Isotopic Analysis of Sporocarp Protein and Structural Material Improves Resolution of Fungal Carbon Sources

Fungal acquisition of resources is difficult to assess in the field. To determine whether fungi received carbon from recent plant photosynthate, litter or soil-derived organic (C:N bonded) nitrogen, we examined differences in δ13C among bulk tissue, structural carbon, and protein extracts of sporocarps of three fungal types: saprotrophic fungi, fungi with hydrophobic ectomycorrhizae, or fungi with hydrophilic ectomycorrhizae. Sporocarps were collected from experimental plots of the Duke Free-air CO2 enrichment experiment during and after CO2 enrichment. The differential 13C labeling of ecosystem pools in CO2 enrichment experiments was tracked into fungi and provided novel insights into organic nitrogen use. Specifically, sporocarp δ13C as well as δ15N of protein and structural material indicated that fungi with hydrophobic ectomycorrhizae used soil-derived organic nitrogen sources for protein carbon, fungi with hydrophilic ectomycorrhizae used recent plant photosynthates for protein carbon and both fungal groups used photosynthates for structural carbon. Saprotrophic fungi depended on litter produced during fumigation for both protein and structural material

Isotopic Analysis of Sporocarp Protein and Structural Material Improves Resolution of Fungal Carbon Sources

Fungal acquisition of resources is difficult to assess in the field. To determine whether fungi received carbon from recent plant photosynthate, litter or soil-derived organic (C:N bonded) nitrogen, we examined differences in δ13C among bulk tissue, structural carbon, and protein extracts of sporocarps of three fungal types: saprotrophic fungi, fungi with hydrophobic ectomycorrhizae, or fungi with hydrophilic ectomycorrhizae. Sporocarps were collected from experimental plots of the Duke Free-air CO2 enrichment experiment during and after CO2 enrichment. The differential 13C labeling of ecosystem pools in CO2 enrichment experiments was tracked into fungi and provided novel insights into organic nitrogen use. Specifically, sporocarp δ13C as well as δ15N of protein and structural material indicated that fungi with hydrophobic ectomycorrhizae used soil-derived organic nitrogen sources for protein carbon, fungi with hydrophilic ectomycorrhizae used recent plant photosynthates for protein carbon and both fungal groups used photosynthates for structural carbon. Saprotrophic fungi depended on litter produced during fumigation for both protein and structural material

Mycorrhizal roots in a temperate forest take up organic nitrogen from 13C- and 15N-labeled organic matter

Background and Aims The importance of the uptake of nitrogen in organic form by plants and mycorrhizal fungi has been demonstrated in various ecosystems including temperate forests. However, in previous experiments, isotopically labeled amino acids were often added to soils in concentrations that may be higher than those normally available to roots and mycorrhizal hyphae in situ, and these high concentrations could contribute to exaggerated uptake. Methods We used an experimental approach in which we added 13C-labeled and 15N-labeled whole cells to root-ingrowth cores, allowing proteolytic enzymes to release labeled organic nitrogen at a natural rate, as roots and their associated mycorrhizal fungi grew into the cores. We employed this method in four forest types representing a gradient of soil pH, nitrogen mineralization rate, and mycorrhizal type. Results Intact uptake of organic nitrogen was detected in mycorrhizal roots, and accounted for at least of 1-14% of labeled nitrogen uptake. Forest types did not differ significantly in the importance of organic uptake. Conclusions The estimates of organic N uptake here using 13C-labeled and 15N-labeled whole cells are less than those reported in other temperate forest studies using isotopically labelled amino acids, and likely represent a minimum estimate of organic N-use. The two approaches each have different assumptions, and when used in tandem should complement one another and provide upper and lower bounds of organic N use by plants

Collembola’s role in regulating mass fluxes in soil and the effects of contrasting life histories

The study determined metabolic rates and elemental pools for two Collembola species with contrasting life histories. The fittest of the two species, P. minuta, excreted the equivalent of 10–12% of the elemental body content per day, and P. armata 7–10%. Most elements are lost to excretion (CO2 and N-waste). These figures in combination with stoichiometry and life histories indicate that the cost of P. minuta’s better fitness is a requirement for a higher quality diet than P. armata. The data produced in this study can be used to estimate the collembolan contribution to C and N fluxes in the soil

Nutrient allocations and metabolism in two collembolans with contrasting reproduction and growth strategies

Physiological mechanisms such as allocation and release of nutrients are keys to understanding an animal\u27s adaptation to a particular habitat. This study investigated how two detrivores with contrasting life‐history traits allocated carbon (C) and nitrogen (N) to growth, reproduction and metabolism. As model organisms we used the collembolans, Proisotoma minuta (Tullberg 1871) and Protaphorura fimata (Gisin 1952). To estimate allocations of C and N in tissue, we changed the isotopic composition of the animal\u27s yeast diets when they became sexually mature and followed isotope turnover in tissue, growth and reproduction for 28 days. In addition, we measured the composition of C, N and phosphorus (P) to gain complementary information on the stoichiometry underlying life‐history traits and nutrient allocation. For P. minuta, the smallest and most fecund of the two species, the tissue turnover of C and N were 13% and 11% day−1, respectively. For P. fimata, the equivalent rates were 5% and 4% d−1, respectively. Protaphorura fimata had the lowest metabolic rate relative to total body mass but the highest metabolic rates relative to reproductive investment. Adult P. fimata retained approximately 17% of the nutrient reserves acquired while a juvenile and adult P. minuta about 11%. N and P contents of total tissue were significantly higher in P. minuta than in P. fimata, suggesting that tissue turnover was correlated with high protein‐N and RNA‐P. Our results suggest that the lower metabolism and nutritional requirements by P. fimata than P. minuta is an adaptation to the generally low availability and quality of food in its natural habitat. The methodological approach we implemented tracking mass balance, isotope turnover and elemental composition is promising for linking nutrient budgets and life‐history traits in small invertebrates such as Collembola

Increased C3 productivity in Midwestern lawns since 1982 revealed by carbon isotopes in Amanita thiersii

How climate and rising carbon dioxide concentrations (pCO2) have influenced competition between C3 and C4 plants over the last 50 years is a critical uncertainty in climate change research. Here we used carbon isotope (δ13C) values of the saprotrophic lawn fungus Amanita thiersii to integrate the signal of C3 and C4 carbon in samples collected between 1982 and 2009 from the Midwestern USA. We then calculated 13C fractionation (Δ) to assess the balance between C3 and C4 photosynthesis as influenced by mean annual temperature (MAT), mean annual precipitation over a 30 year period (MAP‐30), and pCO2. Sporocarp Δ correlated negatively with MAT (−1.74‰ °C−1, 79% of variance) and positively with MAP (9.52‰ m−1, 15% of variance), reflecting the relative productivity of C3 and C4 grasses in lawns. In addition, Δ values correlated positively with pCO2 (0.072‰ ppm−1, 5% of variance). Reduced photorespiration with rising pCO2 accounted for 20% of this increased Δ, but the remaining 80% is consistent with increased assimilation of C3‐derived carbon by Amanita thiersii resulting from increased productivity of C3 grasses with rising pCO2. Between 1982 and 2009, pCO2 rose by 46 ppm and the relative contribution of C3 photosynthesis to Amanita thiersii carbon increased 18.5%. The δ13C value of Amanita thiersii may integrate both lawn maintenance practices and the physiological responses of turf grasses to rising CO2 concentrations

Long-term carbon and nitrogen dynamics at SPRUCE revealed through stable isotopes in peat profiles

Peatlands encode information about past vegetation dynamics, climate, and microbial processes. Here, we used δ15N and δ13C patterns from 16 peat profiles to deduce how the biogeochemistry of the Marcell S1 forested bog in northern Minnesota responded to environmental and vegetation change over the past  ∼ 10000 years. In multiple regression analyses, δ15N and δ13C correlated strongly with depth, plot location, C∕N, %N, and each other. Correlations with %N, %C, C∕N, and the other isotope accounted for 80% of variance for δ15N and 38% of variance for δ13C, reflecting N and C losses. In contrast, correlations with depth and topography (hummock or hollow) reflected peatland successional history and climate. Higher δ15N in plots closer to uplands may reflect upland-derived DON inputs and accompanying shifts in N dynamics in the lagg drainage area surrounding the bog. The Suess effect (declining δ13CO2 since the Industrial Revolution) lowered δ13C in recent surficial samples. High δ15N from −35 to −55cm probably indicated the depth of ectomycorrhizal activity after tree colonization of the peatland over the last 400 years, as confirmed by the occasional presence of wood down to −35cm depth. High δ13C at  ∼ 4000 years BP (−65 to −105cm) could reflect a transition at that time to slower rates of peat accumulation, when 13C discrimination during peat decomposition may increase in importance. Low δ13C and high δ15N at −213 and −225cm ( ∼ 8500 years BP) corresponded to a warm period during a sedge-dominated rich fen stage. The above processes appear to be the primary drivers of the observed isotopic patterns, whereas there was no clear evidence for methane dynamics influencing δ13C patterns

Linalool attenuates oxidative stress and mitochondrial dysfunction mediated by glutamate and NMDA toxicity

Mitochondrial dysfunction and inflammation contribute to the initiation and development of several brain pathological conditions, including Alzheimer's disease and cerebral ischemia. Linalool is an aromatic plant-derived monoterpene alcohol with reported anti-inflammatory, and anti-oxidant properties. We investigated the role of linalool on glutamate-induced mitochondrial oxidative stress in immortalized neuronal HT-22 cells. Glutamate induced oxidative stress in neuronal cells, as detected by real-time cell impedance measurements, MTT assay, and analysis of Annexin V/PI. Administration of linalool 100 μM reduced cell death mediated by glutamate. Staining of glutamate-stimulated mitochondria by MitoTracker revealed improved morphology in the presence of linalool. Furthermore, we demonstrated a potential neuroprotective effect of linalool in conditions of oxidative stress by a reduction of mitochondrial ROS and mitochondrial calcium levels, and by preserving mitochondrial membrane potential. Experiments using both high-resolution respirometry and Seahorse Extracellular flux analyzer showed that linalool was able to promote an increase in uncoupled respiration that could contribute to its neuroprotective capacity. Linalool protection was validated using organotypic hippocampal slices as ex vivo model with NMDA as a stimulus to induce excitotoxity cell damage. These results demonstrate that linalool is protective in an in vitro model of glutamate-induced oxidative stress and in an ex-vivo model for excitotoxity, proposing linalool as a potential therapeutic agent against neurodegenerative brain diseases where oxidative stress contributes to the pathology of the disease

Importance of Co-operative Hydrogen Bonding in the Apramycin-Ribosomal Decoding A-Site Interaction

An intramolecular hydrogen bond between the protonated equatorial 7'-methylamino group of apramycin and the vicinal axial 6'-hydroxy group acidifies the 6'-hydroxy group leading to a strong hydrogen bond to A1408 in the ribosomal drug binding pocket in the decoding A site of the small ribosomal subunit. In 6'-epiapramycin, the trans-nature of the 6'-hydroxy group and the 7'-methylamino group results in a much weaker intramolecular hydrogen bond, and a consequently weaker cooperative hydrogen bonding network with A1408, resulting overall in reduced inhibition of protein synthesis and antibacterial activity

Exploring the phylogenetic affiliations and the trophic mode of Sedecula pulvinata (Sedeculaceae)

Sedecula is a monotypic genus of hypogeous fungi that is rare and endemic to dry conifer forests of the western United States. The only known species, Sedecula pulvinata, was described in 1941 and its taxonomic placement and trophic status have remained uncertain ever since. Here we employ isotopic and molecular phylogenetic analyses to determine its nutritional mode and placement on the fungal tree of life. Phylogenetic analysis indicates that S. pulvinata is closely related to the genus Coniophora, in Coniophoraceae (Boletales). Stable isotope comparisons with known ectomycorrhizal and saprotrophic fungi together with phylogenetic evidence also suggest that S. pulvinata is saprotrophic. We conclude that Sedecula likely represents a unique morphological transition between a resupinate basidiocarp morphology (in Coniophora and relatives) and a hypogeous, sequestrate basidiocarp morphology (in Sedecula). Spore dimensions are amended from the original description.This is the publisher’s final pdf. The published article is copyrighted by Mycological Society of America and can be found at: http://msafungi.org/mycologia/Keywords: isotopes, Coniophoraceae, mycorrhizal, Boletales, saprotrophic, Great Basi