Formas de nitrogênio e níveis de potássio sobre a absorção de fósforo por milho

A study, was made on the effects of N-sources (N1 - 100 ppm N-NO3 x N2 = 100 ppm NH4) and K levels (32 and 64 ppm) on dry matter accumulation, P-uptake, root volume, and rhizocylinder pH (pHr) of corn (Zea mays L.). Plants (cv. Centralmex) were grown in 5 liter pots, and harvested at 15, 30 and 45 days after-emergence. NH4 - plants showed reduced growth at the first harvest, K overcame that effect. This effect of NH4 was attributed either to soluble-N accumulation in tissues or to NH4 - phosphate complexes in the soil. The beneficial effect of K on plant growth should then be due to development of K-NH4 - phosphate complexes. NO3 and K affected positively root volume. There was a decrease in pHr between 15 and 45 days, and NH4-N pots had the lowest pH. In the NO3-N treatments, decrease in pHr could be attributed to the small N + P/K relationships (0,8 for N1 plants and 0,66- 0,90 for N1K1 plants at 30 and 45 days). There was a negative relationship between pH and P-uptake (except for NH4 - only treatments).Foi estudado o efeito de formas de N (N1 - 100 ppm N-NO3 x N2 = 100 ppm N-NH4 ) e doses de K (32 e 64 ppm) sobre a acumulação de matéria seca, volume de raízes, pH do rizocilindro (PHr) e absorção de fósforo (P) por milho (Zea mays L.) (cv. Centralmex), aos 15, 30 e 45 dias após a emergência. Houve um efeito inicial negativo do N-NH4 sobre o crescimento. K corrige o efeito negativo do NH4. Os efeitos negativos do N-NH4 podem ter sido causados pelo acúmulo de N solúvel em detrimento do N protéico, ou pela formação de complexos NH4 -fosfato, reduzindo a disponibilidade de P na solução do solo. O efeito positivo do K seria através da formação de complexos K-NH4 -fosfatos. Houve acidificação do rizocilindro (PHr) no período de 15 a 45 dias em todos os tratamentos, com menor pH nos tratamentos que receberam N-NH4. A queda de pHr nos tratamentos sob NO3 explica-se pela relação N + P/K (0,8 para o tratamento N1 e 0,66-0,99 para os tratamentos N1K1, aos 30 e 45 dias, respectivamente). Houve uma correlação negativa entre pHr e acumulação de P na parte aérea (exceto para os tratamentos N2)

Transformations of mineral N in a Red-Yellow Podzolic soil under stillage application

Foram feitos dois experimentos para observar as transformações do N-NO-3 em solos Podzólicos Vermelho-Amarelos (PVA) da região de Campos, RJ, tratados com vinhaça. No primeiro experimento, vasos foram incubados com 50 ml de vinhaça/dm3 de solo (equivalente a 100 m3/ha) ou 100 µg de N-NO-3 /g de solo, isoladamente ou em combinação com vinhaça ou dose equivalente em K+ na forma de K2SO4. Em seguida foram cultivados com milho por um período de 60 dias. Os teores de N-NO-3 e N-NH+4no solo, assim como o N nas plantas, foram determinados quinzenalmente. No segundo experimento, amostras indeformadas de solos foram incubadas com 0, 100, 200, 400 e 800 m3/ha de vinhaça com adição de 300 µg N-NO-3/g de solo. Seguiram-se os teores de N-NO-3, N-NH+4, N-NO-2 e N-N2O semanalmente, durante 63 dias. Em conjunto, os experimentos sugerem que a incorporação de N-NO-3 e vinhaça no solo produz uma rápida queda no teor de N-NO-3, atribuída antes a um processo redutor do que à absorção radicular. Durante os primeiros 30 dias aumentaram os teores de N-NH+4 , em ambos os experimentos. Nos primeiros quinze dias evoluiu apreciável quantidade de N-N20. O lento acúmulo de N-orgânico durante as primeiras seis semanas determinou um aumento na disponibilidade de N-NO-3 mineral, após esse período. Esse aumento não se refletiu em um aumento na acumulação de N na parte aérea da planta.The transformations of N-NO-3 in Red-Yellow Podzolic (RYP) soils from the region of Campos, Rio de Janeiro, Brazil, treated with stillage were followed along two experiments. For the first experiment, pots were incubated with 50 ml of stillage/dm3 of soil (corresponding to 100 m3/ha) or 100/µg of N-NO-3/g of soil, separately or in combination with stillage, or K+ as K2SO4 equivalent to the applied stillage. Corn was grown for a period of 60 days. The amount of N-NO-3 and N-NH+4 in the soil, as well as the amount of N in the plants, were determined every fifteen days. For the second experiment, undisturbed samples of soils were incubated with volumes of stillage corresponding to 0, 100, 200, 400 e 800 m3/ha of stillage and addition of 300 µg N-NO-3/g of soil, followed weekly by the amounts of N-NO-3, N-NH4, N-NO-2 and N-N2O for 63 days. The two experiments, together combined, suggest that the incorporation of N-NO-3 and stillage to the soil causes a fast decrease in the amount of N-NO-3, which is mainly due to a reduction process rather than to root absorption. During the first 30 days the amounts of N-NH+4 increased in both experiments. Large amounts of N-N2O evolved along the first fifteen days, and N-organic slowly accumulated during the first six weeks produced an increase in the disponibility of N-NO-3 afterwards. This increase did not correspond to an increase in the N accumulation in the plants

Protein Design: Toward Functional Metalloenzymes

The scope of this Review is to discuss the construction of metal sites in designed protein scaffolds. We categorize the effort of designing proteins into redesign, which is to rationally engineer desired functionality into an existing protein scaffold,(1-9) and de novo design, which is to build a peptidic or protein system that is not directly related to any sequence found in nature yet folds into a predicted structure and/or carries out desired reactions.(10-12) We will analyze and interpret the significance of designed protein systems from a coordination chemistry and biochemistry perspective, with an emphasis on those containing constructed metal sites as mimics for metalloenzymes

Astrobiology and the possibility of life on Earth and elsewhere…

Astrobiology is an interdisciplinary scientific field not only focused on the search of extraterrestrial life, but also on deciphering the key environmental parameters that have enabled the emergence of life on Earth. Understanding these physical and chemical parameters is fundamental knowledge necessary not only for discovering life or signs of life on other planets, but also for understanding our own terrestrial environment. Therefore, astrobiology pushes us to combine different perspectives such as the conditions on the primitive Earth, the physicochemical limits of life, exploration of habitable environments in the Solar System, and the search for signatures of life in exoplanets. Chemists, biologists, geologists, planetologists and astrophysicists are contributing extensively to this interdisciplinary research field. From 2011 to 2014, the European Space Agency (ESA) had the initiative to gather a Topical Team of interdisciplinary scientists focused on astrobiology to review the profound transformations in the field that have occurred since the beginning of the new century. The present paper is an interdisciplinary review of current research in astrobiology, covering the major advances and main outlooks in the field. The following subjects will be reviewed and most recent discoveries will be highlighted: the new understanding of planetary system formation including the specificity of the Earth among the diversity of planets, the origin of water on Earth and its unique combined properties among solvents for the emergence of life, the idea that the Earth could have been habitable during the Hadean Era, the inventory of endogenous and exogenous sources of organic matter and new concepts about how chemistry could evolve towards biological molecules and biological systems. In addition, many new findings show the remarkable potential life has for adaptation and survival in extreme environments. All those results from different fields of science are guiding our perspectives and strategies to look for life in other Solar System objects as well as beyond, in extrasolar worlds