation in plants in a changing world

Climate change is having dramatic effects on the diversity and distribution of species. Many of these effects are mediated by how an organism's physiological patterns of resource allocation translate into fitness through effects on growth, survival and reproduction. Empirically, resource allocation is challenging to measure directly and so has often been approached using mathematical models, such as Dynamic Energy Budget (DEB) models. The fact that all plants require a very similar set of exogenous resources, namely light, water and nutrients, integrates well with the DEB framework in which a small number of variables and processes linked through pathways represent an organism's state as it changes through time. Most DEB theory has been developed in reference to animals and microorganisms. However, terrestrial vascular plants differ from these organisms in fundamental ways that make resource allocation, and the trade-offs and feedbacks arising from it, particularly fundamental to their life histories, but also challenging to represent using existing DEB theory. Here, we describe key features of the anatomy, morphology, physiology, biochemistry, and ecology of terrestrial vascular plants that should be considered in the development of a generic DEB model for plants. We then describe possible approaches to doing so using existing DEB theory and point out features that may require significant development for DEB theory to accommodate them. We end by presenting a generic DEB model for plants that accounts for many of these key features and describing gaps that would need to be addressed for DEB theory to predict the responses of plants to climate change. DEB models offer a powerful and generalizable framework for modelling resource allocation in terrestrial vascular plants, and our review contributes a framework for expansion and development of DEB theory to address how plants respond to anthropogenic change.

The functional role of ericoid mycorrhizal plants and fungi on carbon and nitrogen dynamics in forests

Ericoid mycorrhizal (ErM) shrubs commonly occur in forest understories and could therefore alter arbuscular (AM) and/or ectomycorrhizal (EcM) tree effects on soil carbon and nitrogen dynamics. Specifically, ErM fungi have extensive organic matter decay capabilities, and ErM plant and fungal tissues have high concentrations of secondary compounds that can form persistent complexes in the soil. Together, these traits could contribute to organic matter accumulation and inorganic nutrient limitation. These effects could also differ in AM- vs EcM-dominated stands at multiple scales within and among forest biomes by, for instance, altering fungal guild interactions. Most work on ErM effects in forests has been conducted in boreal forests dominated by EcM trees. However, ErM plants occur in c. 96, 69 and 29% of boreal, temperate and tropical forests, respectively. Within tropical montane forests, the effects of ErM plants could be particularly pronounced because their traits are more distinct from AM than EcM trees. Because ErM fungi can function as free-living saprotrophs, they could also be more resilient to forest disturbances than obligate symbionts. Further consideration of ErM effects within and among forest biomes could improve our understanding of how cooccurring mycorrhizal types interact to collectively affect soil carbon and nitrogen dynamics under changing conditions.

Tree mycorrhizal type mediates conspecific negative density dependence effects on seedling herbivory, growth, and survival

Tree mycorrhizal type plays an important role in promoting plant species diversity and coexistence, via its mediating role in conspecific negative density dependence (CNDD), i.e., the process by which an individual's performance is impaired by the density of conspecific plants. Previous findings suggest that ectomycorrhizal (EM) tree species are generally less susceptible to CNDD than arbuscular mycorrhizal (AM) tree species, due to the chemical and physical protection that EM fungi provide their host with. We examined how CNDD effects on leaf herbivory, seedling growth, and survival differ between AM and EM seedlings of ten tree species collected over 3 years in an old-growth temperate forest in northeastern China. We found that AM and EM seedlings differed in how conspecific density affected their leaf herbivory, seedling growth, and survival. Specifically, AM seedlings leaf herbivory rates significantly increased with increasing conspecific seedling and adult density, and their growth and survival rates decreased with increasing conspecific adult density, these patterns were, however, absent in EM seedlings. Our work suggests that AM seedlings have a performance disadvantage relative to EM seedlings related to the negative effects from conspecific neighbors. We highlight the importance of integrating information on seedling leaf herbivory, seedling growth, to provide further understanding on potential mechanisms driving differences in CNDD between AM and EM tree seedlings.

Interactions with soil fungi alter density dependence and neighborhood effects in a locally abundant dipterocarp species

Seedling recruitment can be strongly affected by the composition of nearby plant species. At the neighborhood scale (on the order of tens of meters), adult conspecifics can modify soil chemistry and the presence of host microbes (pathogens and mutualists) across their combined canopy area or rooting zones. At local or small spatial scales (on the order of one to few meters), conspecific seed or seedling density can influence the strength of intraspecific light and resource competition and also modify the density-dependent spread of natural enemies such as pathogens or invertebrate predators. Intrinsic correlation between proximity to adult conspecifics (i.e., recruitment neighborhood) and local seedling density, arising from dispersal, makes it difficult to separate the independent and interactive factors that contribute to recruitment success. Here, we present a field experiment in which we manipulated both the recruitment neighborhood and seedling density to explore how they interact to influence the growth and survival of Dryobalanops aromatica, a dominant ectomycorrhizal tree species in a Bornean tropical rainforest. First, we found that both local seedling density and recruitment neighborhood had effects on performance of D. aromatica seedlings, though the nature of these impacts varied between growth and survival. Second, we did not find strong evidence that the effect of density on seedling survival is dependent on the presence of conspecific adult trees. However, accumulation of mutualistic fungi beneath conspecifics adults does facilitate establishment of D. aromatica seedlings. In total, our results suggest that recruitment near adult conspecifics was not associated with a performance cost and may have weakly benefitted recruiting seedlings. Positive effects of conspecifics may be a factor facilitating the regional hyperabundance of this species. Synthesis: Our results provide support for the idea that dominant species in diverse forests may escape the localized recruitment suppression that limits abundance in rarer species.

Assessing the dual-mycorrhizal status of a widespread tree species as a model for studies on stand biogeochemistry

Viewing plant species by their mycorrhizal type has explained a range of ecosystem processes. However, mycorrhizal type is confounded with plant phylogeny and the environments in which mycorrhizal partners occur. To circumvent these confounding effects, "dual-mycorrhizal" plant species may be potential models for testing the influence of mycorrhizal type on stand biogeochemistry. To assess their use as models, duality in mycorrhizas within a single host species must be confirmed and factors underlying their variation understood. We surveyed roots, soils, and leaves of mature aspen (Populus tremuloides) across 27 stands in western Canada spanning two biomes: boreal forest and parklands. Aspen roots were mostly ectomycorrhizal with sporadic and rare occurrences of arbuscular mycorrhizas. We further tested whether a climate moisture index predicted abundance of ectomycorrhizal roots (number of ectomycorrhizal root tips m^-1 root length) surveyed at two depths (0-20 cm and 20-40 cm) and found that ectomycorrhizal root abundance in subsoils (20-40 cm) was positively related to the index. We subsequently examined the relationships between ectomycorrhizal root abundance, leaf traits, and slow and fast pools of soil organic carbon and nitrogen. The ratio of leaf lignin:N, but not its components, increased along with ectomycorrhizal root abundance in subsoils. Soil carbon and nitrogen pools were independent of ectomycorrhizal root abundance. Our results suggest that (1) categorizing aspen as dual-mycorrhizal may overstate the functional importance of arbuscular mycorrhizas in this species and life stage, (2) water availability influences ectomycorrhizal root abundance, and (3) ectomycorrhizal root abundance coincides with leaf quality.