A Critical Oxygen Pressure for Root Extension in Rice

Armstrong, W. and Webb, T. 1985. A critical oxygen pressurefor root extension in rice.—J. exp. Bot. 36: 1573–1582. The relationship between oxygen partial pressure and root extensionwas investigated using a method designed to circumvent boundarylayer resistance effects. Roots were made wholly dependent uponoxygen transported longitudinally from the atmosphere throughthe aerenchymatous and intercellular spaces and the internaloxygen pressure in the extension zone was altered when requiredby adjusting the oxygen content of gas mixtures applied to theshoot (whole plants) or basal cut-end of the root (excised roots).Platinum cathodes sleeving the root in the extension zone wereused to monitor root surface oxygen partial pressure continuously,root extension was measured half-hourly by means of travellingmicroscopes. The results confirmed that internal oxygen transport is sufficientto support root extension in rice and that, at least in theshort term, extension is not greatly influenced by oxygen concentrationuntil very low values are reached. A certain degree of variabilitywas noted when using whole plants but this was no longer evidentwith excised roots. The results from the latter suggest a figureof 0.8 kPa for the critical oxygen pressure of root extension,which is much lower than any previously published values. Itis supposed that such a low value is probably not a unique characteristicof rice roots but rather is the result of the measurements havingcircumvented both the boundary layer effects external to theroot and the normal influence of the epidermal and hypodermallayers. Key words: Roots, growth, oxygen, rice     

Oxygen transport in the submerged freshwater macrophyte Egeria densa planch. I. Oxygen production,storage and release

Oxygen exchange in the Egeria densa Planch. (Hydrocharitaceae) lacunar system was investigated using Clark-type oxygen electrodes to monitor root and shoot oxygen release into a bicompartment apparatus. An average root O₂ loss rate of 2.97±0.21 (s.e., n = 50) μl O₂ h⁻¹ cm⁻² root surface area was found, which was of a similar magnitude to values reported by other authors.Root O₂ loss was 4–5 times higher in the light than in the dark, and was approximately 60% higher with still water around the shoot than with a slow, continuous water flow across the shoot surface. Furthermore, both these root O₂ loss rates were reduced when the lower portion of the stem was darkened to simulate self-shading. Under illumination, the boundary layer and stem wall resistances caused thet stem lacunar oxygen partial pressure to be up to 5 kPa higher than in the water.Measurements of lacunar dimensions in Egeria allowed calculation of the oxygen gradient required to drive the observed transport rate. Simple gas-phase diffusion down a gradient of 5.49 × 10⁻² cm³ O₂ cm⁻³ m⁻¹ is sufficient to account for the oxygen transport rates in the experimental material.The ecological significance of the results is discussed, and a schematic model describing the diffusive transport of oxygen in the Egeria lacunar system is developed.     

Exploring the Radial and Longitudinal Aeration of Primary Maize Roots by Means of Clark-Type Oxygen Microelectrodes

Clark-type oxygen microelectrodes were used to measure the radial and longitudinal oxygen distribution in aerenchymatous and nonaerenchymatous primary roots of intact maize seedlings. A radial intake of oxygen from the rooting medium was restricted by embedding the roots in 1% agar causing aeration to be largely dependent upon longitudinal internal transport from the shoot. In both root types, oxygen concentrations declined with distance from the base, and were lower in the stele than in the cortex. Also, the bulk of the oxygen demand was met internally by transport from the shoots, but a little oxygen was received by radial inward diffusion from the surrounding agar, and in some positions the hypodermal layers received oxygen from both the agar and the cortex. Near to the base, the oxygen partial pressure difference between the cortex and the center of the stele could be as much as 6–8 kPa. Nearer to the tip, the differences were smaller but equally significant. In the nonaerenchymatous roots, cortical oxygen partial pressures near the apex were becoming very low (< 1 kPa) as root lengths approached 100 mm, and towards the center of the stele values reached 0.1 kPa or lower. However, the data indicated that respiratory activity did not decline until the cortical oxygen pressure was less than 2 kPa. Mathematical modeling based on Michaelis–Menten kinetics supported this and suggested that the respiratory decline would be mostly restricted to the stele until cortical oxygen pressures approached very low values. At a cortical oxygen pressure of 0.75 kPa, it was shown that respiratory activity in the pericycle and phloem might remain as high as 80–100% of maximum even though in the center of the stele it could be less than 1% of maximum. Aerenchyma production resulted in increases in oxygen concentration throughout the roots with cortical partial pressures of ca. 5–6 kPa and stelar values of ca. 3–4 kPa near the tips of 100 mm long roots. In aerenchymatous roots, there was some evidence of a decline in the oxygen permeability of the epidermal–hypodermal cylinder close to the apex; a decline in stelar oxygen permeability near the base was indicated for both root types. There was some evidence that the mesocotyl and coleoptile represented a very significant resistance to oxygen transport to the root.     

Pulsing of membrane potential in individual mitochondria: a stress-induced mechanism to regulate respiratory bioenergetics in Arabidopsis

Mitochondrial ATP synthesis is driven by a membrane potential across the inner mitochondrial membrane; this potential is generated by the proton-pumping electron transport chain. A balance between proton pumping and dissipation of the proton gradient by ATP-synthase is critical to avoid formation of excessive reactive oxygen species due to overreduction of the electron transport chain. Here, we report a mechanism that regulates bioenergetic balance in individual mitochondria: a transient partial depolarization of the inner membrane. Single mitochondria in living Arabidopsis thaliana root cells undergo sporadic rapid cycles of partial dissipation and restoration of membrane potential, as observed by real-time monitoring of the fluorescence of the lipophilic cationic dye tetramethyl rhodamine methyl ester. Pulsing is induced in tissues challenged by high temperature, H(2)O(2), or cadmium. Pulses were coincident with a pronounced transient alkalinization of the matrix and are therefore not caused by uncoupling protein or by the opening of a nonspecific channel, which would lead to matrix acidification. Instead, a pulse is the result of Ca(2+) influx, which was observed coincident with pulsing; moreover, inhibitors of calcium transport reduced pulsing. We propose a role for pulsing as a transient uncoupling mechanism to counteract mitochondrial dysfunction and reactive oxygen species production.     

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.     

Exchange of oxygen across the epicardial surface distorts estimates of myocardial oxygen consumption

The rate of oxygen consumption of isolated, Langendorff-circulated, saline-perfused hearts of guinea pigs, rats, and rabbits was measured using the classical Fick Principle method. The heart was suspended in a glass chamber the oxygen partial pressure, PO2, of which could be varied. The measured rate of oxygen consumption was found to vary inversely with the ambient (heart chamber) PO2. This result prevailed whether the chamber was filled with air, saline, or oil, and whether the pericardium was present or the heart was wrapped in Saran. The effect varied inversely with heart size both within and across species. It is concluded that the epicardial surface is permeable to oxygen which will diffuse either into or out of the heart as the PO2 gradient dictates. In either case the classically measured rate of oxygen consumption will be in error. The error can be large in studies of cardiac basal metabolism. A simple model is developed to describe the observed rate of oxygen consumption as classically measured. The measured rate is partitioned into two components: the true rate of oxygen consumption of the heart, and the rate of loss of oxygen by diffusive exchange across the epicardial surface. The latter component is proportional to the gradient of oxygen partial pressure from myocardium to environment and to the diffusive oxygen conductance of myocardial tissue. Application of the model allows the true rate of oxygen consumption of the heart to be recovered from measured values which may be considerably in error.     

Stimulation of ethylene production and gas-space (aerenchyma) formation in adventitious roots of Zea mays L. by small partial pressures of oxygen

Adventitious roots of two to four-weekold intact plants of Zea mays L. (cv. LG11) were shorter but less dense after extending into stagnant, non-aerated nutrient solution than into solution continuously aerated with air. Dissolved oxygen in the non-aerated solutions decreased from 21 kPa to 3–9 kPa within 24 h. When oxygen partial pressures similar to those found in non-aerated solutions (3, 5 and 12 kPa) were applied for 7 d to root systems growing in vigorously bubbled solutions, the volume of gas-space in the cortex (aerenchyma) was increased several fold. This stimulation of aerenchyma was associated with faster ethylene production by 45-mm-long apical root segments. When ethylene production by roots exposed to 5 kPa oxygen was inhibited by aminoethoxyvinylglycine (AVG) dissolved in the nutrient solution, aerenchyma formation was also retarded. The effect of AVG was reversible by concomitant applications of 1-aminocyclopropane-1-carboxylic acid, an immediate precursor of ethylene. Addition of silver nitrate, an inhibitor of ethylene action, to the nutrient solution also prevented the development of aerenchyma in roots given 5 kPa oxygen. Treating roots with only 1 kPa oxygen stimulated ethylene production but failed to promote gas-space formation. These severely oxygen-deficient roots seemed insensitive to the ethylene produced since a supplement of exogeneous ethylene that promoted aerenchyma development in nutrient solution aerated with air (21 kPa oxygen) failed to do so in nutrient solution supplied with 1 kPa oxygen. Both ethylene production and aerenchyma formation were almost completely halted when roots were exposed to nutrient solutions devoid of oxygen. Thus both processes require oxygen and are stimulated by oxygen-deficient surroundings in the 3-to 12-kPa range of oxygen partial pressures when compared with rates observed in air (21 kPa oxygen).Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine     

The Critical Oxygen Pressures for Respiration in Intact Plants

Two methods for determining critical respiratory oxygen pressure in whole plants are described. By a polarographic method involving the use of cylindrical platinum electrodes the following critical oxygen pressures for root respiration were found: Rice (cv. Norin 36). 0.024 atm: Rice (cv. Norm 37). 0.026 atm: Eriophorum angustifolium. 0.02 atm. These values contrast markedly with those obtained in vitro, and support earlier criticisms of in vitro measurements: they call into question the use of such data in the modelling of root aeration. When the results were assessed by an electrical analogue system, it was concluded that the respiratory activity in the intact root does not follow the normally accepted hyperbolic relationship with oxygen partial pressure. The experimental data were simulated most closely by assuming the critical oxygen pressure to be a function of respiratory responses in the low porosity (high diffusional impedance) tissues of the root meristem and stele, and respiratory activity in the moderately porous root cortex to be unaffected at values greater than 0.001 atm. A critical oxygen pressure of 0.025–0.04 atm for E. angustifolium was found from analyses of the gas phase oxygen in the leaves of whole plants after submergence in the dark. It was concluded that the higher value found by this method was most likely a function of respiratory responses in root tissue remote from the leaf and should not be regarded as the critical oxygen pressure for leaf respiration. The form of the oxygen concentration vs. time plot again suggested a very much lower critical oxygen pressure for certain of the plant tissues.     

Determination of oxygen saturation and hematocrit of flowing human blood using two different spectrally resolving sensors.

The blood parameters oxygen saturation and hematocrit were determined by two different spectral sensors using reflectance spectra from 550 to 900 nm and partial transmission spectra centered at 660 nm. The spectra were analyzed by the method of partial least squares. One sensor consists of a miniature integrating sphere, while the other was fiber-guided. The results show that the geometry of the sensors and different blood flows do not influence the spectral analysis significantly. Independent of the sensor geometry, both hematocrit and oxygen saturation could be determined with an absolute predicted root mean square error of less than 3%. Furthermore, the analysis showed that hematocrit prediction requires eight wavelength regions and oxygen saturation prediction requires four wavelength regions using reflectance spectroscopy. This implies that if the measurement is restricted to reflectance, a spectrometer is indispensable for determining both blood parameters. Hematocrit determination could be improved using reflectance measurements in combination with transmission.     

The effect of pressure upon the solubility of oxygen in water: Implications of the deviation from the ideal gas law upon measurements of fluorescence quenching

The effect of pressure upon the solubility of oxygen in water compressed up to 500 atmospheres (atm) was directly measured. Pressurized aqueous solutions were allowed to equilibrate with a low pressure atmosphere (air, total pressure, 1 atm; oxygen partial pressure, 0.2 atm) across a gas-permeable, pressure-resistant Teflon membrane, and the equilibrium molar concentration of oxygen determined chemically. The solubility of oxygen in water decreased exponentially with pressure up to approximately 200 atm. At higher pressures, decreases in the molar volume of oxygen in solution resulted in a slight deviation from this initial trend. Implications of these results upon measurements of fluorescence quenching by oxygen under conditions of elevated pressure, a probe for studying the structure of macromolecules, are discussed.     

Enhancement of Anaerobic Respiration in Root Tips of Zea mays following Low-Oxygen (Hypoxic) Acclimation

Root tips (10-millimeter length) were excised from hypoxically pretreated (HPT, 4% [v/v] oxygen at 25°C for 16 hours) or nonhypoxically pretreated (NHPT, 40% [v/v] oxygen) maize (Zea mays) plants, and their rates of respiration were compared by respirometry under aerobic and anaerobic conditions with exogenous glucose. The respiratory quotient under aerobic conditions with 50 millimolar glucose was approximately 1.0, which is consistent with glucose or other hexose sugars being utilized as the predominant carbon source in glycolysis. Under strictly anaerobic conditions (anoxia), glycolysis was accelerated appreciably in both HPT and NHPT root tips, but the rate of anaerobic respiration quickly declined in NHPT roots. [U-¹⁴C]Glucose supplied under anaerobic conditions was taken up and respired by HPT root tips up to five times more rapidly than by NHPT roots. When anaerobic ethanol production was measured with excised root tips in 50 millimolar glucose, HPT tissues consistently produced ethanol more rapidly than NHPT tissues. These data suggest that a period of low oxygen partial pressure is necessary to permit adequate acclimation of the root tip of maize to subsequent anoxia, resulting in more rapid rates of fermentation and generation of ATP.     

Dioxygen transmembrane distributions and partitioning thermodynamics in lipid bilayers and micelles

Cellular respiration, mediated by the passive diffusion of oxygen across lipid membranes, is key to many basic cellular processes. In this work, we report the detailed distribution of oxygen across lipid bilayers and examine the thermodynamics of oxygen partitioning via NMR studies of lipids in a small unilamellar vesicle (SUV) morphology. Dissolved oxygen gives rise to paramagnetic chemical shift perturbations and relaxation rate enhancements, both of which report on local oxygen concentration. From SUVs containing the phospholipid sn-2-perdeuterio-1-myristelaidoyl, 2-myristoyl-sn-glycero-3-phosphocholine (MLMPC), an analogue of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), we deduced the complete trans-bilayer oxygen distribution by measuring (13)C paramagnetic chemical shifts perturbations for 18 different sites on MLMPC arising from oxygen at a partial pressure of 30 bar. The overall oxygen solubility at 45 °C spans a factor of 7 between the bulk water (23.7 mM) and the bilayer center (170 mM) and is lowest in the vicinity of the phosphocholine headgroup, suggesting that oxygen diffusion across the glycerol backbone should be the rate-limiting step in diffusion-mediated passive transport of oxygen across the lipid bilayer. Lowering of the temperature from 45 to 25 °C gave rise to a slight decrease of the oxygen solubility within the hydrocarbon interior of the membrane. An analysis of the temperature dependence of the oxygen solubility profile, as measured by (1)H paramagnetic relaxation rate enhancements, reveals that oxygen partitioning into the bilayer is entropically favored (ΔS° = 54 ± 3 J K(-1) mol(-1)) and must overcome an enthalpic barrier (ΔH° = 12.0 ± 0.9 kJ mol(-1)).     

An inhibitory effect of excess moisture on the early development of Sinapis alba L. seedlings

Abstract. Mustard seedlings in the early stages of growth are sensitive to the presence of excess moisture, growth of the radicle and anthocyanin synthesis being retarded by water at a suction of less than 3 cm water for seedlings growing on a plane surface. This inhibitory effect commences at about 12-15 h from wetting of the seed. It can be counteracted by increasing the partial pressure of oxygen in the atmosphere or by de-coating the seed, suggesting that the inhibition is caused by a restricted flow of oxygen through the mucilaginous seed coat. The positive effect of gravity on anthocyanin synthesis in the developing seedling can be wholly accounted for in terms of the removal of excess moisture. This explanation largely accounts for the improved growth of the root, but a tonic effect of gravity on root growth can also be discerned.     

Pressurized gas transport in two Japanese alder species in relation to their natural habitats

Oxygen uptake measurements have shown that pressurized gas transport, resulting from the physical effect of thermo-osmosis of gases, improves oxygen supply to the roots of the seedlings in two alder speciesAlnus japonica (Thunb.) Steud. andAlnus hirsuta (Spach) Rupr., which are both native in Japan. When gas transport conditions were established by irradiation of the tree stems the internal aeration was increased to a level nearly equal to the oxygen demand of the root system in leafless seedlings ofA. hirsuta, but was higher inA. japonica so that excess oxygen was excreted into the environment. An increase of superoxide dismutase (SOD) activity, which protects plants from toxic oxygen radicals and post-anoxic injury, has been observed in root tissues ofA. japonica when the seedlings were flooded for 3 days. The increase of SOD activity, in concert with high gas transport rates, may enable this tree species to grow in wet sites characterized by low oxygen partial pressure in the soil and by varying water tables. A less effective gas transport, flood-induced reduction of SOD activity in root tissues, and reduced height growth in waterlogged soil may be responsible for the fact thatA. hirsuta is unable to inhabit wettland sites.     

Effect of elicitation on growth, respiration, and nutrient uptake of root and cell suspension cultures of Hyoscyamus muticus

The elicitation of Hyoscyamus muticus root and cell suspension cultures by fungal elicitor from Rhizoctonia solani causes dramatic changes in respiration, nutrient yields, and growth. Cells and mature root tissues have similar specific oxygen uptake rates (SOUR) before and after the onset of the elicitation process. Cell suspension SOUR were 11 and 18 micromol O2/g FW x h for non-elicited control and elicited cultures, respectively. Mature root SOUR were 11 and 24 micromol O2/g FW x h for control and elicited tissue, respectively. Tissue growth is significantly reduced upon the addition of elicitor to these cultures. Inorganic yield remains fairly constant, whereas yield on sugar is reduced from 0.532 to 0.352 g dry biomass per g sugar for roots and 0.614 to 0.440 g dry biomass per g sugar for cells. This reduction in yield results from increased energy requirements for the defense response. Growth reduction is reflected in a reduction in root meristem (tip) SOUR, which decreased from 189 to 70 micromol O2/g FW x h upon elicitation. Therefore, despite the increase in total respiration, the maximum local oxygen fluxes are reduced as a result of the reduction in metabolic activity at the meristem. This distribution of oxygen uptake throughout the mature tissue could reduce mass transfer requirements during elicited production. However, this was not found to be the case for sesquiterpene elicitation, where production of lubimin and solavetivone were found to increase linearly up to oxygen partial pressures of 40% O2 in air. SOUR is shown to similarly increase in both bubble column and tubular reactors despite severe mass transfer limitations, suggesting the possibility of metabolically induced increases in tissue convective transport during elicitation.     

Free radical involvement in the generation of trans‐root potential

The identity of the naturally occurring compounds that accept electrons from plasma membrane-bound redox systems in vivo is obscure. We analysed the effect of ascorbate, oxygen, iron, as well as their free radical forms, and also the free radical-generating and -quenching systems on the trans-root electrical potential, which had previously been shown to be coupled to plasma membrane-bound redox systems. The material was the primary root of 8-day-old maize (Zea mays L.) seedlings. Trans-root electrical potential difference was measured across excised roots. Different ascorbate (ascorbate, dehydroascorbate and ascorbate free radical) and oxygen redox forms (superoxide and hydroxide radicals and hydrogen peroxide), as well as scavenging agents of oxygen species (superoxide dismutase, catalase, mannitol), and ferric and ferrous ions were added to the solution flowing around the root. Ascorbate free radical induced the greatest depolarization of the trans-root potential when compared to other ascorbate redox forms, which is consistent with its suggested role as a natural electron acceptor. Addition of xanthine oxidase, with or without xanthine, also produced depolarizing effects. The presence of SOD magnified this effect both with ascorbate free radical and xanthine oxidase. When ferric or ferrous chloride and ferric EDTA were applied to the bathing medium, only free ferric ion produced a very pronounced depolarization. The magnitude and kinetics of trans-root potential depolarization, induced by the ascorbate redox forms and systems for the generation and scavenging of oxygen species, argue in favour of the mutually competing electron transfer role of ascorbate free radicals and superoxide radicals in the extracellular space of the root. These results provide evidence that at least a part of the electrical potential difference occurring across plant roots arises from current flow from the symplast, via the plasma membrane-bound redox systems, to naturally occurring compounds in the apoplast, and that this transfer is achieved through the mediation of their free radical forms.     

Effect of percolation rate on nutrient kinetics and rice yield in tropical rice soils

A model is presented with which the contribution of longitudinal oxygen diffusion to total oxygen requirement of a root can be estimated. Oxygen transport in and respiration of the soil are taken into account. Given the air-filled root porosity, root diameter, coefficient of oxygen transfer between root and soil, root and soil respiration rate, and the coefficient for oxygen diffusion in the soil, the maximum length a root can attain with an adequate oxygen supply to the root tip can be calculated. Results show the importance of root porosity for root aeration, also in unsaturated soils. For thick roots (radius >0.03 cm), diffusion along the internal pathway can provide 50–75% of the total oxygen requirement even, at modest values of the root porosity.     

Reduced oxygen diffusion across the shell of Gray gull (Larus modestus) eggs

Gray gulls, Larus modestus, nest 1500 m above sea level in northern Chile's Atacama Desert, one of the driest in the world. Their eggshell gas permeability, one third of that found in other Larus species, is an adaptation that reduces water loss, but at the expense of oxygen diffusion into the air cell with resultant hypoxia and reduced metabolic rate. This contrasts with characteristics found in birds nesting at very high altitudes where oxygen diffusion across the egg shell is maximized at the expense of water conservation. The oxygen consumption (MO2) of Larus modestus is 66% that of Larus argentatus; the oxygen conductance (GO2) is equivalent to 48% of that obtained in 5 other bird species. The oxygen partial pressure (PAO2) in the air chamber of Larus modestus (84 Torr) is lower than that of 10 other bird species whose average (PAO2) is 106 Torr. The CO2 partial pressure (PACO2) in the air chamber of Larus modestus is 68 Torr, a higher value than that found in 9 other bird species whose average (PACO2) is 39 Torr.     

Prediction of in situ root decomposition rates in an interspecific context from chemical and morphological traits

Background and Aims

We quantitatively relate in situ root decomposition rates of a wide range of trees and herbs used in agroforestry to root chemical and morphological traits in order to better describe carbon fluxes from roots to the soil carbon pool across a diverse group of plant species.

Methods

In situ root decomposition rates were measured over an entire year by an intact core method on ten tree and seven herb species typical of agroforestry systems and were quantified using decay constants (k values) from Olson''s single exponential model. Decay constants were related to root chemical (total carbon, nitrogen, soluble carbon, cellulose, hemicellulose, lignin) and morphological (specific root length, specific root length) traits. Traits were measured for both absorbing and non-absorbing roots.

Key Results

From 61 to 77 % of the variation in the different root traits and 63 % of that in root decomposition rates was interspecific. N was positively correlated, but total carbon and lignin were negatively correlated with k values. Initial root traits accounted for 75 % of the variation in interspecific decomposition rates using partial least squares regressions; partial slopes attributed to each trait were consistent with functional ecology expectations.

Conclusions

Easily measured initial root traits can be used to predict rates of root decomposition in soils in an interspecific context.     

光照和生长阶段对菖蒲根系泌氧的影响

以自然湖泊沉积物为研究基质,利用微型电机控制溶氧微电极实现纵向精确微位移,在照光与遮光条件下,对典型湿地植物菖蒲幼苗、成株根系根基部起总根长1/4处(根1/4)、根系中部(根1/2)、从根基部起总根长3/4处(根3/4)及根尖(根1)处根系微界面径向溶氧浓度变化进行原位精确测定。结果表明:无论有无光照,菖蒲幼苗、成株根系不同部位均存在从根表面至沉积物氧饱和度由高到低的氧扩散层,其厚度0.18—0.68 mm;根1/2、3/4、1处氧扩散能力菖蒲成株较幼苗显著增强(P<0.01),根1/4处二者则无显著差异(P>0.05);光照对菖蒲幼苗、成株根系不同部位氧扩散能力的影响存在差异,光照对菖蒲幼苗根1/2及菖蒲成株根1/2、根3/4处影响显著(照光组显著高于遮光组,P<0.01),而对菖蒲幼苗根1/4、根3/4、根1及菖蒲成株根1/4、根1处无显著影响(P>0.05);从根系泌氧空间差异上看,照光条件下菖蒲幼苗、成株分别表现为根1/2>根3/4≈根1≈根1/4(P<0.01,P>0.05)和根1/2>根3/4>根1>根1/4(P<0.01),遮光条件下菖蒲幼苗、成株分别表现为根1/2≈根3/4≈根1≈根1/4(P>0.05)和根1/2>根3/4≈根1>根1/4(P<0.01,P>0.05)。