Absorption microphotometry of irregular-shaped objects

Summary A new microphotometric method (mainly for the evaluation of microchemical color reactions) which uses measurements at two wave lengths (developed byOrnstein and, independently, by the author) is presented in a form which greatly reduces the computational labor (for an illustration, see Table 3).Contribution from the Program in Cytology, Department of Botany, University of Wisconsin, Madison, supported in part by grants to Dr.C. Leonard huskins from the Research Committee of the Graduate School with funds supplied by the Wisconsin Alumni Research Foundation.     

The Effects of Gibberellin4+7 on the Vase Life and Flower Quality of Alstroemeria Cut Flowers

Leaf yellowing is a major problem in Alstroemeria and absence of leaf senescence symptoms is an important quality attribute. Two Alstroemeria cultivars ‘Yellow King’ and ‘Marina’ were sourced from a commercial farm and harvested when sepals began to reflex. Stems were re-cut under water and kept in vase solutions of gibberellin A₄₊₇ (0, 2.5, 5.0, 7.5, 10.0, 12.5 or 15.0 mg l⁻¹ [Provide^r]). Treatments and cultivars were combined in a factorial fashion and arranged in a completely randomised design. Application of GA₄₊₇ in the holding solution at 2.5–10.0 mg l⁻¹ significantly delayed the onset of leaf senescence by around 7 days and significantly increased days to 50% petal fall by ca. 2 days. Additionally, these GA₄₊₇ concentrations resulted in higher retention of leaf nitrogen, leaf chlorophyll and also increased leaf water content, while reducing leaf dry weight, all relative to untreated controls. Cultivar ‘Yellow King’ had significantly longer vase life and a better retention of leaf quality than ‘Marina’. Our results suggest that a concentration of 10 mg l⁻¹ GA₄₊₇ can be used to prolong vase life, delay leaf senescence and enhance post-harvest quality of Alstroemeria cut flowers during their transport to market.     

Chiral resolution of phenylalanine by d-Phe imprinted membrane considering rejection property

An enantio-selective d-Phe imprinted P(AA-co-AN) membrane was prepared using the wet-phase inversion method. The membrane not only selectively adsorbed phenylalanine but also rejected it with a rejection selectivity of 0.82–0.64 and 0.91–0.63 during the filtration of 100 and 10 ppm (g m⁻³) racemate solutions, respectively. The fluxes of d-Phe and l-Phe during filtration of 10 ppm racemate solution were 0.0077–0.0229 and 0.0064–0.0208 mg m⁻² s⁻¹, respectively, and the fluxes of d-Phe and l-Phe during filtration of 100 ppm racemate solution were 0.1287–0.2522 and 0.1174–0.2458 mg m⁻² s⁻¹, respectively. The adsorption selectivity was higher at low concentration. The adsorption selectivities varied from 1.11 to 1.65 and from 1.64 to 2.78 during filtration of 100 and 10 ppm racemate solutions, respectively. In respect to desorption, the fractional difference between d-Phe and l-Phe in the recovered solution from 10 ppm was higher than that from 100 ppm.     

Regulation of Cell Volume by β2-adrenergic Stimulation in Rat Fetal Distal Lung Epithelial Cells

Cell-volume changes induced by terbutaline (a specific β₂-agonist) were studied morphometrically in rat fetal distal lung epithelium (FDLE) cells. Cell-volume changes qualitatively differed with the concentration of terbutaline. Terbutaline of 10⁻¹⁰–10⁻⁸ m induced transient cell swelling. Terbutaline of 10⁻⁷ m induced transient cell swelling followed by slow cell shrinkage. Terbutaline of 10⁻⁶–10⁻⁵ m induced rapid cell shrinkage followed by slow cell shrinkage. Terbutaline of 10⁻³ m induced transient cell shrinkage; then cell volume oscillated during stimulation. Benzamil of 10⁻⁶ m suppressed the cell swelling induced by 10⁻¹⁰–10⁻⁸ m terbutaline and quinine of 10⁻³ m inhibited the cell shrinkage induced by 10⁻⁶–10⁻⁵ m terbutaline. These results suggest that cell swelling would be induced by NaCl influx and the cell shrinkage is by KCl efflux. Dibutyryl cyclic AMP (DBcAMP) also induced similar cell-volume changes over a wide range of concentrations (10⁻⁹–10⁻³ m): a low concentration induced transient cell swelling; a high concentration, rapid and slow cell shrinkage. Forskolin (10⁻⁴ m), like terbutaline (10⁻⁵ m), induced rapid cell shrinkage followed by slow cell shrinkage, and this decrease in the cell volume was enhanced by the presence of benzamil. On the other hand, cell shrinkage was induced by ionomycin (even low concentration; 3 × 10⁻¹⁰ m ionomycin), and after that cell volume remained at a plateau level. Removal of extracellular Ca²⁺ abolished the cell swelling caused by terbutaline of 10⁻¹⁰–10⁻⁸ m. With removal of extracellular Ca²⁺, the initial, rapid cell shrinkage induced by 10⁻⁵ m terbutaline became transient, but we still detected slow cell shrinkage similar to that in the presence of extracellular Ca²⁺. Overall, at low concentrations (10⁻¹⁰–10⁻⁸ m), terbutaline induced benzamil-sensitive cell swelling in FDLE cells, which was cAMP- and Ca²⁺-dependent; high concentrations (≥⁻⁶) induced quinine-sensitive rapid cell shrinkage, which was Ca²⁺-dependent; high concentrations (≥⁻⁷) induced slow cell shrinkage, which was cAMP-dependent. These findings suggest that terbutaline regulates cell volume in FDLE cells by cytosolic cAMP and Ca²⁺ through activation of Na⁺ and K⁺ channels. Received: 13 March 1995/Revised: 17 January 1996     

Simultaneous utilization of D-cellobiose, D-glucose, and D-xylose by recombinant Corynebacterium glutamicum under oxygen-deprived conditions

Corynebacterium glutamicum R was metabolically engineered to broaden its sugar utilization range to d-xylose and d-cellobiose contained in lignocellulose hydrolysates. The resultant recombinants expressed Escherichia coli xylA and xylB genes, encoding d-xylose isomerase and xylulokinase, respectively, for d-xylose utilization and expressed C. glutamicum R bglF ^317A and bglA genes, encoding phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) β-glucoside-specific enzyme IIBCA component and phospho-β-glucosidase, respectively, for d-cellobiose utilization. The genes were fused to the non-essential genomic regions distributed around the C. glutamicum R chromosome and were under the control of their respective constitutive promoter trc and tac that permitted their expression even in the presence of d-glucose. The enzyme activities of resulting recombinants increased with the increase in the number of respective integrated genes. Maximal sugar utilization was realized with strain X5C1 harboring five xylA–xylB clusters and one bglF ^317A –bglA cluster. In both d-cellobiose and d-xylose utilization, the sugar consumption rates by genomic DNA-integrated strain were faster than those by plasmid-bearing strain, respectively. In mineral medium containing 40 g l⁻¹ d-glucose, 20 g l⁻¹ d-xylose, and 10 g l⁻¹ d-cellobiose, strain X5C1 simultaneously and completely consumed these sugars within 12 h and produced predominantly lactic and succinic acids under growth-arrested conditions.     

Olfactory sensitivity to amino acids in the blackspot sea bream (<Emphasis Type="Italic">Pagellus bogaraveo</Emphasis>): a comparison between olfactory receptor recording techniques in seawater

The current study investigated the olfactory sensitivity of the blackspot sea bream to amino acids, odorants associated with food detection in fish, and compared the efficacy of two different experimental methods: multi-unit recording from the olfactory nerve and the electro-olfactogram (EOG). Twenty essential amino acids plus l-DOPA evoked clear, concentration-dependent olfactory responses using both methods, with estimated thresholds of 10^−8.5–10^−6.2 M (nerve recording) and 10^−7.5–10^−4.8 M (EOG). The most potent amino acids were l-cysteine, l-methionine (both sulphur-containing), l-alanine, l-leucine (both neutral), l-glutamine (amide-containing) and l-serine (hydroxyl-containing). The least potent were l-proline (secondary α-amino group), the aromatic amino acids and glycine (simplest). Although the rank order of olfactory potency was similar for the two methods used, and the calculated thresholds given by the two methods were positively correlated, the sensitivity of the EOG was consistently lower than multi-unit recording by approximately one order of magnitude, presumably due to the electrical shunting effect of seawater. As in freshwater, the EOG could be a valid method for comparing olfactory potency of different odorants in stenohaline marine fish; however, for absolute ‘biological’ thresholds, a more invasive recording technique, such as multi-unit recording from the olfactory nerve, should be used.     

Bioconversion of L-tyrosine to L-DOPA by a novel bacterium Bacillus sp. JPJ

l-DOPA is an amino acid derivative and most potent drug used against Parkinson’s disease, generally obtained from Mucuna pruriens seeds. In present communication, we have studied the in vitro production of l-DOPA from l-tyrosine by novel bacterium Bacillus sp. JPJ. This bacterium produced 99.4% of l-DOPA from l-tyrosine in buffer (pH 8) containing 1 mg ml⁻¹ cell mass incubated at 40°C for 60 min. The combination of CuSO₄ and l-ascorbic acid showed the inducing effect at concentrations of 0.06 and 0.04 mg ml⁻¹, respectively. The activated charcoal 2 mg ml⁻¹ was essential for maximum bioconversion of l-tyrosine to l-DOPA and the crude tyrosinase activity was 2.7 U mg⁻¹ of tyrosinase. Kinetic studies showed significant values of Y _p/s (0.994), Q _s (0.500) and q _s (0.994) after optimization of the process. The production of l-DOPA was confirmed by analytical techniques such as HPTLC, HPLC and GC–MS. This is the first report on rapid and efficient production of l-DOPA from l-tyrosine by bacterial source which is more effective than the plant, fungal and yeast systems.     

Elevated [CO2], temperature increase and N supply effects on the turnover of below-ground carbon in a temperate grassland ecosystem

The effects of elevated [CO₂] (700 μl l^-1 CO₂) and temperature increase (+3 °C) on carbon turnover in grassland soils were studied during 2.5 years at two N fertiliser supplies (160 and 530 kg N ha^-1 y^-1) in an experiment with well-established ryegrass swards (Lolium perenne) supplied with the same amounts of irrigation water. During the growing season, swards from the control climate (350 μl l^-1 [CO₂] at outdoor air temperature) were pulse labelled by the addition of ¹³CO₂. The elevated [CO₂] treatments were continuously labelled by the addition of fossil-fuel derived CO₂ (^{13 C} of -40 to -50 ‰). Prior to the start of the experimental treatments, the carbon accumulated in the plant parts and in the soil macro-organic matter (‘old’ C) was at −32‰. During the experiment, the carbon fixed in the plant material (‘new’ C) was at −14 and −54‰ in the ambient and elevated [CO₂] treatments, respectively. During the experiment, the ¹³C isotopic mass balance method was used to calculate, for the top soil (0–15 cm), the carbon turnover in the stubble and roots and in the soil macro-organic matter above 200 μ (MOM). Elevated [CO₂] stimulated the turnover of organic carbon in the roots and stubble and in the MOM at N+, but not at N−. At the high N supply, the mean replacement time of ‘old’ C by ‘new’ C declined in elevated, compared to ambient [CO₂], from 18 to 7 months for the roots and stubble and from 25 to 17 months for the MOM. This resulted from increased rates of ‘new’ C accumulation and of ‘old’ C decay. By contrast, at the low N supply, despite an increase in the rate of accumulation of ‘new’ C, the soil C pools did not turnover faster in elevated [CO₂], as the rate of ‘old’ C decomposition was reduced. A 3 °C temperature increase in elevated [CO₂] decreased the input of fresh C to the roots and stubble and enhanced significantly the exponential rate for the ‘old’ C decomposition in the roots and stubble. An increased fertiliser N supply reduced the carbon turnover in the roots and stubble and in the MOM, in ambient but not in elevated [CO₂]. The respective roles for carbon turnover in the coarse soil OM fractions, of the C:N ratio of the litter, of the inorganic N availability and of a possible priming effect between C-substrates are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Energy recovery from energy rich vegetable products with microbial fuel cells

Two types of rapidly biodegradable vegetable products (the liquid fraction of clover and the glycerol-containing sidestream from biodiesel production) were selected for anodic oxidation in microbial fuel cells (MFC) equipped with a biocathode. As benchmark references, five abundant amino-acids in plant sap (l-glutamine, l-glutamic acid, l-asparagine, l-aspartic acid and l-alanine) were tested separately. Their performance was in the same order of magnitude of clover sap oxidation (145–225 A m⁻³ MFC; 39–95 W m⁻³ MFC). Glycerol oxidation resulted in competitive current and power outputs (111 A m⁻³ MFC; 23 W m⁻³ MFC).     

Biomass carbon stocks in China’s forests between 2000 and 2050: A prediction based on forest biomass-age relationships

China’s forests are characterized by young forest age, low carbon density and a large area of planted forests, and thus have high potential to act as carbon sinks in the future. Using China’s national forest inventory data during 1994–1998 and 1999–2003, and direct field measurements, we investigated the relationships between forest biomass density and forest age for 36 major forest types. Statistical approaches and the predicted future forest area from the national forestry development plan were applied to estimate the potential of forest biomass carbon storage in China during 2000–2050. Under an assumption of continuous natural forest growth, China’s existing forest biomass carbon (C) stock would increase from 5.86 Pg C (1 Pg=10¹⁵ g) in 1999–2003 to 10.23 Pg C in 2050, resulting in a total increase of 4.37 Pg C. Newly planted forests through afforestation and reforestation will sequestrate an additional 2.86 Pg C in biomass. Overall, China’s forests will potentially act as a carbon sink for 7.23 Pg C during the period 2000–2050, with an average carbon sink of 0.14 Pg C yr⁻¹. This suggests that China’s forests will be a significant carbon sink in the next 50 years.     

Production of d-hydantoinase by halophilic Pseudomonas sp. NCIM 5109

About 1000 bacterial colonies isolated from sea water were screened for their ability to convert dl-5-phenylhydantoin to d(−)N-carbamoylphenylglycine as a criterion for the determination of hydantoinase activity. The strain M-1, out of 11 hydantoinase-producing strains, exhibited the maximum ability to convert dl-5-phenylhydantoin to d(−)N-carbamoylphenylglycine. The strain M-1 appeared to be a halophilic Pseudomonas sp. according to morphological and physiological characteristics. Optimization of the growth parameters revealed that nutrient broth with 2% NaCl was the preferred medium for both biomass and enzyme production. d-Hydantoinase of strain M-1 was not found to be inducible by the addition of uracil, dihydrouracil, β-alanine etc. The optimum temperature for enzyme production was about 25 °C and the organism showed a broad pH optimum (pH 6.5–9.0) for both biomass and hydantoinase production. The organism seems to have a strict requirement of NaCl for both growth and enzyme production. The optimum pH and temperature of enzyme activity were 9–9.5 and 30 °C respectively. The biotransformation under the alkaline conditions allowed the conversion of 80 g l⁻¹ dl-5-phenylhydantoin to 82 g l⁻¹ d(−)N-carbamoylphenylglycine within 24 h with a molar yield of 93%. Received: 15 September 1997 / Received revision: 5 January 1998 / Accepted: 6 January 1998     

High-level expression of a truncated 1,3-1,4-β-<Emphasis Type="SmallCaps">d</Emphasis>-glucanase from <Emphasis Type="Italic">Fibrobacter succinogenes</Emphasis> in <Emphasis Type="Italic">Pichia pastoris</Emphasis> by optimization of codons and fermentation

1,3-1,4-β-d-glucanase is an important endoglycosidase in the brewing and animal feed industries. To achieve high-level expression of recombinant glucanase in Pichia pastoris, we designed sequences encoding the α-factor signal peptide from Saccharomyces cerevisiae and the truncated 1,3-1,4-β-d-glucanase from Fibrobacter succinogenes as a whole. The codons encoding the 52 amino acids of the signal peptide and 106 residues of the glucanase protein were optimized for expression in P. pastoris; 189 nucleotides were changed. The G + C content was adjusted to 48–49%, and AT-rich stretches were eliminated to avoid premature termination. The messenger ribonucleic acid secondary structure near the AUG start codon was also adjusted to ensure efficient translation; the resulting glucanase production was twofold higher compared with that achieved with gene structure optimization alone. We also propose a new fermentation strategy for the induction phase, in which 5/95% glycerol/methanol mixed feed was used in days 1–3 and 100% methanol was used on days 4–6. By comparison with methanol feed and glycerol/methanol-mixed feed alone, the yield of recombinant glucanase increased by 38.5 and 16.5%, respectively. The expressed optimized recombinant 1,3-1,4-β-d-glucanase constituted ~90% of the total secreted protein, reaching up to 3 g l⁻¹ in the medium.     

Production of <Emphasis Type="SmallCaps">l</Emphasis>-phenylalanine from glycerol by a recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis>

The production of l-phenylalanine is conventionally carried out by fermentations that use glucose or sucrose as the carbon source. This work reports on the use of glycerol as an inexpensive and abundant sole carbon source for producing l-phenylalanine using the genetically modified bacterium Escherichia coli BL21(DE3). Fermentations were carried out at 37°C, pH 7.4, using a defined medium in a stirred tank bioreactor at various intensities of impeller agitation speeds (300–500 rpm corresponding to 0.97–1.62 m s⁻¹ impeller tip speed) and aeration rates (2–8 L min⁻¹, or 1–4 vvm). This highly aerobic fermentation required a good supply of oxygen, but intense agitation (impeller tip speed ~1.62 m s⁻¹) reduced the biomass and l-phenylalanine productivity, possibly because of shear sensitivity of the recombinant bacterium. Production of l-phenylalanine was apparently strongly associated with growth. Under the best operating conditions (1.30 m s⁻¹ impeller tip speed, 4 vvm aeration rate), the yield of l-phenylalanine on glycerol was 0.58 g g⁻¹, or more than twice the best yield attainable on sucrose (0.25 g g⁻¹). In the best case, the peak concentration of l-phenylalanine was 5.6 g L⁻¹, or comparable to values attained in batch fermentations that use glucose or sucrose. The use of glycerol for the commercial production of l-phenylalanine with E. coli BL21(DE3) has the potential to substantially reduce the cost of production compared to sucrose- and glucose-based fermentations.     

Efficient micropropagation of Robinia ambigua var. idahoensis (Idaho Locust) and detection of genomic variation by ISSR markers

Robinia ambigua var. idahoensis, presumably originated from interspecific hybridization of R. pseudoacacia L. and R. hispida L., is a multipurpose tree. Several reports have showed that in vitro micropropagation is a feasible method to produce large quantities of ‘clonal’ plants from R. pseudoacacia, however, no information is available on micropropagation of R. ambigua or the other assumed parental species, R. hispida. Here, we report on a tissue culture system for efficient micropropagation of R. ambigua plants by enhanced branching of axillary buds taken from a single branch of a donor tree. The culture system consists of sequential use of three media, namely, the bud-induction medium (MS medium supplemented with 0.8–1.4 mg l⁻¹ 6-BA, 0.05–0.08 mg l⁻¹ NAA and 0.07–0.1 mg l⁻¹ GA), elongation medium (MS medium added with 0.35–0.5 mg l⁻¹ 6-BA, 0.05–0.08 mg l⁻¹ NAA and 0.07–0.1 mg l⁻¹ GA) and root-induction medium (1/4 MS medium fortified with 1.7–2.5 mg l⁻¹ IAA and 0.1–0.5 mg l⁻¹ IBA). In addition, we investigated the genetic stability (relative to the donor plant) of a sample of 41 morphologically normal plants randomly taken from ca. 13,000 micropropagated plants, by using the inter-simple sequence repeat (ISSR) marker with 32 selected primers. We found that of the 226 reproducible bands scored, 24 were polymorphic (10.62%), thus pointing to the occurrence, though at a relatively low level compared with an earlier study on R. pseudoacacia, of genomic variation in these micropropagated plants. Further sequencing on seven loci underlying the variations showed that two had significant homology to known or predicted plant genes.     

Engineering <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis> for the production of pyruvate

A Corynebacterium glutamicum strain with inactivated pyruvate dehydrogenase complex and a deletion of the gene encoding the pyruvate:quinone oxidoreductase produces about 19 mM l-valine, 28 mM l-alanine and about 55 mM pyruvate from 150 mM glucose. Based on this double mutant C. glutamicum △aceE △pqo, we engineered C. glutamicum for efficient production of pyruvate from glucose by additional deletion of the ldhA gene encoding NAD⁺-dependent l-lactate dehydrogenase (LdhA) and introduction of a attenuated variant of the acetohydroxyacid synthase (△C–T IlvN). The latter modification abolished overflow metabolism towards l-valine and shifted the product spectrum to pyruvate production. In shake flasks, the resulting strain C. glutamicum △aceE △pqo △ldhA △C–T ilvN produced about 190 mM pyruvate with a Y _P/S of 1.36 mol per mol of glucose; however, it still secreted significant amounts of l-alanine. Additional deletion of genes encoding the transaminases AlaT and AvtA reduced l-alanine formation by about 50%. In fed-batch fermentations at high cell densities with adjusted oxygen supply during growth and production (0–5% dissolved oxygen), the newly constructed strain C. glutamicum △aceE △pqo △ldhA △C–T ilvN △alaT △avtA produced more than 500 mM pyruvate with a maximum yield of 0.97 mol per mole of glucose and a productivity of 0.92 mmol g_(CDW)⁻¹ h⁻¹ (i.e., 0.08 g g_(CDW) ⁻¹ h⁻¹) in the production phase.     

High frequency embryogenesis in immature zygotic embryos of sunflower

In the present investigation, nutritional requirements for induction of a high frequency of well formed somatic embryos (SEs) from zygotic embryos (ZEs) of sunflower were assessed. Variables like genotype, embryo size (0.5–10 mm), sucrose concentration (30–240 g l⁻¹), carbohydrate source (sucrose, glucose, maltose), agar strength (0.2–1.0%), basal media (MS, Gamborg, Nitsch, White), photoperiod (light/dark) and temperature (20–36°C) were tested. All these variables except photoperiod had significant effect on the frequency of embryogenesis. Highest frequency of embryogenesis was facilitated by Gamborg basal salt media, 120–210 g l⁻¹ sucrose, 0.8–1.0% agar, smaller sized embryos (0.5–2 mm) and incubation temperature of 28–32°C. In addition to these, growth regulator combinations (2,4-D, 2,4-D+kinetin, BA+NAA) in varying concentrations were tried. Media supplemented with 2,4-D promoted direct embryogenesis, BA+NAA facilitated formation of single/multiple shoots while there was no response on 2,4-D+kinetin supplemented media. Zygotic embryos with well differentiated embryos were transferred to growth regulator free half strength MS medium for whole plantlet development. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ethanol fermentation of mixed-sugars using a two-phase, fed-batch process: method to minimize D-glucose repression of Candida shehatae D-xylose fermentations

Candida shehatae cells pre-grown on D-xylose simultaneously consumed mixtures of D-xylose and D-glucose, under both non-growing (anoxic) and actively growing conditions (aerobic), to produce ethanol. The rate of D-glucose consumption was independent of the D-xylose concentration for cells induced on D-xylose. However, the D-xylose consumption rate was approximately three times lower than the D-glucose consumption rate at a 50% D-glucose: 50% D-xylose mixture. Repression was not observed (substrate utilization rates were approximately equal) when the percentage of D-glucose and D-xylose was changed to 22% and 78%, respectively. In fermentations with actively growing cells (50% glucose and D-xylose), ethanol yields from D-xylose increased, the % D-xylose utilized increased, and the xylitol yield was significantly reduced in the presence of D-glucose, compared to anoxic fermentations (Y_ETOH,xylose = 0.2–0.40 g g⁻¹, 75–100%, and Y_xylitol = 0–0.2 g g⁻¹ compared to Y_ETOH,xylose = 0.15 g g⁻¹, 56%, Y_xylitol = 0.51 g g⁻¹, respectively). To increase ethanol levels and reduce process time, fed-batch fermentations were performed in a single stage reactor employing two phases: (1) rapid aerobic growth on D-xylose (μ = 0.32 h⁻¹) to high cell densities; (2) D-glucose addition and anaerobic conditions to produce ethanol (Y_ETOH,xylose = 0.23 g g⁻¹). The process generated high cell densities, 2 × 10⁹ cells ml⁻¹, and produced 45–50 g L⁻¹ ethanol within 50 h from a mixture of D-glucose and D-xylose (compared to 30 g L⁻¹ in 80 h in the best batch process). The two-phase process minimized loss of cell viability, increased D-xylose utilization, reduced process time, and increased final ethanol levels compared to the batch process. Received 23 February 1998/ Accepted in revised form 15 July 1998     

Overgrazing and soil carbon dynamics in eastern Inner Mongolia of China

Eastern Inner Mongolia of China is a typical ecotone between sandy forests and steppe. Little is known about the effect of overgrazing on carbon loss from soil in semiarid steppe and sandy forests of the north of China. The soil carbon parameters were measured in a 10,000 ha natural reserve in eastern Inner Mongolia of China (43°30′–43°36′N, 117°06′–117°16′E). Three situations were compared: primary protected (PP), moderately protected (MP) and highly degraded (HD). Soil and litter samples were recovered in spring and summer. Soil organic carbon (SOC) and CO₂–C values decreased from the PP (9.23 kg m⁻² and 157 g m⁻²) to the HD (1.69 kg m⁻² and 57 g m⁻²) sites whereas the C mineralization rate increased toward the less restored sites (1.06–2.37). Surface-litter C was different in both sites under protection (PP 648 and MP 408 g m⁻²), an was low at the HD site (17 g m⁻²). Leaves from woody species dominated the surface litter at the PP site, whereas grass material was predominant at the MP site. During summer, both CO₂–C and SOC decreased, whereas the C mineralization rate increased. We calculated that C loss since the introduction of cattle into the forest was 77 M g ha⁻¹, reaching a total of 1.1×10¹⁵ g for eastern Inner Mongolia. These values are higher than those caused by the conversion of steppe and other ecosystems into agriculture or cultivated pastures. The amount of C fixed at the PP site (650 g ha⁻¹year⁻¹) indicates that the sandy soils have a significant potential as atmospheric carbon sinks. Foundation item: The National Natural Science Foundation of China (No. 39900019, 30070129).     

Simultaneous utilization of glucose and D-xylose by Candida shehatae in a chemostat

The kinetics of biomass formation, D-xylose utilization, and mixed substrate utilization were determined in a chemostat using the yeast Candida shehatae. The maximum growth rate of C. shehatae grown aerobically on D-xylose was 0.42 h⁻¹ and the Monod constant, K _s, was 0.06 g L⁻¹. The biomass yield, Y _{X/S}, ranged from 0.40 to 0.50 g g⁻¹ over a dilution rate range of 0.2–0.3 h⁻¹, when C. shehatae was grown on pure D-xylose. Mixtures of D-xylose and glucose (∼1 : 1) were simultaneously utilized over a dilution rate from 0.15 to 0.35 h⁻¹ at pH 3.5 and 4.5, but pH 3.5 reduced μ_max and reduced the dilution rate range over which D-xylose was utilized in the presence of glucose. At pH 4.5, μ_max was not reduced with the mixed sugar feed and the overall or lumped K _s value was not significantly increased (0.058 g L⁻¹ vs 0.06 g L⁻¹), when compared to a pure D-xylose feed. Kinetic data indicate that C. shehatae is an excellent candidate for chemostat production of value added products from renewable carbon sources, since simultaneous mixed substrate utilization was observed over a wide range of growth rates on a 1 : 1 mixture of glucose and D-xylose. Received 21 August 1997/ Accepted in revised form 28 May 1998     

Measurements and Modeling of Carbon and Nitrogen Cycling in Agroecosystems of Southern Wisconsin: Potential for SOC Sequestration during the Next 50 Years

Landmanagement practices such as no-tillage agriculture and tallgrass prairie restoration have been proposed as a possible means to sequester atmospheric carbon, helping to refurbish soil fertility and replenish organic matter lost as a result of previous agricultural management practices. However, the relationship between land-use changes and ecosystem structure and functioning is not yet understood. We studied soil and vegetation properties over a 4-year period (1995–98), and assembled measurements of microbial biomass, soil organic carbon (SOC) and nitrogen (N), N-mineralization, soil surface carbon dioxide (CO₂) flux, and leached C and N in managed (maize; Zea mays L.) and natural (prairie) ecosystems near the University of Wisconsin Agricultural Research Station at Arlington. Field data show that different management practices (tillage and fertilization) and ecosystem type (prairie vs maize) have a profound influence on biogeochemistry and water budgets between sites. These measurements were used in conjunction with a dynamic terrestrial ecosystem model, called IBIS (the Integrated Biosphere Simulator), to examine the long-term effects of land-use changes on biogeochemical cycling. Field data and modeling suggest that agricultural land management near Arlington between 1860 and 1950 caused SOC to be depleted by as much as 63% (native SOC approximately 25.1 kg C m⁻²). Reductions in N-mineralization and microbial biomass were also observed. Although IBIS simulations depict SOC recovery in no-tillage maize since the 1950s and also in the Arlington prairie since its restoration was initiated in 1976, field data suggest otherwise for the prairie. This restoration appears to have done little to increase SOC over the past 24 years. Measurements show that this prairie contained between 28% and 42% less SOC (in the top 1 m) than the no-tillage maize plots and 40%–47% less than simulated potential SOC for the site in 1999. Because IBIS simulates competition between C3 and C4 grass species, we hypothesized that current restored prairies, which include many forbs not characterized by the model, could be less capable of sequestering C than agricultural land planted entirely in monocultural grass in this region. Model output and field measurements show a potential 0.4 kg C m⁻² y⁻¹ difference in prairie net primary production (NPP). This study indicates that high-productivity C4 grasslands (NPP = 0.63 kg C m⁻² y⁻¹) and high-yield maize agroecosystems (10 Mg ha⁻¹) have the potential to sequester C at a rate of 74.5 g C m⁻² y⁻¹ and 86.3 g C m⁻² y⁻¹, respectively, during the next 50 years across southern Wisconsin. Received 28 December 1999; accepted 11 December 2000.