Interaction between Ammonium Toxicity and Green Tide Development Over Seagrass Meadows:A Laboratory Study

Eutrophication affects seagrasses negatively by increasing light attenuation through stimulation of biomass of fast-growing, bloom-forming algae and because high concentrations of ammonium in the water can be toxic to higher plants. We hypothesized nevertheless, that moderate amounts of nitrophilic macroalgae that coexists with seagrasses under eutrophic conditions, can alleviate the harmful effects of eutrophication on seagrasses by reducing ammonium concentrations in the seawater to non-toxic levels because such algae have a very large capacity to take up inorganic nutrients. We studied therefore how combinations of different ammonium concentrations (0, 25 and 50 μM) and different standing stocks of macroalgae (i.e. 0, 1 and 6 layers of Ulva sp.) affected survival, growth and net production of the seagrass Zostera noltei. In the absence of Ulva sp., increasing ammonium concentrations had a negative influence on the performance of Z. noltei. The presence of Ulva sp. without ammonium supply had a similar, but slightly smaller, negative effect on seagrass fitness due to light attenuation. When ammonium enrichment was combined with presence of Ulva sp., Ulva sp. ameliorated some of negative effects caused by high ammonium availability although Ulva sp. lowered the availability of light. Benthic microalgae, which increased in biomass during the experiment, seemed to play a similar role as Ulva sp.--they contributed to remove ammonium from the water, and thus, aided to keep the ammonium concentrations experienced by Z. noltei at relatively non-toxic levels. Our findings show that moderate amounts of drift macroalgae, eventually combined with increasing stocks of benthic microalgae, may aid seagrasses to alleviate toxic effects of ammonium under eutrophic conditions, which highlights the importance of high functional diversity for ecosystem resistance to anthropogenic disturbance

Índices para avaliar o estado de nitrogênio da batata multiplicada por distintos materiais propagativos

Melhoria na eficiência de aplicação do N pode ser conseguida pela sincronização da demanda da planta com o suprimento de N durante o ciclo da batateira. O objetivo do trabalho foi determinar os valores ótimos de índices relacionados com o estado de nitrogênio ao longo do ciclo da batata cultivada em ambiente protegido, utilizando distintos materiais propagativos, tubérculo-semente, minitubérculo e broto, comuns na produção de tubérculo-semente básica. Os índices, determinados na quarta folha e na mais velha, foram intensidade da cor verde, avaliada pelo índice SPAD e pela tabela de cor, e características agronômicas: comprimento, largura, área e número de folíolos. Foram realizados três experimentos em vaso, em casa de vegetação na Universidade Federal de Viçosa. Em cada experimento, instalado no delineamento de blocos ao acaso, com quatro repetições, foram utilizadas seis doses de nitrogênio (0; 25; 50; 100; 200 e 400 mg dm-3). Os índices foram determinados a cada 10 dias iniciando-se aos 20 dias após a emergência. Com cada material de propagação, o índice SPAD medido tanto na QF quanto na FV respondeu de forma diferenciada ao incremento na dose de N e atingiu os valores ótimos de 41,3; 40,5; 37,0; 35,8; 36,0; 31,9 e 29,8 dos 20 aos 80 DAE, respectivamente, ao ser utilizado o tubérculo-semente básica. Com todos os materiais de propagação, a idade da planta influencia significativamente todas as variáveis, exceto o número de hastes ou o número de folhas, quando é utilizado broto ou minitubérculo, respectivamente. O valor ótimo dos índices relacionados com a intensidade da cor das folhas e das características agronômicas da planta foram estabelecidos e variam com o material de propagação e idade da planta de batata

Intracellular pH regulation in maize root tips exposed to ammonium at high external pH.

Ammonium-induced changes in the cytoplasmic and vacuolar pH values of excised maize (Zea mays L.) root tips, measured by in vivo 31P nuclear magnetic resonance (NMR) spectroscopy, were correlated with the ammonium content of the tissue, determined by 14N NMR. Calculations based on these measurements indicated that the pH changes observed during exposure to 10 mM ammonium for 1 h at pH 9.0, and in the recovery following the removal of the external ammonium supply, were largely determined by the influx and efflux of the weak base NH3. Carboxylate synthesis, detected by both in vivo 13C NMR and the incorporation of [14C]bicarbonate, was stimulated by the ammonium-induced alkalinization of the root tips, but the contribution that this proton-generating process made to pH regulation during and after the ammonium treatment was quantitatively insignificant. Similarly, ammonium assimilation, which was shown to occur via the proton-generating glutamine synthetase/glutamate synthase pathway using in vivo 15N NMR, was also quantitatively insignificant in comparison with the large changes in ammonium content that occurred during the ammonium treatment and subsequent recovery. The results are discussed in relation to several recent studies in which ammonium was used to perturb intracellular pH values, and it is argued (i) that a new method for probing the subcellular compartmentation of amino acids, based on an ammonium-induced alkalinization of the cytoplasm may be difficult to implement in dense heterogeneous tissues; and (ii) that observations on the apparently proton-consuming effect of ammonium assimilation in rice root hairs may actually reflect unusually rapid assimilation

Effect of differential N and S competition 1 in inter- and sole cropping of Brassica species and lettuce on glucosinolate concentration

Field and greenhouse pot experiments were conducted to evaluate the potential to use intercropping as an alternative method to increase glucosinolates in Brassicas by manipulating nitrogen (N) and sulphur (S) balance by intercropping with lettuce (Lactuca sativa L. var. capitata). In both experiments, four combinations of N and S fertilization were used. In the field experiment no effect of intercropping on the total glucosinolates was found as the growing lettuce was strongly inhibited by the presence of broccoli (Brassica oleracea L. var italic). The reduction in neoglucobrassicin in broccoli from intercropping was probably attributed to the lower N concentrations in broccoli florets. In contrast to this, in the pot experiment both total and individual glucosinolate concentrations in red leaf mustard(Brassica juncea L.) increased by intercropping. Fertilization treatments influenced glucosinolate concentrations in both experiments, and an N by S interaction was observed