Efeitos da nutrição mineral sobre o crescimento, aspecto, composição elementar e fixação de nitrogênio em Azolla

The mineral nutrition of Azolla feliculoides Lam was studied in solutions deficient in phosphorus, potassium, calcium, magnesium, sulfur, iron and molybdenum, and in excess of Mn and Al. Dry weight, N2 fixation and mineral composition of Azolla were determined after 3 weeks. Phosphorus, potassium, calcium and magnesium deficiencies and excess of manganese and aluminium decressed growth severely and also depressed the activity of nitrogenase. Phosphorus deficiency improved the uptake of iron and zinc. Potassium deficiency increased the levels of phosphorus in dry matter. Magnesium deficiency caused lower uptake of K and better uptake of Ca, Fe and Mn. Sulfur deficiency reduced aluminium uptake and promoted the best growth. Positive correlations were found between: N content and dry matter, nitrogenase activity and N content.Azolla filiculoides Lam foi cultivado em solução nutritiva arejada, sempre desprovida de N combinado, sendo submetida aos seguintes tratamentos: omissão de P, K, Ca, Mg, S, Fe e Mo, excesso de Mn e Al. As plantas foram colhidas depois de 3 semanas da inoculação. Verificou-se que as deficiências de P, K, Ca e Mg provocaram diminuição na produção de matéria seca e na atividade de nitrogenase. A análise mineral mostrou que: a falta de um elemento provoca redução no seu teor; grande acumulo de Mo; diminuição no teor de Al (do inóculo ou contaminação) no tratamento menos S que garantiu o maior crescimento; efeitos inibitórios ou sinergísticos semelhantes aos descritos no caso de plantas superiores. A toxidez de Al e Mn causou, principalmente a primeira, redução no crescimento e na atividade da nitrogenase. Houve correlações positivas entre: N total e crescimento, atividade de nitrogenase e N total

Cost Overruns in Hydrocarbon Megaprojects: A Critical Review and Implications for Research

Cost overruns are prevalent in hydrocarbon (oil and gas) megaprojects. A recent report indicates that 64% of ongoing megaprojects globally are facing cost overruns. Despite their increasing occurrence, there has been limited published research in the mainstream literature that has specifically examined why and how they occur. Consequently, suggestions regarding how to constructively address cost overruns in hydrocarbon megaprojects are scant. To better understand the causal nature of cost overruns in hydrocarbon megaprojects, this article provides a critical review of the extant literature. Findings from the research indicate that complex interactions between project characteristics, people, technology, and structure and culture contribute to cost overruns occurring. As a result, it is suggested that chaos theory can be used to explain how cost overruns arise in hydrocarbon megaprojects. This article provides a reference point for engendering future research in this pervasive and fertile area