Arbuscular mycorrhizal diversity increases across a plant productivity gradient driven by soil nitrogen availability.

Arbuscular mycorrhizal fungi (AMF) are widespread obligate symbionts of plants. This dynamic symbiosis plays a large role in successful plant performance, given that AMF help to ameliorate plant responses to abiotic and biotic stressors. Although the importance of this symbiosis is clear, less is known about what may be driving this symbiosis, the plant's need for nutrients or the excess of plant photosynthate being transferred to the AMF, information critical to assess the functionality of this relationship.

Fungal community composition and genetic potential regulate fine root decay in northern temperate forests.

Understanding how genetic differences among soil microorganisms regulate spatial patterns in litter decay remains a persistent challenge in ecology. Despite fine root litter accounting for ~50% of total litter production in forest ecosystems, far less is known about the microbial decay of fine roots relative to aboveground litter. Here, we evaluated whether fine root decay occurred more rapidly where fungal communities have a greater genetic potential for litter decay.

Decay by ectomycorrhizal fungi couples soil organic matter to nitrogen availability.

Interactions between soil nitrogen (N) availability, fungal community composition, and soil organic matter (SOM) regulate soil carbon (C) dynamics in many forest ecosystems, but context dependency in these relationships has precluded general predictive theory. We found that ectomycorrhizal (ECM) fungi with peroxidases decreased with increasing inorganic N availability across a natural inorganic N gradient in northern temperate forests, whereas ligninolytic fungal saprotrophs exhibited no response. Lignin-derived SOM and soil C were negatively correlated with ECM fungi with peroxidases and were positively correlated with inorganic N availability, suggesting decay of lignin-derived SOM by these ECM fungi reduced soil C storage.

Anthropogenic N deposition alters soil organic matter biochemistry and microbial communities on decaying fine roots.

Fine root litter is a primary source of soil organic matter (SOM), which is a globally important pool of C that is responsive to climate change. We previously established that ~20 years of experimental nitrogen (N) deposition has slowed fine root decay and increased the storage of soil carbon (C; +18%) across a widespread northern hardwood forest ecosystem. However, the microbial mechanisms that have directly slowed fine root decay are unknown.

Anthropogenic N deposition, fungal gene expression, and an increasing soil carbon sink in the Northern Hemisphere.

Terrestrial ecosystems in the Northern Hemisphere are a globally important sink for anthropogenic CO in the Earth's atmosphere, slowing its accumulation as well as the pace of climate warming. With the use of a long-term field experiment (ca. 20 yr), we show that the expression of fungal class II peroxidase genes, which encode enzymes mediating the rate-limiting step of organic matter decay, are significantly downregulated (-60 to -80%) because of increases in anthropogenic N deposition; this response was consistent with a decline in extracellular peroxidase enzyme activity in soil, the slowing of organic-matter decay, and greater soil C storage.

Soil microbial communities and elk foraging intensity: implications for soil biogeochemical cycling in the sagebrush steppe.

Foraging intensity of large herbivores may exert an indirect top-down ecological force on soil microbial communities via changes in plant litter inputs. We investigated the responses of the soil microbial community to elk (Cervus elaphus) winter range occupancy across a long-term foraging exclusion experiment in the sagebrush steppe of the North American Rocky Mountains, combining phylogenetic analysis of fungi and bacteria with shotgun metagenomics and extracellular enzyme assays. Winter foraging intensity was associated with reduced bacterial richness and increasingly distinct bacterial communities.

Microbial Potential for Ecosystem N Loss Is Increased by Experimental N Deposition.

Fossil fuel combustion and fertilizer use has increased the amount of biologically available N entering terrestrial ecosystems. Nonetheless, our understanding of how anthropogenic N may alter the physiological mechanisms by which soil microorganisms cycle N in soil is still developing. Here, we applied shotgun metagenomics to a replicated long-term field experiment to determine how two decades of experimental N deposition, at a rate expected by mid-century, has affected the genetic potential of the soil microbial community to cycle N in soils.

Anthropogenic N deposition increases soil organic matter accumulation without altering its biochemical composition.

Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (SOM). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of SOM. Here, we used size-density fractionation and solid-state C-NMR spectroscopy to explore the extent to which declines in microbial decay in a long-term (ca.

Active microorganisms in forest soils differ from the total community yet are shaped by the same environmental factors: the influence of pH and soil moisture.

Predicting the impact of environmental change on soil microbial functions requires an understanding of how environmental factors shape microbial composition. Here, we investigated the influence of environmental factors on bacterial and fungal communities across an expanse of northern hardwood forest in Michigan, USA, which spans a 500-km regional climate gradient. We quantified soil microbial community composition using high-throughput DNA sequencing on coextracted rDNA (i.

Anthropogenic N Deposition Slows Decay by Favoring Bacterial Metabolism: Insights from Metagenomic Analyses.

Litter decomposition is an enzymatically-complex process that is mediated by a diverse assemblage of saprophytic microorganisms. It is a globally important biogeochemical process that can be suppressed by anthropogenic N deposition. In a northern hardwood forest ecosystem located in Michigan, USA, 20 years of experimentally increased atmospheric N deposition has reduced forest floor decay and increased soil C storage.

Dispersal limitation and the assembly of soil Actinobacteria communities in a long-term chronosequence.

It is uncertain whether the same ecological forces that structure plant and animal communities also shape microbial communities, especially those residing in soil. We sought to uncover the relative importance of present-day environmental characteristics, climatic variation, and historical contingencies in shaping soil actinobacterial communities in a long-term chronosequence. Actinobacteria communities were characterized in surface soil samples from four replicate forest stands with nearly identical edaphic and ecological properties, which range from 9500 to 14,000 years following glacial retreat in Michigan.

Slowed decomposition is biotically mediated in an ectomycorrhizal, tropical rain forest.

Bacteria and fungi drive the cycling of plant litter in forests, but little is known about their role in tropical rain forest nutrient cycling, despite the high rates of litter decay observed in these ecosystems. However, litter decay rates are not uniform across tropical rain forests. For example, decomposition can differ dramatically over small spatial scales between low-diversity, monodominant rain forests, and species-rich, mixed forests.

Isolation of fungal cellobiohydrolase I genes from sporocarps and forest soils by PCR.

Cellulose is the major component of plant biomass, and microbial cellulose utilization is a key step in the decomposition of plant detritus. Despite this, little is known about the diversity of cellulolytic microbial communities in soil. Fungi are well known for their cellulolytic activity and mediate key functions during the decomposition of plant detritus in terrestrial ecosystems.

Isolation of polymer-degrading bacteria and characterization of the hindgut bacterial community from the detritus-feeding larvae of Tipula abdominalis (Diptera: Tipulidae).

The Tipula abdominalis larval hindgut microbial community presumably facilitates digestion of the lignocellulosic diet. The microbial community was investigated through characterization of bacterial isolates and analysis of 16S rRNA gene clone libraries. This initial study revealed novel bacteria and provides a framework for future studies of this symbiosis.