The metabolism of 4-methyl-2-oxopentanoate in rat pancreatic islets.

1. Radioactively labelled 4-methyl-2-oxopentanoate was taken up by isolated pancreatic islets in a concentration- and pH-dependent manner and led to the intracellular accumulation of labelled amino acid and to a decrease in the intracellular pH. Uptake of 4-methyl-2-oxopentanoate did not appear to be either electrogenic or Na+-dependent. The islet content of 2-oxo acid radioactivity was not affected by either 2-cyano-3-hydroxy-cinnamate (10mM) or pyruvate (10mM), although both these substances inhibited the oxidation of [U-14C]4-methyl-2-oxopentanoate by islet tissue. 2. 4-Methyl-2-oxopentanoate markedly stimulated islet-cell respiration, ketone-body formation and biosynthetic activity. The metabolism of endogenous nutrients by islets appeared to be little affected by the compound. 3. Studies with the 3H- and 14C-labelled substrate revealed that 4-methyl-2-oxopentanoate was incorporated by islets into CO2, water, acetoacetate, L-leucine and to a lesser extent into islet protein and lipid. Carbon atoms C-2, C-3 and C-4 of the acetoacetate produced were derived from the carbon skeleton of the 4-methyl-2-oxopentanoate, but the acetoacetate carboxy group was derived from the incorporation of CO2. These results, and consideration of the relative rates of 14CO2 and acetoacetate formation from 1-14C-labelled as opposed to U-14C-labelled 4-methyl-2-oxopentanoate, led to the conclusion that the pathway of catabolism of this 2-oxo acid in pancreatic islets is identical with that described in other tissues. The amination of 4-methyl-2-oxopentanoate by islets was attributed to the presence of a branched-chain amino acid aminotransferase (EC 2.6.1.42) activity in the tissue. Although glutamate dehydrogenase activity was demonstrated in islet tissue, the reductive amination of 2-oxoacids did not seem to be of importance in the formation of leucine from 4-methyl-2-oxopentanoate. 4. The results of experiments with respiratory inhibitors and uncouplers, and the finding that 14CO2 production and islet respiration were linked in a 1:1 stoicheiometry suggested that 4-methyl-2-oxopentanoate catabolism was coupled to mitochondrial oxidative phosphorylation. The catabolism of 4-methyl-2-oxopentanoate in islet tissue appeared to be regulated at the level of the initial 2-oxo acid dehydrogenase (EC 1.2.1.25) reaction.     

Underestimation of metabolic rates owing to reincorporation of 14CO2 in the perfused rat liver

(14)CO(2) production by perfused rat livers was simulated by infusing NaH(14)CO(3) into the perfusate. Recovery of label as (14)CO(2) gas + perfusate bicarbonate was 45-85%. Rates of (14)CO(2) exchange in the liver are 3-70 times greater than net rates of CO(2) production. Therefore (14)CO(2) reincorporation can lead to significant underestimations of rates of oxidation of (14)C-labelled substrates in liver.     

A simple (14)C-respirometric method for assessing microbial catabolic potential and contaminant bioavailability

This paper describes the validation and application of a simple flask-based (14)C-respirometer system designed to assess mineralisation of (14)C-labelled substrates under defined conditions. Validation of this respirometer system indicated stoichiometric CO(2) trapping up to a maximum of 400 micromol of CO(2) (in a single trap). Polycyclic aromatic hydrocarbon (PAH)-degrading bacteria were used to measure growth-linked biodegradation of [(14)C]naphthalene to (14)CO(2). A (14)C activity balance of 101.7+/-8.9% (n=6), after 74 h incubation time and 10 respirometer-opening events, indicated the suitability of the system for monitoring substrate mineralisation. This respirometric apparatus was then successfully applied to assess: (i) the PAH catabolism of microbes in a field contaminated soil, where naphthalene and phenanthrene were rapidly mineralised and (ii) soil-associated organic contaminant bioavailability, where increased soil-phenanthrene contact time resulted in a reduction in phenanthrene mineralisation in the soil. The described respirometer system differs from existing respirometer systems in that the CO(2) trap can be removed and replaced quickly and easily. The system is efficient, reproducible, adaptable to many situations, easy to construct and simple to use, it therefore affords advantages over existing systems.     

Importance of chemical structure on the development of hydrocarbon catabolism in soil

A soil was amended with (14)C-analogues of naphthalene, phenanthrene, pyrene, B[a]P or hexadecane at 50 mg kg(-1) and the development of catabolic activity was assessed by determining the rate and extent of (14)CO(2) evolution at time points over 180 days. The catabolic potential of the soil was hexadecane>naphthalene>phenanthrene>pyrene>B[a]P, determined by the decrease in lag time (as defined by the time taken for 5%(14)CO(2) to be evolved from the minerialization of the (14)C-labeled hydrocarbons). The results clearly showed the difference between constitutive and inducible biodegradation systems. The 0 day time point showed that hexadecane minerialization was rapid and immediate, with a 45.4 +/- 0.6% mineralization extent, compared with pyrene minerialization at 1.0 +/- 0.1%. However, catabolism for pyrene developed over time and after a 95 days soil-pyrene contact time, mineralization extent was found to be 63.1 +/- 7.8%. Strong regression was found (r(2)>0.99) between the maximum rates of mineralization and the partioning coefficient between the mineralized hydrocarbons, which may indicate linearity in the system.     

Oxidation of 2-oxoisocaproate and 2-oxoisovalerate by the perfused rat heart. Interactions with fatty acid oxidation

The interactions between fatty acid oxidation and the oxidation of the 2-oxo acids of the branched chain amino acids were studied in the isolated Langendorff-perfused heart. 2-Oxoisocaproate inhibited the oxidation of oleate, but 2-oxoisovalerate and 2-oxo-3-methylvalerate did not. This difference was not attributable to the magnitude of the flux through the branched chain 2-oxo acid dehydrogenase, which was slightly higher with 2-oxoisovalerate than with 2-oxoisocaproate. Oxidation of 2-oxoisocaproate in the perfused heart was virtually complete, since more than 80% of the isovaleryl-CoA formed from 2-oxo[1-14C]isocaproate was further metabolized to CO2, as determined by comparing 14CO2 production from 2-oxo[14C(U)]isocaproate with that from the 1-14C-labelled compound. Only twice as much 14CO2 was produced from 2-oxo[14C(U)]isovalerate as from the 1-14C-labelled compound, indicating incomplete oxidation. This was confirmed by the accumulation in the perfusion medium of substantial quantities of labelled 3-hydroxyisobutyrate (an intermediate in the pathway of valine catabolism), when hearts were perfused with 2-oxo[14C(U)]isovalerate. The failure of 2-oxoisovalerate to inhibit fatty acid oxidation, then, can be attributed to the fact that its partial metabolism in the heart produces little ATP. We have previously shown that 3-hydroxyisobutyrate is a good gluconeogenic substrate in liver and kidney, and postulate that 3-hydroxyisobutyrate serves as an interorgan metabolite such that valine can serve as a glucogenic amino acid, even when its catabolism proceeds beyond the irreversible 2-oxo acid dehydrogenase in muscle.     

GDP binding to brown-adipose-tissue mitochondria of mice treated chronically with corticosterone.

A procedure is described to convert rates of (14)CO(2) production into rates of mitochondrial acetyl-CoA production from a (14)C-labelled substrate. The principle is illustrated in perfused rat liver and kidney by the differential yield of (14)CO(2) from 4-methyl-2-oxo[1-(14)C]valerate and 4-methyl-2-oxo[2-(14)C]valerate.     

Changes in pattern of respiration and glucose utilisation in Candida utilis during the cell cycle: some variations with growth rate.

The release of 14CO2 from 14C-labelled glucose(G-1(-14)C, G-3,4(-14)C, G-6(-14)C) was followed in phased cultures of Candida utilis grown in a glucose- mineral salts medium under altered conditions of carbon:nitrogen limitation at doubling times of 2,4 and 6, h. Changes in oxygen uptake and CO2 evolution were observed and respirometric studies showed that the relative contributions of the Embden-Meyerhof-Parnas and hexose monophosphate pathways varied over the cell cycle and changed with growth rate. The results are discussed in relation to the growth metabolism of the cells.     

Biodegradation of organic compounds in vadose zone and aquifer sediments.

The microbial processes that occur in the subsurface under a typical Midwest agricultural soil were studied. A 26-m bore was installed in November of 1988 at a site of the Purdue University Agronomy Research Center. Aseptic collections of soil materials were made at 17 different depths. Physical analysis indicated that the site contained up to 14 different strata. The site materials were primarily glacial tills with a high carbonate content. The N, P, and organic C contents of sediments tended to decrease with depth. Ambient water content was generally less than the water content, which corresponds to a -0.3-bar equivalent. No pesticides were detected in the samples, and degradation of added 14C-labeled pesticides (atrazine and metolachlor) was not detected in slurry incubations of up to 128 days. The sorption of atrazine and metolachlor was correlated with the clay content of the sediments. Microbial biomass (determined by direct microscopic count, viable count, and phospholipid assay) in the tills was lower than in either the surface materials or the aquifer located at 25 m. The biodegradation of glucose and phenol occurred rapidly and without a lag in samples from the aquifer capillary fringe, saturated zone, and surface soils. In contrast, lag periods and smaller biodegradation rates were found in the till samples. Subsurface sediments are rich in microbial numbers and activity. The most active strata appear to be transmissive layers in the saturated zone. This implies that the availability of water may limit activity in the profile.     

Biodegradation of organic compounds in vadose zone and aquifer sediments.

The microbial processes that occur in the subsurface under a typical Midwest agricultural soil were studied. A 26-m bore was installed in November of 1988 at a site of the Purdue University Agronomy Research Center. Aseptic collections of soil materials were made at 17 different depths. Physical analysis indicated that the site contained up to 14 different strata. The site materials were primarily glacial tills with a high carbonate content. The N, P, and organic C contents of sediments tended to decrease with depth. Ambient water content was generally less than the water content, which corresponds to a -0.3-bar equivalent. No pesticides were detected in the samples, and degradation of added 14C-labeled pesticides (atrazine and metolachlor) was not detected in slurry incubations of up to 128 days. The sorption of atrazine and metolachlor was correlated with the clay content of the sediments. Microbial biomass (determined by direct microscopic count, viable count, and phospholipid assay) in the tills was lower than in either the surface materials or the aquifer located at 25 m. The biodegradation of glucose and phenol occurred rapidly and without a lag in samples from the aquifer capillary fringe, saturated zone, and surface soils. In contrast, lag periods and smaller biodegradation rates were found in the till samples. Subsurface sediments are rich in microbial numbers and activity. The most active strata appear to be transmissive layers in the saturated zone. This implies that the availability of water may limit activity in the profile.     

Fetal CO2 kinetics

Knowledge of CO2 kinetics in the fetus is important for the design and interpretation of fetal metabolic studies that use carbon-labelled tracers. To study fetal CO2 kinetics, four fetal sheep were infused at constant rate with NaH14CO3 to simulate a constant rate of fetal 14CO2 production from the metabolism of a 14C-labelled substrate. Uterine and umbilical blood flows, and concentrations of 14CO2 and total CO2 in umbilical arterial and venous blood and in uterine arterial and venous blood were measured. During steady state, the excretion of 14CO2 via the umbilical circulation was 99.6 +/- 1.0 (SEM)% of the NaH14CO3 infusion rate. The irreversible disposal rate of CO2 molecules from the fetal CO2 pool was approximately 5 times greater than the metabolic production of CO2 by the fetus. This evidence demonstrates that measurements of fetal 14CO2 excretion via the umbilical circulation can provide an accurate measurement of fetal 14CO2 production and that the exchange rate of CO2 molecules between placenta and fetal blood is much greater than the net rate of excretion of CO2 molecules from fetus to placenta.     

Thermoanaerobacteriaceae oxidize acetate in methanogenic rice field soil at 50°C

Rice field soils contain a thermophilic microbial community. Incubation of Italian rice field soil at 50°C resulted in transient accumulation of acetate, but the microorganisms responsible for methane production from acetate are unknown. Without addition of exogenous acetate, the δ(13)C of CH(4) and CO(2) indicated that CH(4) was exclusively produced by hydrogenotrophic methanogenesis. When exogenous acetate was added, acetoclastic methanogenesis apparently also operated. Nevertheless, addition of [2-(13)C]acetate (99% (13)C) resulted in the production not only of (13)C-labelled CH(4) but also of CO(2), which contained up to 27% (13)C, demonstrating that the methyl group of acetate was also oxidized. Part of the (13)C-labelled acetate was also converted to propionate which contained up to 14% (13)C. The microorganisms capable of assimilating acetate at 50°C were targeted by stable isotope probing (SIP) of ribosomal RNA and rRNA genes using [U-(13)C] acetate. Using quantitative PCR, (13)C-labelled bacterial ribosomal RNA and DNA was detected after 21 and 32 days of incubation with [U-(13)C]acetate respectively. In the heavy fractions of the (13)C treatment, terminal restriction fragments (T-RFs) of 140, 120 and 171 bp length predominated. Cloning and sequencing of 16S rRNA showed that these T-RFs were affiliated with the bacterial genera Thermacetogenium and Symbiobacterium and with members of the Thermoanaerobacteriaceae. Similar experiments targeting archaeal RNA and DNA showed that Methanocellales were the dominant methanogens being consistent with the operation of syntrophic bacterial acetate oxidation coupled to hydrogenotrophic methanogenesis. After 17 days, however, Methanosarcinacea increasingly contributed to the synthesis of rRNA from [U-(13)C]acetate indicating that acetoclastic methanogens were also active in methanogenic Italian rice field soil under thermal conditions.     

Spatial Patterns of Soil Microbial Communities in a Norway Spruce (Picea abies) Plantation

The phospholipid fatty acid (PLFA) profiles of soil microbial communities were determined in relation to the patterns of tree cover in a mature Norway spruce plantation. Replicate samples of the surface organic layers were taken close to the trunk, at 1 m and at 2 m (under the edge of the canopy) beneath five trees. Samples were analyzed for standard PLFAs to assess the initial composition of the microbial communities. Replicate samples were then incubated under constant or fluctuating moisture conditions for 30 d to test the hypothesis that the patterns of microbial community structure (or its physiological state) might be determined by biophysical conditions under the tree canopies. The PLFA profiles near the trunks and at 2 m were similar, but samples taken 1 m from the bases of the trees contained lower concentrations of polyunsaturated (fungal) and monounsaturated PLFAs, and higher concentrations of saturated PLFAs. These differences in PLFA profiles were maintained during laboratory incubation under a regime of drying and wetting cycles, but there was some evidence of convergence in community structure under constant moisture conditions resulting from significant increases and decreases in specific bacterial PLFA concentrations. There were no effects of either moisture treatment on fungal PLFA concentrations. It is concluded that variation in the soil biophysical environment beneath the tree canopies resulted in the differentiation of spatially defined bacterial communities that were tolerant of moisture stress. The anomaly that differences in community structure were largest at an intermediate position of 1 m between the trunk and below the canopy edge was not explained but may relate to tree root distribution.     

Larval behavior in Lymantria dispar increases risk of fungal infection

Late-instar larvae of the forest defoliator Lymantria dispar display relatively unusual behavior for Lepidoptera. Late instars move down from the tree canopy and wander and rest in dark locations during daylight hours. When we sampled the area extending from below 3 m and within 200 cm of tree trunks during daylight hours, 71% of L. dispar late instar larvae were found at ground level. Providing dark resting locations on the soil surface where there was no litter resulted in rapid location and colonization of these sites by late instar larvae. L. dispar larvae were always more prevalent in leaf litter 0-50 cm from tree trunks compared with 50-200 cm away. In an area where the fungal insect pathogen Entomophaga maimaiga is established, larvae were caged on tree trunks, in the foliage, or on top of soil during photophase or scotophase to determine in which locations risk of infection was greatest. At both times of day, highest infection levels always occurred on the soil, with least infection among larvae caged in the foliage. Infection levels were greater during photophase than scotophase. When larvae were exposed to soil for shorter periods during daylight hours to mimic wandering, 4.7 and 6.1% became infected after 30- and 60-min exposure intervals, respectively, with increasing infection associated with longer exposure times. The high levels of infection by E. maimaiga that have been documented in L. dispar populations since this pathogen was first found in North America are consistent with the strong litter-dwelling behavior of late-instar L. dispar larvae. Rarity of other lepidopteran larvae at ground level could help to explain the host specificity of this pathogen in the field.     

Are tree trunks habitats or highways? A comparison of oribatid mite assemblages from hoop-pine bark and litter

Abstract Oribatid mites (Acari: Oribatida) are among the most diverse and abundant inhabitants of forest soil and litter, but also have species-rich assemblages on bark and in the canopies of trees. It is unclear whether the trunk of a tree acts simply as a 'highway' for movement of mites into and out of the canopy, or whether the trunk has a distinctive acarofauna. We compare oribatid assemblages from the trunk bark of hoop pine ( Araucaria cunninghamii ) with those from litter collected beneath the same trees. A 1.0 by 0.5 m area of bark was sampled from three trees at each of five sites using a knockdown insecticide. A 1-L sample of leaf litter was collected as close as possible to the base of each sampled tree. Mites were extracted using Tullgren funnels, identified to genus and morphospecies, and counted. Assemblages were almost 100% distinct, with only one oribatid morphospecies ( Pseudotocepheus sp.) collected from both litter and bark. Litter had a higher taxon richness than bark in total and per sample, but oribatids made up a greater percentage of the acarofauna in the bark samples. We had expected that the more consistent physical substrate of bark would be reflected in greater similarity of oribatid faunas on trunks than in litter; however, the opposite proved to be the case. We conclude that hoop-pine trunks are habitats rather than highways for oribatid mites. Based on the observed higher turnover among bark faunas, tree trunks may represent habitat islands whose colonisation by particular oribatid species is more stochastic than that of the more continuous 'sea' of litter.     

Carbon and nitrogen allocation in Lolium perenne in response to elevated atmospheric CO2 with emphasis on soil carbon dynamics

The effect of elevated CO2 on the carbon and nitrogen distribution within perennial ryegrass (L. perenne L.) and its influence on belowground processes were investigated. Plants were homogeneously 14C-labelled in two ESPAS growth chambers in a continuous 14C-CO2 atmosphere of 350 and 700 L L-1 CO2 and at two soil nitrogen regimes, in order to follow the carbon flow through all plant and soil compartments.After 79 days, elevated CO2 increased the total carbon uptake by 41 and 21% at low (LN) and high nitrogen (HN) fertilisation, respectively. Shoot growth remained unaffected, whereas CO2 enrichment stimulated root growth by 46% and the root/soil respiration by 111%, irrespective of the nitrogen concentration. The total 14C-soil content increased by 101 and 28% at LN and HN, respectively. The decomposition of the native soil organic matter was not affected either by CO2 or by the nitrogen treatment.Elevated CO2 did not change the total nitrogen uptake of the plant either at LN or at HN. Both at LN and HN elevated CO2 significantly increased the total amount of nitrogen taken up by the roots and decreased the absolute and relative amounts translocated to the shoots.The amount of soil nitrogen immobilised by micro-organisms and the size of the soil microbial biomass were not affected by elevated CO2, whereas both were significantly increased at the higher soil N content.Most striking was the 88% increase in net carbon input into the soil expressed as: 14C-roots plus total 14C-soil content minus the 12C-carbon released by decomposition of native soil organic matter. The net carbon input into the soil at ambient CO2 corresponded with 841 and 1662 kg ha-1 at LN and HN, respectively. Elevated CO2 increased these amounts with an extra carbon input of 950 and 1056 kg ha-1. Combined with a reduced decomposition rate of plant material grown at elevated CO2 this will probably lead to carbon storage in grassland soils resulting in a negative feed back on the increasing CO2 concentration of the atmosphere.     

北京山区典型暖温带落叶阔叶林大气CO_2浓度、草本层光合作用及土壤释放CO_2变化特点(英文)

为探讨森林生态系统植被、土壤等不同组分与大气CO_2交换特点,利用中型同化箱(40cm×40cm×2Ocm)及红外CO_2分析仪装置对北京山区典型暖温带森林生态系统辽东栎(Quercus liaotungensisKoidz.)林草本层净光合作用、土壤释放CO_2及林外(高出林冠2m)与林内(低于林冠2m)大气CO_2变化进行测定。结果表明:夏季及秋季大气CO_2浓度分别为(323±10)μmol·mol~(-1)和(330±1)μmol·mol~(-1);在一天内连续24h的测定中,大气与林内CO_2浓度的差值最大时可分别达-46和-61μmol·mol~(-1)。夏季草本层净光合强度为(2.59±1.05)μmol CO_2·m~(-2)·s~(-1),是秋季((1.31±0.39)μmol CO_2·m~(-2)·s~(-1))的2倍;夏季土壤呼吸释放CO_2的强度明显高于秋季,分别为(5.18±0.75)μmol CO_2·m~(-2)·s~(-1)和(1.96±0.57)μmol CO_2·m~(-2)·s~(-1)。土壤释放CO_2强度与地面温度之间存在显著相关,其关系式为Y=-0.8642 0.3101X(r=0.7164,P<0.001,n=117)。大气CO_2浓度的低值及草本层光合强度高值约出现在14:00左右;而在夜间土壤释放CO_2强度增加,表现为大气CO_2浓度升高。     

Biogeochemical cycle of methane in the northwestern shelf of the Black Sea

Seasonal investigations of methane distribution and rates of its oxidation and generation in the water column and sediments of the Black Sea northwestern shelf were carried out within the framework of the interdisciplinary projects "European River-Ocean Systems" (EROS-2000, EROS-21) and "Biogenic Gases Exchange in the Black Sea" (BigBlack) in August 1995, May 1997, and December 1999. Experiments that involved the addition of 14CH3COONa and 14CO2 to sediment samples showed the main part of methane to be formed from CO2. Maximum values of methane production (up to 559 mumol/(m2 day)) were found in coastal sediments in summer time. In winter and spring, methane production in the same sediments did not exceed 3.6-4.2 mumol/(m2 day). The delta 13C values of methane ranged from -70.7 to -81.8@1000, demonstrating its microbial origin and contradicting the concept of the migration of methane from cold seeps or from the oil fields located at the Black Sea shelf. Experiments that involved the addition of 14CH4 to water and sediment samples showed that a considerable part of methane is oxidized in the upper horizons of bottom sediments and in the water column. Nevertheless, it was found that, in summer, part of methane (from 6.8 to 320 mumol/(m2 day)) arrives in the atmosphere.     

Does the Prostrate-leaved Geophyte Brunsvigia orientalis Utilize Soil-derived CO2 for Photosynthesis?

BACKGROUND AND AIMS: A test was made of the hypothesis that the prostrate growth habit of the leaves of the geophyte Brunsvigia orientalis enables utilization of soil-derived CO(2) and is related to the presence of lysigenous air-filled channels characteristic of B. orientalis leaves. METHODS: Brunsvigia orientalis was sampled at a field site. Leaf anatomy, stomatal density, leaf/soil gas exchange characteristics and soil atmosphere and leaf delta(13)C isotope abundances were examined. KEY RESULTS: The leaves of B. orientalis have large lysigenous air-filled channels separating the upper and lower surfaces of the leaves. The upper surface comprised approx. 70 % of the leaf mass and 75 % of the leaf N (mmol g(-1)). Between 20 % and 30 % of the stomatal conductance and CO(2) assimilation was through the lower surface of the leaf. CO(2) efflux rates from the soil surface were up to 5.4 micromol m(-2) s(-1) while photosynthetic fluxes through the lower surface of the leaves were approx. 7 micromol m(-2) s(-1). However, the utilization of soil-derived CO(2) only altered the leaf delta(13)C isotope abundance of the prostrate leaves by a small amount. Using delta(13)C values it was estimated that 7 % of the leaf tissue C was derived from soil-derived CO(2). CONCLUSIONS: A small proportion of photosynthetically fixed CO(2) was derived from the soil, with minimal associated transpirational H(2)O loss into the space between the leaf and soil. The soil-derived CO(2), taken up through the lower surface was probably assimilated by the palisade tissue in the upper surface of the leaf which was exposed to sunlight and where most of the leaf N was located. The occurrence of lysigenous air channels in the leaves may provide longitudinal strength without impaired transfer of CO(2) taken up through the lower surface to the upper surface.     

Mechanical Properties of Black Locust (Robinia pseudoacacia L.) Wood. Size- and Age-dependent Variations in Sap- and Heartwood

Variations in the density and stiffness (Young's elastic modulus)of fresh wood samples drawn from different parts of the threemain trunks of a 32-year-old black locust tree,Robinia pseudoacacia(measuring 19.8 m at its highest point), were studied to determinewhether tree ontogeny can achieve a constant safety factor againstmechanical failure. Based on the properties of isolated woodsamples, the fresh density of sapwood decreased along radialtransects from bark to pith, while that of progressively olderheartwood samples increased, on average, towards the centreof each of the three trunks. Along the same radial transects,the Young's elastic modulus of sap- and heartwood increased.In terms of longitudinal changes in wood properties, mean woodmoduli (averages of sap- and heartwood samples) increased, onaverage, towards the base of each of the three trunks of thetree. However, the mean fresh densities of wood samples increasedtowards the top and the bottom of each trunk and were lowestroughly near trunk mid-length. The mean density-specific stiffness(the quotient of Young's modulus and fresh density) of woodwas thus lower toward the top and the bottom of the trunks andhighest near trunk mid-length. Mean values of fresh wood density-specificstiffness were used to estimate the critical buckling heightsfor sections of the trunks differing in diameter and age. Theseestimates indicated that ontogenetic variation in the physicalproperties and relative amounts of sap- and heartwood in trunkscould maintain a constant factor of safety (approximately equalto 2) as a sapling grows in height and girth into a mature tree.This expectation was supported by data from 16 black locusttrees differing in height and diameter at breast height (DBH). Wood; elastic properties; tree height; biomechanics     

Biodegradation of pentachlorophenol in soil: the response to physical, chemical, and biological treatments

The effects of physical, chemical, and biological treatments on biodegradation of pentachlorophenol (PCP) were studied in a silt-loam soil contaminated with 175 mg PCP/kg and uniformly 14C-labelled PCP. Biodegradation of 14C-labelled PCP and technical-grade PCP were monitored over 210 days incubation. Mineralization of labelled PCP was significantly (p=0.05) influenced by soil treatments. Negligible biodegradation occurred in either the sterile control soil or the uninoculated control soil, with less than 1% of added 14C recovered as 14 CO2. Inoculation of unamended soil with a strain of Flavobacterium (ATCC 39723) known to degrade PCP increased biodegradation of PCP; approximately 60% of the [14C]PCP was recovered as 14CO2. Increased soil water content (60% versus 30% w/w) enhanced biodegradation (67% recovery of 14C as CO2), while increased chloride ion concentration and anoxic conditions were inhibitory (20 and 1% recoveries, respectively). Residual soil PCP concentrations were also influenced by various treatments. In the sterile control soil and noninoculated control, after 210 days incubation, concentrations of PCP were 143 and 1223 mg/kg, respectively, while the PCP concentration in the inoculated soil was 21 mg/kg. When soil organic matter was increased by adding finely ground red clover leaf and stem material, the residual PCP concentration was reduced to 6 mg/kg after 210 days. Increased soil water content resulted in a residual PCP concentration of 5 mg/kg. High-pressure liquid chromatography of soil extracts revealed no accumulation of partial PCP degradation products. The results indicated that biodegradation of PCP in soil was significantly influenced by various soil amendments.