硝酸盐对毛萼田菁茎瘤固氮的影响

ＫＮＯ３对毛萼田菁（Ｓｅｓｂａｎｉａｒｏｓｔｒａｔａ）茎瘤和根瘤固氮的抑制作用与瘤中积累，碳水化合物减少（特别是蔗糖）以及豆血红蛋白（ｌｇｈｅｍｏｇｌｏｂｉｎ，Ｌｂ）浓度减少和功能受阻相关．经ＫＮＯ３处理的植株的茎瘤类菌体的呼吸作用和固氮活性明显下降．从ＫＮＯ３处理的植株茎瘤中提取的类菌体悬液加上未经ＫＮＯ３处理的正常Ｌｂ可提高固氮活性和耐ｐＯ２；加５ｍｍｏｌ／ＬＫＮＯ２于正常的茎瘤类菌体悬液和Ｌｂ反应体系，引起固氮活性和耐ｐＯ２都降低，证明是Ｌｂ功能受阻的重要因素．施ＫＮＯ３可能还导致茎瘤Ｏ２扩散的阻力增加．     

暹罗于腥藻氢代谢的调节

暹罗鱼腥藻（Ａｎａｂａｅｎａ ｓｉａｍｅｍｓｉｓ）能代谢分子氢，基固氮酶和氢酶的放和吸氢均受其生长环境因子的影响。ＣＯ２对暹罗鱼腥藻之固氮酶的放氢和氢酶的放氢及吸氢显示不同程度的促进作用。在含５％ＣＯ２的空气条件下生长，藻细胞的氢酶放氢和吸氢活性分别为空气条件下的２．５倍和１．３倍；固氮酶的放氢活性为９６ｎｍｏｌ Ｈ２ｍｇ＾－１ｃｈｌ＾－１ｈ＆－１，而在空气中生长的细胞则检测不出该活性，培养基中加     

暹罗鱼腥藻氢代谢的调节

暹罗鱼腥藻（Ａｎａｂａｅｎａｓｉａｍｅｍｓｉｓ）能代谢分子氢，其固氮酶和氢酶的放氢和吸氢均受其生长环境因子的影响。ＣＯ２对暹罗鱼腥藻之固氮酶的放氢和氢酶的放氢及吸氢显示不同程度的促进作用。在含５％ＣＯ２的空气条件下生长，藻细胞的氢酶放氢和吸氢活位分别为空气条件下的２．５倍和１．３倍；固氮酶的放氢活性为９６ｎｍｏｌＨ２ｍｇ－１ｃｈｌ－１ｈ－１，而在空气中生长的细胞则检测不出该活性，培养基中加１０ｍｍｏｌ／ＬＫＮＯ３和／或１０ｍｍｏｌ／ＬＮａＮＯ２，对其氢酶放氢活性影响不大，但其需氧吸氢和固氮酶的放氢均明显受到抑制。ＤＣＭＵ和Ｋ３Ｆｅ（ＣＮ）６等抑制剂对氢酶活性有不同程度的影响，一些金属离子对氢酶放氢有刺激作用，其中尤以Ｎｉ２＋和Ｍｏ２＋明显。     

甘蒙柽柳与沙棘抗旱性研究

在野外条件下，应用ＰＶ技术研究了中龄的甘蒙柽柳和沙棘的水分参数［ｐｓ（ｓａｔ）、ｐｓ（ｔｌｐ）］及其生理生态学意义、季节变化规律．探讨了水分胁迫条件下树木的适应性．结果表明，水分参数具有一定的的季节变化规律．干旱胁迫条件下树木具有一定的渗透调节能力，其幅度大小随季节而发生变化；嫩枝生长时期，树木的抗旱性和渗透调节能力都很弱，随着枝条的木质化和叶子的革质化程度的增强，树木的抗旱性逐渐增强．     

施垃圾堆肥拌CaCO3对蔬菜中重金属的累积影响

垃圾堆肥拌施ＣａＣＯ３对蔬菜中重金属的累积效应试验结果显示：单施垃圾肥会增加蔬菜中重金属的累积量，但若施垃圾堆肥同时拌施ＣａＣＯ３（按施垃圾堆肥量的０．５％或１％），则可有效地降低蔬菜中重金属的累积水平．与单施垃圾堆肥相比，拌施ＣａＣＯ３能使番茄中Ｐｂ含量下降２９％－４１％；Ｃｒ下降５％－４６％，Ｃｄ下降９％－４２％；Ｃｕ下降２％－２４％；ＡＳ下降４％－６０％；有的元素如Ｐｂ和Ｃｄ甚至能降到本底值（即不施垃圾肥者）以下。青菜中Ｐｂ、Ｃｕ、Ａｓ的含量下降较明显。试验还显示：施垃圾堆肥拌施ＣａＣＯ３，土壤中重金属可提取总量低于单施垃圾堆肥者。     

嗜热厌氧细菌Clostridium sp.EVA4菌株直接转化纤维素产乙醇的研究

用分离获得的嗜热厌氧纤维素降解细菌 Ｃｌｏｓｔｒｉｄｉｕｍ ｓｐ ． Ｅ Ｖ Ａ４ 菌株进行了直接转化纤维素产生乙醇的动力学、发酵最适条件及其影响因子的研究．结果表明, Ｅ Ｖ Ａ４ 菌株在ｐ Ｈ６ ．２ ～８ ．９ ,θ４５ ℃～６０ ℃的范围内能直接转化纤维素滤纸产生乙醇,最适ｐ Ｈ 为７ ．５ ～８ ．０ ,最适θ为５５ ～６０ ℃． Ｅ Ｖ Ａ４ 菌株能利用纤维素滤纸,纤维素粉 Ｗｈａｔｍａｎ Ｃ Ｆ Ｉ Ｉ,微晶纤维素,纤维素粉 Ｍ Ｎ３００ 和未经处理的玉米秆芯,甘蔗渣,水稻秸秆产生乙醇．乙醇浓度 ,纤维素降解率和培养基还原糖浓度均随培养时间延长而增大．不同的纤维素材料、ｐ Ｈ、θ、底物浓度、酵母粉含量、振荡、培养气相、外加 Ｏ２ 和乙醇等条件均能影响 Ｅ Ｖ Ａ４ 菌株转化纤维素为乙醇的能力．最适条件下 Ｅ Ｖ Ａ４ 菌株利用１ ％ 纤维素滤纸培养１２０ ｈ 产乙醇浓度为１ １２３ ｍｇ／ Ｌ,纤维素降解率为５９ ％     

利用氧化亚铁硫杆菌抗砷工程菌Tf—59（pSDX3）处理含砷金精矿

利用构建的氧化亚铁硫杆菌抗砷工程菌对含砷金精矿进行了有关试验，结果表明：含有抗砷质粒的氧化亚铁硫杆菌Ｔｆ－５９（ｐＳＤＸ３）的生长和产酸能力不低于对照菌Ｔｆ－５９加入硫酸亚铁和提高接种量可明显缩短生长延迟期，并加快脱砷速度；可将矿浆浓度从２０％提高到３０％，抗胂试验显示，当ｃ（ＮａＡｓＯ２）达到８０ｍｍｏｌ／Ｌ时，Ｔｆ－５９的生长受到严重预制，而对Ｔｆ－５９（ｐＳＤＸ３）的生长影响较少，说明Ｔｆ＝     

不同菌源的微生物对邻苯二甲酸二甲酯生物降解性的比较

从处理石化厂废水的活性污泥中分离出１ 株邻苯二甲酸酯降解菌 Ｆ Ｓ１（ 荧光假单胞菌 Ｐｓｅｕｄｏｍｏｎａｓｆｌｕｏｒｅｓｃｅｎｓ Ｆ Ｓ１） ,从处理焦化厂废水的活性污泥中分离出２ 株邻苯二甲酸酯降解菌 Ｆ Ｓ２（ 铜绿假单胞菌 Ｐｓｅｕｄｏｍｏｎａｓａｅｒｕｇｉｎａｓａ Ｆ Ｓ２） 和 Ｆ Ｓ３（ 短杆菌 Ｂｒｅｖｉｂａｃｔｅｒｉｕｍ ｓｐ ． Ｆ Ｓ３） ． 研究了邻苯二甲酸酯降解菌 Ｆ Ｓ１ , Ｆ Ｓ２ 和 Ｆ Ｓ３ 对邻苯二甲酸二甲酯（ Ｄ Ｍ Ｐ） 的最适降解条件,比较了其降解特性． Ｆ Ｓ１ 、 Ｆ Ｓ２ 和 Ｆ Ｓ３ 最适酸度分别为ｐ Ｈ６ ．５ ～８ ．０ 、ｐ Ｈ７ ．０ ～８ ．０ 和ｐ Ｈ７ ．０ ～８ ．０ ,温度为２０ ～３５ ℃、１５ ～３５ ℃和１５ ～３５ ℃．邻苯二甲酸酯降解菌 Ｆ Ｓ１ 、 Ｆ Ｓ２ 和 Ｆ Ｓ３ 对邻苯二甲酸二甲酯的降解的半寿期： Ｆ Ｓ１ ＜ Ｆ Ｓ２ ＜ Ｆ Ｓ３ ,邻苯二甲酸酯降解菌 Ｆ Ｓ１ 是一株高效的邻苯二甲酸二甲酯降解菌     

城市生活垃圾中酞酸酯的微生物降解

从酞酸酯生产厂排污沟中分离到４株酞酸酯降解菌，分属镰孢属（Ｆｕｓａｒｉｕｍ　ｓｐ．）、醇母属（Ｓａｃｃｈａｒｏｍｙｃｅｓ　ｓｐ．）、不动杆菌属（Ａｃｉｎｅｔｏｂａｃｔｅｒ　ｓｐ．）、黄单孢菌属（Ｘａｎｔｈｏｍｏｎａｓ　ｓｐ．）。在酞酸酯剂量为５０、２５μｇ／ｍＬ水平的纯培养条件下，４株单菌对酞酸酯的降解率达到７２％－７７％，混合菌的降解率还可提高近１０％。在垃圾堆肥中酞酸酯剂量为１９７μｇ／ｇ的水平下，将降解菌回接堆肥后，不动杆菌属和混合菌对酞酸酯的降解率最高，分别达到７２％和６９％。     

皮革废物铬革屑的微生物学处理研究Ⅱ:降解革屑微生物的发酵条件及其蛋白酶的降解研究

在以皮胶原为碳、氮源时其最适产酶条件为ｐ Ｈ７ ,３０ ℃,高产酶时间为４ ｄ ．经 Ｃａ（ Ｏ Ｈ）２ 预处理革屑不能有效促进该菌对革屑的降解,但可使大部分 Ｃｒ３ ＋ 沉淀而除去．经该株蛋白酶的粗提及性质实验,确定酶的最适反应条件为４０ Ｃ、ｐ Ｈ７ ．０ ～８ ．０ , Ｃｒ３ ＋ 对酶有轻度的抑制作用,以２ ．２６ ％ 的粗酶作用于革屑,水解率达５０ ％ 以上     

玉米-花生混作系统中的氮铁营养效应

采用盆栽试验的方法研究了不同施氮水平和种间相互作用对花生铁营养、根瘤固氮能力以及系统氮营养的影响。结果表明,在本试验种植密度下,施氮水平和种植方式对下针期单株花生生物量无显著影响。在不同施氮水平下,玉米-花生混作不仅均显著改善了花生铁营养,而且玉米对氮素的大量吸收显著降低了混作花生根际土壤硝态氮的质量分数,从而使得花生根瘤数增加,根瘤固氮酶活性增强。混作花生铁营养受混作玉米氮营养及作物发育状况的影响较大,并且下针期花生固氮酶活性受施氮抑制及花生铁营养改善的促进。这说明,根际土壤硝态氮的质量分数的降低和花生铁营养的改善是石灰性土壤上花生固氮能力增强的关键因素,而花生生物固氮作用的增强是该混作系统体现氮营养优势的主要原因。     

Nitrogen fixation associated with the cyanobacterial mat of a marine laminated microbial ecosystem

The nitrogenase activity in the cyanobacterial mat of a laminated microbial ecosystem was investigated by the acetylene reduction method. Measurements under several conditions such as light and dark, aerobic and anaerobic and by inhibiting photosystem II by 10^-5 M DCMU showed the nitrogenase activity to be light stimulated and to some degree inhibited by oxygen. An appreciable amount of activity was also present under complete aerobic conditions. We estimated 8 to 15 kg N fixed per hectare per year for that part of the intertidal flat supporting growth of cyanobacteria. By measuring a vertical sediment profile, nitrogenase was shown to be associated with the cyanobacterial mat. Diurnal measurements of nitrogenase showed two activity peaks, one at sunrise and one at sunset. Following population dynamics in the cyanobacterial mat showed Microcoleus sp., Oscillatoria spp., Spirulina sp., Gloeocapsa sp. and sometimes Merismopedia sp. to be present. During four years of observations we never found any heterocystous cyanobacteria. Non-heterocystous cyanobacteria apparently play an important role in nitrogen fixation in this marine intertidal environment.     

Hydrogen production by nitrogenase as a potential crop rotation benefit

Both climate change and the adverse effects of chemical use on human and environmental health are recognized as serious issues of global concern. Nowhere is this more apparent than in the agricultural sector where release of greenhouse gases such as carbon dioxide, nitrous oxide and methane continues to be problematic and where use of nitrogen fertilizer is responsible for negative impacts on both human populations and ecosystems. The manipulation of biological nitrogen fixation (BNF) could help alleviate part of the difficulty by decreasing the need for nitrogen fertilizers, which require huge quantities of fossil fuel to produce and contribute to the release of nitrous oxide from soil as well as being responsible for the contamination of drinking water systems and natural habitats. BNF is performed by a variety of microorganisms. One of the most studied examples is the BNF carried out by rhizobial bacteria in symbiosis with their plant hosts such as pea and soybean. Hydrogen gas is an energy-rich, obligate by-product of BNF. Legume symbioses with rhizobia lacking hydrogenase enzymes (which can recycle hydrogen) have traditionally been viewed as energetically inefficient. However, recent studies suggest hydrogen release to soil may be beneficial, increasing soil carbon sequestration and promoting growth of hydrogen-oxidizing bacteria beneficial to plant growth; the alleged superiority of symbiotic performance in rhizobia possessing functional hydrogenases (HUP⁺) over those rhizobia without functional hydrogenases (HUP⁻) has also not been conclusively shown. The structure of the iron-molybdenum cofactor or FeMo-co of nitrogenase (the active site of the enzyme) has been elucidated through X-ray crystallography but the mechanism of nitrogen fixation remains unknown. However, studies of effects of hydrogen production on BNF have revealed potential candidate intermediates involved in the nitrogenase reaction pathway and have also shown the role of hydrogen as a competitive inhibitor of N₂, with hydrogen now considered to be the primary regulator of the nitrogenase electron allocation coefficient. The regulation of oxygen levels within legume root nodules is also being investigated; nitrogen fixation is energetically expensive, requiring a plentiful oxygen supply but too high an oxygen concentration can irreversibly damage nitrogenase, so some regulation is needed. There is evidence from gas diffusion studies suggesting the presence of a diffusion barrier in nodules; leghaemoglobin is another potential O₂ regulator. Possible functions of hydrogenases include hydrogen recycling, protection of nitrogenase from damaging O₂ levels and prevention of inhibitory H₂ accumulation; there is evidence for H₂ recycling only in studies where H₂ uptake has been strongly coupled to ATP production and where this is not the case, it is believed that the hydrogenase acts as an O₂ scavenger, lowering O₂ concentrations. The distribution of hydrogenases in temperate legumes has been found to be narrow and root and shoot grafting experiments suggest the host plant may exert some influence on the expression of hydrogenase (HUP) genes in rhizobia that possess them. Many still believe that HUP⁺ rhizobia are superior in performance to HUP⁻ species; to this end, many attempts to increase the relative efficiency of nitrogenase through the introduction of HUP genes into the plasmids or chromosomes of HUP⁻ rhizobia have been carried out and some have met with success but many other studies have not revealed an increase in symbiotic performance after successful insertion of HUP genes so the role of HUP in increasing parameters such as N₂ fixation and plant yield is still unclear. One advantage of the hydrogen production innate to BNF is that the H₂ evolved can be used to measure N₂ fixation using new open-flow gas chamber techniques seen as superior to the traditional acetylene reduction assay (ARA) conducted in closed chambers, although H₂ cannot be used for field studies yet as the ARA can. However, the ARA is now believed to be unreliable in field studies and it is recommended that other measures such as dry weight, yield and total nitrogen content are more accurate, especially in determining real food production, particularly in the developing nations. Another potential benefit of H₂ release from root nodules is that it stays in the soil and has been found to be consumed by H₂-oxidizing bacteria, many of which show plant growth–promoting properties such as the inhibition of ethylene biosynthesis in the host plant, leading to root elongation and increased plant growth; they may well be promising as biofertilizers if they can be successfully developed into seed inoculants for non-leguminous crop species, decreasing the need for chemical fertilizers. It has been suggested that rhizobia can produce nitrous oxide through denitrification but this has never been shown; it is possible that hydrogen release may provide more ideal conditions for denitrifying, free-living bacteria and so increase production of nitrous oxide that way and this issue will require more study. However, it seems unlikely that a natural system would release nitrous oxide to the same degree that chemical fertilizers have been shown to do.     

Effects of Nitrate Nitrogen Additions on Physical, Chemical and Biological Parameters in Lake Enclosures

The effects of nitrate additions on the physics, chemistry and biology of lake water were studied in 5 × 10 m polyethylene enclosures installed in Lake Kastoria, a shallow eutrophic lake in Northern Greece. The water physics, chemistry, chlorophyll a and nitrogenase activity were monitored from July 10 till October 17 1985 at 2 week intervals. The experiment included a control enclosure.

Water confinement in the control enclosure resulted in ammonia accumulation, a slight decrease in chlorophyll a, a significant reduction of nitrogenase activity and an increase in phosphorus release from the sediments at the end of the experimental period.

The addition of KNO₃ resulted in higher than the control accumulation of NH₃, chlorophyll reduction, increase in water transparency and reduction of nitrogenase activity. Large losses of nitrogen added were measured which were attributed to denitrification, organic matter sedimentation and ammonia volatilization. Anaerobic but not aerobic phosphorus release from sediments was inhibited at the end of the period. The reduction of nitrogenase activity and of chlorophyll a concentration are attributed to changes in phytoplankton composition from blue-greens to small-sized species grazed by zooplankters.     

Nitrogen fixation by blue-green algae associated with the siphonous green seaweed Codium decorticatum: effects on ammonium uptake

Nitrogen fixation (acetylene reduction) at rates of up to 1.2 g N₂ g dry wt^-1 h^-1 was measured for the siphonous green seaweed Codium decorticatum. No nitrogenase activity was detected in C. isthmocladum. The nitrogenase activity was light sensitive and was inhibited by the addition of DCMU and triphenyl tetrazolium chloride. Additions of glucose did not stimulate nitrogen fixation. Blue-green algae (Calothrix sp., Anabaena sp., and Phormidium sp.) were implicated as the organisms responsible for the nitrogenase activity. They occurred in a reduced microzone within the C. decorticatum thallus where nitrogen fixation was optimized. Nitrogen fixation did not affect the kinetic constants for ammonium uptake in C. decorticatum (K_s=12.0 M, V_max=13.4 mol NH₃ g dry wt^-1 h^-1) determined using the perturbation method. Nevertheless, C. decorticatum thalli which fixed nitrogen had internal dissolved nitrogen concentrations which were over 1.4 times higher than in non-fixing thalli. This suggests that if C. decorticatum does derive part of its nitrogen requirement from the blue-green algae which it harbors, the transfer does not involve competition between this process and the uptake of ambient ammonium.     

Physiology and chemical composition of nitrogen-fixing phytoplankton in the central North Pacific Ocean

The magnitude and physiological characteristics of biological nitrogen fixation have been studied in the oligotrophic waters of the North pacific gyre. The filamentous blue-green algae Trichodesmium spp. and Richelia intracellularis were the important nitrogen-fixing phytoplankton. Most of the nitrogen fixation occurs in the upper 40 m of the water column, with detectable fixation as deep as 90 m, which corresponds to about the 1 % light depth. There was no evidence of photoinhibition of nitrogen fixation, although CO₂ reduction was depressed slightly at the highest light levels. The rate of nitrogen fixation in the water column varied throughout the day, being highest in mid-morning and in late afternoon. Relatively high fixation rates were also found during periods of darkness. Elevated oxygen concentrations had a marked inhibitory effect on rates of nitrogen fixation, a pO₂ of 0.4 atm causing a 75% inhibition. Data from studies of nitrogen fixation and assimilation rates of ¹⁵N-labelled nitrate, ammonium, and urea indicate that nitrogen fixation furnished about 3% of the total daily fixed nitrogen requirement for phytoplankton growth. Studies with isolated colonies of Trichodesmium spp. indicated that 100% of their nitrogen requirement was met by nitrogen fixation. Chemical composition of the Trichodesmium colonies showed that the C:N ratio was 4.1 and that their phosphorus content relative to carbon or nitrogen was much lower than that of the total particulate material in the water column. Elevated ratios of carbon: adenosine triphosphate (ATP) also suggest that phosphorus deficiency may be limiting the growth of Trichodesmium. The magnitude of nitrogen fixation in the gyre is seasonally dependent, with high rates in late summer and autumn. At these times the water column is stratified, with phosphate and nitrate barely detectable in the upper 100 m. Our data suggest that during these months of stratification, biological fixation of nitrogen amounts to about 33 g-at N/m²/day.     

The association of N2-fixing bacteria with sea urchins

Dinitrogen fixation associated with bacteria in the gastrointestinal tract of sea urchins appears to be a widespread phenomenon: sea urchins from the tropics (Diadema antillarum, Echinometra lacunter, Tripneustes ventricosus), the temperature zone (Strongylocentrotus droebachiensis) and the arctic (S. droebachiensis) exhibited nitrogenase activity (C₂H₂ reduction). Pronounced seasonal variation was found in nitrogenase activity of temperate sea urchins feeding on kelp (Laminaria spp.) and eelgrass (Zostera marina). The mean monthly nitrogenase activity was inversely correlated with the nitrogen content of the sea urchin's food, which varied up to fivefold over the course of a year. The highest rate of nitrogenase activity recorded for a temperate sea urchin during the 14 month sampling period was 11.6g N fixed g wet wt^-1 d^-1, with a yearly mean activity of 1.36 g N fixed g wet wt^-1 d^-1. Studies with ¹⁵N confirmed the C₂H₂ reduction results and showed incorporation of microbially-fixed nitrogen into S. droebachiensis demonstrating that N₂ fixation can be a source of N for the sea urchin. Laboratory experiments indicated that part of the sea urchin's (S. droebachiensis) normal gastrointestinal microflora is responsible for the observed nitrogenase activity.     

Effects of oxygen,mannitol and ammonium concentrations on nitrogenase [C2H2] activity in a marine skeletal carbonate sand

Following a lag of 3 to 18 h, acetylene reduction in mannitol-amended sand systems proceeded at approximately constant and high rates for periods up to 4 days. Carbon dioxide production and O₂ consumption were low in these systems in comparison to similar systems additionally amended with ammonium, indicating N-limitation of growth in the former. Thus, long-term acetylene assays of mannitol-amended sand and suspensions from the sand incubated at various partial pressures of oxygen could be used to characterize the O₂-sensitivity of the N₂-fixing bacterial population as a whole, in batch-type systems with a minimal degree of enrichment or change in pO₂ during the course of the assays. Results of various studies suggested that aerobic or microaerophilic N₂-fixing bacteria were absent or scarce in the sand, and that nitrogenase activity occurring in aerobically incubated systems occurred in anaerobic microenvironments. Hydrogen stimulated acetylene-reducing activity, but the time course differed from that of mannitol-supported activity, and proceeded with shorter lags in systems incubated at 0.2 and 0.05 atm O₂ than in systems incubated anaerobically. Efficiency of N₂ fixation [C₂H₂] increased with decreasing initial mannitol concentration. For sand washed with seawater to remove native combined inorganic nitrogen, and amended with 0.015% mannitol, 374 μmoles added NH₄-N/kg wet sand caused almost complete repression of nitrogenase activity, while concentrations as low as 12 μmoles added NH₄-N/kg wet sand appeared to cause at least partial repression of nitrogenase activity. Some implications of these results for the existence of anaerobic microenvironments in the cavities of skeletal carbonates, and for N₂-fixation in the seagrass rhizosphere are discussed.     

慈姑(Sagittaria trifolia)根系泌氧特征

借助高精度溶解氧微电极,研究了自然沉积物中慈姑(Sagittaria trifolia)根不同部位的泌氧能力差异以及光照对根系泌氧能力的影响。结果表明,慈姑根系不同部位的泌氧能力存在差异,光照和黑暗条件下根区氧气扩散层厚度由大到小依次为1/2根长(0.98、0.72 mm)、3/4根长(0.68、0.28 mm)、根尖(0.58、0.44 mm)和1/4根长(0.42、0.32 mm);光照条件下不同根长部位根表面溶解氧含量由大到小依次为1/2根长〔64.56%(以%空气饱和度计)〕、3/4根长(52.73%)、根尖(38.55%)和1/4根长(20.55%),这与根部泌氧屏障、通气组织发育程度和根组织呼吸代谢有关。无论有无光照,慈姑根均有泌氧产生,光照条件下根表面溶解氧含量和根区氧气扩散层厚度均高于黑暗条件;在光照和黑暗条件下1/2根长处根表面溶解氧含量均显著高于其他测定点(P<0.05);除1/2根长处以外的其他测定点,在光照条件下的根表面溶解氧含量差异显著(P<0.05),但在黑暗条件下趋于相同(P>0.05)。