Changes in growth,porosity, and radial oxygen loss from adventitious roots of selected mono‐ and dicotyledonous wetland species with contrasting types of aerenchyma

Growth in stagnant, oxygen‐deficient nutrient solution increased porosity in adventitious roots of two monocotyledonous (Carex acuta and Juncus effusus) and three dicotyledonous species (Caltha palustris, Ranunculus sceleratus and Rumex palustris) wetland species from 10 to 30% under aerated conditions to 20–45%. The spatial patterns of radial oxygen loss (ROL), determined with root‐sleeving oxygen electrodes, indicated a strong constitutive ‘barrier’ to ROL in the basal root zones of the two monocotyledonous species. In contrast, roots of the dicotyledonous species showed no significant ‘barrier’ to ROL when grown in aerated solution, and only a partial ‘barrier’ when grown in stagnant conditions. This partial ‘barrier’ was strongest in C. palustris, so that ROL from basal zones of roots of R. sceleratus and R. palustris was substantial when compared to the monocotyledonous species. ROL from the basal zones would decrease longitudinal diffusion of oxygen to the root apex, and therefore limit the maximum penetration depth of these roots into anaerobic soil. Further studies of a larger number of dicotyledonous wetland species from a range of substrates are required to elucidate the ecophysiological consequences of developing a partial, rather than a strong, ‘barrier’ to ROL.     

Root porosity and oxygen movement in waterlogging-tolerant Trifolium tomentosum and -intolerant Trifolium glomeratum

Trifolium tomentosum and T. glomeratum are small (< 0·5 mg) seeded pasture legumes which are considered to be waterlogging tolerant and intolerant, respectively. The root porosity of the two species was compared for plants raised for 10 d in aerated nutrient solution and then transferred to either aerated (0·25 mol O₂ m^–3) or ‘hypoxic’ (0·031–0·069 mol O₂ m^–3) solutions for a further 7 and 21 d. After 21 d, T. tomentosum developed a root porosity of 11·2% in ‘hypoxic’ solution, which was significantly higher than the 6·1% developed by T. glomeratum. When grown in aerated solution, T. tomentosum also had a larger constitutive porosity (6·7%) than T. glomeratum (3·9%). Cylindrical root-sleeving O₂ electrodes were used to measure the rates of radial O₂ loss (ROL) from roots of the two species when in an O₂-free medium. In general, roots previously grown in ‘hypoxic’ solution had higher rates of ROL than roots grown in aerated solution. Moreover, the rates of ROL along the main root of T. tomentosum were ≈ 5-fold faster than from equivalent locations along roots of T. glomeratum. Manipulations of the shoot O₂ concentration resulted in rapid changes in ROL near the root tip of T. tomentosum plants raised in aerated or ‘hypoxic’ solutions, whereas for T. glomeratum ROL only increased for roots of plants raised in ‘hypoxic’ solution. Thus, the cortical air spaces in roots of both species raised in ‘hypoxic’ solution formed a continuous, low resistance pathway for O₂ diffusion from the shoots to the roots. ROL from the lateral roots was also evaluated and it was 3-fold faster from T. tomentosum than from T. glomeratum. Moreover, ROL from lateral roots of T. tomentosum was 10–20-fold higher than from a position on the primary root axis the same distance from the root/shoot junction. Relatively, high rates of ROL were also recorded for young (40 mm in length) lateral roots of T. glomeratum which were previously grown in ‘hypoxic’ solution, but the ROL was low for the older lateral roots of this species. The substantial amounts of ROL from the lateral roots may limit O₂ supply to the lower parts of the primary root axis, so that the laterals probably become the main functional root system in waterlogged soils.     

The native subspecies of Juncus effusus (Juncaceae) in western North America

Juncus effusus s. str. has two native representatives on the coast of western North America. A new combination is provided forJuncus effusus subsp.pacificus, ranging from California to British Columbia.Juncus effusus subsp.austrocalifornicus is newly described from southernmost California, Arizona, and Baja California, México. It differs from subsp.pacificus by its pale sheaths, with less thickened and less overlapping margins, and its disjunct distribution. A key is provided for the subspecies ofJ. effusus in North America.     

Potential of Indigenous Plant Species for the Phytoremediation of Arsenic Contaminated Land in Kurdistan (Iran)

To evaluate the potential of the indigenous plant species for Arsenic (As) phytoremediation, a total of 138 plant samples and 138 soil samples from rooting zones were collected from two As-contaminated areas in Kurdistan, western Iran. The areas were the Sari Gunay Gold Mine (SG) and Ali Abad Village (AA). The soil of both areas naturally contains As, with mining activities at SG. Soil and plant samples were collected at five sites in the SG (SG1 to SG5) and at two sites in the AA (AA1 and AA2). Soil samples were analyzed for total and water-soluble As concentration, as well as for the main soil physical and chemical properties such as electrical conductivity (Ec), pH, organic carbon (C_org.), available phosphorus (P_ava.), and soil texture. Plant samples were analyzed for As concentration in their shoots and roots.

The average total and water–soluble As concentrations in soil were 751.6 and 6.2 ppm at SG and 920.8 and 8.0 ppm at AA, respectively. The highest root and shoot As concentration was found in Juncus inflexus (751.5 ppm) at AA2 and in Astragalus gossypinus (158.7 ppm) at AA1, respectively. With regard to phytoremediation strategies, Acantholimon brachystachyum, Astragalus gossypinus, Stipa barbata, and Ephedra major with a high translocation factor (TF) can be potentially used for As phytoextraction. However, Juncus inflexus, Phragmites australis, Bromus tomentellus, and Elymus sp., which show high bioconcentration factor (BCF) and low TF, are suggested as good candidates for As phytostabilization. In general, the TF values of terrestrial plants were higher than those of amphibious plants; meanwhile, BCF values showed the opposite behavior.     

Spatial heterogeneity and short‐term oxygen dynamics in the rhizosphere of Vallisneria spiralis: Implications for nutrient cycling

相似文献   

Enhancement of docosahexaenoic acid production by Schizochytrium sp. using a two-stage oxygen supply control strategy based on oxygen transfer coefficient

Aims: To improve the yield and productivity of docosahexaenoic acid (DHA) by Schizochytrium sp. in terms of the analysis of microbial physiology. Methods and Results: A two‐stage oxygen supply control strategy, aimed at achieving high concentration and high productivity of DHA, was proposed. At the first 40 h, K_La was controlled at 150·1 h^?1 to obtain high μ for cell growth, subsequently K_La was controlled at 88·5 h^?1 to maintain high q_p for high DHA accumulation. Finally, the maximum lipid, DHA content and DHA productivity reached 46·6, 17·7 g l^?1 and 111 mg l^?1 h^?1, which were 43·83%, 63·88% and 32·14% over the best results controlled by constant K_La. Conclusions: This paper described a two‐stage oxygen supply control strategy based on the kinetic analysis for efficient DHA fermentation by Schizochytrium sp. Significance and Impact of the study: This study showed the advantage of two‐stage control strategy in terms of microbial physiology. As K_La is a scaling‐up parameter, the idea developed in this paper could be scaled‐up to industrial process and applied to other industrial biotechnological processes to achieve both high product concentration and high productivity.     

Testing nitrogen and water co-limitation of primary productivity in a temperate steppe

Background and aims

Studies have found significant differences in methane (CH₄) emissions among rice cultivars; however, it is unclear whether this difference is related to radial oxygen loss (ROL) from the roots.

Methods

Based on a 2-year in situ field study and solution culture experiments on 16 rice cultivars, we investigated CH₄ emission levels and their dependence on ROL.

Results

We detected significant differences in CH₄ emission and ROL among rice cultivars. The lowest and highest CH₄ emission levels were 4.10 and 7.35 g m^?2 for early rice, and 14.36 and 23.33 g m^?2 for late rice, respectively. The maximum and minimum ROL values were 3.77 and 1.73 mmol plant^?1 h^?1 for early rice, and 4.18 and 2.08 mmol plant^?1 h^?1 for late rice, respectively. Seasonal total CH₄ emission was negatively correlated with ROL in the early rice season (p?<?0.01), and (p?<?0.01) in the late rice season. ROL was positively correlated with the number of roots per plant (RN), root tips per plant (RT), and root volume per plant (RV).

Conclusions

We suggest that ROL can be used as a predictive index for CH₄ emissions. RN, RT, and RV were the most important factors influencing ROL in rice cultivars.

     

Waterlogging tolerance in the tribe Triticeae: the adventitious roots of Critesion marinum have a relatively high porosity and a barrier to radial oxygen loss

Nine species from the tribe Triticeae – three crop, three pasture and three ‘wild’ wetland species – were evaluated for tolerance to growth in stagnant deoxygenated nutrient solution and also for traits that enhance longitudinal O₂ movement within the roots. Critesion marinum (syn. Hordeum marinum) was the only species evaluated that had a strong barrier to radial O₂ loss (ROL) in the basal regions of its adventitious roots. Barriers to ROL have previously been documented in roots of several wetland species, although not in any close relatives of dryland crop species. Moreover, the porosity in adventitious roots of C. marinum was relatively high: 14% and 25% in plants grown in aerated and stagnant solutions, respectively. The porosity of C. marinum roots in the aerated solution was 1·8–5·4‐fold greater, and in the stagnant solution 1·2–2·8‐fold greater, than in the eight other species when grown under the same conditions. These traits presumably contributed to C. marinum having a 1·4–3 times greater adventitious root length than the other species when grown in deoxygenated stagnant nutrient solution or in waterlogged soil. The length of the adventitious roots and ROL profiles of C. marinum grown in waterlogged soil were comparable to those of the extremely waterlogging‐tolerant species Echinochloa crus‐galli L. (P. Beauv.). The superior tolerance of C. marinum, as compared to Hordeum vulgare (the closest cultivated relative), was confirmed in pots of soil waterlogged for 21 d; H. vulgare suffered severe reductions in shoot and adventitious root dry mass (81% and 67%, respectively), whereas C. marinum shoot mass was only reduced by 38% and adventitious root mass was not affected.     

Effect of broken dead culms of Phragmites australis on radial oxygen loss in relation to radiation and temperature

The amount of oxygen released from the roots of Phragmites australis was quantified to examine the effects of airflow through dead culms, radiation, and temperature on radial oxygen loss (ROL). To investigate the effect of dead culms on ROL quantitatively, the ROL of individual plants with open dead culms was compared to that of plants with sealed dead culms as a function of light intensity and temperature. The relationship between ROL and plant morphology (aboveground biomass, shoot diameter, shoot height) was investigated. When exposed to 300, 600, and 900 μmol m⁻² s⁻¹ light, the ROL was 15.6, 22.5, and 30.9 μmol O₂ g⁻¹ dry root day⁻¹, respectively, from plants with open dead culms and 11.0, 16.4, and 23.3 μmol O₂ g⁻¹ dry root day⁻¹, respectively, from plants with sealed dead culms. The ROL from plants with open dead culms was obviously higher than that from plants with sealed dead culms in every condition. The ROL from plants with open culms was 37% and 30% higher than that from plants with sealed culms at 20°C and 30°C, respectively. The effects of plant-specific parameters such as leaf area and shoot diameter on radial oxygen loss were evident. From the point of view of rhizosphere oxidation during the growing season, the existence of open dead culms should be taken into consideration for optimal plant management in constructed wetlands. This study provides a theoretical understanding of the effects of open dead culms, light conditions, and temperature on radial oxygen loss. Handling editor: S. M. Thomaz     

A Method to Estimate Practical Radial Oxygen Loss of Wetland Plant Roots

The estimation of practical radial oxygen loss (ROL) of wetland plant roots was attempted in this study. We have devised a new method to measure ROL of wetland plant roots. The whole root system was bathed in an anoxic nutrient solution. Oxygen released from the root was removed immediately by introducing oxygen-free nitrogen gas (O₂ < 4 nmol L⁻¹) to mimic natural habitats where released oxygen is consumed rapidly due to chemical and biological oxidation processes. Oxygen removed from the root-bathing chamber was simultaneously detected colorimetrically by use of the highly oxygen-sensitive anthraquinone radical anion (AQ·⁻) in a cell outside the root-bathing chamber, which decolorized by a rapid reaction with oxygen. An emergent macrophyte Typha latifolia L. was incubated, and its ROL was measured by both the new method and one of the conventional methods, the closed chamber/electrode method, by which the ROL of Typha latifolia L. had not yet been measured. The new method succeeded in detecting the ROL, whereas the conventional method was not able to detect oxygen, due to the level being below the detection limit of the oxygen electrode. The oxygen supply via the seedlings of Typha latifolia L. was ca. 10 times higher compared with control measurements without plant. Light illumination significantly enhanced the ROL of Typha latifolia L. (0.33 nmol O₂ g⁻¹ root dry weight s⁻¹ under light and 0.18 nmol O₂ g⁻¹ root dry weight s⁻¹ in the dark). Theses values fall between those previously reported by the closed chamber/titanium citrate method and the open chamber/electrode method.     

Bimodal oxygen uptake in a freshwater air-breathing fish,Notopterus chitala

Measurements of bimodal oxygen uptake have been made in a freshwater air-breathing fish,Notopterus chitala at 29.0±1(S.D.)°C. xhe mean oxygen uptake from continuously flowing water without any access to air, was found to be 3.58±0.37 (S.E.) ml O₂ · h^?1 and 56.84+4.29 (S.E.) ml O₂ · kg^?1 · h^?1 for a fish weighing 66.92 + 11.27 (S.E.) g body weight. In still water with access to air, the mean oxygen uptake through the gills were recorded to be 2.49 ± 0.31 (S.E.) ml O₂ · h^?1 and 38.78 ± 1.92 (S.E.) ml O₂ · kg^?1 · h^?1 and through the accessory respiratory organs (swim-bladder) 6.04±0.87 (S.E.) ml O₂ · h^?1 and 92.32±2.91 (S.E.) ml O₂ · kg^?1 · h^?1 for a fish averaging 66.92±11.27 (S.E.) g. Out of the total oxygen uptake (131.10 ml O₂ · kg^?1 · h^?1), about 70% was obtained through the aerial route and the remainder 30% through the gills.     

Abilities of Helophyte Species to Release Oxygen into Rhizospheres with Varying Redox Conditions in Laboratory-Scale Hydroponic Systems

Plantlets of the wetland species cattail (Typha latifolia), reed (Phragmites australis), rush (Juncus effusus), and yellow flag (Iris pseudacorus) grown from seedlings or cuttings were investigated in laboratory-scale hydroponic systems in order to determine the intensity of oxygen release into the rhizosphere under various redox conditions. The initial redox conditions of the rhizosphere were modified by adding different amounts of titanium (III) citrate.

All the plantlets investigated released oxygen into the rhizosphere (0.01 mg/h ^* plant to 1.41 mg/h ^* plant), depending on the actual conditions of each experiment. The intensity of release was found to be controlled by the external oxygen demand in the rhizosphere for the whole range of conditions from extremely reduced to oxidized. The capacities of the plantlets to release oxygen were found to be species-specific under reduced conditions in the rhizosphere (–400 mV to +200 mV). Under conditions of higher redox potential (>+200 mV) the oxygen release depends on the physiological status of the individual plant.

Oxygen release rates are highest in the range–250 mV < Eh < ?150 mV. For the species investigated, the highest rates were observed for Typha latifolia (1.41 mg/h ^* plant) followed by Phragmites australis (1 mg/h ^* plant), Juncus effusus (0.69 mg/h ^* plant), and Iris pseudacorus (0.34 mg/h ^* plant). In general, the plantlets released oxygen with different rates into a nonbuffered rhizosphere until highly oxidized conditions in the root-near environment prevailed. The presented oxygen-releasing behavior is a process dominating natural conditions within the rhizosphere and is relevant to wetland systems and for conceptual approaches in phytoremediation.     

Decomposition of standing litter of the freshwater emergent macrophyte Juncus effusus

1. Standing dead plant litter of emergent macrophytes frequently constitutes a significant fraction of the detrital mass in many freshwater wetland and littoral habitats. Rates of leaf senescence and decomposition of the emergent macrophyte Juncus effusus were examined in a small freshwater wetland in central Alabama, U.S.A. Juncus effusus leaves in the initial stages of senescence were tagged in random plant tussocks and monitored periodically to determine in situ rates of leaf senescence and death. Fully senescent leaves were collected, placed in litter bags, and suspended above the sediments to simulate standing dead decay conditions. Litter bags were periodically retrieved over 2 years and analysed for weight loss, litter nutrient contents (N, P), associated fungal biomass and fungal taxa. 2. Senescence and death of J. effusus leaves proceeds from the leaf tip to the base at an exponential rate. The rate of senescence and death of leaf tissue increased with increasing temperatures. Plant litter decomposition was slow (k = 0.40 yr^–1), with 49% weight loss observed in 2 years. Both the nitrogen (N) and phosphorus (P) concentration (%) of litter increased during decomposition. However, the total amount of nitrogen (mg) in litter bags remained stable and phosphorus increased slightly during the study period. 3. Fungal biomass associated with plant litter, as measured by ergosterol concentrations, varied between 3 and 8% of the total detrital weight. Values were not significantly different among sampling dates (P > 0.05, ANOVA, Tukey). Fungi frequently identified on decaying litter were Drechslera sp., Conioscypha lignicola (Hyphomycetes), Phoma spp. (Coelomycetes), Panellus copelandii and Marasmiellus sp. (Basidiomycota). 4. These results support previous findings that plant litter of emergent macrophytes does not require submergence or collapse to the sediment surface to initiate microbial colonization and litter decomposition.     

Radial oxygen loss, a plastic property of dune slack plant species

Mean and environmentally induced differences in radial oxygen loss (ROL) were investigated for three pioneer species (i.e. Schoenus nigricans L., Juncus articulatus L. and Samolus valerandi L.) and two late-successional dune slack species (i.e. Calamagrostis epigejos L. and Carex flacca Schreber). These species were grown in a factorial design at conditions differing in moisture, light, nutrient availability and Fe²⁺ and Mn²⁺ concentrations. On average, ROL was twice as low for late-successional species compared to pioneer species, but it increased on average by a factor 1.5 for these species upon flooding while ROL was unaffected by flooding in pioneer species. Other effects of treatments on pioneer and late-successional species groups were insignificant. Species-specific plasticity in ROL was stronger than that of the species groups and varied highly with the different combinations of – interactions between – environmental cultivation conditions flooding, concentrations of Fe²⁺ and Mn²⁺, nutrient and light levels, but was not affected by differences in relative growth rates. Moreover, ROL activity was almost 20×, and significantly, higher for seedlings than for adults of Schoenus nigricans. This implies that ROL of a species depends on the stage of the life cycle and on growth conditions, something that should be considered when determining ROL. ROL activity of most species increased at (a combination of) high nutrient and at low light levels: ROL activity was strongly negatively correlated to the root/shoot ratio, which was presumably caused by a higher gas transport capacity compared to root oxygen consumption at low root/shoot ratios. The plasticity in ROL leads to a highly dynamic rhizosphere in which the oxygen influx is a function of plant species and particularly of the interactions between plant species and environmental conditions.     

Pulse-radiolytic investigations of catechols and catecholamines II. Reactions of Tiron with oxygen radical species

Transient spectra and kinetic data of Tiron (1,2-dihydroxybenzene-3,5-disulphonic acid) are reported, obtained after pulse-radiolytic oxidation by hydroxyl radicals (°OH), superoxide anions (O₂^?) or a combination of both oxygen radicals. The rate constant with °OH radicals was determined at 1.0·10⁹ M^?1·s^?1. Contrary to a previous report (Greenstock, C.L. and Miller, R.W. (1975) Biochim. Biophys. Acta 396, 11–16), the rate constant with O₂^? of 1.0·10⁷ M^?1·s^?1 is lower by one order of magnitude; also the semiquinone absorbs at 300 nm rather than at 400 nm. The ratio of the rate constants with °OH and O₂^? of 100 again demonstrates that any oxidation reaction by the latter radical is unspecific due to the more efficient reaction of °OH radicals, leading to the same products with catechol compounds.     

Profiling coral reef productivity and calcification using pH and oxygen electrodes

An instrument package carrying pH and oxygen electrodes and a thermister was floated across a reef flat. Using equations associated with the alkalinity anomaly technique, and by making certain assumptions, the productivity and calcification rates of the reef flat were calculated. At an average light intensity of 800 μE · m^?2 · s^?1, the average net oxygen production was 21.5 mmol O₂ · m^?2 · h^?1 and the average rate of calcification was 11.0 mmol CaCO₃ · m^?2 · h^?1. Results showed three metabolic zones within the transect which corresponded to zonation seen in an aerial photograph and confirmed by benthic surveys.     

The relationship between Rb+ influx and K+-stimulated Mg2+-ATPase activity in oat roots of different K+ status flexible coupling?

The relationship between Rb⁺ influx and microsomal ATPase activity stimulated by K⁺ and Mg²⁺+ K⁺ was investigated for roots of 7-day-old seedlings of oat (Avena sativa L., cv. Brighton). Different concentrations of K⁺ in the roots, K⁺_root were produced by cultivating plants in complete nutrient solutions of different dilutions and dFifferent K⁺ concentrations at various temperatures. Experiments were performed in both light and darkness. The range of the influx/ATPase ratios was large with a factor of 5 or more between the highest and lowest values. In most cases, the highest ratios were obtained at low K⁺_root and at high temperatures, and the lowest at high K⁺_root and at low temperatures. At high temperatures (20 and 25°C) in the light, the influx/ATPase ratio was constant, independently of K⁺_root, if K⁺ in the medium was kept constant but the bulk of the nutrient solution diluted. If K⁺ was varied and the other components of the medium kept constant, the normal relation of decreasing influx/ATPase ratio at increasing K⁺_root was found; thus, Rb⁺ influx appears regulated by both the internal and external potassium conditions. Also in darkness, at 15°C and with K ⁺ in the medium varied, the influx/ATPase ratio was independent of K⁺_root but in the corresponding light experiments, ratio and K⁺_root had the normal, inverse relationship. The difference between light and dark conditions appears to indicate that growth rate is of importance for the relationship between energy input and transport. Our data lead to the concept of “flexible coupling” between transducers) of energy and ion carrier. Without excluding other possibilities, this may be one of the mechanisms for ecological adaptation to variations in the root medium.     

Environmental factors regulating the radial oxygen loss from roots of Myriophyllum spicatum and Potamogeton crispus

Myriophyllum spicatum and Potamogeton crispus are common species of shallow eutrophic lakes in north-eastern Germany, where a slow recovery of the submersed aquatic vegetation was observed. Thus, the characterisation of the root oxygen release (ROL) as well as its implication for geochemical processes in the sediment are of particular interest. A combination of microelectrode measurements, methylene blue agar and a titanium(III) redox buffer was used to investigate the influence of the oxygen content in the water column on ROL, diel ROL dynamics as well as the impact of sediment milieu. Oxygen gradients around the roots revealed a maximum oxygen diffusion zone of up to 250 μm. During a sequence with a light/dark cycle as well as alternating aeration of the water column, maximum ROL with up to 35% oxygen saturation at the root surface occurred under light/O₂-saturated conditions. A decrease to about 30% was observed under dark/O₂-saturated conditions, no ROL was detected at dark/O₂-depleted conditions and only a weak ROL with 5–10% oxygen saturation at the root surface was measured under light but O₂-depleted water column. These results indicate, that during darkness, ROL is supplied by oxygen from the water column and even during illumination and active photosynthesis production, ROL is modified by the oxygen content in the water column. Visualisation of ROL patterns revealed an enhanced ROL for plants which were grown in sulfidic littoral sediment in comparison to plants grown in pure quartz sand. For both plant species grown in sulfidic littoral sediment, a ROL rate of 3–4 μmol O₂ h⁻¹ plant⁻¹ was determined with the Ti(III) redox buffer. For plants grown in pure quartz sand, the ROL rate decreased to 1–2 μmol O₂ h⁻¹ plant⁻¹. Hence, aside from the oxygen content in the water column, the redox conditions and microbial oxygen demand in the sediment has to be considered as a further major determinant of ROL.     

Respiration,energy balance and development during growth and starvation of Carcinus maenas L. larvae (Decapoda:Portunidae)

In all larval stages of Carcinus maenas L. oxygen consumption was measured at three temperatures (12,18,25 °C). Values increased during development and were in the range of 0.037 ± 0.01 (zoea-1, 12°C, $\text{x}\text{?}\text{± 95\% CL}$) to 0.734 ± 0.047 μl O₂ · h^?1 · ind^?1 (megalopa, 25 °C). Growing larvae showed temperature dependent trends in weight specific respiration rates (referred to dry wt; DW), with values between ≈2.4 and 9.4 μl O₂· h^?1·mg DW^?1. Increase in oxygen consumption of megalops did not differ much at temperatures between 18 and 25 °C. This points to an exceptional physiological position of this stage. Fed zoea-1 of C. maenas (18 °C) revealed growth rates in terms of 40% DW, 20% carbon (C), 30% nitrogen (N) and 65% hydrogen (H). At the same time larvae gained individual energy by 13% (J · ind^?1), while weight specific energy dropped by ≈ 19% (J · mg DW^?1) during the first day and remained constant until the moult. Starved zoea-1 of C. maenas (18 ° C) gained ≈ 20 % in DW through the first day, probably caused by inorganic salts which enter the organism after the moult of the prezoea. DW dropped to ≈ 25 % of initial value, when starvation continued. Single components decreased by ≈50% (C), 54% (N), 57% (J · ind^?1). Weight specific energy (J · mg DW^?1) decreased by 40% during the first 4 days of starvation, remaining constant thereafter. Individual respiration rate (R) dropped by 61 %, weight specific respiration rate (QO₂) by 55 %. Individual energy loss in starved zoea-1 was 0.077 J over a period of 11 days. In this period ≈ 9.3 μl O₂·ind^?1 were consumed. Thus effective oxygen capacity was lower than in growing larvae. It dropped to 5.3 J·mlO₂^?1 after 4 days and remained constant if starvation continued, i.e. 65 % of possible energy loss occurred during the first 4 days. Decrease in requirement for oxygen and its effective capacity were both recognized as independent components of survival during starvation. Partitioning of energy through individual larval development of C. maenas was investigated for all five larval stages. The cumulative budget could be calculated: consumption (C) = 28.23 J, growth (G) = 0.92 J, exoskeleton (Ex) = 0.20 J, metabolism (M) = 5.30 J, egestion and excretion (E) = 21.82 J. Mean gross and net growth efficiency were, K₁ = 3.3% and K₂ = 14.8%, respectively.     

Radial Oxygen Losses from Intact Rice Roots as Affected by Distance from the Apex, Respiration and Waterlogging

Radial oxygen losses (ROL) from the roots of intact rice plants were assayed by the cylindrical Pt electrode technique. At 23°C losses from roots grown in waterlogged soil proved to be about double those from non-waterlogged plants. Cooling which lowers respiratory activity led to increased ROL and it was estimated that at 23°C respiratory activity had been reducing oxygen loss by 8 to 10 10^–8g O₂ cm^–2 root surface min^–1 (c. 50 %) in the non waterlogged, and by 4.5 to 5.5 10^–8g O₂ cm^–2 min^–1 (2C–30 %) in the waterlogged roots. Lacunae formation occurred nearer to the apex and was eventually more extensive in the waterlogged roots while the presence of more intact and presumably functional tissue in the non-waterlogged roots coincides with the greater respiratory effect noted. Estimated flux rates at 23°C (respiration inactive) were respectively 15–17 × 10^–8g O₂ cm^–2 min^–1 (non-waterlogged) and 20–23 × 10^–8g O₂ cm^–2 min^–1 (waterlogged). A major part of this difference can probably be accounted for directly by the differences in root porosity, and Meakiness' superimposed upon lower porosity in the non-waterlogged plants may account for the remainder. ROL was also examined in relation to distance from the apex. With respiratory activity lowered by cooling, two patterns of oxygen loss were detected. Pattern I was a property of younger roots of length between 5–9 cm, while pattern 2 was found in longer roots 11–16 cm bearing numerous emergent laterals. In both, ROL fell rapidly towards the base and at 4–5 cm approached zero in pattern 1 and near zero to about 16% of the maximum in pattern 2. The rapid drop in oxygen loss in both patterns which indicates a concomitant decrease in root wall permeability was associated with the appearance of cortical lacunae at 2–3 cm from the apex. In pattern 2 a rise in ROL began at 5–6 cm from the apex. The presence of lateral root initials in both the pericycle and unbroken segments of cortex was associated with maintained permeability in this pattern as well as with the basal increase in ROL. With a 3-electrode system placed around the apical 3 cm regions of waterlogged roots, it was found that ROL was substantially affected by respiratory activity at 0.5 cm, a little less so at 1.7 cm, but much less or not at all at 3 cm from the apex. The drop in respiratory effect parallelled the formation of cortical lacunae.