Warming and disturbance alter soil microbiome diversity and function in a northern forest ecotone

Seasonal effects of long-term warming on ecosystem function and bacterial diversity

Across biomes, soil biodiversity promotes ecosystem functions. However, whether this relationship will be maintained within ecosystems under climate change is uncertain. Here, using two long-term soil warming experiments, we investigated how warming affects the relationship between ecosystem functions and bacterial diversity across seasons, soil horizons, and warming duration. Soils were sampled from these warming experiments located at the Harvard Forest Long-Term Ecological Research (LTER) site, where soils had been heated +5°C above ambient for 13 or 28 years at the time of sampling. We assessed seven measurements representative of different ecosystem functions and nutrient pools. We also surveyed bacterial community diversity. We found that ecosystem function was significantly affected by season, with autumn samples having a higher intercept than summer samples in our model, suggesting a higher overall baseline of ecosystem function in the fall. The effect of warming on bacterial diversity was similarly affected by season, where warming in the summer was associated with decreased bacterial evenness in the organic horizon. Despite the decreased bacterial evenness in the warmed plots, we found that the relationship between ecosystem function and bacterial diversity was unaffected by warming or warming duration. Our findings highlight that season is a consistent driver of ecosystem function as well as a modulator of climate change effects on bacterial community evenness.

Above- and belowground fungal biodiversity of Populus trees on a continental scale

Understanding drivers of terrestrial fungal communities over large scales is an important challenge for predicting the fate of ecosystems under climate change and providing critical ecological context for bioengineering plant-microbe interactions in model systems. We conducted an extensive molecular and microscopy field study across the contiguous United States measuring natural variation in the Populus fungal microbiome among tree species, plant niche compartments and key symbionts. Our results show clear biodiversity hotspots and regional endemism of Populus-associated fungal communities explained by a combination of climate, soil and geographic factors. Modelling climate change impacts showed a deterioration of Populus mycorrhizal associations and an increase in potentially pathogenic foliar endophyte diversity and prevalence. Geographic differences among these symbiont groups in their sensitivity to environmental change are likely to influence broader forest health and ecosystem function. This dataset provides an above- and belowground atlas of Populus fungal biodiversity at a continental scale.

Shifting microbial communities can enhance tree tolerance to changing climates

Climate change is pushing species outside of their evolved tolerances. Plant populations must acclimate, adapt, or migrate to avoid extinction. However, because plants associate with diverse microbial communities that shape their phenotypes, shifts in microbial associations may provide an alternative source of climate tolerance. Here, we show that tree seedlings inoculated with microbial communities sourced from drier, warmer, or colder sites displayed higher survival when faced with drought, heat, or cold stress, respectively. Microbially mediated drought tolerance was associated with increased diversity of arbuscular mycorrhizal fungi, whereas cold tolerance was associated with lower fungal richness, likely reflecting a reduced burden of nonadapted fungal taxa. Understanding microbially mediated climate tolerance may enhance our ability to predict and manage the adaptability of forest ecosystems to changing climates.

Spatiotemporal variations of microbial assembly, interaction, and potential risk in urban dust

Community and composition of dust-borne microbes would affect human health and are regulated by microbial community assembly. The dust in kindergarten is always collected to evaluate the microbial exposure of children, yet the microbial assembly, their interactions, and potential pathogens in kindergarten dust remain unclear. Here, we aim to investigate the microbial community assembly and structures, and potential bacterial pathogens in outdoor dust of kindergartens, and reveal the factors influencing the assembly and composition of microbial community. A total of 118 urban dust samples were collected on the outdoor impervious surfaces of 59 kindergartens from different districts of Xiamen in January and June 2020. We extracted microbial genomic DNA in these dusts and characterized the microbial (i.e., bacteria and fungi) community compositions and diversities using target gene-based (16S rRNA genes for bacterial community and ITS 2 regions for fungal community) high-throughput sequencing. Potential bacterial pathogens were identified and the interactions between microbes were determined through a co-occurrence network analysis. Our results showed the predominance of Actinobacteria and α-Proteobacteria in bacterial communities and Capnodiales in fungal communities. Season altered microbial assembly, composition, and interactions, with both bacterial and fungal communities exhibiting a higher heterogeneity in summer than those in winter. Although stochastic processes predominated in bacterial and fungal community assembly, the season-depended environmental factors (e.g., temperature) and interactions between microbes play important roles in dust microbial community assembly. Potential bacterial pathogens were detected in all urban dust, with significantly higher relative abundance in summer than that in winter. These results indicated that season exerted more profound effects on microbial community composition, assembly, and interactions, and suggested the seasonal changes of potential risk of microbes in urban dust. Our findings provide new insights into microbial community, community assembly, and interactions between microbes in the urban dust, and indicate that taxa containing opportunistic pathogens occur commonly in urban dust.

Experimental warming increases fungal alpha diversity in an oligotrophic maritime Antarctic soil

The climate of maritime Antarctica has altered since the 1950s. However, the effects of increased temperature, precipitation and organic carbon and nitrogen availability on the fungal communities inhabiting the barren and oligotrophic fellfield soils that are widespread across the region are poorly understood. Here, we test how warming with open top chambers (OTCs), irrigation and the organic substrates glucose, glycine and tryptone soy broth (TSB) influence a fungal community inhabiting an oligotrophic maritime Antarctic fellfield soil. In contrast with studies in vegetated soils at lower latitudes, OTCs increased fungal community alpha diversity (Simpson's index and evenness) by 102-142% in unamended soil after 5 years. Conversely, OTCs had few effects on diversity in substrate-amended soils, with their only main effects, in glycine-amended soils, being attributable to an abundance of Pseudogymnoascus. The substrates reduced alpha and beta diversity metrics by 18-63%, altered community composition and elevated soil fungal DNA concentrations by 1-2 orders of magnitude after 5 years. In glycine-amended soil, OTCs decreased DNA concentrations by 57% and increased the relative abundance of the yeast Vishniacozyma by 45-fold. The relative abundance of the yeast Gelidatrema declined by 78% in chambered soil and increased by 1.9-fold in irrigated soil. Fungal DNA concentrations were also halved by irrigation in TSB-amended soils. In support of regional- and continental-scale studies across climatic gradients, the observations indicate that soil fungal alpha diversity in maritime Antarctica will increase as the region warms, but suggest that the accumulation of organic carbon and nitrogen compounds in fellfield soils arising from expanding plant populations are likely, in time, to attenuate the positive effects of warming on diversity.

Reduction of microbial diversity in grassland soil is driven by long-term climate warming

Anthropogenic climate change threatens ecosystem functioning. Soil biodiversity is essential for maintaining the health of terrestrial systems, but how climate change affects the richness and abundance of soil microbial communities remains unresolved. We examined the effects of warming, altered precipitation and annual biomass removal on grassland soil bacterial, fungal and protistan communities over 7 years to determine how these representative climate changes impact microbial biodiversity and ecosystem functioning. We show that experimental warming and the concomitant reductions in soil moisture play a predominant role in shaping microbial biodiversity by decreasing the richness of bacteria (9.6%), fungi (14.5%) and protists (7.5%). Our results also show positive associations between microbial biodiversity and ecosystem functional processes, such as gross primary productivity and microbial biomass. We conclude that the detrimental effects of biodiversity loss might be more severe in a warmer world.

Influence of Intraspecific Competition Stress on Soil Fungal Diversity and Composition in Relation to Tree Growth and Soil Fertility in Sub-Tropical Soils under Chinese Fir Monoculture

Soil microorganisms provide valuable ecosystem services, such as nutrient cycling, soil remediation, and biotic and abiotic stress resistance. There is increasing interest in exploring total belowground biodiversity across ecological scales to understand better how different ecological aspects, such as stand density, soil properties, soil depth, and plant growth parameters, influence belowground communities. In various environments, microbial components of belowground communities, such as soil fungi, respond differently to soil features; however, little is known about their response to standing density and vertical soil profiles in a Chinese fir monoculture plantation. This research examined the assemblage of soil fungal communities in different density stands (high, intermediate, and low) and soil depth profiles (0–20 cm and 20–40 cm). This research also looked into the relationship between soil fungi and tree canopy characteristics (mean tilt angle of the leaf (MTA), leaf area index (LAI), and canopy openness index (DIFN)), and general growth parameters, such as diameter, height, and biomass. The results showed that low-density stand soil had higher fungal alpha diversity than intermediate- and high-density stand soils. Ascomycota, Basidiomycota, Mucromycota, and Mortierellomycota were the most common phyla of the soil fungal communities, in that order. Saitozyma, Penicillium, Umbelopsis, and Talaromyces were the most abundant fungal genera. Stand density composition was the dominant factor in changing fungal community structure compared to soil properties and soil depth profiles. The most significant soil elements in soil fungal community alterations were macronutrients. In addition, the canopy openness index and fungal community structure have a positive association in the low-density stand. Soil biota is a nutrient cycling driver that can promote better plant growth in forest ecosystems by supporting nutrient cycling. Hence, this research will be critical in understanding soil fungal dynamics, improving stand growth and productivity, and improving soil quality in intensively managed Chinese fir plantations.

Soil Disturbance Affects Plant Productivity via Soil Microbial Community Shifts

Recent advances in climate research have discovered that permafrost is particularly vulnerable to the changes occurring in the atmosphere and climate, especially in Alaska where 85% of the land is underlain by mostly discontinuous permafrost. As permafrost thaws, research has shown that natural and anthropogenic soil disturbance causes microbial communities to undergo shifts in membership composition and biomass, as well as in functional diversity. Boreal forests are home to many plants that are integral to the subsistence diets of many Alaska Native communities. Yet, it is unclear how the observed shifts in soil microbes can affect above ground plant communities that are relied on as a major source of food. In this study, we tested the hypothesis that microbial communities associated with permafrost thaw affect plant productivity by growing five plant species found in Boreal forests and Tundra ecosystems, including low-bush cranberry and bog blueberry, with microbial communities from the active layer soils of a permafrost thaw gradient. We found that plant productivity was significantly affected by the microbial soil inoculants. Plants inoculated with communities from above thawing permafrost showed decreased productivity compared to plants inoculated with microbes from undisturbed soils. We used metagenomic sequencing to determine that microbial communities from disturbed soils above thawing permafrost differ in taxonomy from microbial communities in undisturbed soils above intact permafrost. The combination of these results indicates that a decrease in plant productivity can be linked to soil disturbance driven changes in microbial community membership and abundance. These data contribute to an understanding of how microbial communities can be affected by soil disturbance and climate change, and how those community shifts can further influence plant productivity in Boreal forests and more broadly, ecosystem health.