Application of a membrane recycle bioreactor for continuous ethanol production

Summary A series of continuous fermentations were carried out with a production strain of the yeast Saccharomyces cerevisiae in a membrane bioreactor. A membrane separation module composed of ultrafiltration tubular membranes retained all biomass in a fermentation zone of the bioreactor and allowed continuous removal of fermentation products into a cell-free permeate. In a system with total (100%) cell recycle the impact of fermentation conditions [dilution rate (0.03–0.3 h^–1); substrate concentration in the feed (50–300 g·1^–1); biomass concentration (depending on the experimental conditions)] was studied on the behaviour of the immobilized cell population and on ethanol formation. Maximum ethanol productivity (15 g·1^–1·h^–1) was attained at an ethanol concentration of 81 g·1^–1. The highest demands of cells for maintenance energy were found at the maximum feed substrate concentration (300 g·1^–1) and at very low concentrations of cells in the broth.     

New cell recycle ethanol fermentation with periodic cleaning of filter with gas

High ethanol productivities were obtained by cell recycle cultures of yeast and bacterial strains at a dry cell concentration of 200 kg cells m^–3 using a new membrane bioreactor system. The filtration rates of the cultures were stabilized by removing the microbial cake on the filter with periodic back flows of the fermentation gas through the filter. For instance, the filtration flux of 0.023 m³m^–2h^–1 was maintained for 30 h with the periodic cleaning of the filter, whereas it decreased at a half time of 2 h without the cleaning. Ethanol productivity, ethanol concentration and filtration flux attained were: 68.7 kg/(m³ · h), 62.7 kg/m³ and 0.029 m³m^–2h^–1 for Saccharomyces carlsbergensis, LAM1068, the respective values for Zymomonas mobilis, ZM4, were: 93.7, 33 5 and 0.074.     

Suspension feeding in Bithynia tentaculata (Prosobranchia,Bithyniidae), as affected by body size,food and temperature

The suspension feeding of Bithynia tentaculata was tested in laboratory experiments. The animals were fed in 1-1 aerated glass beakers, and filtration rates were calculated from changes in cell concentrations during the 6-h experiment. Temperature influenced the filtering rate, with minimum values of 5ml · ind^–1 · h^–1 at 5° C and maxima of 17.2 ml · ind^–1 · h^–1 at 18° C. Three food species of different size, motility and cell surface characteristics (Chlamydomonas reinhardii, Chlorella vulgaris and Chlorogonium elongatum) did not affect filtration rates. Suspension feeding increased with increasing food concentrations up to 12 nl · ml^–1, above which feeding rate was kept constant by lowering the filtering rates. Even the smallest animals tested (<4 mm body length) were found to be feeding on suspended food at a rate of 2.7 ml · ind^–1 · h^–1, and increasing rates up to 8.4 ml were found in the 6–7 mm size class. All size classes of Bithynia showed a circannual fluctuation of their filtration rates. The ecological consequences of Bithynia's ability to switch between two feeding modes, grazing and suspension feeding, are discussed.     

Continuous lactic acid fermentation with concentrated product recovery by ultrafiltration and electrodialysis

Lactose of sweet whey permeate was converted into sodium lactate byLactobacillus helveticus. To increase the, productivity of the lactic acid fermentation and to reduce the amounts of effluents, the bioreactor was coupled with an ultrafiltration module and an electrodialysis unit. Without the electrodialyzer, with total cell recycling and at a dilution rate of 0.88 h^–1, a cellular concentration of 64 gl^–1 and a productivity of 22 gl^–1 h^–1 were obtained. When the electrodialysis unit is coupled, the outlet concentration of lactate was stabilized at 85±5 gl^–1.     

The production of 2,3-butanediol by fermentation of high test molasses

Summary Klebsiella oxytoca fermented 199 g·l^–1 high test or invert molasses using batch fermentation with substrate shift to produce 95.2–98.6 g 2,3-butanediol·l^–1 and 2,4–4.3 g acetoin·l^–1 with a diol yield of 96–100% of the theoretical value and a diol productivity of 1.0–1.1 g·l^–1·h^–1. Fermentation was performed numerous times with molasses in repeated batch culture with cell recovery. Such repeated batch fermentation, in addition to a high product yield, also showed a very high product concentration. For example, 118 g 2,3-butanediol·l^–1 and 2.3 g acetoin·l^–1 were produced from 280 g·l^–1 of high test molasses. The diol productivity in this fermentation amounted to 2.4 g·l^–1·h^–1 and can undoubtedly be further increased by increasing the cell concentration. Because the Klebsiella cultures ferment 2,3-butanediol at an extremely high rate once the sugar has been consumed, the culture was inhibited completely by the addition of 15 g ethanol·l^–1 and switching off aeration. Offprint requests to: A. S. Afschar     

Adaptation of renal function to hypotonic medium in the winter flounder (Pseudopleuronectes americanus)

Summary The kidneys of winter flounders transferred to hypotonic medium were investigated for glomerular and tubular handling of fluid and electrolytes and for the urinary excretion of proteins. Media were sea water (925 mosm·kg^–1) and brackish water (70 mosm·kg^–1).In sea water, the urine was hypertonic to the plasma in 7 fish of this study. Urine flow rate was correlated with the GFR. After adaptation to brackish water a delay of 1 to 3 days was observed until the kidneys switched from fluid retention to the excretion of large amounts of dilute urine. GFR and urine flow rate were increased from 0.61±0.08 to 1.58±0.29 ml·h^–1·kg^–1 and from 0.14±0.02 to 0.68±0.08 ml·h^–1·kg^–1, respectively . With increased filtered load the tubular reabsorption of fluid decreased from 74±2.4% to 45±11.2%. The excretion rates of sodium and potassium were increased due to decreased fractional sodium and potassium reabsorption. The urinary excretion of divalent cations, however, was reduced because the net tubular reabsorption of calcium was increased and the net secretion of magnesium was diminished.Both the urinary total protein concentration and the protein pattern showed no significant change, but the rate of protein excretion was increased from 0.21±0.04 to 0.60±0.05 mg·h^–1·kg^–1. The comparison of protein patterns obtained from urine and serum samples revealed that high molecular weight (HMW) proteins prevail in the serum whereas low molecular weight (LMW) proteins dominate in the urine. The diminished quantity of the HMW-protein fraction in the urine thus may reflect size selectivity of the glomerular filtration barrier for serum proteins also in the winter flounder.Abbreviations BW brackish water - SW sea water - GFR glomerular filtration rate - HMW heigh molecular weight - LMW low molecular weight     

Bacterial productivity and microbial biomass in tropical mangrove sediments

Bacterial productivity (³H-thymidine incorporation into DNA) and intertidal microbenthic communities were examined within five mangrove estuaries along the tropical northeastern coast of Australia. Bacteria in mangrove surface sediments (0–2 cm depth) were enumerated by epifluorescence microscopy and were more abundant (mean and range: 1.1(0.02–3.6)×10¹¹ cells·g DW^–1) and productive (mean: 1.6 gC·m^–2· d^–1) compared to bacterial populations in most other benthic environments. Specific growth rates (¯x=1.1) ranged from 0.2–5.5 d^–1, with highest rates of growth in austral spring and summer. Highest bacterial numbers occurred in winter (June–August) in estuaries along the Cape York peninsula north of Hinchinbrook Island and were significantly different among intertidal zones and estuaries. Protozoa (10⁵–10⁶·m^–2, pheopigments (0.0–24.1g·gDW^–1) and bacterial productivity (0.2–5.1 gC·m^–2·d^–1) exhibited significant seasonality with maximum densities and production in austral spring and summer. Algal biomass (chlorophylla) was low (mean: 1.6g·gDW^–1) compared to other intertidal sediments because of low light intensity under the dense forest canopy, especially in the mid-intertidal zone. Partial correlation analysis and a study of possible tidal effects suggest that microbial biomass and bacterial growth in tropical intertidal sediments are regulated primarily by physicochemical factors and by tidal flushing and exposure. High microbial biomass and very high rates of bacterial productivity coupled with low densities of meiofaunal and macroinfaunal consumers observed in earlier studies suggest that microbes may be a sink for carbon in intertidal sediments of tropical mangrove estuaries.     

A scalable membrane gradostat reactor for enzyme production using Phanerochaete chrysosporium

This is the first demonstration of process scale-up of a membrane gradostat reactor for continuous enzyme production using Phanerochaete chrysosporium ME446. The fungus was immobilised by reverse filtration on to externally unskinned, ultrafiltration capillary membranes and then nutrient gradients were induced across the biofilm. A 10-fold scale-up from a single capillary bioreactor to a 2.4 l multi-capillary unit resulted in a 7-fold increase in enzyme productivity with a peak at 209 U l^–1 d^–1. Subsequent scale effects on the spore distribution, continuous manganese peroxidase production profile and biofilm development are discussed.     

Batch and continuous ribonuclease production by immobilized Aspergillus clavatus cells in a bubble-collumn bioreactor

Summary Ribonuclease production using immobilized cells (IC) of Aspergillus clavatus has been studied under batch, repeated-batch and continuous fermentation conditions in a bubble-column bioreactor and compared with production by free cells, Immobilization was achieved by the method of cryostructurization in polyvinyl alcohol beads. The effect of various aeration rates in a column bioreactor has been investigated. Enzyme production by IC [42 000 units (U)·l^–1] during batch fermentations was comparable to that of a free-cell system. The specific productivity of IC was 8.5 times higher than that of free cells. In repeated batch fermentation at various aeration rates, successful reuse of IC was obtained, with comparable levels of enzyme production. Continuous ribonuclease production was achieved for 44 days at 1 vvm aeration and a dilution rate of 0.0 h^–1 with volumetric productivity (450 U·1^–1) and yield.     

Organic reduction of tapioca wastewaters using modified RBC

A modified Rotating Biological Contactor (RBC) was used for the treatability studies of synthetic tapioca wastewaters. The RBC used was a four stage laboratory model and the discs were modified by attaching porous nechlon sheets to enhance biofilm area. Synthetic tapioca wastewaters were prepared with influent concentrations from 927 to 3600 mg/l of COD. Three hydraulic loads were used in the range of 0.03 to 0.09 m³·m^–2·d^–1 and the organic loads used were in the range of 28 to 306 g COD· m^–2·d^–1. The percentage COD removal were in the range from 97.4 to 68. RBC was operated at a rotating speed of 18 rpm which was found to be the optimal rotating speed. Biokinetic coefficients based on Kornegay and Hudson models were obtained using linear analysis. Also, a mathematical model was proposed using regression analysis.List of Symbols A m² total surface area of discs - d m active depth of microbial film onany rotating disc - K _s mg ·l^–1 saturation constant - P mg·m^–2·^–1 area capacity - Q l·d^–1 hydraulic flow rate - q m³·m^–2·d^–1 hydraulic loading rate - S ₀ mg·l^–1 influent substrate concentration - S _e mg·l^–1 effluent substrate concentration - w rpm rotational speed - V m³ volume of the reactor - X _f mg·l^–1 active biomass per unit volume ofattached growth - X _s mg·l^–1 active biomass per unit volume ofsuspended growth - X mg·l^–1 active biomass per unit volume - Y _s yield coefficient for attachedgrowth - Y _A yield coefficient for suspendedgrowth - Y yield coefficient, mass of biomass/mass of substrate removed Greek Symbols hr mean hydraulic detention time - (_max)_A d^–1 maximum specific growth rate forattached growth - (_max)_s d^–1 maximum specific growth rate forsuspended growth - _max d^–1 maximum specific growth rate - d^–1 specific growth rate - _v mg·l^–1·hr^–1 maximum volumetric substrateutilization rate coefficient     

Production of hirudin by recombinant Saccharomyces cerevisiae in a membrane-recycle fermentor

Summary Recombinant Saccharomyces cerevisiae was employed to continuously produce hirudin in a membrane cell recycle fermentor. The gene cooing for the anticoagulant protein was combined with the GAL10 promoter for controlled expression and the MF 1 signal sequence for secretion to the fermentation broth. A dilution rate of 0.1h^–1 yielded a maximum hirudin concentration of 59mg / l with a specific hirudin concentration of 2.4 mg /g cell mass among dilution rates studied ranging from 0.05h^–1 to 0.3h^–1. Cell bleeding gave the same fermentation results as cell recycle fermentation without cell bleeding. The productivity of the cell recycle fermentation process was 6.0mg hirudin/l · hr, corresponding to a 1.7-fold increase compared with a conventional continuous culture.     

Microbial communities in southern Victoria Land streams (Antarctica) I. Photosynthesis

The glacier-fed ephemeral streams of southern Victoria Land (ca. 78° S, 64° E) are colonised by an epilithon dominated by cyanobacterial mats and films. Biomass levels are often high (> 15 µg Chl a · cm^–2). The mat structure, pigment and photosynthetic characteristics of these communities have been investigated on site. The mats in high light environments have a layered structure with high levels of light shielding accessory pigments in the upper layers and elevated chlorophyll a and phycocyanin concentrations in the lower layers. Photosynthetic rates per unit area (0.4–3.5 µg C · cm^{– 2} · hr^–1) fall within the range reported for temperate communities. P vs I curves were used to separate high, intermediate and low light communities. I_k values for high light communities were at or lower than PAR recorded at midnight in the polar midsummer (ca 100 µ E m^–2 · s^–1). We did not detect photoinhibitory responses at the midday light intensities. In situ continuous nutrient enrichment experiments failed to demonstrate N or P limitation to pigment content or photosynthetic rates. We suggest that the growth of these communities is controlled by factors other than light and nutrients.     

Water conservation and protein metabolism in northern elephant seal pups during the postweaning fast

Urine production and N output were monitored in northern elephant seal (Mirounga angustirostris) pups progressing through 10 weeks of a natural postweaning fast. Urine output declind by 84% (to 69±12 ml·day^–1) at 10 weeks (P<0.05). Glomerular filtration rate at 10 weeks was 51% of the 67±3 ml serum·min^–1 observed during week 1 (P<0.05). Urine N excretion fell by 69% to 1.2±0.17 g·day^–1, while urinary concentration increased (P<0.05). Serum urea declined from an initial 11 mmol·1^–1 to 5–7 mmol·1^–1 by 5 weeks. The fall in urinary N loss (and thus amino acid oxidation) was concomitant with depressed metabolic rate. Therefore, protein contributed little toward meeting energy demands (i.e., <4% of average metabolic rate) throughout fasting. These data indicate that fasting pups improve water conservation and minimize protein catabolism during prolonged natural fasts without an exogenous source of water.Abbreviations AA amino acid(s) - AMR average metabolic rate - ANOVA one-way analysis of variance - BMR basal metabolic rate - BUN blood urea nitrogen - EP end product - EWL evaporative water loss - [Gr]_s serum creatinine concentration - GFR glomerular filtration rate - LBM lean body mass - LML Long Marine Laboratory - MR metabolic rate - NEFA non-esterified fatty acids - RMR resting metabolic rate - TCA tricarboxylic acid - U:C ulinary urea: creatinine concentration ratio     

Direct alcoholic fermentation of starchy biomass using amylolytic yeast strains in batch and immobilized cell systems

Summary Direct alcoholic fermentation of dextrin or soluble starch with selected amylolytic yeasts was studied in both batch and immobilized cell systems. In batch fermentations, Saccharomyces diastaticus was capable of fermenting high dextrin concentrations much more efficiently than Schwanniomyces castellii. From 200 g·l^–1 of dextrin S. diastaticus produced 77 g·l^–1 of ethanol (75% conversion efficiency). The conversion efficiency decreased to 59% but a higher final ethanol concentration of 120 g·l^–1 was obtained with a medium containing 400 g·l^–1 of dextrin. With a mixed culture of S. diastaticus and Schw. castellii 136 g·l^–1 of ethanol was produced from 400 g·l^–1 of dextrin (67% conversion efficiency). S. diastaticus cells attached well to polyurethane foam cubes and a S. diastaticus immobilized cell reactor produced 69 g·l^–1 of ethanol from 200 g·l^–1 of dextrin, corresponding to an ethanol productivity of 7.6g·l^–1·h^–1. The effluent from a two-stage immobilized cell reactor with S. diastaticus and Endomycopsis fibuligera contained 70 g·l^–1 and 80 g·l^–1 of ethanol using initial dextrin concentrations of 200 and 250 g·l^–1 respectively. The corresponding values for ethanol productivity were 12.7 and 9.6 g·l^–1·h^–1. The productivity of the immobilized cell systems was higher than for the batch systems, but much lower than for glucose fermentation.     

Factors which influence the sedimentation characteristics of Torulopsis glabrata after growth in a recirculation system

Summary Some environmental affects on cell aggregation described in the literature are briefly summarized. By means of a biomass recirculation culture (Contact system), using the yeast Torulopsis glabrata, the aggregation behavior of cells in static and in dynamic test systems is described. Sedimentation times required to obtain 50 g · l^–1 yeast dry matter in static systems were always higher than in dynamic ones.In addition to, influencing the biomass yield, the specific growth rate of the yeast also affected cell aggregation. The specific growth rate and therefore the aggregation could be regulated by the biomass recirculation rate as well as by the sedimenter volume.Abbreviations f_o Overflow flow rate (l·h^–1) - f_R Recycle flow rate (l·h^–1) - f_t0t Total flow rate through the fermenter (l·h^–1) - g Gram - h Hour - D_R Fermenter dilution rate due to recycle (h^–1) - D_S Fermeter dilution rate due to substrate (h^–1) - D_tot Total fermenter dilution rate (h^–1) - l Liter - Specific growth rate (h^–1) - P_F Fermenter productivity (g·l^–1·h^–1) - P_FS Overall productivity (g·l^–1·h^–1) - R_pM Rates per minute - RS Residual sugar content in the effluent with respect to the substrate concentration (%) - Y Yield of biomass with respect to sugar concentration (%) - Sed 50 Sedimentation time to reach a YDM of 50 g·l^–1 (min) - V Volume (l) - V_F Fermenter volume (l) - V_Sed Sedimenter volume (l) - VVM Volumes per volume and minute - X_F YDM in the fermenter (g·l^–1) - X_F YDM in the recycle (g·l^–1) - X_S Yeast dry matter due to substrate concentration (g·l^–1) - YDM Yeast dry matter (g·l^–1)     

Excretion of photosynthetically fixed organic carbon by metalimnetic phytoplankton

The effects of light intensity, oxygen concentration, and pH on the rates of photosynthesis and net excretion by metalimnetic phytoplankton populations of Little Crooked Lake, Indiana, were studied. Photosynthetic rates increased from 1.42 to 3.14 mg C·mg^–1 chlorophylla·hour^–1 within a range of light intensities from 65 to 150E·m^–2·sec^–1, whereas net excretion remained constant at 0.05 mg C·mg^–1 chlorophylla·hour^–1. Bacteria assimilated approximately 50% of the carbon released by the phytoplankton under these conditions. Excreted carbon (organic compounds either assimilated by bacteria or dissolved in the lake water) was produced by phytoplankton at rates of 0.02–0.15 mg C·mg^–1 chlorophylla·hour^–1. These rates were 6%–13% of the photosynthetic rates of the phytoplankton. Both total excretion of carbon and bacterial assimilation of excreted carbon increased at high light intensities whereas net excretion remained fairly constant. Elevated oxygen concentrations in samples incubated at 150E· m^–2·sec^–1 decreased rates of both photosynthesis and net excretion. The photosynthetic rate increased from 3.0 to 5.0 mg C·mg^–1 chlorophylla· hour^–1 as the pH was raised from 7.5 to 8.8. Net excretion within this range decreased slightly. Calculation of total primary production using a numerical model showed that whereas 225.8 g C·m^–2 was photosynthetically fixed between 12 May and 24 August 1982, a maximum of about 9.3 g C·m^–2 was released extracellularly.     

Effects of 12 weeks of aerobic exercise plus dietary restriction on body composition, resting energy expenditure and aerobic fitness in mildly obese middle-aged women

This study investigated the effects of 12 weeks of aerobic exercise plus voluntary food restriction on the body composition, resting metabolic rate (RMR) and aerobic fitness of mildly obese middle-aged women. The subjects were randomly assigned to exercise/diet (n = 17) or control (n = 15) groups. The exercise/diet group participated in an aerobic training programme, 45–60 min · day ^–1 at 50%–60% of maximal oxygen uptake (VO_2max), 3–4 days · week^–1, and also adopted a self-regulated energy deficit relative to predicted energy requirements (–1.05 MJ · day ^–1 to –1.14 MJ · day ^–1 ). After the regimen had been followed for 12 weeks, the body mass of the subjects had decreased by an average of 4.5 kg, due mainly to fat loss, with little change of fat free mass (m _ff). The absolute RMR did not change, but the experimental group showed significant increases in the RMR per unit of body mass (10%) and the RMR per unit of m _ff (4%). The increase in RMR/m _ff was not correlated with any increase in VO_2max/m _ff. The resting heat production per unit of essential body mass increased by an average of 21%, but the resting heat production rate per unit of fat tissue mass remained unchanged. We concluded that aerobic exercise enhances the effect of moderate dietary restriction by augmenting the metabolic activity of lean tissue.     

Pulmonary diffusing capacity in reptiles (Relations to temperature and O2-uptake)

Summary Pulmonary CO-diffusing capacity (D l _CO), lung volume, pulmonary perfusion and O₂-uptake were measured by non-invasive techniques in the lizardsVaranus exanthematicus andTupinambis teguixin (mean body weight 2.2 kg for both species).The CO-diffusing capacity was at 25–27°C 0.059 mlstpd·kg^–1·min^–1·Torr^–1 inVaranus, which is 47% greater than the value of 0.040 mlstpd·kg^–1·min^–1·Torr^–1 inTupinambis. The lung volume ofVaranus was 36 ml·kg^–1 and that ofTupinambis 20 ml·kg^–1. At 35–37°C the diffusing capacity of lizard lungs are about 25% of those for mammals of comparable size.InVaranus pulmonary CO-diffusing capacity increased with temperature from 0.027 mlstpd·kg^–1·min^–1·Torr^–1 at 17–19 °C to 0.075 mlstpd·kg^–1·min^–1·Torr^–1 at 35–37 °C. This change closely matched a concomitant increase of O₂-uptake. Pulmonary perfusion increased from 27 ml·kg^–1·min^–1 to 55 ml·kg^–1·min^–1 within this temperature range.The study emphasizes that pulmonary diffusing capacity cannot be fully evaluated without information on pulmonary perfusion and O₂-uptake. In reptiles and other ectotherms diffusing capacity must be reported at specified body temperature.     

Digestion and energy metabolism in a small arboreal marsupial,the Greater Glider (Petauroides volans), fed high-terpeneEucalyptus foliage

Summary The digestion and metabolism ofEucalyptus radiata foliage was studied in a small (1–1.5 kg) arboreal marsupial, the greater glider (Petauroides volans). Mean dry matter intake was 44 g·kg^–0.75·d^–1 and mean cell wall digestibility was 34%; these values fall within the range of other marsupials fedEucalyptus foliage. Digestible energy content ofE. radiata was high compared to other eucalypts because of the high content and digestibility of essential oils. However, excretion of essential oils and their metabolites in the urine meant that greater gliders retained only 55% of their digestible energy intakes (0.61 MJ · kg^–0.75· d^–1) as metabolizable energy (ME). Low ME intakes were not offset by low standard metabolic rates (2.39 W · kg^–0.75), but the efficiency with which ME substituted for tissue energy was high (94%), so that greater gliders were able to maintain energy balance and body mass onE. radiata foliage.Abbreviations ME metabolizable energy - DE digestible energy - RQ respiratory quotient - FHP fasting heat production     

The nitrogen cycle in lodgepole pine forests,southeastern Wyoming

Storage and flux of nitrogen were studied in several contrasting lodgepole pine (Pinus contorta spp.latifolia) forests in southeastern Wyoming. The mineral soil contained most of the N in these ecosystems (range of 315–860 g · m^–2), with aboveground detritus (37.5–48.8g · m^–2) and living biomass (19.5–24.0 g · m^–2) storing much smaller amounts. About 60–70% of the total N in vegetation was aboveground, and N concentrations in plant tissues were unusually low (foliage = 0.7% N), as were N input via wet precipitation (0.25 g · m^–2 · yr^–1), and biological fixation of atmospheric N (<0.03 g · m^–2 · yr^–1, except locally in some stands at low elevations where symbiotic fixation by the leguminous herbLupinus argenteus probably exceeded 0.1 g · m^–2 · yr^–1).Because of low concentrations in litterfall and limited opportunity for leaching, N accumulated in decaying leaves for 6–7 yr following leaf fall. This process represented an annual flux of about 0.5g · m^–2 to the 01 horizon. Only 20% of this flux was provided by throughfall, with the remaining 0.4g · m^–2 · yr^–1 apparently added from layers below. Low mineralization and small amounts of N uptake from the 02 are likely because of minimal rooting in the forest floor (as defined herein) and negligible mineral N (< 0.05 mg · L^–1) in 02 leachate. A critical transport process was solubilization of organic N, mostly fulvic acids. Most of the organic N from the forest floor was retained within the major tree rooting zone (0–40 cm), and mineralization of soil organic N provided NH₄ for tree uptake. Nitrate was at trace levels in soil solutions, and a long lag in nitrification was always observed under disturbed conditions. Total root nitrogen uptake was calculated to be 1.25 gN · m^–2 · yr^–1 with estimated root turnover of 0.37-gN · m^–2 · yr^–1, and the soil horizons appeared to be nearly in balance with respect to N. The high demand for mineralized N and the precipitation of fulvic acid in the mineral soil resulted in minimal deep leaching in most stands (< 0.02 g · m^–2 · yr^–1). These forests provide an extreme example of nitrogen behavior in dry, infertile forests.