From 13C-lignin to 13C-mycelium: Agaricus bisporus uses polymeric lignin as a carbon source

Plant biomass conversion by saprotrophic fungi plays a pivotal role in terrestrial carbon (C) cycling. The general consensus is that fungi metabolize carbohydrates, while lignin is only degraded and mineralized to CO2. Recent research, however, demonstrated fungal conversion of 13C-monoaromatic compounds into proteinogenic amino acids. To unambiguously prove that polymeric lignin is not merely degraded, but also metabolized, carefully isolated 13C-labeled lignin served as substrate for Agaricus bisporus, the world's most consumed mushroom. The fungus formed a dense mycelial network, secreted lignin-active enzymes, depolymerized, and removed lignin. With a lignin carbon use efficiency of 0.14 (g/g) and fungal biomass enrichment in 13C, we demonstrate that A. bisporus assimilated and further metabolized lignin when offered as C-source. Amino acids were high in 13C-enrichment, while fungal-derived carbohydrates, fatty acids, and ergosterol showed traces of 13C. These results hint at lignin conversion via aromatic ring-cleaved intermediates to central metabolites, underlining lignin's metabolic value for fungi.

Ecological Functions of Agricultural Soil Bacteria and Microeukaryotes in Chitin Degradation: A Case Study

Chitin provides a valuable carbon and nitrogen source for soil microorganisms and is a major component of particulate organic matter in agricultural soils. To date, there is no information on interaction and interdependence in chitin-degrading soil microbiomes. Since microbial chitin degradation occurs under both oxic and anoxic conditions and both conditions occur simultaneously in soil, the comparison of the active microbiome members under both conditions can reveal key players for the overall degradation in aerated soil. A time-resolved 16S rRNA stable isotope probing experiment was conducted with soil material from the top soil layer of a wheat-covered field. [¹³C_U]-chitin was largely mineralized within 20 days under oxic conditions. Cellvibrio, Massilia, and several Bacteroidetes families were identified as initially active chitin degraders. Subsequently, Planctomycetes and Verrucomicrobia were labeled by assimilation of ¹³C carbon either from [¹³C_U]-chitin or from ¹³C-enriched components of primary chitin degraders. Bacterial predators (e.g., Bdellovibrio and Bacteriovorax) were labeled, too, and non-labeled microeukaryotic predators (Alveolata) increased their relative abundance toward the end of the experiment (70 days), indicating that chitin degraders were subject to predation. Trophic interactions differed substantially under anoxic and oxic conditions. Various fermentation types occurred along with iron respiration. While Acidobacteria and Chloroflexi were the first taxa to be labeled, although at a low ¹³C level, Firmicutes and uncultured Bacteroidetes were predominantly labeled at a much higher ¹³C level during the later stages, suggesting that the latter two bacterial taxa were mainly responsible for the degradation of chitin and also provided substrates for iron reducers. Eventually, our study revealed that (1) hitherto unrecognized Bacteria were involved in a chitin-degrading microbial food web of an agricultural soil, (2) trophic interactions were substantially shaped by the oxygen availability, and (3) detectable predation was restricted to oxic conditions. The gained insights into trophic interactions foster our understanding of microbial chitin degradation, which is in turn crucial for an understanding of soil carbon dynamics.

Comprehensive Multiphase (CMP) NMR Monitoring of the Structural Changes and Molecular Flux Within a Growing Seed

A relatively recent technique termed comprehensive multiphase (CMP) NMR spectroscopy was used to investigate the growth and associated metabolomic changes of ¹³C-labeled wheat seeds and germinated seedlings. CMP-NMR enables the study of all phases in intact samples (i.e., liquid, gel-like, semisolid, and solid), by combining all required electronics into a single NMR probe, and can be used for investigating biological processes such as seed germination. All components, from the most liquid-like (i.e., dissolved metabolites) to the most rigid or solid-like (seed coat) were monitored in situ over 4 days. A wide range of metabolites were identified, and after 96 h of germination, the number of metabolites in the mobile phase more than doubled in comparison to 0 h (dry seed). This work represents the first application of CMP-NMR to follow biological processes in plants.

Comprehensive multiphase NMR spectroscopy of intact ¹³C-labeled seeds

Seeds are complex entities composed of liquids, gels, and solids. NMR spectroscopy is a powerful tool for studying molecular structure but has evolved into two fields, solution and solid state. Comprehensive multiphase (CMP) NMR spectroscopy is capable of liquid-, gel-, and solid-state experiments for studying intact samples where all organic components are studied and differentiated in situ. Herein, intact (13)C-labeled seeds were studied by a variety of 1D/2D (1)H/(13)C experiments. In the mobile phase, an assortment of metabolites in a single (13)C-labeled wheat seed were identified; the gel phase was dominated by triacylglycerides; the semisolid phase was composed largely of carbohydrate biopolymers, and the solid phase was greatly influenced by starchy endosperm signals. Subsequently, the seeds were compared and relative similarities and differences between seed types discussed. This study represents the first application of CMP-NMR to food chemistry and demonstrates its general utility and feasibility for studying intact heterogeneous samples.

Carbon and nitrogen cycles in European ecosystems respond differently to global warming

The global climate is predicted to become significantly warmer over the next century. This will affect ecosystem processes and the functioning of semi natural and natural ecosystems in many parts of the world. However, as various ecosystem processes may be affected to a different extent, balances between different ecosystem processes as well as between different ecosystems may shift and lead to major unpredicted changes. In this study four European shrubland ecosystems along a north-south temperature gradient were experimentally warmed by a novel nighttime warming technique. Biogeochemical cycling of both carbon and nitrogen was affected at the colder sites with increased carbon uptake for plant growth as well as increased carbon loss through soil respiration. Carbon uptake by plant growth was more sensitive to warming than expected from the temperature response across the sites while carbon loss through soil respiration reacted to warming in agreement with the overall Q10 and response functions to temperature across the sites. Opposite to carbon, the nitrogen mineralization was relatively insensitive to the temperature increase and was mainly affected by changes in soil moisture. The results suggest that C and N cycles respond asymmetrically to warming, which may lead to progressive nitrogen limitation and thereby acclimation in plant production. This further suggests that in many temperate zones nitrogen deposition has to be accounted for, not only with respect to the impact on water quality through increased nitrogen leaching where N deposition is high, but also in predictions of carbon sequestration in terrestrial ecosystems under future climatic conditions. Finally the results indicate that on the short term the above-ground processes are more sensitive to temperature changes than the below ground processes.

No evidence for substantial aerobic methane emission by terrestrial plants: a 13C-labelling approach

* The results of a single publication stating that terrestrial plants emit methane has sparked a discussion in several scientific journals, but an independent test has not yet been performed. * Here it is shown, with the use of the stable isotope (13)C and a laser-based measuring technique, that there is no evidence for substantial aerobic methane emission by terrestrial plants, maximally 0.3% (0.4 ng g(-1) h(-1)) of the previously published values. * Data presented here indicate that the contribution of terrestrial plants to global methane emission is very small at best. * Therefore, a revision of carbon sequestration accounting practices based on the earlier reported contribution of methane from terrestrial vegetation is redundant.

Taking mycocentrism seriously: mycorrhizal fungal and plant responses to elevated CO2

The aim here was to separately assess mycorrhizal fungal and plant responses under elevated atmospheric CO2, and to test a mycocentric model that assumes that increased carbon availability to the fungus will not automatically feed back to enhanced plant growth performance. Meta-analyses were applied across independent studies. Responses were compared in ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi, and ECM and AM plants. Responses of both mycorrhizal fungi and mycorrhizal plants to elevated CO2 were significantly positive. The response ratio for ECM fungi was 1.34 (an increase of 34%) and for AM fungi 1.21 (21%), indicating a significantly different response. The response ratio for ECM plants was 1.26, similar to that of AM plants (1.25). Fractional colonization proved to be an unsuitable fungal parameter. Evidence was found for the mycocentric view in ECM, but not in AM systems. Fungal identity and plant identity were important parameters that affected response ratios. The need for better descriptors of fungal and plant responses is emphasized.

Pig slurry reduces the survival ofRalstonia solanacearumbiovar 2 in soil

The effect of added pig slurry and solarization on the survival of Ralstonia solanacearum biovar 2 strain 1609 in soil was analysed in soil microcosms and field plots. In addition, the invasion of potato plants by R. solanacearum and the development of disease symptoms were determined, as measures of induced disease suppressiveness. In untreated soil, R. solanacearum showed slow population declines in both microcosms and the field from, initially, 106–107to 103–104CFU·(g dry soil)–1in about 9 weeks. The suppressiveness assays of these untreated soils after this period revealed that most of the plants that were used developed wilting symptoms and (or) contained the pathogen in their lower stem parts, as shown by immunofluorescence colony staining and PCR. The addition of pig slurry resulted in a significantly lower population size of R. solanacearum as well as reduced numbers of infected and (or) diseased plants in the soil suppressiveness tests. On the other hand, solarization of soil also decreased R. solanacearum survival but did not enhance soil suppressiveness as measured by development of disease symptoms and (or) plant invasion after 9 weeks. Combined soil solarization and pig slurry addition showed an additive effect of both treatments. Healthy-looking plants, primarily from soils treated with pig slurry and solarization, incidentally revealed the latent presence of R. solanacearum in the lower stem parts. The mechanism behind the enhanced population declines and disease suppressiveness induced by pig slurry is unclear but shifts in community profiles were clearly discernible by PCR – denaturing gradient gel electrophoresis 9 weeks after pig slurry addition in the field experiment, indicating induced changes in the bacterial community structure.Key words: soil suppressiveness, organic amendment, solarization, DGGE analysis, immunofluorescence colony staining.

MR angiography as a screening tool for intracranial aneurysms: feasibility, test characteristics, and interobserver agreement

OBJECTIVE

MR angiography may be an appropriate tool to screen for unruptured intracranial aneurysms. Feasibility, test characteristics, and interobserver agreement in evaluation of MR angiograms were assessed by members of the MARS (Magnetic resonance Angiography in Relatives of patients with Subarachnoid hemorrhage) Study Group.

SUBJECTS AND METHODS

We screened 626 first-degree relatives of a consecutive series of 193 patients with subarachnoid hemorrhage examined at two institutions. We used MR imaging and MR angiography (three-dimensional time-of-flight imaging at both institutions and additional three-dimensional phase-contrast imaging at one institution). Three observers independently assessed the MR angiograms. Conventional angiography was performed in relatives with possible or definite aneurysms on MR angiography and was considered the standard of reference.

RESULTS

Thirty-three aneurysms were found in 25 (4%; 95% confidence interval [CI], 3-6%) of 626 relatives. Thirteen (8%) of 169 relatives who refused screening had MR-related reasons; an additional six persons could not be screened because of contraindications for MR imaging (pregnancy, n = 1; claustrophobia, n = 5). The positive predictive value of MR angiography was 100% (95% CI, 79-100%) for "definite" aneurysms and 58% (95% CI, 28-85%) for "possible" aneurysms. Sensitivity of MR angiography was estimated at 83% (95% CI, 65-94%) and specificity at 97% (95% CI, 94-98%). Interobserver agreement in the evaluation of MR angiograms was poor (kappa < .30), probably because different diagnostic strategies used by individual observers resulted in different use of the assessment category "possible aneurysm."

CONCLUSION

MR angiography is a feasible screening tool for detection of intracranial aneurysms. Positive predictive value, sensitivity, and specificity are acceptable when at least two neuroradiologists independently assess MR angiograms.

Elevated CO2 enhances below-ground C allocation in three perennial grass species at different levels of N availability

Three perennial grass species, Lolium perenne L., Agrottis capillaris L. and Festuca uvina L., were homogeneously labelled in phytotrons with ¹⁴ CO₂ at two CO₂ concentrations (350 and 700μl l^-1 ). Plants were grown under two nitrogen regimes: one with a minor addition of 8 kg N ha^-1 , the other with an addition of 278 kg N ha^-1 . Carbon allocation over the different compartments of the plant/soil systems was measured: shoots, roots, rhizosphere soil (soil solution, microbial biomass and soil residue), and bulk soil. Elevated CO., increased total net ¹⁴ C recovery in all species by 14%, and significantly enhanced the below-ground ¹⁴ C allocation by 26%, this enhancement was 24%, 39% and 21 % for root, rhizosphere soil and bulk soil, respectively. Within the rhizosphere soil, the ¹⁴ C amounts in the soil solution (+ 69%) and soil residue (+ 49%,) increased significantly. Total microbial biomass-C in the rhizosphere soil was also increased (15 %) by the elevated CO₂ treatment, but only in proportion to the increased root mass. No interactions were observed between the elevated CO₂ , and N treatments. The N treatment increased total net ¹⁴ C recovery by more than 300% and ¹⁴ C was preferentially allocated to the shoots, leading to a significant increase in shoot-to-root ratio. However, N fertilization also increased (+111%) the absolute amount of ¹⁴ C in soil. The three species behaved differently, but no interactions were observed between CO₂ treatment and plant species. These results show that elevated CO₂ induces an increased C input into soil for all three grass species at both N levels. However, the highest absolute amounts were found in the soils of the fastest growing species and at the highest N level.

Carbon allocation and water use in juvenile Douglas fir under elevated CO2

In this study the impact of an elevated CO₂ level on allocation of assimilates and water use efficiency of Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] was investigated. Juvenile Douglas firs were exposed to a long-term treatment at 350 and 700 μ 1^-1 CO₂ for 14 months and subsequently crosswise transferred to phytotrons for a short-term treatment with 350 and 700 μ l ^-1 CO₂ for 4 wk in an atmosphere continuously labelled with ¹⁴ CO₂ . No interactive effects on total net uptake of ¹⁴ CO₂ between long-term treatment and short-term treatment were observed. The short-term treatment with 700 μ 1^-1 CO₂ increased the total net uptake of ¹⁴ CO₂ by 22%, compared with the 350 μ l ^-1 CO₂ treatment. The long-term pretreatment did not affect the total net uptake, suggesting that photosynthetic acclimation had not occurred. However, expressed per unit of needle mass a 14% reduction was observed in the trees pretreated at 700 μ l^-1 CO₂ . This was not because of a reduced sink strength of the root system. This reduced uptake per unit of needle mass after long-term treatment may have implications for carbon storage in forest ecosystems. The results showed that an initial growth stimulation can eventually be annulled by developing physiological or morphological adaptions. ¹⁴ CO₂ in the root/soil respiration increased in the short-term treatment with 700 μ l^-1 CO₂ , indicating a stimulated use of current carbon compounds either by roots or microorganisms. The water use efficiency during the short-term treatment with 700 μ l^-1 CO₂ increased by 32 %, but was not affected by the long-term pretreatment. Water use per unit needle mass during the short-term treatment was decreased both by the short-term treatment and by the long-term pretreatment by about 15%. Some of the observed effects appeared to be persistent, such as decreased water use per unit needle mass, whereas others, stimulation of total net ¹⁴ CO₂ uptake and water use efficiency, were transient.

Effects of short-term ozone exposure on the carbon economy of mature and juvenile Douglas firs [Pseudotsuga menziesii (Mirb.) Franco]

Effects of short-term ozone exposure of mature trees were compared with those of seedlings. Both 25-yr-old Douglas firs [Pseudotsuga menziesii (Mirb.) Franco] and 3-yr-old Douglas fir seedlings were exposed to 0, 200 and 400 μgm^-1 ozone for about 1.5 wk and then labelled with ¹⁴ CO₂ to study the effect on net photosynthesis, translocation and partitioning of assimilates. In the seedling experiment, two identical growth cabinets with separated shoot and root compartments were used for ozone fumigation and ¹⁴ C-labelling. Seedlings were harvested and ^H C contents in the needles (subdivided into starch, ethanol-soluble and residue fractions), branches, roots, root/soil respiration and soil residue were determined, together with the total starch content of the needles. Ozone increased the retention of ¹⁴ C-photosynthates in the needles. Translocation of carbon to the branches and roots seemed to be inhibited by the highest ozone treatment. The increased ¹⁴ C-retention was mainly recovered in the residue fraction of the needles. Total starch content of the needles decreased in the highest ozone treatment. In the experiment with mature trees, terminal shoots were fumigated with ozone and labelled with ¹⁴ C using three small branch chambers. Carbon distribution was studied after harvest of the branches. Total ¹⁴ C contents in the needle fractions and the branches were determined, together with the total starch content of the needles. Ozone was found to inhibit net ¹⁴ CO₂ assimilation as well as translocation of ¹⁴ C-labelled assimilates from exposed needles to the branch. No effects of ozone were found on the partitioning of ¹⁴ C among the starch, ethanol-soluble, and residue fractions of the needles, although amounts in the ethanol-soluble fraction tended to increase after exposure to ozone. The results indicate that mature and juvenile Douglas firs respond in a similar way to short-term ozone exposure with regard to carbon translocation. If this similarity also applies to other species, then results from phytotron experiments on ozone and translocation of carbon might gain importance with respect to extrapolation to forest ecosystems.

Effects of short-term ozone exposure and soil water availability on the carbon economy of juvenile Douglas-fir

Effects of ozone and soil water availability on partitioning and translocation of assimilates were studied in three-year-old Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings exposed, in separate experiments, to 0 and 106 or 0 and 514 micro g m(-3) ozone for 8 h day(-1) for 9 days. The dynamics of carbon from assimilated (14)CO(2) were followed. No interactions between ozone and soil water content were observed. Total net uptake of carbon was reduced by low soil water content, but was unaffected by ozone. Both ozone and low soil water content increased the amount of (14)C-photosynthates retained in the current-year needles. Total starch content in old and current-year needles was unaffected by ozone, but was reduced by low water availability. Translocation of carbon to the root-soil compartment was additively affected by ozone and low soil water content. The results suggest that dry periods in summer combined with high ozone concentrations cause the greatest reduction in the supply of carbon compounds to the root-soil compartment.

Effects of ozone and ammonium sulphate on carbon partitioning to mycorrhizal roots of juvenile Douglas fir

In this study the impact of two components of air pollution, i.e., ozone and ammonium sulphate, on carbon transport to mycorrhizal roots of Douglas fir was investigated. Juvenile Douglas fir (Pseudulsuga menziesii [Mirb.] Franco) were inoculated with Rhizopogon vinicolor A. H. Smith and Lactarius rufus (Scop.: Fr.) Fr., and allowed to grow outdoors for a period of four months. Subsequently, they were transferred to a phytotron and treated with 0 or 200μg m^-3 ozone for 28 days. During these treatments, they were watered with a solution of ammonium sulphate of concentrations corresponding to 5, SO and 200 kg N ha^-1 yr^-1 , During the last three days, the trees were pulse-labelled with 14CO₂ . Ozone increased the amounts of ¹⁴ C recovered in the new needle fraction, whereas the amounts recovered in the roots and root/soil respiration tended to decrease. Mycorrhizal frequency tended to increase during ozone treatment. Ammonium sulphate did not affect the distribution pattern of ¹⁴ C over the trees, but seemed to stimulate the activity of the root system and mycorrhizal frequency at the intermediate nitrogen level.

Temporary disturbance of translocation of assimilates in douglas firs caused by low levels of ozone and sulfur dioxide

Douglas firs (Pseudotsuga menziesii [Mirb.] Franco) are suffering strongly from air pollution in western Europe. We studied the effect of low concentrations of ozone (200 micrograms per cubic meter during 3 days) and sulfur dioxide (53 micrograms per cubic meter during 28 days) on translocation of assimilates in 2 year old Douglas firs. The trees were exposed to the pollutants and afterward transferred to a growth chamber adapted to the use of (14)CO(2). Root/soil respiration was measured daily. The results showed a significant decrease of the (14)CO(2) root/soil respiration during the first 1 to 2 weeks after exposure to either ozone or sulfur dioxide. The ultimate level of (14)CO(2) root/soil respiration did not differ significantly, which suggests a recovery of the exposed trees during the first weeks after exposure.