Aerobic and anaerobic degradation and mineralization of 14C-chitin by water column and sediment inocula of the York River estuary, Virginia.

Potential rates of chitin degradation (Cd) and mineralization (Cm) by estuarine water and sediment bacteria were measured as a function of inoculum source, temperature, and oxygen condition. In the water column inoculum, 88 to 93% of the particulate chitin was mineralized to CO2 with no apparent lag between degradation and mineralization. No measurable dissolved pool of radiolabel was found in the water column. For the sediment inocula, 70 to 90% of the chitin was degraded while only 55 to 65% was mineralized to CO2. 14C label recoveries in the dissolved pool were 19 to 21% for sand, 17 to 24% in aerobic mud, and 12 to 21% for the anaerobic mud. This uncoupling between degradation and mineralization occurred in all sediment inocula. More than 98% of the initial 14C-chitin was recovered in the three measured fractions. The highest Cd and Cm values, 30 and 27% day-1, occurred in the water column inoculum at 25 degrees C. The lowest Cd and Cm values were found in the aerobic and anaerobic mud inocula incubated at 15 degrees C. Significant differences in Cd and Cm values among water column and sediment inocula as well as between temperature treatments were evident. An increased incubation temperature resulted in shorter lag times before the onset of chitinoclastic bacterial growth, degradation, and mineralization and resulted in apparent Q10 values of 1.1 for water and 1.3 to 2.1 for sediment inocula. It is clear that chitin degradation and mineralization occur rapidly in the estuary and that water column bacteria may be more important in this process than previously acknowledged.     

Characteristics of a photorespiratory mutant of barley (Hordeum vulgare L.) deficient in phosphogly collate phosphatase

A barley mutant RPr84/90 has been isolated by selecting for plants which grow poorly in natural air, but normally in air enriched to 0.8% CO₂. After 5 minutes of photosynthesis in air containing¹⁴CO₂ this mutant incorporated 26% of the¹⁴C carbon into phosphoglycollate, a compound not normally labelled in wild type (cv. Maris Mink) leaves.The activity of phosphoglycollate phosphatase (EC 3.1.1.18) was 1.2 nkat mg^–1 protein at 30°C in RPr 84/90 compared to 19.2 nkat mg^–1 protein in the wild-type leaves. Phosphoglycollate phosphatase activity was not detected after protein separation by electrophoresis of leaf extracts from the mutant on polyacrylamide gels; on linear 5% acrylamide gels three bands with enzyme activity were separated from extracts of wild type plants. Gradient gel electrophoresis followed by activity staining showed two bands in Maris Mink tracks of MW 86,000 and 96,000, but no bands in 84/90. This is the first report of isozymes of phosphoglycollate phosphatase in barley which were absent in the mutant extracts. Our results confirm an earlier report of isozymes of this phosphatase in Phaseolus vulgaris [18].The photosynthetic rate of RPr 84/90 in 1% O₂, 350 l CO₂ l^–1 was 9–12 mg CO₂ dm^–2 h^–1 at 20°C, whereas the wild-type rate was 27–29 mg CO₂ dm^–2 h^–1 at 20°C. In 21% O₂, 350 l CO₂ l^–1 the rate was 2–3 mg CO₂ dm^–2 h^–1 in the mutant and 20 mg CO₂ dm^–2 h^–1 in the wild type.Genetic analysis has shown that the mutation segregates as a single recessive nuclear gene.     

Respiration of individual honeybee larvae in relation to age and ambient temperature

The CO₂ production of individual larvae of Apis mellifera carnica, which were incubated within their cells at a natural air humidity of 60–80%, was determined by an open-flow gas analyzer in relation to larval age and ambient temperature. In larvae incubated at 34 °C the amount of CO₂ produced appeared to fall only moderately from 3.89±1.57 µl mg^–1 h^–1 in 0.5-day-old larvae to 2.98±0.57 µl mg^–1 h^–1 in 3.5-day-old larvae. The decline was steeper up to an age of 5.5 days (0.95±1.15 µl mg^–1 h^–1). Our measurements show that the respiration and energy turnover of larvae younger than about 80 h is considerably lower (up to 35%) than expected from extrapolations of data determined in older larvae. The temperature dependency of CO₂ production was determined in 3.5-day-old larvae, which were incubated at temperatures varying from 18 to 38 °C in steps of 4 °C. The larvae generated 0.48±0.03 µl mg^–1 h^–1 CO₂ at 18 °C, and 3.97±0.50 µl mg^–1 h^–1 CO₂ at 38 °C. The temperature-dependent respiration rate was fitted to a logistic curve. We found that the inflection point of this curve (32.5 °C) is below the normal brood nest temperature (33–36 °C). The average Q₁₀ was 3.13, which is higher than in freshly emerged resting honeybees but similar to adult bees. This strong temperature dependency enables the bees to speed up brood development by achieving high temperatures. On the other hand, the results suggest that the strong temperature dependency forces the bees to maintain thermal homeostasis of the brood nest to avoid delayed brood development during periods of low temperature.Abbreviations m body mass - R rate of development or respiration - T_I inflexion point of a logistic (sigmoid) curve - T_L lethal temperature - T_O temperature of optimum (maximum) developmentCommunicated by G. Heldmaier     

Nitrite uptake by Chlamydomonas reinhardtii cells immobilized in calcium alginate

When an initial cell loading of about 30–40 µg chlorophyll (Chl)·g^–1 gel and alginate suspension of 3% (w/v) were used for immobilization of Chlamydomonas reinhardtii, the resulting cell beads showed optimum nitrite uptake rate, at 30° C and pH 7.5, of 14 µmol NO _inf2 ^sup– ·mg^–1 Chl·h^–1, the photosynthetic and respiratory activities being about 120 µmol O₂ produced·mg^–1 Chl·h^–1, and 40 µmol O₂ consumed ·mg^–1 Chl·h^–1, respectively. The nitrite uptake activity required CO₂ in the culture and persisted after 8 days of cells immobilization, or in the presence of 0.2 mm ammonium in the medium. Our data indicate that alginate-entrapped C, reinhardtii cells may provide a stable and functional system for removing nitrogenous contaminants from waste-waters.Correspondence to: C. Vílchez     

Stimulation of potato tuber respiration by cold stress is associated with an increased capacity of both plant uncoupling mitochondrial protein (PUMP) and alternative oxidase

The CO₂ evolution of intact potato tubers (Solanum tuberosum, L., var. Bintje) was analyzed during a 10-day period of their warm (25 ± 2°C) or cold (5 ± 1°C) storage, to evaluate cold-stress effects on expression and activities of plant uncoupling mitochondrial protein (PUMP) and alternative oxidase (AOX). CO₂ evolution rates were analyzed at 20°C, to reflect their possible capacities. The 20°C CO₂ production declined from 13 to 8 mg kg^–1 h^–1 after 2 days of warm storage and then (after 3 to 7 days) decreased from 8 to 6.5 mg kg^–1 h^–1. In contrast, 20°C CO₂ evolution did not change after the first day of cold storage, increased up to 14.5 mg kg^–1 h^–1 after 2 days, and decreased to about 12 mg kg^–1 h^–1 after 3 to 7 days of cold storage. Cold storage increased PUMP expression as detected by Western blots and led to elevated capacities of both PUMP (44%) and CN-resistant AOX (10 times), but not the cytochrome pathway. Since we found that cold storage led to about the same mitochondrial respiration of 40 nmol O₂ min^–1 mg^–1 attributable to each of the respective proteins, we conclude that both AOX and PUMP equally contribute to adaptation of potato tubers to cold.     

Pyruvate metabolism of the hyperthermophilic archaebacterium Pyrococcus furiosus

The hyperthermophilic anaerobe Pyrococcus furiosus was found to grow on pyruvate as energy and carbon source. Growth was dependent on yeast extract (0.1%). The organism grew with doublings times of about 1 h up to cell densities of 1–2×10⁸ cells/ml. During growth 0.6–0.8 mol acetate and 1.2–1.5 mol CO₂ and 0.8 mol H₂ were formed per mol of pyruvate consumed. The molar growth yield was 10–11 g cells(dry weight)/mol pyruvate. Cell suspensions catalyzed the conversion of 1 mol of pyruvate to 0.6–0.8 mol acetate, 1.2–1.5 mol CO₂, 1.2 mol H₂ and 0.03 mol acetoin. After fermentation of [3-¹⁴C]pyruvate the specific radioactivities of pyruvate, CO₂ and acetate were equal to 1:0.01:1. Cellfree extracts contained the following enzymatic activities: pyruvate: ferredoxin (methyl viologen) oxidoreductase (0.2 U mg^-1, T=60°C, with Clostridium pasteurianum ferredoxin as electron acceptor; 1.4 U mg^-1 at 90°C, with methyl viologen as electron acceptor); acetyl-CoA synthetase (ADP forming) [acetyl-CoA+ADP+Piacetate+ATP+CoA] (0.34 U mg^-1, T=90°C), and hydrogen: methyl viologen oxidoreductase (1.75 U mg^-1). Phosphate acetyl-transferase activity, acetate kinase activity, and carbon monoxide:methyl viologen oxidoreductase activity could not be detected. These findings indicate that the archaebacterium P. furiosus ferments pyruvate to acetate, CO₂ and H₂ involving only three enzymes, a pyruvate:ferredoxin oxidoreductase, a hydrogenase and an acetyl-CoA synthetase (ADP forming).Non-standard abbreviations DTE dithioerythritol - MV methyl viologen - MOPS morpholinopropane sulfonic acid - Tricine N-tris(hydroxymethyl)-methylglycine Part of the work was performed at the Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, Karlvon-Frisch-Strasse, W-3550 Marburg/Lahn, Federal Republic of Germany     

Microbial biomass and nitrogen cycling responses to fertilization and litter removal in young northern hardwood forests

The influence of site fertility on soil microbial biomass and activity is not well understood but is likely to be complex because of interactions with plant responses to nutrient availability. We examined the effects of long-term (8 yr) fertilization and litter removal on forest floor microbial biomass and N and C transformations to test the hypothesis that higher soil resource availability stimulates microbial activity. Microbial biomass and respiration decreased by 20–30 % in response to fertilization. Microbial C averaged 3.8 mg C/g soil in fertilized, 5.8 mg C/g in control, and 5.5 mg C/g in litter removal plots. Microbial respiration was 200 µg CO₂-C g^–1 d^–1 in fertilized plots, compared to 270 µg CO₂-C g^–1 d^–1 in controls. Gross N mineralization and N immobilization did not differ among treatments, despite higher litter nutrient concentrations in fertilized plots and the removal of substantial quantities of C and N in litter removal plots. Net N mineralization was significantly reduced by fertilization. Gross nitrification and NO₃ ^– immobilization both were increased by fertilization. Nitrate thus became a more important part of microbial N cycling in fertilized plots even though NH₄ ⁺ availability was not stimulated by fertilization.Soil microorganisms did not mineralize more C or N in response to fertilization and higher litter quality; instead, results suggest a difference in the physiological status of microbial biomass in fertilized plots that influenced N transformations. Respiration quotients (qCO₂, respiration per unit biomass) were higher in fertilized plots (56 µg CO₂-C mg C^–1 d^–1) than control (48 µg CO₂-C mg C^–1 d ^–1) or litter removal (45 µg CO₂-C mg C^–1 d^–1), corresponding to higher microbial growth efficiency, higher proportions of gross mineralization immobilized, and lower net N mineralization in fertilized plots. While microbial biomass is an important labile nutrient pool, patterns of microbial growth and turnover were distinct from this pool and were more important to microbial function in nitrogen cycling.     

End Products of Anaerobic Chitin Degradation by Salt Marsh Bacteria as Substrates for Dissimilatory Sulfate Reduction and Methanogenesis

The anaerobic pathway of chitin decomposition by chitinoclastic bacteria was examined with an emphasis on end product coupling to other salt marsh bacteria. Actively growing chitinoclastic bacterial isolates produced primarily acetate, H₂, and CO₂ in broth culture. No sulfate-reducing or methanogenic isolates grew on chitin as sole carbon source or produced any measurable degradation products. Mixed cultures of chitin degraders with sulfate reducers resulted in positive sulfide production. Mixed cultures of chitin-degrading isolates with methanogens resulted in the production of CH₄ with reductions in headspace CO₂ and H₂. The combination of all three metabolic types resulted in the simultaneous production of methane and sulfide, with more methane being produced in mixed cultures containing CO₂-reducing methanogens and acetoclastic sulfate reducers because of less interspecific H₂ competition.     

Elevated CO2 effects on carbon and nitrogen cycling in grass/clover turves of a Psammaquent soil

Effects of elevated CO₂ (525 and 700 L L^–1), and a control (350 L L^–1 CO₂), on biochemical properties of a Mollic Psammaquent soil in a well-established pasture of C3 and C4 grasses and clover were investigated with continuously moist turves in growth chambers over four consecutive seasonal temperature regimes from spring to winter inclusive. After a further spring period, half of the turves under 350 and 700 L L^–1 were subjected to summer drying and were then re-wetted before a further autumn period; the remaining turves were kept continuously moist throughout these additional three consecutive seasons. The continuously moist turves were then pulse-labelled with ¹⁴C-CO₂ to follow C pathways in the plant/soil system during 35 days.Growth rates of herbage during the first four seasons averaged 4.6 g m^–2 day^–1 under 700 L L^–1 CO₂ and were about 10% higher than under the other two treatments. Below-ground net productivity at the end of these seasons averaged 465, 800 and 824 g m^–2 in the control, 525 and 700 L L^–1 treatments, respectively.in continuously moist soil, elevated CO₂ had no overall effects on total, extractable or microbial C and N, or invertase activity, but resulted in increased CO₂-C production from soil, and from added herbage during the initial stages of decomposition over 21 days; rates of root decomposition were unaffected. CO₂ produced h^–1 mg^–1 microbial C was about 10% higher in the 700 L L^–1 CO₂ treatment than in the other two treatments. Elevated CO₂ had no clearly defined effects on N availability, or on the net N mineralization of added herbage.In the labelling experiment, relatively more ¹⁴C in the plant/soil system occurred below ground under elevated CO₂, with enhanced turnover of ¹⁴C also being suggested.Drying increased levels of extractable C and organic-N, but decreased mineral-N concentrations; it had no effect on microbial C, but resulted in lowered microbial N in the control only. In soil that had been previously summer-dried, CO₂ production was again higher, but net N mineralization was lower, under elevated CO₂ than in the control after autumn pasture growth.Over the trial period of 422 days, elevated CO₂ generally appears to have had a greater effect on soil C turnover than on soil C pools in this pasture ecosystem.     

Control of carbon mineralization to CH4 and CO2 in anaerobic,Sphagnum-derived peat from Big Run Bog,West Virginia

The mineralization of organic carbon to CH₄ and CO₂ inSphagnum-derived peat from Big Run Bog, West Virginia, was measured at 4 times in the year (February, May, September, and November) using anaerobic, peat-slurry incubations. Rates of both CH₄ production and CO₂ production changed seasonally in surface peat (0–25 cm depth), but were the same on each collection date in deep peat (30–45 cm depth). Methane production in surface peat ranged from 0.2 to 18.8 mol mol(C)^–1 hr^–1 (or 0.07 to 10.4 g(CH₄) g^–1 hr^–1) between the February and September collections, respectively, and was approximately 1 mol mol(C)^–1 hr^–1 in deep peat. Carbon dioxide production in surface peat ranged from 3.2 to 20 mol mol(C)^–1 hr^–1 (or 4.8 to 30.3 g(CO₂) g^–1 hr^–1) between the February and September collections, respectively, and was about 4 mol mol(C)^–1 hr^–1 in deep peat. In surface peat, temperature the master variable controlling the seasonal pattern in CO₂ production, but the rate of CH₄ production still had the lowest values in the February collection even when the peat was incubated at 19°C. The addition of glucose, acetate, and H₂ to the peat-slurry did not stimulate CH₄ production in surface peat, indicating that CH₄ production in the winter was limited by factors other than glucose degradation products. The low rate of carbon mineralization in deep peat was due, in part, to poor chemical quality of the peat, because adding glucose and hydrogen directly stimulated CH₄ production, and CO₂ production to a lesser extent. Acetate was utilized in the peat by methanogens, but became a toxin at low pH values. The addition of SO₄ ^2– to the peat-slurry inhibited CH4 production in surface peat, as expected, but surprisingly increased carbon mineralization through CH4 production in deep peat. Carbon mineralization under anaerobic conditions is of sufficient magnitude to have a major influence on peat accumulation and helps to explain the thin (< 2 m deep), old (> 13,000 yr) peat deposit found in Big Run Bog.     

Turnover and distribution of root exudates of Zea mays

Decomposition and distribution of root exudates of Zea mays L. were studied by means of ¹⁴CO₂ pulse labeling of shoots on a loamy Haplic Luvisol. Plants were grown in two-compartment pots, where the lower part was separated from the roots by monofilament gauze. Root hairs, but not roots, penetrated through the gauze into the lower part of the soil. The root-free soil in the lower compartment was either sterilized with cycloheximide and streptomycin or remained non-sterile. In order to investigate exudate distribution, 3 days after the ¹⁴C labeling, the lower soil part was frozen and sliced into 15, one-mm thick layers using a microtome. Cumulative ¹⁴CO₂ efflux from the soil during the first 3 days after ¹⁴C pulse labeling did not change during plant growth and amounted to about 13–20% of the total recovered ¹⁴C (41–55% of the carbon translocated below ground). Nighttime rate of total CO₂ efflux was 1.5 times lower than during daytime because of tight coupling of exudation with photosynthesis intensity. The average CO₂ efflux from the soil with Zea mays was about 74 g C g^–1 day^–1 (22 g C m^–2 day^–1), although, the contribution of plant roots to the total CO₂ efflux from the soil was about 78%, and only 22% was respired from the soil organic matter. Zea mays transferred about 4 g m^–2 of carbon under ground during 26 days of growth. Three zones of exudate concentrations were identified from the distribution of the ¹⁴C-activity in rhizosphere profiles after two labeling periods: (1) 1–2 (3) mm (maximal concentration of exudates) 2) 3–5 mm (presence of exudates is caused by their diffusion from the zone 1); (3) 6–10 mm (very insignificant amounts of exudates diffused from the previous zones). At the distance further than 10 mm no exudates were found. The calculated coefficient of exudate diffusion in the soil was 1.9 × 10^–7 cm² s^–1.     

The fate of carbon in pulse-labelled crops of barley and wheat

Wheat (cv. Gutha) and barley (cv. O'Connor) were grown as field crops on a shallow duplex soil (sand over clay) in Western Australia with their root systems contained within pvc columns. At four stages during growth, the shoots were pulse-labelled for 1.5h with¹⁴CO₂; immediately prior to labelling, the soil was isolated from the shoot atmosphere by pvc sheets. After labelling, the soil atmosphere was pumped through NaOH to trap respired CO₂ and after 2.5, 5, 7.5 and 24 h from the start of labelling, columns were destructively sampled to recover¹⁴C from the roots, soil and shoot.Both species showed similar patterns of¹⁴C distribution and changes in distribution through the growing season. During early tillering, 15–25% of the¹⁴C recovered after 24 h had been respired by the roots and rhizosphere, 17–27% was retained in the roots, 0.4–1.8% was recovered as water-soluble¹⁴C in the soil and the remainder (45–67%) was present in the shoot. These percentages changed during growth so that during grain filling only 2–3% of the¹⁴C recovered after 24 h was as respired CO₂, 2–6% was in the roots, 0.2% was in the soil and over 90% was in the shoot.The distribution of¹⁴C in components of the soil-plant system changed during the 24 h after labelling with the most rapid changes occurring generally during the first 7.5 h after labelling.Using growth measurements from adjacent plots, the amounts of C added to the soil were estimated for the whole season. Carbon input to the soil was about 48 gC m^–2 for wheat and 58 gC m^–2 for barley; the crops produced total shoot dry matter of 494 (wheat) and 735 g m^–2 (barley). Of the C input to the soil, 27.8% (wheat) and 40.3% (barley) was as respired C and only 3.3 (wheat) and 4.1% (barley) was collected as exudate (water-soluble material).     

Degradation of 14C-labelled poplar wood lignin by selected white-rot fungi

Summary Of eight white-rot fungi examined, seven fungi grew on nitrogen-limited poplar wood meal medium and degraded ¹⁴C-lignin in wood meal to ¹⁴CO₂. Increased oxygen enhanced both the rate and extent of degradation. However, whereas Pleurotus ostreatus, Pycnoporus cinnabarinus 115 and Pycnoporus cinnabarinus A-360 degraded 12–17% of ¹⁴C-(U)-lignin of poplar wood to ¹⁴CO₂ also in an air atmosphere, Sporotrichum pulverulentum, Phlebia radiata 79 and Phanerochaete sordida 37 degraded only 1–5% under these conditions. Addition of cellulose and glucose to the poplar wood medium stimulated degradation of ¹⁴C-(RING)-lignin of poplar wood by Phlebia radiata 79 but repressed degradation by Polyporus versicolor and Pleurotus ostreatus. Cellulose added to the wood meal medium had no effect on the degradation of lignin by Phanerochaete sordida 37 and Sporotrichum pulverulentum but glucose slightly repressed lignin degradation by these fungi. Those white-rot fungi which were considered as preferentially lignin attacking fungi could degrade ¹⁴C-(RING)-lignin of poplar wood efficiently under 100% oxygen. They did not require an extra energy source in addition to wood meal polysaccharides for rapid ring cleavage and they degraded up to 50–60% of the ¹⁴C-lignin to ¹⁴CO₂ in 6–7 weeks at a maximum rate of 3–4% per day.These results were reported in part at the Journées Internationales d'Etudes du Groupe Polyphenols, 29. 9.–1. 10. 1982, Université Paul Sabatier, Toulouse, France     

Glucose and lactate utilization by the amygdala of male and female rats

Gonadal hormones appear to modulate brain energy metabolism, and morphological and functional sexual differences are found in the amygdaloid complex (AC) of rats. Our aim was to study the CO₂ production and lipid synthesis, measured by the rate of L-[U-¹⁴C]lactate or D-[U-¹⁴C]glucose utilization (in pmol.hr^–1.mg^–1), by AC slices in vitro of male and female rats. Lactate was more used than glucose as energy substrate (p < 0.01) but no sex-related difference was observed in glucose or lactate oxidation to CO₂ (p > 0.05) or on lipid synthesis obtained from both substrates (p > 0.05). In addition, there was no effect of the estrous cycle on lactate oxidation to CO₂ by the AC of females (p > 0.05). Based on the present data, it appears that the endogenous normal levels of gonadal hormones are not able to promote sex-related differences in the in vitro glucose or lactate utilization by the AC of rats.     

Anaerobic degradation of phenol via carboxylation to 4-hydroxybenzoate: in vitro study of isotope exchange between 14CO2 and 4-hydroxybenzoate

Extracts of denitrifying bacteria grown anaerobically with phenol and nitrate catalyzed an isotope exchange between ¹⁴CO₂ and the carboxyl group of 4-hydroxybenzoate. This exchange reaction is ascribed to a novel enzyme, phenol carboxylase, initiating the anaerobic degradation of phenol by para-carboxylation to 4-hydroxybenzoate. Some properties of this enzyme were determined by studying the isotope exchange reaction. Phenol carboxylase was rapidly inactivated by oxygen; strictly anoxic conditions were essential for preserving enzyme activity. The exchange reaction specifically was catalyzed with 4-hydroxybenzoate but not with other aromatic acids. Only the carboxyl group was exchanged; [U-¹⁴C]phenol was not exchanged with the aromatic ring of 4-hydroxybenzoate. Exchange activity depended on Mn²⁺ and inorganic phosphate and was not inhibited by avidin. Ortho-phosphate could not be substituted by organic phosphates nor by inorganic anions; arsenate had no effect. The pH optimum was between pH 6.5–7.0. The specific activity was 100 nmol ¹⁴CO₂ exchange · min^-1 · mg^-1 protein. Phenol grown cells contained 4-hydroxybenzoyl CoA synthetase activity (40 nmol · min^-1 · mg^-1 protein). The possible role of phenol carboxylase and 4-hydroxybenzoyl CoA synthetase in anaerobic phenol metabolism is discussed.     

The decomposition of tylosin fermentation waste in soil at four temperatures

Summary Aerobic decomposition of tylosin fermentation waste was studied by O₂ uptake and CO₂, NH₄ ⁺ and NO₃ ^– release over 10 weeks in a light compost-soil at 3 concentrations and 4 temperatures. Comparisons of O₂ uptake and CO₂ release at each temperature showed that aerobic conditions were maintained in the system. Maximal rates of respiration (C mineralization) increased with temperature. At 23°C 50% of the substrate C had been mineralized in 10 weeks. At 10–15°C and at 4°C C mineralization was approximately 38% and 22% respectively. Except at 4°C mineralization had almost ceased within 10 weeks. There was evidence of a permanent inhibition of C mineralization at 10–15°C compared with 23°C, and a temporary inhibition at 10°C compared with 15°C.At 10 weeks 25% of the N had been mineralized at 23, 15 and 10°C, while 14% had been mineralized at 4°C. The time taken to reach maximum N mineralization was reduced by increase in temperature and by 10 weeks mineralization had almost ceased at 15 and 23°C. In terms of the fertilizing effect of tylosin fermentation, 25% of the total N was available within 10 weeks at 10–23°C. Nitrification was strongly inhibited at 4 and 10°C. Both C and N mineralization were in direct proportion to the concentration of tylosin fermentation waste added to the soil.     

Carbon turnover in peatland mesocosms exposed to different water table levels

Changes of water table position influence carbon cycling in peatlands, but effects on the sources and sinks of carbon are difficult to isolate and quantify in field investigations due to seasonal dynamics and covariance of variables. We thus investigated carbon fluxes and dissolved carbon production in peatland mesocosms from two acidic and oligotrophic peatlands under steady state conditions at two different water table positions. Exchange rates and CO₂, CH₄ and DOC production rates were simultaneously determined in the peat from diffusive-advective mass-balances of dissolved CO₂, CH₄ and DOC in the pore water. Incubation experiments were used to quantify potential CO₂, CH₄, and DOC production rates. The carbon turnover in the saturated peat was dominated by the production of DOC (10–15 mmol m^–2 d^–1) with lower rates of DIC (6.1–8.5 mmol m^–2 d^–1) and CH₄ (2.2–4.2 mmol m^–2 d^–1) production. All production rates strongly decreased with depth indicating the importance of fresh plant tissue for dissolved C release. A lower water table decreased area based rates of photosynthesis (24–42%), CH₄ production (factor 2.5–3.5) and emission, increased rates of soil respiration and microbial biomass C, and did not change DOC release. Due to the changes in process rates the C net balance of the mesocosms shifted by 36 mmol m^–2 d^–1. According to our estimates the change in C mineralization contributed most to this change. Anaerobic rates of CO₂ production rates deeper in the peat increased significantly by a factor of 2–3.5 (DOC), 2.9–3.9 (CO₂), and 3–14 (CH₄) when the water table was lowered by 30 cm. This phenomenon might have been caused by easing an inhibiting effect by the accumulation of CO₂ and CH₄ when the water table was at the moss surface.     

Soil C and N responses to woody plant expansion in a mesic grassland

Changes in land management and reductions in fire frequency have contributed to increased cover of woody species in grasslands worldwide. These shifts in plant community composition have the potential to alter ecosystem function, particularly through changes in soil processes and properties. In semi-arid grasslands, the invasion of shrubs and trees is often accompanied by increases in soil resources and more rapid N and C cycling. We assessed the effects of shrub encroachment in a mesic grassland in Kansas (USA) on soil CO₂ flux, extractable inorganic N, and N mineralization beneath shrub communities (Cornus drummondii) and surrounding undisturbed grassland sites. In this study, a shift in plant community composition from grassland to shrubland resulted in a 16% decrease in annual soil CO₂ flux(4.78 kg CO₂ m^–2 year^–1 for shrub dominated sites versus 5.84 kg CO₂ m^–2 year^–1 for grassland sites) with no differences in total soil C or N or inorganic N. There was considerable variability in N mineralization rates within sites, which resulted in no overall difference in cumulative N mineralized during this study (4.09 g N m^–2 for grassland sites and 3.03 g N m^–2 for shrub islands). These results indicate that shrub encroachment into mesic grasslands does not significantly alter N availability (at least initially), but does alter C cycling by decreasing soil CO₂ flux.     

The kinetics of the degradation of chloroform and benzene in anaerobic sediment from the River Rhine

In anaerobic methanogenic sediment microcosms¹⁴C labelled chloroform was degraded mainly to carbon dioxide. At a concentration of 4 g.l^–1 the mineralization followed first order kinetics with a half life of 12 days at 10°C and 2.6 days at 20°C. At a concentration of 400 g.l^–1 the mineralization rate increased with time and followed logarithmic kinetics with a _max of 0.02.d^–1 at 10°C. The logarithmic kinetics can be explained by growth of the bacteria on the higher concentration of chloroform with a generation time of 35 days. Shaking and oxygenation did not inhibit the mineralization of chloroform, probably because of bacterial consumption of the dissolved oxygen. ¹⁴C labelled benzene was mineralized only for a small percentage to¹⁴C labelled carbon dioxide while other, not acid extractable, degradation products were formed. Under anaerobic conditions after one day when 5% of the benzene was degraded to carbon dioxide, the mineralization ceased, while the disappearance of benzene proceeded. With air in the headspace of the incubation bottles 25% of the benzene was mineralized to carbon dioxide. The anaerobic degradation of benzene at a concentration of 100 .l^–1 showed similar kinetics as the degradation at 1 g.l^–1. Hence no adaptation of the microflora in the sediment occurred during the 63 days of the experiment at 100 g.l^–1.     

Net nitrogen mineralization,nitrification and CO2 production in alternating moisture conditions in an unfertilized low-humus sandy soil from the Sahel

In this study the rates of net mineralization, net immobilization and net nitrification have been quantified under laboratory conditions in a sandy low-humus soil from a semi-arid region, in absence of plant growth. Incubation experiments were carried out under constant humidity and under alternating wet and dry conditions to simulate field conditions during the rainy season. The ammonium and nitrate content of the incubates were determined and their CO₂ production measured.The rate of net mineralization at field capacity was 0.6 kg N ha^–1d^–1 during the first 40 days and decreased to 0.06 kg N ha^–1d^–1 after 400 days. This rate was twice as high on wet days under alternating wet and dry conditions. The rate of net nitrification during alternating wet and dry conditions was also higher (1.9 kg N ha^–1d^–1) than at constant field capacity (1.3 kg N ha^–1d^–1) until the ammonium was almost completely depleted. These rates of net mineralization and net nitrification are in agreement with field observations.Net immobilization did not occur in the experiments, unless glucose was added to the soil.The data on CO₂ production and net mineralization showed that the C/N ratio of the degraded material was around 9 or below. It is much lower than the ratio of total carbon over total nitrogen in the soil. This indicates that microorganisms and compounds high in nitrogen were mineralized. Certainly after about 30 days the only growth taking place is based on turnover of material of the microbial biomass itself.A decrease in the amount of inorganic nitrogen was observed upon drying of the soil, while it returned to the original content after rewetting. It is postulated that this might be due to temporary uptake of nitrogen in an inorganic form in microorganisms as part of their osmoregulation.