红薯叶片浸提液对5种主要农田杂草种子萌发及幼苗生长的化感作用

以发芽率、发芽势、根长、茎长和鲜重变化为种子萌发和幼苗生长参数,研究了作物红薯叶片水浸液对云南省农田5种恶性杂草牛膝菊、藿香蓟、鬼针草、马唐和稗草的化感作用。结果表明,红薯叶片水浸液对5种受体杂草种子发芽率的影响不明显,但对发芽势有显著抑制作用。牛膝菊、藿香蓟、鬼针草和马唐的根长和生物量随红薯叶片水浸液浓度增加而显著降低,其中对马唐的抑制最强,高浓度0.1 g/m L时对根长和生物量抑制率分别为92.04%和73.33%,而低浓度0.0125 g/m L时分别为40.99%和46.67%;其次为鬼针草、藿香蓟、牛膝菊;最差的是稗草,随浓度的变化趋势均不明显。随红薯叶片水浸液浓度增加牛膝菊、鬼针草和马唐的茎长显著地降低,其中对马唐的抑制最强,高浓度0.1 g/m L和低浓度0.0125 g/m L时分别为86.85%和70.64%;其次为鬼针草和牛膝菊;相反藿香蓟和稗草的茎长随浓度增加而显著增加,高浓度0.1 g/m L和低浓度0.0125 g/m L时对藿香蓟的促进率分别为86.97%和16.03%。红薯叶片水浸液低浓度0.0125 g/m L时对牛膝菊的茎长和生物量有促进作用(低促高抑)。从化感作用响应指数和综合效应指数的综合对比来看,红薯对牛膝菊、藿香蓟、鬼针草、马唐具有显著的化感抑制作用,随浓度增加其抑制能力显著增加;其中对马唐的为最强,其次为鬼针草、牛膝菊和藿香蓟,相反对稗草具有促进作用(除了浓度0.1 g/m L)。所有这些表明,红薯叶片水浸液对5种杂草化感作用的敏感性趋势总体为:马唐鬼针草牛膝菊藿香蓟,最不敏感或者具有促进作用的是稗草。     

Influence of microbial concentration on the rheology of non-Newtonian fermentation broths

The objective of this study was to quantify the effect of fungal biomass concentration on the rheology of non-Newtonian fermentation systems. Batch fermentations of Penicillium chrysogenum were carried out with glucose as the sole carbon source. The flow behavior of the system was characterized at various fermentation times and was adequately described by the power-law model. The apparent viscosity of the fermentation broth was significantly affected by biomass concentrations in the fermenter. Fermentation broths containing 17.71 g/l biomass as dry weight were characterized by an apparent viscosity of 0.25 Pa s at a shear rate of 50 s⁻¹. Microbial concentration also affected the power-law flow-behavior index and the consistency index. The value of the consistency index ranged from 0.002 Pa s ⁿ at a biomass concentration of 0.1 g/l to 6.14 Pa s ⁿ at a biomass concentration of 17.71 g/l. The flow-behavior index decreased from an initial value of 1 to a final value of 0.17. Simple empirical correlations have been proposed to quantify the dependence of the power-law parameters on fungal biomass concentration. Experimental data obtained in this study were accurately described by these correlations. The general applicability of these relationships was tested, using previously published rheological data on Aspergillus awamori and Aspergillus niger fermentation broths, and good agreement was seen between experimental data and the predictions from the empirical correlations. Received: 24 March 1998 / Received revision: 10 September 1998 / Accepted: 16 October 1998     

Nonvascular contribution to ecosystem NPP in a subarctic heath during early and late growing season

Bryophytes and lichens abound in many arctic ecosystems and can contribute substantially to the ecosystem net primary production (NPP). Because of their growth seasonality and their potential for growth out of the growing season peak, bryophyte and lichen contribution to NPP may be particularly significant when vascular plants are less active and ecosystems act as a source of carbon (C). To clarify these dynamics, nonvascular and vascular aboveground NPP was compared for a subarctic heath during two contrasting periods of the growing season, viz. early-mid summer and late summer-early autumn. Nonvascular NPP was determined by assessing shoot biomass increment of three moss species (Hylocomium splendens, Pleurozium schreberi and Dicranum elongatum) and by scaling to ecosystem level using average standing crop. For D. elongatum, these estimates were compared with production estimates obtained from measurements of shoot length increase. Vascular NPP was determined by harvesting shrub and herb apical growth and considering production due to stem secondary growth of shrubs. Hylocomium splendens and Pleurozium schreberi showed highest biomass growth in late summer, whereas for D. elongatum this occurred in early summer. Maximum relative growth rates were ca. 0.003–0.007 g g⁻¹ d⁻¹. For D. elongatum, production estimates from length growth differed from estimations from biomass growth, likely because of an uncoupling between length growth and biomass shoot growth. Nonvascular NPP was 0.37 and 0.46 g dry weight m⁻² d⁻¹, in early and late summer, respectively, whereas in the same periods vascular NPP was 3.6 and 1.1 g dry weight m⁻² d⁻¹. The contribution of nonvascular NPP to total aboveground NPP was therefore minor in early summer but substantial in late summer, when 25% of the C accumulated by the vegetation was incorporated into nonvascular plant tissue. The expected global change-induced reduction of nonvascular plant biomass in subarctic heath is likely therefore to enhance C release during the late part of the growing season.     

Seasonal growth and biomass ofTrapa japonica Flerov in Ojaga-Ike Pond,Chiba, Japan

In order to determine the seasonal growth and biomass ofTrapa japonica Flerov, field observations were carried out at Ojaga-ike Pond, Chiba, Japan, during 1979 and 1980. In spring, the plant showed exponential growth (c. 0.080 g g⁻¹ day⁻¹) and shoot elongation was as rapid as 10 cm day⁻¹. The plant attained its maximum biomass (380.5±35.1 g m⁻²) in late August, and about 50% of this was concentrated in the topmost 30-cm stratum (645.7±33.1 g m⁻³); maximum total stem length exceeded 6m. The plant produced large (500–800 mg per fruit), but small numbers of nut-like fruit (maximum, 5 fruits per rosette). Defoliation occurred almost linearly with time at a rate of 30.6 leaves m⁻² day⁻¹; annual net leaf production was estimated to be about twice as large as the seasonal maximum leaf biomass. While the number of leaves per rosette showed moderate seasonal change, rosette density, rosette area and leaf dry weight changed considerably during the year. From the negative log-log correlation between mean total leaf dry weight per rosette and rosette density, density-dependent rosette growth was assumed. The cause of the wide spread of this species in aquatic habitats is briefly discussed in terms of its seed size and morphology.     

Structure, above-ground biomass and dynamics of mangrove ecosystems: new data from French Guiana

The article presents new results on the structure and the above-ground biomass of the various population types of mangroves in French Guiana. Nine mangrove stands were studied, each composed of three to ten adjoining plots with areas that varied depending on the density of the populations. Structural parameters and indices were calculated. Individuals representative of the three groups of taxa present were felled:Avicennia germinans (L) Stearn, Rhizophora spp., and Laguncularia racemosa (L) Gaertn. The trunks, branches and leaves were sorted and weighed separately. The biomass was obtained by determining the allometric relationships, the general equation selected being of the type y = a _o x ^a1, where the diameter (x) is the predictive variable. The total above-ground biomass varied from 31 t ha⁻¹ for the pioneer stages to 315 t ha⁻¹ for mature coastal mangroves, but with large variations depending on the structural characteristics at each site. The results place the Guianese mangroves among those with high biomass, although lower than those reported for Asia. Based on the relationships between structural parameters and standing biomass, in particular with the use of the “self-thinning rule”, population dynamics models are proposed. Received: 16 August 1996 / Accepted 17 January 1998     

Light, nutrients and the growth of herbaceous forest species

The herb layer of forests planted on former agricultural land often differs from that of old-growth forest. This study investigates if the expected increased nutrient availability in the shaded conditions of newly planted forests and the plasticity of the species to adjust their biomass allocation to different levels of light and nutrients help to explain these differences in the herb layers of the two forest types. In a greenhouse experiment biomass distribution and production of two species characteristic for the highly shaded forest floor, Circaea lutetiana and Mercurialis perennis, and two species more common in the forest-edge, Aegopodium podagraria and Impatiens parviflora were studied at different levels of light (2%, 8% and 66% of the full light level) and nutrients (30 and 300 kg N ha^–1 per year). The main factor affecting allocation and biomass production was light availability. Nutrient supply only had a significant effect at the higher light levels. Species were mainly plastic to changes in light and the two species from the forest floor showed to be more rigid in allocation pattern than the species from the forest-edge. So, although the species from the forest-edge were more plastic, they did not profit from the increased nutrient supply because the main factor affecting biomass distribution and production was light availability.     

甘肃南部7种高寒杜鹃生物量模拟

精确测定与模拟高山-亚高山灌丛生物量是了解陆地生态系统碳功能的重要基础工作。以甘肃南部高山-亚高山地区常见的7种高寒杜鹃（Rhododendron spp.）灌木为对象,通过标准植株收获法,建立易测因子与各器官生物量及总生物量的方程并检验拟合精度,筛选最优拟合方程。结果表明：（1）自变量和函数的类型对杜鹃生物量的模拟效果影响较大,700组方程中以D和D²H为自变量和以幂函数为模型拟合的R²相对集中、中位数都较高。（2）遴选出的35组单物种最优生物量模型的R²介于0.66-0.99之间、中位数为0.92,除山光杜鹃（Rh.oreodoxa）的茎、叶生物量和地上生物量模型为线性函数、麻花杜鹃（Rh.maculiferum）的所有模型为指数函数外,其余的生物量模型均为幂函数;D和D²H是单物种生物量模型的最佳预测变量,H仅是黄毛杜鹃（Rh.rufum）除根外、美容杜鹃（Rh.calophytum）叶生物量的最佳预测变量。（3）混合物种最优模型是以D²H为自变量的幂函数,除对叶生物量的模拟精度相对较低外,对其它生物量的模拟均较好。甘肃南部7种高寒杜鹃灌木生物量模型的建立为高寒地区灌丛生态系统碳汇功能的研究提供了支撑。     

Studies on the dynamic properties of terrestrial ecosystems based on a simulation model II. Tropical rainforest dynamics and stability as influenced by stem mortality

Further analysis of tropical rainforest dynamics and stability in relation to stem mortality has been conducted using a microcomputer model developed in a previous study (Oikawa, 1985). By simulation experiments covering a period of 100 years, the effects of changing stem mortality (δc) upon a tropical rainforest were investigated. Increasing stem mortality ranging from a standard value (3%yr⁻¹) to a 4-fold value (12%yr⁻¹) brings about decreases in stem biomass and thus total living biomass, and a contrasting increase of stem litterfall flux at the steady state of the forest ecosystem. At the same time, the decreased stem biomass at the steady state is predicted to result in increases of gross production (P _g) and net production (P _n), and an improvement in production efficiency of the model rainforest expressed as theP _n/P_g ratio. similar simulation experiments predict that the improved production efficiency in the forest with a 4-fold stem mortality is able to enhance tolerance to less productive environments such as a prolonged dry season or a reduced incident light flux density. On the other hand, the standard stem mortality (δ_c=3%yr⁻¹), which was estimated as a probable value for the Pasoh forest, West Malaysia, is considered to approximate the lower threshold necessary for attaining forest stability. Based on the results obtained, the significance of δ_c for the dynamics and stability of a tropical rainforest ecosystem is discussed in relation to the competition and tolerance of trees. In addition, the effectiveness of the simulation approach adopted here is emphasized. Titles are tentative translations by the author for original titles in Japanese.     

Evidence against the involvement of phytochrome in UVB-induced inhibition of stem growth in green tomato plants

The effects of UVB on the kinetics of stem elongation of wild type (WT) and photomorphogenic mutants of tomato were studied by using linear voltage transducers connected to a computer. Twenty-one or twenty-six-day-old plants, grown in 12 h white light (150 μmol m⁻² s⁻¹ PAR)/12 h dark cycles, were first transferred to 200 μmol m⁻² s⁻¹ monochromatic yellow light for 12 h, then irradiated with 0.1 or 4.5 μmol m⁻² s⁻¹ UVB for 12 h and finally kept in darkness for another 24 h. The measurements of the kinetics of stem elongation started after 4 h under yellow light. Significant differences in stem growth during the irradiation with yellow light, as well as during the dark period, were found between the genotypes. In darkness, the magnitude of stem growth followed the order: tri > AC = fri > MMau > hp1. Two factors determined the large differences of growth in darkness: 1) the different stem elongation rate (SER) and 2) the different duration of the growing phase among the genotypes. In darkness the stem growth of au and hp1 mutants lasted for about 18 h, whereas it continued for the whole experimental period (36 h) in the other genotypes. UVB irradiation substantially reduced elongation growth of all genotypes (4.5 μmol m⁻² s⁻¹ being more effective than 0.1 μmol m⁻² s⁻¹). Both fluence rates of UVB induced a detectable reduction of SER already after 15 min of irradiation. Red light inhibited, while far red light promoted stem growth of all the genotypes tested. fri (phyA null), tri (phyB1 null), hp1 (exhibiting exaggerated phytochrome responses) mutants and WT tomato showed similar levels of UVB–induced inhibition of growth, while the aurea mutant showed the largest growth inhibition during the 12 h of irradiation. These results indicate that phytochrome is not directly involved in UVB control of stem elongation. The results of dichromatic irradiations UVB + red or UVB + far red indicate the presence of distinct and additive action of UVB photoreceptor and of the phytochrome system in the photoregulation of stem growth. This revised version was published online in June 2006 with corrections to the Cover Date.     

Use of Phanerochaete chrysosporium biomass for the removal of textile dyes from a synthetic effluent

Summary The use of Phanerochaete chrysosporium biomass for the removal of Reactofix Golden Yellow from aqueous solution and eight textile dyes (four azo and four anthraquinone) from a synthetic effluent (0.6 g/l) at different pH, temperature and biomass concentrations was studied. Adsorption was maximum at pH 2.0 and 40 °C using 2.45 g mycelial biomass. The rate constant of adsorption was 1.95×10⁻¹/min for Reactofix Golden Yellow and 1.64×10⁻¹/min for synthetic effluent. In both cases, the equilibrium data fitted well in the Langmuir but not the Freundlich model of adsorption, and the adsorption was biphasic. Adsorption decreased the COD of Reactofix Golden Yellow and synthetic effluent by 54 and 57%, respectively. Desorption (80–84%) of dyes from P. chrysosporium mycelial surface occurred as the pH increased from 2 to 10.     

Production Ecology of the Non-indigenous Seagrass, Dwarf Eelgrass (Zostera japonica Ascher. & Graeb.), in a Pacific Northwest Estuary, USA

The non-indigenous seagrass Zostera japonica Ascher. & Graeb. (dwarf eelgrass) was first identified in central Oregon (USA) estuaries about 30 years ago. The autecology of this species is poorly described at the southern end of its non-native range although several process oriented studies have been conducted. I examined the production ecology of Z. japonica in the Yaquina Bay estuary. Strong seasonal patterns in light and temperature appeared to control the seasonal variations in biomass and growth. Above- and below-ground biomass ranged between 40–100 and 70–170 gdw m⁻² respectively and seasonal changes in the root:shoot ratio were controlled by above-ground biomass dynamics. Shoot density ranged between 4000 and 11 000 shts m⁻². Areal leaf growth ranged between 0.1 and 1.7 gdw m⁻² d⁻¹ and annual production was about 314 ± 60 gdw m⁻² y⁻¹ (mean ± SD). Nutrients were not limiting in this system as a result of coastal upwelling and watershed inputs. The Z. japonica population studied in Oregon exhibited different patterns of persistence, phenology and flowering intensity relative to other populations along its native and non-native range. These differences suggest that management policies developed for one site may not be appropriate for other sites. The data presented here greatly expands our knowledge base on Z. japonica and provides insight to the processes controlling the dynamics and spread of this non-indigenous seagrass. An erratum to this article is available at .     

Effect of crab shell size on bio-demineralization with lactic acid-producing bacterium, <Emphasis Type="Italic">Lactobacillus paracasei</Emphasis> subsp. <Emphasis Type="Italic">tolerans</Emphasis> KCTC-3074

Demineralization (DM) from crab shell (CS) waste was carried out using a lactic acid-producing bacterium, Lactobacillus paracasei subsp. tolerans KCTC-3074 for 7 days at 25, 30, and 35°C. DM rates were 89∼92% and slightly affected by temperature. DM was also performed for four particle-sized shell samples (0.84∼3.35, 3.35∼10, 10∼20, and 20∼35 mm) with 10% inoculum, 5% shell, and 10% glucose at 30°C and 180 rpm for 7 days. It was found out that the shell size had a slight effect on the rate of DM. Negative relationships were found between DM and residual dry weight (r² = 0.960), and between DM and pH (r² = 0.906). Conversely, positive relationships were found between DM and medium protein (r² = 0.696), and between DM and total titratable acidity (r² = 0.630).     

Vegetative growth and productivity ofEichhornia azurea with special emphasis on leaf dynamics

The lifeform and the biological production of pure stands ofEichhornia azurea Kunth in three lakes in tropical Brazil were studied. The lifeform ofE. azurea is termed ‘semi-emergent’, because the plant has well developed trailing stems just under the water, and the aerial lamina emerges with the thick petiole. The density of shoot apices was 9.9, 17.2 and 17.1 m⁻² in Lake Dom Helvecio, Lake Jacaré and Lake Carioca, respectively. The mean daily increment of the apical shoot biomass was between 1.8 and 4.8 g m⁻² day⁻¹. The mean leaf life-span in Lake Dom Helvecio, Lake Jacaré and Lake Carioca was estimated to be 78, 49 and 64 days in the wet season and 73, 70 and 73 days in the dry season, respectively. The stem life-span was estimated to be about 28 months. Starch content in the current years' stem ranged from 24 to 118 mg g⁻¹ dry matter with fluctuations, the amplitude of which decreased with age. The differences for most of the growth parameters, such as density of shoot apices, daily increment of biomass and leaf life-span, between dry and wet season are smaller than those among the three lakes. Both the decrease in daily dry matter production and the increase in leaf life-span occurred in order from Lake Dom Helvecio to Lake Jacaré and Lake Carioca. The low productivity ofE. azurea is considered to be related to a low leaf area index, a long time interval for the emergence of new leaves, long leaf life-span and a low capacity for branching.     

Tolerance and phytoaccumulation of Chromium by three Azolla species

Azolla, an aquatic fern is ideal candidate for exploitation in constructed wetlands for treating metal-contaminated wastewaters. This study demonstrates the potential of Azolla spp. namely A. microphylla, A. pinnata and A.␣filiculoides to tolerate Cr ions in the growth environment and bioconcentrate them. These species could grow in presence of up to 10 μg ml⁻¹ Cr and showed biomass production 30–70% as compared to controls. Nitrogenase activity was not affected at 1–5 μg ml⁻¹ but at higher concentrations it diminished. There was no growth at higher concentrations of chromium. However, the necrosed biomass harvested from treatments containing higher concentrations of chromium, accumulated Cr to the levels 5000–15,000 μg g⁻¹. At increased levels of Cr, the metal was accumulated in higher amount in dry biomass. Bioconcentration Factor (BCF) ranged between 243 and 4617 for the three species. A. microphylla showed highest bioconcentration potential. Thus, these Azolla spp. can be exploited for treatment of tannery and other Cr contaminated wastewaters.     

Performance of a flat plate,air-lift reactor for the growth of high biomass algal cultures

A flat plate, multi-pass air lift reactor (FPALR) for the culture of photosynthetic organisms was constructed from twin wall acrylic sheet and its performance characterised. When operated at an air input of 2.01 min⁻¹ the multi-pass system had a Reynolds number of 5200 indicating fully turbulent flow. Chlorella vulgaris 211/11c was found to have a stationary phase biomass of 1.48 g 1⁻¹ when grown in the flat plate air lift reactor (FPALR) at 100 μmol m⁻²s⁻¹ compared to 1.11 g 1⁻¹ when cultured in the continually stirred tank reactor (CSTR) at the same PFD (photon flux density). The same organism cultured at 200 μmol m⁻²s⁻¹ achieved a stationary phase biomass of 1.71 g 1⁻¹ in the FPALR. In contrast, Scenedesmus sp. produced a stationary phase biomass of 2.27 g1⁻¹ and 1.27 g1⁻¹, when cultured at 100 μmol m⁻²s⁻¹ in the FPALR and the CSTR respectively. The growth rates of both organisms were also higher in the PFALR.     

Growth characteristics of Rhodopseudomonas palustris cultured outdoors, in an underwater tubular photobioreactor, and investigation on photosynthetic efficiency

The underwater tubular photobioreactor is a fully controlled outdoor system to study photosynthetic bacteria. Before growing bacteria cells outdoors, two modified van Niel medium (vN-A, vN-B) were tested under artificial light. During exponential growth, the specific growth rates were 0.0416 and 0.0434 h⁻¹, respectively; vN-B was chosen for outdoor experiments. The growth behavior of Rhodopseudomonas palustris was investigated under a natural light–dark cycle (sunrise–sunset, 15L/9D) and a forced light–dark cycle (9:00–19:00, 10L/14D). Relationships between solar radiations, daily growth rates, and biomass output rates were also investigated. After determining the elemental biomass molar composition and its combustion heat, some trends of photosynthetic efficiency (PE) were obtained over daylight. The PE trends were always of the oscillatory type, with the exception of that achieved at low biomass concentration. Under a natural light/dark cycle, the maximum PE (11.2%) was attained at sunset, while under a forced light/dark cycle, the highest PE (8.5%) was achieved in the morning. Three initial biomass concentrations were investigated (0.65, 1.01, and 1.54 g l⁻¹). The stoichiometric equation for bacteria cells indicated that 87.7% of the carbon of acetic acid was converted to biomass and only 12.3% was lost as CO₂.     

Carbon-limited fed-batch production of medium-chain-length polyhydroxyalkanoates from nonanoic acid by <Emphasis Type="Italic">Pseudomonas putida</Emphasis> KT2440

Pseudomonas putida KT2440 grew on glucose at a specific rate of 0.48 h⁻¹ but accumulated almost no poly-3-hydroxyalkanoates (PHA). Subsequent nitrogen limitation on nonanoic acid resulted in the accumulation of only 27% medium-chain-length PHA (MCL-PHA). In contrast, exponential nonanoic acid-limited growth (μ = 0.15 h⁻¹) produced 70 g l⁻¹ biomass containing 75% PHA. At a higher exponential feed rate (μ = 0.25 h⁻¹), the overall productivity was increased but less biomass (56 g l⁻¹) was produced due to higher oxygen demand, and the biomass contained less PHA (67%). It was concluded that carbon-limited exponential feeding of nonanoic acid or related substrates to cultures of P. putida KT2440 is a simple and highly effective method of producing MCL-PHA. Nitrogen limitation is unnecessary.     

QTL for yield in bioenergy Populus: identifying G×E interactions from growth at three contrasting sites

Populus is a genus of fast growing trees that may be suitable as a bioenergy crop grown in short rotation, but understanding the genetic nature of yield and genotype interactions with the environment is critical in developing new high-yield genotypes for wide-scale planting. In the present study, 210 genotypes from an F₂ population (Family 331; POP1) derived from a cross between Populus trichocarpa 93-968 and P. deltoides ILL-129 were grown in southern UK, central France and northern Italy. The performance of POP1, based upon first- and second-year main stem traits and biomass production, improved from northern to southern Europe. Trees at the Italian site produced the highest mean biomass ranging from 0.77 to 18.06 oven-dried tonnes (ODT) ha⁻¹ year⁻¹, and the UK site produced the lowest mean biomass ranging from 0.18 to 10.31 ODT ha⁻¹ year⁻¹. Significant genotype × environment interactions were seen despite heritability values across sites being moderate to high. Using a pseudo-testcross analysis, 37 quantitative trait loci (QTL) were identified for the maternal parent and 45 for the paternal parent for eight stem and biomass traits across the three sites. High genetic correlations between traits suggested that collocating QTL could be inferred as a single pleiotropic QTL, reducing the number of unique QTL to 23 and 24 for the maternal and paternal parent, respectively. Additive genetic effects were seen to differ significantly for eight QTL on the maternal map and 20 on the paternal map across sites. An additive main effects and multiplicative interaction analysis was carried out to obtain stability parameters for each trait. These parameters were mapped as QTL, and collocation to trait QTL was accessed. Two of the eight stability QTL collocate to trait QTL on the maternal map, and 8 of the 20 stability QTL collocate to trait QTL on the paternal map, suggesting that a regulatory gene model is prevalent over an allele sensitivity model for stem trait stability across these environments.     

TheParasponia parviflora — Rhizobium symbiosis. Isotopic nitrogen fixation,hydrogen evolution and nitrogen-fixation efficiency,and oxygen relations

Summary Isotopic¹⁵N₂ experiments confirmed nitrogen fixation inParasponia parviflora. The conversion ratio C₂H₄/N₂ was 6.7 under the experimental conditions employed. Measurements of the δ¹⁵N in leaves of Parasponia and Trema showed on the basis of these determinations thatParasponia parviflora possesses N₂-fixing capacity and can be distinguished in this respect from the non-nitrogen-fixingTrema cannabina tested by the same method. Therefore, δ¹⁵N can be used to monitor N₂ fixation in natural ecosystems. Hydrogen evolution and the relative efficiency of N₂ fixation in this relation have been determined. DetachedParasponia parviflora root nodules grown in soil and tested in an argon/oxygen atmosphere produced appr. 4 μmol H₂.h⁻¹.g⁻¹ fresh weight root nodules. The relative efficiency of hydrogen utilization as measured in argon, air, and in the presence of C₂H₂ 10% (v/v) was for both equations used for to express this efficiency 0.96 and 0.97, respectively. This indicates that Parasponia like the root nodules of some actinorhizal symbioses (Alnus, Myrica, Elaeagnus) and some tropical legumes (Vigna sinensis) has evolved mechanisms of minimizing net hydrogen production in air, thus increasing the efficiency of electron transfer to nitrogen. The oxygen relation of nitrogen fixation (C₂H₂) inParasponia parviflora root nodules was determined. The nitrogenase activity of Parasponia root nodules increased at increasing oxygen concentrations up till c. 40% O₂. At oxygen levels above 40% O₂, the nitrogenase activity of the root nodules was nil or very erratic suggesting that at these oxygen levels the nitrogenase is not longer protected against the harmful effect of oxygen. In this respect Parasponia root nodules differ from actinorhizal root nodules in other nonlegumes, where optimal nitrogenase activity was observed in the range of 12–25% oxygen. Respiration experiments with Parasponia root nodules showed that in the range 10, 20, and 40% oxygen, the respiration rate (CO₂ evolution) increased concomitantly with an increase of the acetylene reduction rate. The CO₂/C₂H₄ values obtained varied between 8.1 and 19.2, being therefore 2–3 times higher than similar estimations in some actinorhizal and legume root nodules. The respiratory quotient (RQ) of detachedParasponia parviflora root nodules was in air initially approximately 2.0, but this value dropped to about 1.0 in a 3-hours period.     

Effect of light and temperature on the cyanobacterium <Emphasis Type="Italic">Arthronema africanum</Emphasis> - a prospective phycobiliprotein-producing strain

The effect of light intensity (50–300 μmol photons m⁻² s⁻¹) and temperature (15–50°C) on chlorophyll a, carotenoid and phycobiliprotein content in Arthronema africanum biomass was studied. Maximum growth rate was measured at 300 μmol photons m⁻² s⁻¹ and 36°C after 96 h of cultivation. The chlorophyll a content increased along with the increase in light intensity and temperature and reached 2.4% of dry weight at 150 μmol photons m⁻² s⁻¹ and 36°C, but it decreased at higher temperatures. The level of carotenoids did not change significantly under temperature changes at illumination of 50 and 100 μmol photons m⁻² s⁻¹. Carotenoids were about 1% of the dry weight at higher light intensities: 150 and 300 μmol photons m⁻² s⁻¹. Arthronema africanum contained C-phycocyanin and allophycocyanin but no phycoerythrin. The total phycobiliprotein content was extremely high, more than 30% of the dry algal biomass, thus the cyanobacterium could be deemed an alternative producer of C-phycocyanin. A highest total of phycobiliproteins was reached at light intensity of 150 μmol photons m⁻² s⁻¹ and temperature of 36°C, C-phycocyanin and allophycocyanin amounting, respectively, to 23% and 12% of the dry algal biomass. Extremely low (<15°C) and high temperatures (>47°C) decreased phycobiliprotein content regardless of light intensity.