Contributions of ectomycorrhizal fungal mats to forest soil respiration

Distinct aggregations of fungal hyphae and rhizomorphs, or "mats", formed by some genera of ectomycorrhizal (EcM) fungi are common features of soils in coniferous forests of the Pacific Northwest. We measured in situ respiration rates of Piloderma mats and neighboring non-mat soils in an old-growth Douglas-fir forest in western Oregon to investigate whether there was higher respiration from mats, and to estimate mat contributions to total soil respiration. We found that areas where Piloderma mats colonized the organic horizon often had higher soil surface flux than non-mats, with the relative increase in respiration averaging 16% across two growing seasons. Both soil physical factors and biochemistry were related to the higher surface flux of mat soils. When soil moisture was high, soil CO₂ production was concentrated into near-surface soil horizons where mats tend to colonize, resulting in greater apparent differences in respiration between mat and non-mat soils. Respiration rates were also correlated with the activity of chitin-degrading soil enzymes. This finding supports the notion that the abundance of fungal biomass in EcM mats is an important driver of C and N cycling. We found Piloderma mats present across 57% of the exposed soil, and use this value to estimate a respiratory contribution from mats at the stand-scale of about 9% of total soil respiration. The activity of EcM mats, which includes both EcM fungi and microbial associates, appeared to constitute a substantial portion of total soil respiration in this old-growth Douglas-fir forest

Experimental determination of the transient transport and of fluctuations relevant to transport in ASDEX

Particle transport was studied in ASDEZ with modulated puffing of the discharge gas and of impurities. The energy transport is investigated by numerical simulation of the heat pulse after the swatooth crash. Small scale density fluctuations are investigated in the confinement region with far infrared scattering and reflectometry and in the edge plasma with langmuir probes and Ha diagnostic. In addition to a diffuse component of the particle transport, a strong inward drift is observed in all discharges. In ohmic discharges the transport coefficients decrease and saturate like 1/TE with increasing density. They are smaller in deuterium that in hydrogen. In the improved ohmic confinement (IOC)regime mainly D in the outer region is reduced. D increases proportionally to the heating power in L-mode discharges. The improvement of particle confinement in the H-mode is explained by a increase of the inward drift at the edge rather than a decrease of D. The impurity diffusion coefficient is independent of the impurity mass and charge. In ohmic discharges, it varies with ne like the bulk diffusion coefficient, is independent of B or increases weakly with B and increases with Ip. In L-mode discharges, Dimp increases linearly with the heating power. The electron thermal condustivity determined by heat pulse propagation exceeds the stationary value by a factor of 3-4, assuming merely diffusive heat transport. Convection does not significantly reduce this factor. however, non-diagonal terms

Adaptive root foraging strategies along a boreal–temperate forest gradient

The tree root–mycorhizosphere plays a key role in resource uptake, but also in the adaptation of forests to changing environments. The adaptive foraging mechanisms of ectomycorrhizal (EcM) and fine roots of Picea abies, Pinus sylvestris and Betula pendula were evaluated along a gradient from temperate to subarctic boreal forest (38 sites between latitudes 48°N and 69°N) in Europe. Variables describing tree resource uptake structures and processes (absorptive fine root biomass and morphology, nitrogen (N) concentration in absorptive roots, extramatrical mycelium (EMM) biomass, community structure of root-associated EcM fungi, soil and rhizosphere bacteria) were used to analyse relationships between root system functional traits and climate, soil and stand characteristics. Absorptive fine root biomass per stand basal area increased significantly from temperate to boreal forests, coinciding with longer and thinner root tips with higher tissue density, smaller EMM biomass per root length and a shift in soil microbial community structure. The soil carbon (C) : N ratio was found to explain most of the variability in absorptive fine root and EMM biomass, root tissue density, N concentration and rhizosphere bacterial community structure. We suggest a concept of absorptive fine root foraging strategies involving both qualitative and quantitative changes in the root–mycorrhiza–bacteria continuum along climate and soil C : N gradients.Peer reviewe

Contributions of ectomycorrhizal fungal mats to forest soil respiration

Distinct aggregations of fungal hyphae and rhizomorphs, or "mats", formed by some genera of ectomycorrhizal (EcM) fungi are common features of soils in coniferous forests of the Pacific Northwest. We measured in situ respiration rates of <i>Piloderma</i> mats and neighboring non-mat soils in an old-growth Douglas-fir forest in western Oregon to investigate whether there was higher respiration from mats, and to estimate mat contributions to total soil respiration. We found that areas where <i>Piloderma</i> mats colonized the organic horizon often had higher soil surface flux than non-mats, with the relative increase in respiration averaging 16% across two growing seasons. Both soil physical factors and biochemistry were related to the higher surface flux of mat soils. When soil moisture was high, soil CO<sub>2</sub> production was concentrated into near-surface soil horizons where mats tend to colonize, resulting in greater apparent differences in respiration between mat and non-mat soils. Respiration rates were also correlated with the activity of chitin-degrading soil enzymes. This finding supports the notion that the abundance of fungal biomass in EcM mats is an important driver of C and N cycling. We found <i>Piloderma</i> mats present across 57% of the exposed soil, and use this value to estimate a respiratory contribution from mats at the stand-scale of about 9% of total soil respiration. The activity of EcM mats, which includes both EcM fungi and microbial associates, appeared to constitute a substantial portion of total soil respiration in this old-growth Douglas-fir forest

Testicular development and endocrine function in boars fed altrenogest

Crossbred male pigs were used to evaluate the influence of a synthetic progestogen on reproductive development. Concentrations of luteinizing hormone (LH) and testosterone in blood serum were reduced while boars were being fed altrenogest (15 to 21 wk of age). At 25 wk of age (4 wk after withdrawal from altrenogest), weights of the testes and accessory reproductive glands and testicular content of sperm were reduced in boars that had been fed altrenogest. However, testicular weight and content of sperm had returned to control values following 12 wk after withdrawal from altrenogest. In addition, concentration of LH and testosterone in blood serum were similar for control boars and boars previously fed altrenogest. We conclude that suppression of normal reproductive development of growing boars by altrenogest merely delays the onset of sexual maturation but does not permanently affect testicular function

Growth, carcass and boar-odor traits in male pigs fed altrenogest

Two experiments were conducted to examine the effects of a synthetic progestogen (altrenogest) on growth and carcass characteristics of boars. Altrenogest inhibited both the growth of the testes and the pubertal rise in testosterone that is associated with maleness. Growth rate, feed intake, and feed/gain were unaffected by feeding altrenogest in both experiments; however, in Exp. 2. growth rate and feed intake during the 4-wk withdrawal of altrenogest were less than those in the control boar or barrow groups. These changes appeared to be related to marked mounting activity of boars beginning 5 days after withdrawal of altrenogest from the feed. Feeding altrenogest to growing boars had no negative effects on carcass qualitative traits, but intensity of boar odor in fat was not diminished in treated boars. It is possible that altrenogest would have to be fed until about 1 wk before slaughter or later to allow marketing of boars without significant boar odor

Atomic structure of carbon-induced Si (001) c (4x4) reconstruction as a Si-Si homodimer and C-Si heterodimer network

A combination of low-energy electron diffraction, x-ray and ultraviolet photoelectron spectroscopy, and scanning-tunneling microscopy studies, in conjunction with ab initio calculations leads us to suggest a model for the carbon (C)-induced Si(001)c(4x4) atomic structure. This surface superstructure is obtained in a defined range of C2H4 exposures at 600 degreesC. Experimental probes show that the c(4x4) superstructure involves C atoms in both surface and subsurface sites. This is reflected in well-marked features in photoemission valence- and core-level spectra. Surface carbon atoms are stabilized in Si-C heterodimers, with a surface density of about 0.25 monolayer (ML) [i.e., two C atoms per c(4x4) unit cell of eight atoms]. In the subsurface region, carbon atoms substitute for Si atoms in well-defined sites of the third or fourth layers of the Si substrate. The subsurface C density increases with C2H4 exposure time up to a limit value of about 0.5 ML, within the c(4x4) surface structure. Further exposure disrupts the c(4x4) reconstruction and leads to a (2x1) low-energy electron diffraction pattern. Interaction with atomic hydrogen shows that the surface contains a mixture of heterodimers (Si-C) and homodimers (Si-Si), with an 1:1 proportion. These assignments are supported by first-principle calculations, which yield valence band and core level states in fairly good agreement with the experiment. Furthermore, total energy calculations strongly favor C incorporation in surface Si-C dimers and in third and fourth layer sites, and rule out C incorporation in sites of the second Si layer. The most stable c(4x4) surface configuration, suggested by our calculations, consists of alternate Si-C and Si-Si dimer lines. In such a configuration, surface carbon atoms in Si-C dimers induce a surface stress that leads to charge redistribution and atomic relaxation of the adjacent Si-Si dimers, consistent with scanning-tunneling microscopy images. Additional C atoms (in excess of those accommodated in surface sites) are forced in selected compressive (alpha) sites of the third and fourth layers. This model is discussed with respect to the previous models published in the literatur

Soil microbial community variation correlates most strongly with plant species identity, followed by soil chemistry, spatial location and plant genus

Soil ecologists have debated the relative importance of dispersal limitation and ecological factors in determining the structure of soil microbial communities. Recent evidence suggests that ‘everything is not everywhere’, and that microbial communities are influenced by both dispersal limitation and ecological factors. However, we still do not understand the relative explanatory power of spatial and ecological factors, including plant species identity and even plant relatedness, for different fractions of the soil microbial community (i.e. bacterial and fungal communities). To ask whether factors such as plant species, soil chemistry, spatial location and plant relatedness influence rhizosphere community composition, we examined field-collected rhizosphere soil of seven congener pairs that occur at Bodega Bay Marine Reserve, CA, USA. We characterized differences in bacterial and fungal communities using terminal-restriction fragment length polymorphism. Plant species identity was the single best statistical predictor of both bacterial and fungal community composition in the root zone. Soil microbial community structure was also correlated with soil chemistry. The third best predictor of bacterial and fungal communities was spatial location, confirming that everything is not everywhere. Variation in microbial community composition was also related to combinations of spatial location, soil chemistry and plant relatedness, suggesting that these factors do not act independently. Plant relatedness explained less of the variation than plant species, soil chemistry, or spatial location. Despite some congeners occupying different habitats and being spatially distant, rhizosphere fungal communities of plant congeners were more similar than expected by chance. Bacterial communities from the same samples were only weakly similar between plant congeners. Thus, plant relatedness might influence soil fungal, more than soil bacterial, community composition