Nitrogen dynamics in subtropical fringe and basin mangrove forests inferred from stable isotopes.

Mangroves exhibit low species richness compared to other tropical forests, but great structural and functional diversity. Aiming to contribute to a better understanding of the functioning of mangrove forests, we investigated nitrogen (N) dynamics in two physiographic types of mangroves (fringe and basin forests) in southeastern Brazil. Because fringe forests are under great influence of tidal flushing we hypothesized that these forests would exhibit higher N cycling rates in sediment and higher N losses to the atmosphere compared to basin forests. We quantified net N mineralization and nitrification rates in sediment and natural abundance of N stable isotopes (δ15N) in the sediment-plant-litter system. The fringe forest exhibited higher net N mineralization rates and δ15N in the sediment-plant-litter system, but net nitrification rates were similar to those of the basin forest. The results of the present study suggest that fringe forests exhibit higher N availability and N cycling in sediment compared to basin forests.

Ammonium uptake kinetics and protons efflux in corn varieties / Cinética de absorção de amônio e efluxo de prótons em variedades de milho

The analysis of kinetic parameters for absorption of ions (NO3? e NH4+) is the main experimental procedure for the differentiation of the efficiency of absorption of these nutrients between corn species and cultivars. This work had the aim of evaluating the kinetic parameters of ammonium uptake to elucidate metabolic strategies of corn cultivars at environments with low and high nitrogen concentrations. The selected cultivars were: Catetão, Sol da Manhã, Eldorado and BR 473. The plants were cultivated in pots with N solutions of 1.43 and 8.57 mM at green house conditions. The following kinetic parameters were evaluated 28 days after germination: Vmax, KM and N-amino soluble fraction in the water, nitrate and ammonium. Fresh mass of above groud part and roots, and N-total, P, and Mg in the dried material were determined. Sol da Manhã cultivar presented high development at high affinity uptake systems, while Catetão and Eldorado cultivars presented high development at the low affinity and high capacity of NH4+ uptake system. Sol da Manhã cultivar presented high adaptation at low nitrogen availability conditions. The values of NH4+ uptake kinetic parameters, Vmax and KM can justify the high productivity of this cultivar described in the literature as efficient in nitrogen use.

A análise dos parâmetros cinéticos de absorção de íons (NO3? e NH4+) é o principal procedimento experimental para a diferenciação da eficiência de absorção desses nutrientes entre espécies e variedades de milho. Este trabalho objetivou avaliar parâmetros relativos à cinética de absorção do amônio e o desempenho metabólico de variedades de milho em ambientes com alta e baixa disponibilidade de nitrogênio. As variedades testadas foram: Catetão, Sol da Manhã, Eldorado e BR 473. O experimento foi conduzido em casa de vegetação e as plantas foram cultivadas em vasos com soluções 1,43 e 8,57 mM de N .Aos 28 dias após germinação determinaram-se os parâmetros cinéticos Vmax e KM, e na fração hidrossolúvel, quantificou-se N?amino, nitrato e amônio. Obteve-se a massa fresca da parte aérea e de raiz e, seguido com determinação do N?total, P e Mg no material seco. A variedade Sol da Manhã apresentou maior desenvolvimento de sistemas de absorção de alta afinidade, enquanto, as variedades Catetão e Eldorado mostraram maior desenvolvimento para sistemas de baixa afinidade e alta capacidade de absorção de N-NH4+. A variedade Sol da Manhã apresentou maior adaptação do sistema de absorção à condição de menor disponibilidade de nitrogênio. Os valores obtidos para os parâmetros cinéticos como Vmax e KM confirmam o alto potencial produtivo desta variedade descrita na literatura como eficiente no us

Ammonium uptake kinetics and protons efflux in corn varieties / Cinética de absorção de amônio e efluxo de prótons em variedades de milho

The analysis of kinetic parameters for absorption of ions (NO3? e NH4+) is the main experimental procedure for the differentiation of the efficiency of absorption of these nutrients between corn species and cultivars. This work had the aim of evaluating the kinetic parameters of ammonium uptake to elucidate metabolic strategies of corn cultivars at environments with low and high nitrogen concentrations. The selected cultivars were: Catetão, Sol da Manhã, Eldorado and BR 473. The plants were cultivated in pots with N solutions of 1.43 and 8.57 mM at green house conditions. The following kinetic parameters were evaluated 28 days after germination: Vmax, KM and N-amino soluble fraction in the water, nitrate and ammonium. Fresh mass of above groud part and roots, and N-total, P, and Mg in the dried material were determined. Sol da Manhã cultivar presented high development at high affinity uptake systems, while Catetão and Eldorado cultivars presented high development at the low affinity and high capacity of NH4+ uptake system. Sol da Manhã cultivar presented high adaptation at low nitrogen availability conditions. The values of NH4+ uptake kinetic parameters, Vmax and KM can justify the high productivity of this cultivar described in the literature as efficient in nitrogen use.   

A análise dos parâmetros cinéticos de absorção de íons (NO3? e NH4+) é o principal procedimento experimental para a diferenciação da eficiência de absorção desses nutrientes entre espécies e variedades de milho. Este trabalho objetivou avaliar parâmetros relativos à cinética de absorção do amônio e o desempenho metabólico de variedades de milho em ambientes com alta e baixa disponibilidade de nitrogênio. As variedades testadas foram: Catetão, Sol da Manhã, Eldorado e BR 473. O experimento foi conduzido em casa de vegetação e as plantas foram cultivadas em vasos com soluções 1,43 e 8,57 mM de N .Aos 28 dias após germinação determinaram-se os parâmetros cinéticos Vmax e KM, e na fração hidrossolúvel, quantificou-se N?amino, nitrato e amônio. Obteve-se a massa fresca da parte aérea e de raiz e, seguido com determinação do N?total, P e Mg no material seco. A variedade Sol da Manhã apresentou maior desenvolvimento de sistemas de absorção de alta afinidade, enquanto, as variedades Catetão e Eldorado mostraram maior desenvolvimento para sistemas de baixa afinidade e alta capacidade de absorção de N-NH4+. A variedade Sol da Manhã apresentou maior adaptação do sistema de absorção à condição de menor disponibilidade de nitrogênio. Os valores obtidos para os parâmetros cinéticos como Vmax e KM confirmam o alto potencial produtivo desta variedade descrita na literatura como eficiente no us

Sampling spatial and temporal variation in soil nitrogen availability.

There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part, this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+4) and nitrate (NO-3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in time, we also measured soil NH+4 and NO-3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+4 and NO-3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+4 and NO-3 concentrations decreased with the age of the dune. Soil NO-3 concentration showed strong spatial structure, but soil NH+4 concentration was not spatially structured. Plant-available NH+4 and NO-3 showed relatively little spatial structure: only NO-3 availability in the second sampling period had significant patch structure. Spatial maps of NH+4 and NO-3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different points in time. NO-3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO-3 concentrations, providing some evidence that patches of plant-available NO-3 may reappear at the same spatial locations at irregular points in time.