Factors affecting production of COS and CS2 in Leucaena and Mimosa species

Carbon disulfide (CS₂) and carbonyl sulfide (COS) are colorless, foul-smelling, volatile sulfur compounds with biocidal properties. Some plants produce CS₂ or COS or both. When used as an intercrop or forecrop, these plants may have agronomic potential in protecting other plants. Most of the factors which affect production of these plant-generated organic sulfides are unknown. We determined the effects of sulfate concentration, plant age, nitrogen fixation, drought stress, root injury (through cutting), and undisturbed growth on COS production in Leucaena retusa or Leucaena leucocephala and the effect of some of these factors on CS₂ production in Mimosa pudica. In addition, we determined if organic sulfides were produced in all Leucaena species. When L. retusa and M. pudica seedlings were grown in a plant nutrient medium with different sulfate concentrations (50 to 450 mg SL^-1), COS or CS₂ from crushed roots generally increased with increasing sulfate concentration. COS production was highest (74 ng mg^-1 dry root) for young L. retusa seedlings and declined to low amounts (<5 ng mg^-1 dry root) for older seedlings. Nitrogen fixation reduced the amounts of COS or CS₂ produced in L. leucocephala and M. pudica. Under conditions of undisturbed growth, root cutting, or drought stress, no COS production was detected in 4-to 8-weeks-old L. retusa plants. COS or CS₂ or both was obtained from crushed roots or shoots of all 13 known Leucaena species.     

Past vegetation changes in the Brazilian Pantanal arboreal–grassy savanna ecotone by using carbon isotopes in the soil organic matter

Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in ¹³C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM ¹³C values reflect the change from C₃ to C₄ plants between the sites, as confirmed by measurements of ¹³C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of ¹³C in SOM with depth at both sites are larger than the 3–4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C₃ and C₄ plants at these sites. Mass balances with ¹⁴C and ¹³C suggest that past vegetational changes from C₃ to C₄ plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C₄ to C₃, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime.     

Prediction of the Reaction Equilibrium of Biocatalytic Reactions in Aqueous-Organic Two-Phase Systems

Biocatalytic reactions can be carried out in aqueous-organic two-phase systems. Several models to describe the thermodynamically-determined equilibrium position in such systems have appeared in the literature. Some of these models are only valid for dilute systems, whereas others can also be used for nondilute systems. In this paper, these models are described and compared. It is explained in what way the equilibrium constants of each model can be used to predict the product concentration in different organic solvents.     

Changes in organic matter composition of forest soil treated with a large amount of urea to promote ammonia fungi and the abilities of these fungi to decompose organic matter

Organic matter composition (lignin, holocellulose, 50% (v/v) methanol extract, water-soluble carbohydrate (WSC) and phenolics (WSP), petroleum ether extract, and ash) of A₀ layer soil treated with 700 g/m² of urea to promote ammonia fungi was investigated in a Japanese red pine (Pinus densiflora) forest. Nine species of fungi were found during the study period of 18 months after the treatment. Of these, seven species belong to the ammonia fungi. WSC content of the treated soil was lower than that of the control. Methanol extract content increased initially after the treatment, then decreased to below the control level. There were no consistent differences in other components between the treated plot and the control. The abilities to decompose cellulose, lignin, chitin, protein and lipid in 18 strains in 10 species of the ammonia fungi were also screened. Cellulose was not lysed byPseudombrophila deerata, Hebeloma spp. andLaccaria bicolor. Strong lignolytic activity was shown byLyophyllum tylicolor, Coprinus echinosporus andP. deerata. Chitin was decomposed byAmblyosporium botrytis, L. tylicolor, C. echinosporus andHebeloma vinosophyllum. All strains possessed proteolytic and lipolytic activities. Supply of glucose to the culture media resulted in weaker enzyme activities except for lignolytic ability.     

Effect of support material and enzyme pretreatment on enantioselectivity of immobilized subtilisin in organic solvents

Subtilisin Carlsberg was covalently attached to five macroporous acrylic supports of varying aquaphilicity (a measure of hydrophilicity). Kinetic parameters of the transesterification of S and R enantiomers of secphenethyl alcohol with vinyl butyrate, catalyzed by various immobilized subtilisins, were determined in anhydrous dioxane and acetonitrile. Enzyme enantioselectivity in acetonitrile, but not in dioxane, correlated with the aquaphilicity of the support; a mechanistic rationale for this phenomenon was proposed. Although the catalytic activity of immobilized subtilisin in anhydrous solvents strongly depended on enzyme pretreatment, the enantioselectivity was essential conserved. (c) 1994 John Wiley & Sons, Inc.     

Facilitated transport of lactic acid in a stirred transfer cell

The application of liquid membrane extraction to the recovery of lactic acid from model systems and fermentation media was investigated. An experimental study of the facilitated transport of lactic acid using ALIQUAT 336 as a mobile carrier in a stirred transfer cell is reported. The effect of stirring speed, initial lactic acid concentration, carrier concentration, and NaCl as a reagent in the acceptor phase are considered. (c) 1994 John Wiley & Sons, Inc.     

Biological destruction of CCl(4): I. Experimental design and data

A denitrifying consortium capable of transforming carbon tetrachloride (CCl(4)) was cultured from aquifer sediment from the U.S. Department of Energy's Hanford Site in southeastern Washington State. To understand the kinetics of the biological destruction of CCl(4) by these microbes, a set of experiments, the conditions of which were chosen according to a fractional factorial experimental design, were completed. This article reports on the experimental design along with the results for CCl(4), biomass, acetate, nitrate, and nitrite concentrations. These data indicate that growth is inhibited by high nitrite concentrations, whereas CCl(4) degradation is slowed by the presence of nitrate and/or nitrite. (c) 1994 John Wiley & Sons, Inc.     

Predicting responses of photosynthesis and root fraction to elevated [CO2]a: interactions among carbon,nitrogen, and growth*

At elevated atmospheric CO₂ concentrations ([CO₂]_a), photosynthetic capacity (A_max) and root fraction (η_R, the ratio of root to plant dry mass) increased in some studies and decreased in others. Here, we have explored possible causes of this, focusing on the relative magnitudes of the effects of elevated [CO₂]_a on specific leaf (n_m) and plant (n_p) nitrogen concentrations, leaf mass per unit area (h), and plant nitrogen productivity (α). In our survey of 39 studies with 35 species, we found that elevated [CO₂]_a led to decreased n_m and n_p in all the studies and to increased h and α in most of the studies. The magnitudes of these changes varied with species and with experimental conditions. Based on a model that integrated [CO₂]_a-induced changes in leaf nitrogen into a biochemically based model of leaf photosynthesis, we predicted that, to a first approximation, photosynthesis will be upregulated (A_max will increase) when growth at increased [CO₂]_a leads to increases in h that are larger than decreases in n_m. Photosynthesis will be downregulated (A_max will decrease) when increases in h are smaller than decreases in n_m. The model suggests that photosynthetic capacity increases at elevated [CO₂]_a only when additional leaf mesophyll more than compensates the effects of nitrogen dilution. We considered two kinds of regulatory paradigms that could lead to varying responses of η_R to elevated [CO₂]_a, and compared the predictions of each with the data. A simple static model based on the functional balance concept predicts that η_R should increase when neither n_p nor h is very responsive to elevated [CO₂]_a. The quantitative and qualitative agreement of the predictions with data from the literature, however, is poor. A model that predicts η_R from the relative sensitivities of photosynthesis and relative growth rate to elevated [CO₂]_a corresponds much more closely to the observations. In general, root fraction increases if the response of photosynthesis to [CO₂]_a is greater than that of relative growth rate.     

Speculations on carbon dioxide starvation, Late Tertiary evolution of stomatal regulation and floristic modernization

Ambient atmospheric CO₂ concentration ([CO₂]_a) has apparently declined from values above 200μmol mol⁻¹ to values below 200μmol mol⁻¹ within the last several million years. The lower end of this range is marginal for C₃ plants. I hypothesize that: (1) declining [CO₂]_a imposed a physiological strain on plants, and plant taxa evolving under declining [CO₂]_a tended to develop compensating mechanisms, including increased stomatal efficiency; (2) angiosperms were better able to adjust to declining [CO₂]_a than were gymnosperms and pteridophytes; and (3) angiosperm adjustment has been uneven. Fast-evolving taxa (e.g. grasses and herbs) have been better able to adapt to CO₂ starvation. If these propositions are true, stomatal adjustment mechanisms should show patterned variation, and a single pattern of stomatal regulation cannot be assumed.     

The effects of UV-B radiation on loblolly pine. 3. Interaction with CO2 enhancement

Projected depletions in the stratospheric ozone layer will result in increases in solar ultraviolet-B radiation (290–320 nm) reaching the earth's surface, These increases will likely occur in concert with other environmental changes such as increases in atmospheric carbon dioxide concentrations. Currently very little information is available on the effectiveness of UV-B radiation within a CO₂-enriched atmosphere, and this is especially true for trees. Loblolly pine (Pinus taeda L.) seedlings were grown in a factorial experiment at the Duke University Phytotron with either 0, 8.8 or 13.8 kJ m⁻² of biologically effective UV-B radiation (UV-B_BE). The CO₂ concentrations used were 350 and 650 μmol mol⁻¹. Measurements of chlorophyll fluorescence were made at 5-week intervals and photosynthetic oxygen evolution and leaf pigments were measured after 22 weeks, prior to harvest. The results of this study demonstrated a clear growth response to CO₂ enrichment but neither photosynthetic capacity nor quantum efficiency were altered by CO₂. The higher UV-B irradiance reduced total biomass by about 12% at both CO₂ levels but biomass partitioning was altered by the interaction of CO₂ and UV-B radiation. Dry matter was preferentially allocated to shoot components by UV-B radiation at 350 μmol mol⁻¹ CO₂ and towards root components at 650 μmol mol⁻¹ CO₂. These subtle effects on biomass allocation could be important in the future to seedling establishment and competitive interactions in natural as well as agricultural communities.