黄土高原丘陵沟壑区不同土地利用模式对土壤氮素淋溶的影响

通过对黄土高原丘陵沟壑区不同土地利用模式土壤剖面NO-3-N、NH+4-N、有机质和全氮分布的测定,论述黄土高原丘陵沟壑区不同土地利用模式对土壤氮素淋溶的影响,对当地农业发展提出建议。结果表明:在200 cm内土壤NO-3-N最大值都出现在200 cm处,其中日光温室最大为20.36 mg/kg。土壤NH+4-N在200 cm内是较均匀的分布在10~25 mg/kg。不同土地利用模式对土壤剖面土壤NH+4-N、有机质和全氮分布没有影响。随着深度的变化对土壤NH+4-N分布也没有影响。土壤有机质和全氮在土壤剖面的分布是,随着深度的增加而减少,60 cm以下有机质保持在1.07~5.95 g/kg,全氮保持在0.12~0.35 g/kg。根据试验结果得出,土壤氮素淋溶的主要成分是NO-3-N,土壤NO-3-N淋溶程度与降雨、灌溉、施肥量呈正比,在坡地的淋溶较少。

铵态氮肥对黄土高原典型土壤氮素激发效应的影响

以黄土高原从北向南不同地区典型土壤类型为对象,采用Bremner淹水培养法,研究铵态氮肥对黄土高原典型土壤氮素的激发效应。结果表明,在测定NH4+-N的激发效应时,只有考虑粘土矿物对有机氮矿化产物或者添加NH4+-N的固定,才可获得可靠结果。在培养20 d和60 d时,NH4+-N对不同土类氮素激发效应存在极显著和显著的影响(P≤0.01和<0.05);培养40 d时,尽管不同土类氮素激发效应也存在很大差异,但统计检验不显著。从整体评价,NH4+-N对土垫旱耕人为土和黄土正常新成土表现出正的激发效应,而对干润砂质新成土表现出负的激发效应,对简育干润均腐土在培养20 d和40 d时无激发效应,而在培养60 d时,表现出显著的负激发效应。结果还看出,在培养40 d和60 d时,NH4+-N对农田土壤表现出负激发效应,对林地和裸地土壤表现出正激发效应,而草地土壤在培养40 d时为正激发效应;培养20 d和60 d时无激发效应。添加有机物料在培养20 d和40 d时对激发效应的影响不显著(P=0.0872和0.1641),培养时间延长至60 d时影响显著(P=0.049)。添加紫花苜蓿(Medicago sati-v...

花椒主效化感物质分离鉴定及化感作用研究

近年来，随着对作物重茬障碍原因的深入研究，植物的化感作用越来越受到国内外众多学者的重视。花椒（Zanthoxy piperitum.）为芸香科植物，是一种收益早、用途广、价值高的经济树种，是川西干旱河谷地区的重要经济作物，其连作障碍也倍受关注，系统研究花椒化感作用将有助于理解和最终解决花椒连作障碍问题。本文首先通过萃取、层析等方法分离花椒主效化感成分；通过外加不同浓度的花椒叶水浸液研究了对土壤氮素养分循环的影响；研究了花椒叶水浸液对苜蓿生理生化、光合作用、氮素养分吸收的影响，并对外施氮肥对这种化感影响的缓解作用做了研究；研究了花椒化感潜力对全球变化——UV-B增强辐射的响应。主要研究结果如下： 1．用不同极性的有机溶剂对花椒叶水浸液浓缩浸膏萃取、柱层析，结合生物活性检测，分离得到主效化感作用组分的一种化感物质——对甲氧基苯酚。采用该物质纯品进行生物活性检测，证明其具有化感作用。 2．花椒叶水浸液处理土壤30天后，土壤硝态氮、铵态氮、无机氮（硝态氮＋铵态氮）与对照相比，随着花椒叶水浸液浓度的增加呈现降低的趋势，其中土壤铵态氮含量显著降低，而硝态氮含量的变化则不显著，无机氮含量也显著降低。土壤脲酶和蛋白酶的活性与无机氮含量的变化趋势相同。随着花椒叶水浸液浓度的增加，氨化细菌数量显著降低，固氮菌的数量变化不显著，硝化细菌和反硝化细菌数量有减少的趋势。60天后，硝态氮含量、铵态氮含量、无机氮随水浸液浓度增加的变化趋势与30天时相似；随着花椒叶水浸液浓度的增加，氨化细菌、固氮菌的数量显著减少，硝化细菌数量、反硝化细菌数量仍呈减少趋势；土壤脲酶、蛋白酶活性与第30天的变化趋势相同。第60天与第30天的结果相比，相同水浸液浓度处理的硝态氮、铵态氮、无机氮均有下降的趋势，但除了25g.L－1水浸液处理的外，其它相同浓度的处理间差异均不显著；除了12.5 g.L的处理外土壤脲酶活性均呈增强的趋势；蛋白酶活性都有不同程度的增加；花椒叶水浸液处理的土壤硝化细菌和反硝化细菌数量呈增加趋势。 3．随着花椒叶水浸液浓度的增加，显著抑制了苜蓿根长、地上地下生物量、叶绿素含量、叶片中可溶性蛋白的含量，净光合速率。苜蓿体内四种抗氧化酶（POD、SOD、CAT、APX） 活性随着水浸液浓度的增加而降低，而丙二醛含量则增加。苜蓿氮初级同化相关酶硝酸还原酶（NR）、谷氨酰合成酶(GS)、谷氨酸脱氢酶（GDH）的活性随着水浸液浓度的增加受到不同程度的影响。总的来说，苜蓿硝酸还原酶、谷氨酰合成酶的活性受到抑制，而谷氨酸脱氢酶活性的变化则比较复杂，根呈先降低后增加的趋势，叶片则无显著变化。外施两种不同浓度的硝酸铵氮肥后，对12.5、25 g.L－1花椒叶水浸液处理的苜蓿化感作用有显著的缓解作用，表现在株高、生物量、光合作用等方面，大多达到与对照（0 g.L－1）未施氮肥无显著差异的水平，而对50 g.L－1水浸液处理的苜蓿幼苗，虽有一定的缓解作用，但这种作用均未达到与对照（0 g.L－1）未施氮肥时无显著差异的水平。 4． UV-B增强辐射处理花椒后，花椒的化感潜力显著增强。花椒叶片内UV-B吸收物质的含量和总酚含量均显著增加。 In recent years, with profound research on the reasons of continuous cropping obstacles, allelopathy received increasing attention to many scholars at home and abroad. Zanthoxy bungeanum as a Rutaceae plant is a high economic value species which gains early and uses widely. Zanthoxylum is an important economic crop in the arid valley of western Sichuan region, and its not even has received much concern for the continuous cropping obstacles. The systematic study of allelopathy of Zanthoxylum will contribute to the understanding and final settlement of this issue. The major allelopathic composition was separated through the extraction, chromatography combined with other methods. The impact on soil nutrient cycling was also studied through the addition of different concentrations of water extracts of Zanthoxylum. Furthermore, the effects of water extracts of Zanthoxylum leaves on alfalfa leaf physiological and biochemical indexes, photosynthesis, soil enzymes and nutrient uptake of nitrogen and the mitigation of allelopathy through using external fertilizer were studied to put forward scientific resolvent for Zanthoxylum continuous cropping obstacles .The response of allelopathic potential of Zanthoxylum to global change - UV-B enhanced radiation was studied . The main findings are as follows: 1. Through extraction with different polar organic solvents on concentrated water extract of Zanthoxylum leaf and then using column chromatography combined with detection of biological activity, one of the main allelopathic components- methoxy-phenol was isolated. The biological activity testing of the pure material of methoxy-phenol proved that it does have allelopathic potential. 2. Thirty days after treating soil with water extract of Zanthoxylum leaf, as compared with the control, the contents of soil nitrate, ammonium, nitrate plus ammonium nitrogen showed a trend of decrease with the increase of the concentration of water extract whereas the content of ammonium nitrogen showed a significant reduction, and the content of nitrate did not change significantly, the content of nitrate plus ammonium nitrogen also showed a significant (P <0.05) redction. The activity of soil urease and protease showed the same trend as the content of nitrate nitrogen plus ammonium nitrogen. With the increase in the concentration of water extract, the number of ammonification bacteria significantly reduced but nitrogen-fixing bacteria did not change significantly and there was a decreasing trend in the number of nitrifying bacteria and denitrifying bacteria. Sixty days after the treatment, with the increase in solution concentration of water extract of Zanthoxylum leaf, the content of nitrate、 ammonium nitrogen, nitrate plus ammonium nitrogen showed a similar change trend to 30 days’; the number of ammonification bacteria, nitrogen-fixing bacteria significantly reduced ; the number of nitrifying bacteria, denitrifying bacteria was still an downward trend; the activity of soil urease and protease showed the same trend as the 30th days’. Compared to the results of the 30th days’, the content of nitrate, ammonium, nitrate plus ammonium nitrogen showed a decrease trend between the treatment of same concentration, but there was no significant difference except the treatment of 25g.L-1 between the same concentration; the activity of soil urease showed enhanced trend except the treatment of 12.5 g.L-1; the activity of protease increased to varying degrees; the number of ammonification bacteria、 nitrifying bacteria and denitrifying bacteria were growing while nitrogen-fixing bacteria reduced.. 3. With the increase of the concentration of water extract of Zanthoxylum leaf, the water extract significantly inhibited the root length, aboveground biomass, content of chlorophyll and soluble protein in leaf and net photosynthetic rate. The activity of four antioxidant enzymes (POD, SOD, CAT, APX) reduced with the increase in concentration of the water extract but the content of MDA increased. The activity of enzymes related to primary nitrogen assimilation such nitrate reductase (NR), glutamyl synthetase (GS), glutamate dehydrogenase (GDH) were subject to different degrees with an increase in the concentration of water extracts. In general, the activity of nitrate reductase, glutamyl synthetase were inhibited, while change in the activity of glutamate dehydrogenase was more complex. The activity of glutamate dehydrogenase in leaf was first reduced and then increase,but did not change significantly in root. After using two external different concentrations of nitrogen fertilizer, there was a significant mitigation in inhibiton in plant height, biomass, photosynthesis, etc. in the treatment of 12.5,25 gL-1 of water extract of Zanthoxylum leaf, and most of these indexes showed no significant difference with the control (0 g.L-1, no external fertilizer was added) .Although there showed a certain degree of ease in the treatment of 50 g.L-1 , there was still a significant difference compared with the control (0 gL-1) in which no external fertilizer was used. 4.The allelopathic potential of Zanthoxylum positively responded to enhanced UV-B significantly. The content of UV-B absorbing compounds and the total phenol also significant increased.

氮肥对黄瓜根际土壤线虫群落组成、结构及其多样性的影响

土壤线虫是土壤动物的主要功能类群之一，在土壤养分分解和循环中起到重要的作用。本研究通过施用两种形态氮肥，硝态氮(NO-3–N)和铵态氮(NH+4–N)，对黄瓜整个生长期内根际土壤线虫的群落组成、结构及其多样性等的影响进行了比较研究。为增进土壤健康，提高土壤质量以及合理施用氮肥提供科学的理论依据。研究结果如下： 1. 氮肥处理后，不同浓度NO-3–N处理提高了根际土壤线虫数量，而NH+4–N处理（202.5 kg N/ hm2）抑制了线虫数量的增加。线虫群落结构相对较稳定，营养类群变化不大。且少量优势科/属会对土壤线虫群落特征起着至关重要的作用。 2. 在整个生长季节内，非寄生线虫的群体动态变化与寄生线虫的群体的动态变化具有相反的变化趋势。其中，NO-3–N处理和NH+4–N处理后植物寄生线虫出现频率的变化趋势相近，都是由高到低；非植物寄生线虫出现频率的变化趋势则都是由低到高。这说明非植物寄生线虫数量增长和空间占位对植物寄生线虫群体有一定的抑制作用。另外，也反映了适量氮肥在一定程度上能够减轻植物寄生线虫对黄瓜的危害。 3. 由多样性指数变化可知，NO-3–N和NH+4–N在低肥（67.5 kg N/hm2）和高肥（202.5 kg N/hm2）处理较中肥（135.0 kg N/hm2）处理，更不利于提高土壤线虫多样性地提高和线虫群落的稳定性。中肥不同形态氮肥处理与对照相比，H´指数在初花期和结果期显著增加了土壤线虫的H´指数，说明施入两种形态的氮肥能够提高线虫生物多样性程度。NH+4–N处理在初花期和结果期显著降低了土壤线虫种类的丰富性。土壤线虫生物多样性变化中，H´和SR指数在一定程度上能够反映施用无机氮肥对土壤线虫的多样性的影响，而J指数和λ指数效果不明显。NO-3–N和NH+4–N处理相比较，NO-3–N处理对黄瓜土壤线虫的多样性指数影响更大，促进了土壤线虫群体的多样化和种类的丰富度，更有利于提高土壤线虫的多样性，增加其稳定性。这些结果表明适量无机氮肥特别是NO-3–N的施用对黄瓜土壤线虫的生物多样性有一定的维护和提高作用。 4. 线虫数量与土壤质量指标的相关分析表明：线虫数量与有关土壤理化生指标，如土壤NO-3–N、NH+4–N、有机质含量等的正相关程度高，与总酚含量等显著负相关；与根际土壤微生物，细菌、真菌、放线菌数量等呈显著正相关。另外，线虫数量与土壤含水量未表现出显著相关关系。 Nematodes play a major role in decomposition and nutrient cycling in soil. Nematode community analyses are useful in assessing soil ecosystem status and function. The effects of two forms of mineral nitrogenous fertilizers (NO-3–N and NH+4–N) on nematode community composition, structure and diversity in rhizosphere of cucumber were investigated during different growing seasons of cucumber. Systematically research of effects of nitrogenous fertilizers could help to obtain better undstanding of a healthy soil and using nitrogenous fertilizers in reason. The main results are as follows: 1. The total numbers of nematode were more abundant in NH+4–N treatments than other teatments. However, NH+4–N teatment（202.5 kg N/hm2）dramatically inhibited it. All the tropic groups in the soil nematode communities were stable, and the dominant family or genus had an important function in the nematode community structure. 2. There was similar trend of the frequency of plant parasitic nematodes between NO-3–N and NH+4–N treatment, the similar trend of the frequency of non-plant parasitic nematodes was also found. But the frequency of plant parasitic nematodes exhibited a contrary trend to that of plant parasitic nematodes after different nitrogenous fertilizer treatments. The results showed that the increasing trend of the frequency and the niche of non-plant parasitic nematodes inhibited the plant parasitic nematodes, and indicated that right chemical fertilizers dosage could abate plant parasitic nematodes harm to cucumber. 3. The changes of the biodiversity index showed that the nitrogen treatment（135.0 kg N/hm2）promoted the stabilization of soil nematode diversity than other nitrogen treatments(67.5 kg N/hm2 and 202.5 kg N/hm2). In the treatment（135.0 kg N/hm2）,The changes in nematode diversity between the control plots and treated plots were compared by the biodiversity index (H´, J, SR, λ). Among these tested index, H´ and SR were effective in reflecting the effects of different nitrogenous fertilizers on the diversity of soil nematodes. In comparison with the NH+4–N treatment, the NO-3–N treatment promoted the stabilization of soil nematode diversity. 4. Correlation coefficients between nematode abundance and soil quality indices indicated that the total numbers of nematode were affected positively by NO-3–N, NH+4–N and the organic matter, and negatively by total phenolic acids; the total num- bers of nematode had positive correlation with bacteria, fungi and actinomycetes nu- mbers. Soil water contents had only a weak negative influence on it.

设施条件下氮肥对大青菜硝酸盐及土壤矿质氮累积的影响

采用田间实验研究了施用氮肥对设施条件下大青菜生长发育和产量,以及对土壤硝酸盐含量累积分布的影响。结果表明,在施氮肥0~500 kg hm-2范围内,氮肥施用量越大,产量越高,但到达一定量时,便不能再促进产量的提高,反而会引起减产。土壤铵态氮含量随着土壤剖面向下不断下降,表层的铵态氮含量较高,土壤硝态氮含量在整个土壤剖面的分布变化较小,但也是从表层向下处于一种缓慢减少的趋势,铵态氮的累积主要集中在上部土壤剖面,硝态氮的累积分布在整个土壤剖面,土壤硝态氮含量随施肥量增加而增加;氮肥施用量对硝酸盐含量有很大影响。在施氮肥0~700kg hm-2范围内,氮肥施用量越多,大青菜硝酸盐含量越高。

Physiological and immune responses of zhikong scallop Chlamys farreri to the acute viral necrobiotic virus infection

The Zhikong Scallop, Chlamys farreri, is one of the most Important bivalve mollusks cultured in northern China However, mass mortality of the cultured C farreri has posed a serious threat to the maricultural Industry in recent years. Acute Viral Necrobiotic Virus (AVNV) is believed as an important etiological agent causing the scallop mass mortalities To understand the mechanism behind the AVNV associated scallop disease and mortality, we assessed the physiological and immune responses of C farreri to the virus infection using oxygen consumption rate, ammonium-nitrogen excretion rate, hemocyte copper, zinc superoxide dismutase gene expression, and plasma superoxide dismutase activity and alkaline phosphatase activity as indicators Scallops challenged by AVNV at 25 C developed typical disease signs 2 days after virus injection Before the disease manifested, scallop oxygen consumption and NH4+-N excretion rates rose and then fell back. Real-time PCR revealed that the hemocyte cytosol Cu, Zn SOD gene expression was upregulated followed by recovery The plasma SOD activity, however, augmented consistently following virus injection Moreover, plasma AKP activity first lowered and then elevated gradually to the highest level at 24 h post virus injection Scallops challenged by AVNV at 17 degrees C neither developed notable disease nor showed obvious responses that could be associated with the virus infection. While the results suggested a correlation between the elevated seawater temperature and the AVNV infection associated C farreri mortalities, they also indicated that the viral infection provoked multiple physiological and immune responses in the host scallops (C) 2010 Elsevier Ltd All rights reserved

A preliminary survey of micro-organisms in the gut and pellets of a tropical millipede Doratogonus uncinatus Attems (Diplopoda, Spirostreptida, Spirostreptidae).

Millipede gut microbiology and decomposition of faecal pellets over a period of eight weeks were studied in the laboratory. Bacterial numbers, carbon and nitrogen content, pH and weight loss were monitored. Heterotrophic bacteria were the most abundant and reached a peak in the first two weeks of decomposition. The amount of carbon was constant while ammonium nitrogen decreased from 1.51 % to 0.03 % after eight weeksThe pH of the pellets was slightly acidic and did not change much during the course of decomposition. A succession of micro-organisms was observed on decomposing pellets. Zygomycetes were replaced by Ascomycetes after 20 days of decomposition. Decomposition was significantly affected by temperature. The rate of decomposition was highest at 35[degree]C .

Assessment of trophic change and its probable impact on tropical estuarine environment (the Kodungallur-Azhikode estuary, India)

The cumulative effects of global change, including climate change, increased population density and domestic waste disposal, effluent discharges from industrial processes, agriculture and aquaculture will likely continue and increases the process of eutrophication in estuarine environments. Eutrophication is one of the leading causes of degraded water quality, water column hypoxia/anoxia, harmful algal bloom (HAB) and loss of habitat and species diversity in the estuarine environment. The present study attempts to characterize the trophic condition of coastal estuary using a simple tool; trophic index (TRIX) based on a linear combination of the log of four state variables with supplementary index Efficiency Coefficient (Eff. Coeff.) as a discriminating tool. Numerically, the index TRIX is scaled from 0 to10, covering a wide range of trophic conditions from oligotrophic to eutrophic. Study area Kodungallur-Azhikode Estuary (KAE) was comparatively shallow in nature with average depth of 3.6±0.2 m. Dissolve oxygen regime in the water column was ranged from 4.7±1.3 mgL−1 in Station I to 5.9±1.4 mgL−1 in Station IV. The average nitrate-nitrogen (NO3-N) of KAE water was 470 mg m−3; values ranged from Av. 364.4 mg m−3 at Station II to Av. 626.6 mg m−3at Station VII. The mean ammonium-nitrogen (NH4 +-N) varied from 54.1 mg m−3 at Station VII to 101 mg m−3 at Station III. The average Chl-a for the seven stations of KAE was 6.42±3.91 mg m−3. Comparisons over different spatial and temporal scales in the KAE and study observed that, estuary experiencing high productivity by the influence of high degree of eutrophication; an annual average of 6.91 TRIX was noticed in the KAE and seasonal highest was observed during pre monsoon period (7.15) and lowest during post monsoon period (6.51). In the spatial scale station V showed high value 7.37 and comparatively low values in the station VI (6.93) and station VII (6.96) and which indicates eutrophication was predominant in land cover area with comparatively high water residence time. Eff. Coeff. values in the KAE ranges from −2.74 during monsoon period to the lowest of −1.98 in pre monsoon period. Present study revealed that trophic state of the estuary under severe stress and the restriction of autochthonous and allochthonous nutrient loading should be keystone in mitigate from eutrophication process

PHB Biosynthesis in Catabolite Repression Mutant of Burkholderia sacchari

Due to the effect of catabolite repression, sugar mixtures cannot be metabolized in a rapid and efficient way implicating in lower productivity in bioprocesses using lignocellulosic hydrolysates. In gram-negative bacteria, this mechanism is mediated by the phosphotransferase system (PTS), which concomitantly internalizes and phosphorylates sugars. In this study, we isolated a UV mutant of Burkholderia sacchari, called LFM828, which transports hexoses and pentoses by a non-PTS uptake system. This mutant presented released glucose catabolite repression over the pentoses. In mixtures of glucose, xylose, and arabinose, specific growth rates and the specific sugar consumption rates were, respectively, 10 and 23% higher in LFM828, resulting in a reduced time to exhaust all sugars in the medium. However, in polyhydroxybutyrate (PHB) biosynthesis experiments it was necessary the supplementation of yeast extract to maintain higher values of growth rate and sugar consumption rate. The deficient growth in mineral medium was partially recovered by replacing the ammonium nitrogen source by glutamate. It was demonstrated that the ammonium metabolism is not defective in LFM828, differently from ammonium, glutamate can also be used as carbon and energy allowing an improvement on the carbohydrates utilization for PHB production in LFM828. In contrast, higher rates of ammonia consumption and CO(2) production in LFM828 indicate altered fluxes through the central metabolism in LFM828 and the parental. In conclusion, PTS plays an important role in cell physiology and the elimination of its components has a significant impact on catabolite repression, carbon flux distribution, and PHB biosynthesis in B. sacchari.

Monitoramento de 24 horas do desempenho de reator aeróbio de leito fluidizado trifásico na remoção de amônio num sistema de recirculação para produção de tilápia

O objetivo deste trabalho foi monitorar o desempenho de remoção de nitrogênio amoniacal no tratamento das águas residuárias da produção intensiva de tilápia nilótica em sistema com recirculação de água. O sistema foi constituído por um sedimentador convencional e um reator aeróbio de leito fluidizado trifásico com circulação, operados com tempos de detenção hidráulica de 176.4 e 11.9 minutos respectivamente. O meio suporte utilizado no reator foi o carvão ativado granular com densidade aparente de 1.64 g/cm3 e tamanho efetivo de 0.34 mm; a concentração do meio suporte no reator foi mantida constante em 80 g/L. A eficiência média de remoção do nitrogênio amoniacal total foi de 41.2%. O sistema avaliado é uma alternativa efetiva para o reuso da água em sistemas de recirculação para aqüicultura. Embora a variabilidade das concentrações do nitrogênio amoniacal afluente cujo valor médio foi de 0.136 mg/L, o efluente do reator conservou as características de qualidade da água estáveis, com concentrações médias de nitrogênio amoniacal de 0.079 mg/L e do oxigênio dissolvido de 6.70 mg/L, recomendáveis para a criação dos peixes e nas faixas de valores permitidos pela legislação Brasileira (Resolução CONAMA No. 357 de março 5 de 2005) para lançamento de efluentes finais nos corpos de água receptores.

Dinâmica do nitrogênio no solo em razão da calagem e adubação nitrogenada, com palha na superfície

Em sistemas com semeadura direta, a calagem tem sido aplicada superficialmente, causando excesso de calcário nos primeiros centímetros do perfil do solo, onde também é aplicado o N em cobertura e a densidade de comprimento radicular é alta. O objetivo deste trabalho foi estudar a dinâmica do N e do pH do solo em razão da calagem em superfície e aplicação de N em cobertura, na presença de palha. Plantas de algodão (Gossypium hirsutum) foram cultivadas, por 60 dias, em vasos que receberam calagem superficial ou incorporada e aplicação de doses equivalentes a 0, 50, 100 e 150 kg ha-1 de N em cobertura, na forma de sulfato de amônio; os vasos apresentavam, na superfície, o equivalente a 4 t ha-1 de palha de milheto. A calagem aumentou a mineralização e a nitrificação do N no solo, independentemente do modo de aplicação de calcário, aumentando a sua disponibilidade à planta e também a possibilidade de lixiviação. A absorção de N pela planta, além de sua imobilização pela massa microbiana do solo, neutralizou o efeito do adubo nitrogenado amoniacal no pH do solo. O algodoeiro respondeu melhor à calagem incorporada do que à superficial, mas esta resposta não foi causada por diferenças na disponibilidade de nitrogênio.

Frações nitrogenadas em caldos de diferentes cultivares de cana-de-açúcar

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Atividade da enzima nitrato redutase em cultivares de arroz de terras altas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Soil characteristics and abundance of archaea in samples from the Ross Sea Region, Antarctica

The objective of this study was to examine the presence and diversity of Archaea within mineral and ornithogenic soils from 12 locations across the Ross Sea region. Archaea were not abundant but DNA sufficient for producing 16S rRNA gene clone libraries was extracted from 18 of 51 soil samples, from four locations. A total of 1452 clones were analysed by restriction fragment length polymorphism and assigned to 43 operational taxonomic units from which representatives were sequenced. Archaea were primarily restricted to coastal mineral soils which showed a predominance of Crenarchaeota belonging to group 1.1b (>99% of clones). These clones were assigned to six clusters (A through F), based on shared identity to sequences in the GenBank database. Ordination indicated that soil chemistry and water content determined archaeal community structure. This is the first comprehensive study of the archaeal community in Antarctic soils and as such provides a reference point for further investigation of microbial function in this environment.