Impacts of long-term elevated atmospheric CO2 concentrations on communities of arbuscular mycorrhizal fungi

Extreme environments simplify reassembly of communities of arbuscular mycorrhizal fungi

The ecological impacts of long-term (press) disturbance on mechanisms regulating the relative abundance (i.e., commonness or rarity) and temporal dynamics of species within a community remain largely unknown. This is particularly true for the functionally important arbuscular mycorrhizal (AM) fungi; obligate plant-root endosymbionts that colonize more than two-thirds of terrestrial plant species. Here, we use high-resolution amplicon sequencing to examine how AM fungal communities in a specific extreme ecosystem-mofettes or natural CO2 springs caused by geological CO2 exhalations-are affected by long-term stress. We found that in mofettes, specific and temporally stable communities form as a subset of the local metacommunity. These communities are less diverse and dominated by adapted, "stress tolerant" taxa. Those taxa are rare in control locations and more benign environments worldwide, but show a stable temporal pattern in the extreme sites, consistently dominating the communities in grassland mofettes. This pattern of lower diversity and high dominance of specific taxa has been confirmed as relatively stable over several sampling years and is independently observed across multiple geographic locations (mofettes in different countries). This study implies that the response of soil microbial community composition to long-term stress is relatively predictable, which can also reflect the community response to other anthropogenic stressors (e.g., heavy metal pollution or land use change). Moreover, as AM fungi are functionally differentiated, with different taxa providing different benefits to host plants, changes in community structure in response to long-term environmental change have the potential to impact terrestrial plant communities and their productivity.IMPORTANCEArbuscular mycorrhizal (AM) fungi form symbiotic relationships with more than two-thirds of plant species. In return for using plant carbon as their sole energy source, AM fungi improve plant mineral supply, water balance, and protection against pathogens. This work demonstrates the importance of long-term experiments to understand the effects of long-term environmental change and long-term disturbance on terrestrial ecosystems. We demonstrated a consistent response of the AM fungal community to a long-term stress, with lower diversity and a less variable AM fungal community over time under stress conditions compared to the surrounding controls. We have also identified, for the first time, a suite of AM fungal taxa that are consistently observed across broad geographic scales in stressed and anthropogenically heavily influenced ecosystems. This is critical because global environmental change in terrestrial ecosystems requires an integrative approach that considers both above- and below-ground changes and examines patterns over a longer geographic and temporal scale, rather than just single sampling events.

Elevated O3 Exerts Stronger Effects than Elevated CO2 on the Functional Guilds of Fungi, but Collectively Increase the Structural Complexity of Fungi in a Paddy Soil

Global climate change is characterized by altered global atmospheric composition, including elevated CO₂ and O₃, with important consequences on soil fungal communities. However, the function and community composition of soil fungi in response to elevated CO₂ together with elevated O₃ in paddy soils remain largely unknown. Here we used twelve open-top chamber facilities (OTCs) to evaluate the interactive effect of CO₂ (+ 200 ppm) and O₃ (+ 40 ppb) on the diversity, gene abundance, community structure, and functional composition of soil fungi during the growing seasons of two rice cultivars (Japonica, Wuyujing 3 vs. Nangeng 5055) in a Chinese paddy soil. Elevated CO₂ and O₃ showed no individual or combined effect on the gene abundance or relative abundance of soil fungi, but increased structural complexity of soil fungal communities, indicating that elevated CO₂ and/or O₃ promoted the competition of species-species interactions. When averaged both cultivars, elevated CO₂ showed no individual effect on the diversity or abundance of functional guilds of soil fungi. By contrast, elevated O₃ significantly reduced the relative abundance and diversity of symbiotrophic fungi by an average of 47.2% and 39.1%, respectively. Notably, elevated O₃ exerts stronger effects on the functional processes of fungal communities than elevated CO₂. The structural equation model revealed that elevated CO₂ and/or O₃ indirectly affected the functional composition of soil fungi through community structure and diversity of soil fungi. Root C/N and soil environmental parameters were identified as the top direct predictors for the community structure of soil fungi. Furthermore, significant correlations were identified between saprotrophic fungi and root biomass, symbiotrophic fungi and root carbon, the pathotroph-symbiotroph and soil pH, as well as pathotroph-saprotroph-symbiotroph and soil microbial biomass carbon. These results suggest that climatic factors substantially affected the functional processes of soil fungal, and threatened soil function and food production, highlighting the detrimental impacts of high O₃ on the function composition of soil biota.

Fungal communities in soils under global change

Soil fungi play indispensable roles in all ecosystems including the recycling of organic matter and interactions with plants, both as symbionts and pathogens. Past observations and experimental manipulations indicate that projected global change effects, including the increase of CO₂ concentration, temperature, change of precipitation and nitrogen (N) deposition, affect fungal species and communities in soils. Although the observed effects depend on the size and duration of change and reflect local conditions, increased N deposition seems to have the most profound effect on fungal communities. The plant-mutualistic fungal guilds - ectomycorrhizal fungi and arbuscular mycorrhizal fungi - appear to be especially responsive to global change factors with N deposition and warming seemingly having the strongest adverse effects. While global change effects on fungal biodiversity seem to be limited, multiple studies demonstrate increases in abundance and dispersal of plant pathogenic fungi. Additionally, ecosystems weakened by global change-induced phenomena, such as drought, are more vulnerable to pathogen outbreaks. The shift from mutualistic fungi to plant pathogens is likely the largest potential threat for the future functioning of natural and managed ecosystems. However, our ability to predict global change effects on fungi is still insufficient and requires further experimental work and long-term observations. Citation: Baldrian P, Bell-Dereske L, Lepinay C, Větrovský T, Kohout P (2022). Fungal communities in soils under global change. Studies in Mycology 103: 1-24. doi: 10.3114/sim.2022.103.01.

Interactive influence of elevated CO2 and arbuscular mycorrhizal fungi on sucrose and coumarin metabolism in Ammi majus

The elevated level of CO₂ (eCO₂) and arbuscular mycorrhizal fungi (AMF) have been known as successful eco-friendly agents for plant growth and development as well as quality enhancers. The current investigation was designed to study the influence of eCO₂ (620 μmol CO₂ mol^-1 air) and AMF on sucrose and phenylpropanoid metabolism, including coumarins, the most important bioactive metabolite in Ammi majus. eCO₂ and AMF were applied, and different parameters have been assessed in A. majus such as changes in mycorrhizal colonization, plant biomass production, photosynthesis, and levels of N, P, and Ca besides the key metabolites and enzymes in sucrose and coumarins metabolic pathways. The present outcomes revealed that eCO₂ and AMF individually or combined enhanced the plant biomass and photosynthesis as well as nutrient concentrations. Furthermore, the levels of sucrose, soluble sugars, glucose, fructose, and the activities of some key enzymes in their metabolism besides phenylpropanoids metabolites in shoot and root of A. majus have been enhanced by eCO₂ and AMF especially when combined. Moreover, upregulation of sucrose is linked to phenylpropanoids metabolic pathway via upregulation of phenylalanine ammonia-lyase activity suggesting high coumarin biosynthesis. Generally, the synergistic effect of both treatments was noted for most of the investigated parameters compared to the individual effect. It could be concluded that the combined application of eCO₂ and AMF affects A. majus global metabolism and induces accumulation of phyto-molecules, coumarin, which might improve its medicinal and pharmacological applications.

Elevated CO2, warming, N addition, and increased precipitation affect different aspects of the arbuscular mycorrhizal fungal community

The functional diversity of arbuscular mycorrhizal fungi (AMF) affects the resistance and resilience of plant communities to environmental stress. However, considerable uncertainty remains regarding how the complex interactions among elevated atmospheric CO₂ (eCO₂), nitrogen deposition (eN), precipitation (eP), and warming (eT) affect AMF communities. These global change factors (GCFs) do not occur in isolation, and their interactions likely affect AMF community structure and assembly processes. In this study, the interactive effects of these four GCFs on AMF communities were explored using an open-top chamber field experiment in a semiarid grassland. Elevated CO₂, eN, eT, eP, and their interactions did not affect AMF biomass. The relative abundance of Paraglomus increased with N addition across treatment combinations, whereas that of Glomus decreased with N addition, especially combined with eT and eCO₂. Precipitation, temperature (T), and N affected AMF phylogenetic α-diversity, and the three-way interaction among CO₂, T, and N affected taxonomic and phylogenetic α-diversity. N addition significantly affected the composition of AMF communities. Both variable selection and dispersal limitation played major roles in shaping AMF communities, whereas homogeneous selection and homogenizing dispersal had little effect on AMF community assembly. The contribution of variable selection decreased under eCO₂, eN and eT but not under eP. The contribution of dispersal limitation decreased under eCO₂, eT, and eP but increased under eN. The assembly of AMF communities under the sixteen GCF combinations was strongly affected by dispersal limitation, variable selection and ecological drift. Elevated CO₂, warming, N addition, and increased precipitation affected different aspects of AMF communities. The interactive effects of the four GCFs on AMF communities were limited. Overall, the results of this study suggest that AMF communities in semiarid grasslands can resist changes in global climate.

Ecology and Evolution of Marine Fungi With Their Adaptation to Climate Change

Climate change agitates interactions between organisms and the environment and forces them to adapt, migrate, get replaced by others, or extinct. Marine environments are extremely sensitive to climate change that influences their ecological functions and microbial community including fungi. Fungi from marine habitats are engaged and adapted to perform diverse ecological functions in marine environments. Several studies focus on how complex interactions with the surrounding environment affect fungal evolution and their adaptation. However, a review addressing the adaptation of marine fungi to climate change is still lacking. Here we have discussed the adaptations of fungi in the marine environment with an example of Hortaea werneckii and Aspergillus terreus which may help to reduce the risk of climate change impacts on marine environments and organisms. We address the ecology and evolution of marine fungi and the effects of climate change on them to explain the adaptation mechanism. A review of marine fungal adaptations will show widespread effects on evolutionary biology and the mechanism responsible for it.

Functional redundancy and specific taxa modulate the contribution of prokaryotic diversity and composition to multifunctionality

Observational and experimental evidence has revealed the functional importance of microbial diversity. However, the effects of microbial diversity loss on ecosystem functions are not consistent across studies, which are probably tempered by microbial functional redundancy, specific taxa and functions evaluated. Here we conducted diversity manipulation experiments in two independent soils with distinct prokaryotic communities, and investigated how the initial community traits (e.g., distinct functional redundancy and taxonomic composition) modulate the contribution of prokaryotic diversity loss and composition shift to eight ecosystem functions related to soil nutrient cycling. We found that diversity loss impaired three functions (potential nitrification rate, N₂ -fixation activity and phosphatase) and multifunctionality only in the communities with low functional redundancy, but all examined functions were unaffected in the communities with high functional redundancy. All significantly affected functions belonged to specialized functions, while the broad function (soil basal respiration) was unaffected. Moreover, prokaryotic composition explained more functional variation than diversity, which was ascribed to the crucial role of specific taxa that influence particular functions. Taken together, this study provides empirical evidence for identifying the mechanism underlying the ecosystem response to changes in microbial community, with implications for improving the prediction of ecosystem process models and managing microbial communities to promote ecosystem services.

Impacts of elevated atmospheric CO2 on arbuscular mycorrhizal fungi and their role in moderating plant allometric partitioning

Elevated atmospheric CO₂ concentration (eCO₂) effects on plants depend on several factors including plant photosynthetic physiology (e.g. C₃, C₄), soil nutrient availability and plants' co-evolved soil-dwelling fungal symbionts, namely arbuscular mycorrhizal (AM) fungi. Complicated interactions among these components will determine the outcomes for plants. Therefore, clearer understanding is needed of how plant growth and nutrient uptake, along with root-colonising AM fungal communities, are simultaneously impacted by eCO₂. We conducted a factorial growth chamber experiment with a C₃ and a C₄ grass species (± AM fungi and ± eCO₂). We found that eCO₂ increased plant biomass allocation towards the roots, but only in plants without AM fungi, potentially associated with an eCO₂-driven increase in plant nutrient requirements. Furthermore, our data suggest a difference in the identities of root-colonising fungal taxa between ambient CO₂ and eCO₂ treatments, particularly in the C₄ grass species, although this was not statistically significant. As AM fungi are ubiquitous partners of grasses, their response to increasing atmospheric CO₂ is likely to have important consequences for how grassland ecosystems respond to global change.

Carbon for nutrient exchange between arbuscular mycorrhizal fungi and wheat varies according to cultivar and changes in atmospheric carbon dioxide concentration

Arbuscular mycorrhizal fungi (AMF) form symbioses with most crops, potentially improving their nutrient assimilation and growth. The effects of cultivar and atmospheric CO2 concentration ([CO2 ]) on wheat-AMF carbon-for-nutrient exchange remain critical knowledge gaps in the exploitation of AMF for future sustainable agricultural practices within the context of global climate change. We used stable and radioisotope tracers (15 N, 33 P, 14 C) to quantify AMF-mediated nutrient uptake and fungal acquisition of plant carbon in three wheat (Triticum aestivum L.) cultivars. We grew plants under current ambient (440 ppm) and projected future atmospheric CO2 concentrations (800 ppm). We found significant 15 N transfer from fungus to plant in all cultivars, and cultivar-specific differences in total N content. There was a trend for reduced N uptake under elevated atmospheric [CO2 ]. Similarly, 33 P uptake via AMF was affected by cultivar and atmospheric [CO2 ]. Total P uptake varied significantly among wheat cultivars and was greater at the future than current atmospheric [CO2 ]. We found limited evidence of cultivar or atmospheric [CO2 ] effects on plant-fixed carbon transfer to the mycorrhizal fungi. Our results suggest that AMF will continue to provide a route for nutrient uptake by wheat in the future, despite predicted rises in atmospheric [CO2 ]. Consideration should therefore be paid to cultivar-specific AMF receptivity and function in the development of climate smart germplasm for the future.

Impacts of long-term elevated atmospheric CO2 concentrations on communities of arbuscular mycorrhizal fungi

The ecological impacts of long-term elevated atmospheric CO2 (eCO2 ) levels on soil microbiota remain largely unknown. This is particularly true for the arbuscular mycorrhizal (AM) fungi, which form mutualistic associations with over two-thirds of terrestrial plant species and are entirely dependent on their plant hosts for carbon. Here, we use high-resolution amplicon sequencing (Illumina, HiSeq) to quantify the response of AM fungal communities to the longest running (>15 years) free-air carbon dioxide enrichment (FACE) experiment in the Northern Hemisphere (GiFACE); providing the first evaluation of these responses from old-growth (>100 years) semi-natural grasslands subjected to a 20% increase in atmospheric CO2 . eCO2 significantly increased AM fungal richness but had a less-pronounced impact on the composition of their communities. However, while broader changes in community composition were not observed, more subtle responses of specific AM fungal taxa were with populations both increasing and decreasing in abundance in response to eCO2 . Most population-level responses to eCO2 were not consistent through time, with a significant interaction between sampling time and eCO2 treatment being observed. This suggests that the temporal dynamics of AM fungal populations may be disturbed by anthropogenic stressors. As AM fungi are functionally differentiated, with different taxa providing different benefits to host plants, changes in population densities in response to eCO2 may significantly impact terrestrial plant communities and their productivity. Thus, predictions regarding future terrestrial ecosystems must consider changes both aboveground and belowground, but avoid relying on broad-scale community-level responses of soil microbes observed on single occasions.