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101.
Cyanobacteria are important for global nitrogen cycle and often form complex associations referred to as cyanobacterial mats
or periphyton that are common in tropical, limestone-based wetlands. The objective of this study was to monitor the nitrogen
fixation rate using the acetylene reduction assay of these cyanobacterial mats in a tropical, unfertilized, and protected
wetland. To account for temporal and spatial variation of nitrogenase activity, we were interested in seasons in a hydrological
cycle (dry, rains, and end of rains), sites with different vascular vegetation, and rates of nitrogenase activity in a 24-h
cycle. The annual average of nitrogenase activity was 22 nmol C2H4 cm−2 h−1, with a range of <6 to 35 nmol C2H4 cm−2 h−1, and the annual nitrogen fixation rate of our study site (9.0 g N m−2 year−1) is higher than similar estimates from other freshwater wetlands. There was a clear temporal pattern in nitrogenase activity
with a maximum rate occurring during the rainy season (August) and a maximum nitrogenase activity occurring between 0600 and
1200 hours. We found spatial differences in nitrogenase activity among the four sites that could be attributed to variations
in species composition within the periphyton. 相似文献
102.
Effect of nutrients and liming on changes in pH,redox potential,and uptake of iron and manganese by wetland rice in iron-toxic soil 总被引:2,自引:0,他引:2
In a greenhouse experiment, the nutrients NPK, NPK + lime, K, and Mn were applied to an iron-toxic soil (Typic Haplastulf). Soil pH and dry matter production were increased and Eh and available Fe in the soil were decreased. Though liming the soil decreased available Fe and Mn and increased pH to the greatest extent, the highest dry matter production was obtained with NPK application. NPK + lime produced a smaller yield than NPK without lime. Though the application of K or Mn alone produced much less dry matter than NPK or NPK + lime, no symptoms of Fe toxicity were observed. We conclude that Fe toxicity can be reduced with a balanced use of fertilizers (NPK or NPK + lime) and its occurrence was mostly due to nutrient stress. 相似文献
103.
Søren O. Petersen 《Biology and Fertility of Soils》1993,15(2):137-143
Summary Reduction processes in cultivated soil during the decomposition of liquid cattle manure were studied in laboratory experiments. Anoxic slurries of soil and manure in different proportions or alone were followed over 5 weeks. Upon NO
inf3
sup-
depletion, ferrous Fe appeared in solution in soil-manure slurries. Sulfide levels were generally low in the presence of both soil and manure, probably because of precipitation by Fe2+; Fe thereby counteracted the production of free hydrogen sulfide. Methane formation was the quantitatively most important electron sink under prolonged anoxic conditions. When extra sulfate was added to soil-manure slurries, the concentration of Fe2+ remained low and less methane was produced. The detection of Fe2+ was examined in a model system with a gel-stabilized soil-manure mixture sandwiched between two soil phases with a water content near field capacity. Large methodological problems made it impossible to quantify Fe2+ in this oxic-anoxic environment, but the results indicated that reducing conditions were maintained in the manure-saturated zone for the 20-day period of this experiment. 相似文献
104.
Rhizosphere bacteria may enhance plant uptake of Fe by producing siderophores that chelate sparingly soluble Fe3+ in calcareous soils. To evaluate the extent to which plants benefit from colonization of the roots by prolific siderophore-producing bacteria, we inoculated two oat cultivars with six strains of bacteria that produced high concentrations of siderophores under Felimiting conditions in vitro. Oat cv Coker 227, an Fe-efficient cultivar, which produces the phytosiderophore avenic acid, and cv TAM 0-312, and Fe-inefficient cultivar, which does not produce the phytosiderophore, were grown in a calcareous soil (Weswood silt loam) on a light bench in the laboratory. Half of the plants were fertilized with a nutrient solution containing 5 mM Fe and half with a nutrient solution containing no Fe. After 6 weeks of growth, we compared colonization of the roots by the inoculant bacteria and the dry weight and Fe content of roots and shoots. Three species of Pseudomonas colonized the roots of both oat cultivars in high numbers (106 cells g-1 root dry weight), whereas the remaining bacteria colonized the roots in substantially lower numbers (104 cells g-1 root dry weight). Plants fertilized with 5 mM Fe were larger and supported greater numbers or rhizosphere bacteria per gram of root than plants not supplied with Fe. Comparisons of the Fe content and dry weight of roots and shoots revealed few significant differences between inoculated and uninoculated plants, or among the plants inoculated with the different strains of siderophore-producing bacteria. The differences that were observed revealed no consistent response to inoculation. We conclude that inoculation of the roots of the two oat cultivars with bacteria that produce high concentrations of siderophores in response to an Fe deficiency had little or no effect on Fe acquisition by the plants. 相似文献
105.
从无定河流域“94·8·4”暴雨洪水看林草措施的减蚀作用 总被引:2,自引:0,他引:2
典型调查表明,在无定河流域绥德县80年—遇日降雨量120多mm条件下,林草措施具有显著的减蚀作用:农坡地一次降雨侵蚀模数达36660t/km~2,而一般草地侵蚀模数为5000~12000t/km~2,草地减少侵蚀70%~90%;坡度35°、被覆度70%的林地,加上工程整地措施,侵蚀模数为2000~5000t/km~2,减少侵蚀85%~95%;在相同自然条件下,林地减水效益为27.5%,减沙效益为47.7%,在有整地措施条件下,林地径流量较自然荒坡减少42.2%~77.1%. 相似文献
106.
107.
由于主要粮食作物中微量营养元素(特别是Zn 和Fe)的缺乏导致全世界范围内的人类微量营养元素缺乏症。野生二粒小麦(Triticum turgidum ssp. dicoccoides)是提高小麦籽粒Zn、Fe、蛋白质含量及改良小麦其他性状的重要种质资源。本研究以4 份野生二粒小麦及32 份野生二粒小麦与普通小麦(Triticum aestivum L.)杂交后代为材料, 进行籽粒中富含Zn、Fe 和蛋白质种质资源的筛选和鉴定。野生二粒小麦的后代材料表现出广泛的遗传变异。籽粒Zn、Fe 含量和蛋白质含量之间均呈极显著正相关关系, 说明这些性状能够通过育种方式达到共同提高的目的。试验共筛选到17 份Zn、Fe 和蛋白质含量均显著高于对照品种"石4185"的材料, 说明将来自野生二粒小麦的外源基因导入到普通小麦是提高小麦籽粒Zn、Fe 和蛋白质含量的有效途径。其中5份野生二粒小麦与普通小麦的杂交后代表现出较高籽粒Zn、Fe 和蛋白质含量的同时, 也具有较高的产量和优良的农艺性状。这些材料的获得为小麦生物强化育种提供了重要的物质基础。 相似文献
108.
109.
以黄土高原广泛分布的黑垆土为研究对象,研究了6个粒级团聚体中总有机碳(TOC)、稳定性有机碳(St OC)、矿物保护态有机碳(MOC)、化学稳定性有机碳(ROC)和游离氧化铁(Fed)、无定形氧化铁(Feo)、络合态氧化铁(Fep)以及黏土矿物含量的特征,重点分析了有机碳在各粒级团聚体中的分配及其与黏土矿物和各种形态氧化铁之间的相关性,及探讨了有机碳的保护机制。结果表明:黑垆土中约80%的土壤有机碳赋存于0.5~0.25、0.25~0.05和0.05 mm的3个粒级团聚体中;黑垆土中的有机碳以St OC为主,其含量随着团聚体粒级的减小而增加。在0.5~0.25和0.25~0.05 mm团聚体中,TOC含量与Fed含量呈正相关关系,相关性系数(r)均为0.72(P0.05);在0.25~0.05 mm粒级团聚体中,ROC含量与Fed含量呈正相关关系(r=0.68,P0.05),而St OC和MOC含量与伊利石含量具有正相关关系r分别为0.71(P0.05)和0.68(P0.05)。黑垆土中对有机碳起保护作用的主要是Fed和伊利石,但二者对有机碳的保护机制可能有所不同:Fed与有机碳络合形成化学稳定性有机碳,而伊利石主要通过吸附作用实现对有机碳的保护。 相似文献
110.