Roberto Oscar Pereyra Rossiello

Differences in growth and water relations among Phaseolus vulgaris cultivars in response to induced drought stress

Relatively little ecophysiological research has been conducted to determine the responses to drought of Phaseolus vulgaris. Four bean cultivars (cvs.) from Brazil, A320, Carioca, Ouro Negro and Xodó were submitted to an imposed water deficit in order to evaluate the importance of some adaptive mechanisms of drought resistance through the analysis of growth parameters, water status, gas exchange and indicators of tolerance mechanisms at the cellular level. During the drought treatment, relative growth rates were more reduced for A320 and Xodó than Carioca and Ouro Negro. A320 closed its stomata very rapidly and complete stomatal closure was obtained at Psi(w)=-0.6 MPa, in contrast to the other cvs. where stomata were fully closed only at Psi(w)=-0.9 MPa. Net assimilation rates were closely related to stomatal conductances. Mechanisms at the cellular level appeared to be mostly important for higher tolerance. Carioca and Ouro Negro, when compared to A320 and Xodó, were characterized by having better drought tolerance mechanisms and higher tissue water retention capacity leading to a better growth under water deficits. The leaf dehydration rates of those cvs. were slow whereas those of the drought sensitive cvs. were rapid. The results were confirmed by the electrolyte leakage test and leaf osmotic potential measurements, which indicated higher membrane resistance and osmotic adjustment in the two tolerant cvs. Carioca and Ouro Negro. It appears from this study that despite being cultivated in the same geographical region, the four cvs. of P. vulgaris displayed somewhat different drought adaptive capacities for prolonged drought during the vegetative phase.

Mineral Nitrogen in Plant Physiology and Plant Nutrition

Abstract Nitrogen (N) nutrition enhances metabolic processes that influences the physicochemical environment at the soil-root interface, modifies rhizosphere conditions, interferes with the uptake of cations and anions, and enhances or represses the activity of several enzyme systems. Also, it affects growth patterns, protein content, and protein quality of seeds. Ammonium (NH4)-N nutrition increases anion uptake, free amino-N/protein ratios, and acidity of root free space; it reduces carbohydrate levels in plant tissues. NO3-N nutrition results in higher cation uptake, higher carbohydrate content in tissues, and alkalinization of root free space. N-Assimilation interferes with the allocation of dry matter and energy, which causes different growth rates of plant parts. In this article we review the effects of mineral-N nutrition on uptake of cations and anions, activity of enzymes, growth patterns of roots and shoots, and water use efficiency, protein content, and protein quality of seeds.

Soil bulk density and biomass partitioning of Brachiaria decumbens in a silvopastoral system

O sombreamento em sistemas silvipastoris concorre para o conforto termico dos animais; no entanto pode afetar a producao do pasto e contribuir para a compactacao do solo, pelo aumento da concentracao de animais nas areas sombreadas. Avaliou-se o efeito da distância do renque de arvores (sob a copa das arvores, 6 e 12 m de distancia das arvores) na densidade do solo e na biomassa aerea e de raizes de Brachiaria decumbens, nas epocas seca e chuvosa. O estudo foi conduzido num Latossolo Vermelho-Amarelo no delineamento em blocos casualizados, com duas repeticoes. A faixa de arvores foi composta pelas especies Eucalyptus grandis e Acacia mangium, e os piquetes foram manejados com novilhas Holandes (Bos taurus) × Zebu (Bos indicus) , sob lotacao rotativa. A intensidade de sombreamento foi decrescente com o distanciamento do renque de arvores. A densidade do solo nao variou com a distância do renque de arvores, mas sim com a epoca do ano, tendo sido maior na epoca chuvosa (1,47 g dm-3) do que na seca (1,28 g dm-3). As massas secas de forragem verde e de raizes foram menores sob a copa das arvores e maiores na epoca chuvosa do que na seca. Na faixa arborizada houve reducoes de 22,3 e 41,4% na biomassa aerea e de raizes, respectivamente. A maior relacao parte aerea/raiz da B. decumbens a sombra expressa uma modificacao no padrao de alocacao de biomassa na forrageira, que prioriza a formacao da parte aerea, em detrimento do sistema radicular.

Dinâmica do perfilhamento em capim-elefante sob influência da altura do resíduo pós-pastejo

The objective of this work was to evaluate the effects of two stubble heights (50 and 100 cm) on tiller dynamics, dry mass for tiller and dry mass herbage accumulation of basal and aerial tillers in elephantgrass pastures managed under grazing. A complete randomized block design with split plot arrangement and four replications were used. The stubble heights did not influence the population density, tiller mortality and birth percentage, dry mass per tiller and herbage accumulation of basal and aerial tillers. Basal and aerial tillers showed increase of 47% and reduction of 16% on population density between spring and summer, respectively. Tillers with leaves were 92% of aerial tillers and 52% of basal tillers. Tiller birth percentage was the highest determinant of population density variations. The dry mass herbage accumulation was larger for basal tillers during spring, and the aerial tillers increased it during summer.

Parâmetros morfológicos para estabelecer tolerância diferencial à toxicidade de alumínio em cultivares de arroz

Two nutrient solution greenhouse experiments were conducted to identify morphological parameters that express Al tolerance and to determine the influence of period of plant growth and Al concentration necessary for tolerance discrimination, in two rice cultivars. Plants of known maximum root length were transferred to nutrient solution at four levels of Al (0, 80, 160 and 320 mmol L-1) with a pH 4.0. In each collection, the new maximum root length was measured in addition to root and leaf areas, and root and shoot dry weights. Only the morphological parameters related to the root system differentiated Al tolerance of the cultivars, and relative root elongation was the most sensitive. Four days of exposure to Al were sufficient to detect differences in Al tolerance by means of relative root elongation. The methods established in this study can be useful in evaluating larger number of cultivars.

DIFFERENTIAL ROOT RESPONSES TO ALUMINUM STRESS AMONG BRAZILIAN RICE GENOTYPES

Reports on aluminum (Al) tolerance of local rice varieties (Oryza sativa L.) in Brazil are few. In this paper, we investigate the effects of Al toxicity on root elongation of a local rice variety and three improved rice genotypes in simple and complete growth solutions. Seedlings (4–5 days) were exposed to Al levels of 0 to 640 μM for two days in simple solutions, while seedlings of 12 days were grown for 9 days in solution with levels of Al ranging from 0 to 320 μM. We found that differences in Al tolerance were more distinct in simple growth solution tests than in complete growth solution tests. The local variety Comum Branco, cropped on acid soils, showed higher Al tolerance than the new improved genotypes. Relative root elongation of the local variety seemed to depend on the Al concentration of the growth medium, displaying a reduction in root elongation at low Al levels and a recovery of root growth at moderate Al levels. Further investigation is needed to elucidate if this particular pattern of Al tolerance in primary roots is also expressed in lateral root growth.

Effects of N‐source, light intensity and temperature on nitrogen metabolism of bahiagrass

Abstract Under greenhouse conditions, a study was made on the effects of nitrogen (N) source (N)O3 or NH4), mode of application (single vs. split) and nitrification inhibition on the N‐uptake and metabolism, of bahiagrass. Variations in light and temperature in the greenhouse affected the N‐metabolism of bahiagrass plants. Nitrate fed plants had nitrate reductase activity (NRA) pattern different from that of NH4‐fed plants. Amino‐N accumulation patterns were similar for plants under both N‐sources, although amino‐N levels in leaves of NH4‐fed plants were much smaller than that of NO3 plants. Nitrate accumulation in leaves showed inverse trend to that of roots in plants fed both NO3 or NH4. To the sharp peaks in NO3 levels in roots due to increases in light and temperature corresponds a sharp decrease of its levels in leaves. For both both NO3 or NH4 treatments, soluble‐N accumulated most in the rhizomes of bahiagrass plants, whereas protein N accumulated most in leaves, suggesting that rhizomes had a buff...

Um novo clorofilômetro para estimar os teores de clorofila em folhas do capim Tifton 85

The purpose of this research was to evaluate the performance of a new portable chlorophyll meter in the indirect determination of chlorophyll contents in Tifton 85 bermudagrass leaves. In a field trial of short duration, three N doses (0, 75 and 150kg ha-1) were combined with four sampling dates (8, 16, 24 e 28 days after a cut for sward uniformity) in completely randomized blocks, with treatments arranged in a split-plot design. Analyses were performed in the youngest fully expanded leaf blade. Contents of chlorophylls a, b and total were quantified spectrophotometrically, after extraction with acetone 80%, while chlorophyll meter readings, expressed as Falker Chlorophyll Index (FCI) units, provided the same information. Chlorophyll meter readings were sensitive to both N rates and sampling dates. It were obtained significant positive correlations between both methods (chlorophyll a: r=0.646, chlorophyll b: r=0.797 and for total chlorophyll: r=0.721). It was concluded that this new chlorophyll meter constitutes an appropriate tool for the indirect determination of foliar chlorophyll contents in Tifton 85 pastures.

Root growth and proton efflux rates of rice seedlings in a greenhouse environment

Foram avaliados o crescimento e o efluxo de protons (EH+) em raizes de plântulas de arroz (Oryza sativa cv. IAC 47) cultivadas sob as condicoes de luz de uma casa de vegetacao. Quinze dias apos a emergencia, plântulas foram transplantadas para potes contendo 3,7 L de uma solucao nutritiva com 1,43 mmol N-NH4+ L-1 como fonte exclusiva de nitrogenio, visando induzir quatro ciclos sequenciais de acidificacao da solucao, a partir de um valor de pH inicial de 5,3. Os efluxos medios de protons foram calculados com base em periodos de crescimento radicular de 48 h (de 0 a 192 h). As estimativas de EH+ foram obtidas a partir dos valores calculados para as Taxas de Crescimento Relativo (TCR), expressas com base na area radicular (AR), ou massa fresca radicular (MF), e das pendentes da regressao linear da quantidade de protons livres na solucao (UH+) sobre MF ou AR. Os gradientes de acidificacao (DUH+/DMF) foram melhor associados quando relacionados com MF do que com AR. As taxas de crescimento das raizes foram afetadas por flutuacoes de radiacao fotossintetica e temperatura dentro da casa de vegetacao e nao se relacionaram claramente com os valores de EH+. Todavia, foi concluido que quando existe uma relacao linear entre UH+ e MF, as avaliacoes de EH+ expressas por unidades de MF, podem ser mais confiaveis do que aquelas expressas por unidades de AR.

Aluminum tolerance measured by root growth and mucilage protection in Urochloa brizantha and Urochloa decumbens

Aluminum toxicity on root systems was analyzed through comparing root growth and evaluating the protective function of mucilage in Urochloa decumbens and Urochloa brizantha. Seedlings were grown in a solution with different concentrations of AlCl3 and with mucilage removed or present. The root elongation rate, total length, number of roots and presence of aluminum at the root apex were measured. Root development was inhibited by aluminum and the elongation rate was maintained without any difference between the two species. A significant reduction in root length was found in U. brizantha. Aluminum did not influence root branching in either species and accumulated mostly in the rhizosphere of U. brizantha, where the mucilage has less of a protective function. The greatest aluminum tolerance was found in U. decumbens, observed through maintenance of total root system growth from lower to higher aluminum toxicity.