Long Term Tiller Population Dynamics in Swards of Grasses with Contrasting Persistence Strategy

The lifespan of individual grass tillers usually does not exceed 12-15 months, because of death of tillers after floral induction and development, or randomly from disease or other factors. Persistence of the tiller population over several years, and associated long term maintenance of the sward, thus depends on the rate of turnover of individual tillers. This study aimed to characterise seasonal and management conditions critical for tiller turnover and its components, tiller birth and tiller death. Two grasses were investigated: Festuca arundinacea and Lolium multiflorum, having high and low persistence, respectively

A dialética no pensamento antigo.

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The Effect of Blue Light on Leaf Growth and Plant Development in Two Morphologically Contrasted Perennial Ryegrass Genotypes: Cellular Basis and Ecological Implications

Several major plant responses to competition for light are determined by responses to light signals, in particular to red/far-red ratio (R/FR) and blue light, besides responses mediated through photosynthesis and carbon assimilation (Gautier et al., 1999). These responses to light signals allow plants to react to the presence of neighbours and to anticipate the impact of light competition on photosynthesis. The objective of the study was to evaluate the impact of blue light on leaf growth and its cellular basis, on two short and long leaved populations (FC and FL respectively), which were shown to have different competitive ability (Hazard et al., 1996)

Assessment of Nitrogen Nutrition Status of Grasses under Water Deficit and Recovery

Grasslands are rarely irrigated. They are therefore systematically submitted to more or less severe water deficits: as well as mineral deficiencies, water scarcity often also results in a reduction of nitrogen (N) status. Although identified some time ago, qualitatively, the interaction with N still remains difficult to take into account in quantitative analyses of crop physiology under water deficits. This paper illustrates how the nitrogen (N) status of the crop changes under water deficits. A N nutrition index (INN) was defined as the ratio of the actual N concentration of forage with the theoretical N concentration under optimal conditions, the latter only depending on the above ground biomass. The objective of the paper is to describe the effect of water deficits on INN, using a new assay recently proposed by Faruggia et al. ( 2004)

Phytochrome Control of Assimilate Partitioning in White Clover

Experiments were conducted in controlled conditions to examine the influences of phytochrome on assimilate partitioning between stolons and branches and to determine the effects on plant moq\u3ehogcncsis in white clover (Trifolium repens L.). Far-red (FR) irradiated plants partitioned more 14C-assimilates to petioles of both the main stolon and branches and less to the nodulated COOis than did control plants. Results clearly demonstrated that FR-irradiated plants developed longer petioles and long internodes. Moreover, the branching rate decreased, which induced a lower portion of dry weight allocated to branches. However, the sink strength of the branches which were developing remained high in FR-treated plants, due to the high sink strength of petioles. The ecological significance of the results is discussed

Modelling of Nitrogen Allocation and Partitioning Within Lucerne (\u3cem\u3eMedicago Sativa\u3c/em\u3e) Shoot Tissues During Recovery from Defoliation: An Approach to Estimate Forage Production and Nitrogen Composition

Lucerne has been grown over centuries for forage. Its forage production is strongly correlated to the initial taproot and stubble N reserves (Avice et al., 1996; Meuriot et al., 2004). However, the influence of cutting management on the level of N storage and the contribution of these N reserves to forage production still remain unclear and need to be studied at the whole plant level. For this purpose, a deterministic model of N allocation within the different organs and partitioning within different biochemical N pools was developed for lucerne with high and low initial N status and cutting heights of 6 or 15 cm

Nitrogen Use Efficiency of Timothy Populations

The objective of this study was to determine the variability in N use efficiency among field-grown timothy (Phelum pratense L.) populations. Shoot biomass and N uptake were measured at the end of the spring growth cycle on six timothy populations fertilized with three N rates at two sites in Eastern Canada. The variability in shoot biomass among populations was similar under limiting and nonlimiting N conditions. The ranking of the populations, however, differed under limiting and non-limiting N conditions, and also between the two sites under limiting N conditions. The differences in shoot biomass among populations under highly N deficient conditions were more related to N conversion efficiency than N uptake efficiency. These preliminary results indicate significant interactions between the N nutrition status and timothy populations, and the importance of N conversion efficiency under highly N deficient conditions

Discussão dos processos de construção do complexo granítico São Sepé, RS: feições geológicas e petrográficas

Construction processes for the São Sepé granitic complex (SSGC) are discussed on the basis of geological and structural, field informations complemented by integrated studies of remote sensors (DEM-SRTM and ASTER images) and aeromagnetic maps for analyzing regional tectonic systems, and also by detailed petrographic investigation. The granitic complex, located in the west of the Sul-riograndense Shield (São Gabriel Block), represents the shallow level (250-160 MPa) of a vertical slow-production mush column controlled by N30-35°E and N55-60°W, pre-existents fault zones linked to post-collisional events of the Dom Feliciano Orogeny (640-620 Ma). Its formation occurred during transtensive tectonic event along N15-20°E fault zones, responsible for regional uplifting and extensive magmatic events at the end of the Neoproterozoic (570-560 Ma), as a reflex of some younger orogeny in the north. The SSGC is a moderate-size (473 km²), composite pluton composed of monzogranites in the center and syenogranites in the border, showing wide textural variations. The expansion of the magma system caused by volatile accumulation at the end of its formation, as registered by granitic cupola and wide felsic margins, has induced the reactivation of NW-SE fault zones. Consequently, this leads to infer some emplacement mechanisms involving roof uplifting. According to the model proposed, the SSGC was constructed through progressive and cyclic, mafic recharge at the bottom of a precursor syenogranite sill, which are put in evidence by features of hybridism in monzogranites. The result was the stratification of the resident magma, and the pluton started to crystallize separately: hybridized monzogranites at the base; and syenogranites from residual melts at the top, in which the concentration of F-H2 O-rich volatiles postponed the crystallization successively. Next episodes of mafic replenishments in a cold, partially crystallized intrusion resulted in re-heating leading to textural aging and thermal erosion of crystallized facies; the reactivation of crystal mushes with re-intrusion and co-mingling of hybridized magmas; and large thermal undercooling of the mafic pole. These features suggest the accumulation of highly mobile syenogranitic magmas on the top, which has built up one of the active magma chambers feeding of the coeval volcanism (Acampamento Velho Formation).A construção do complexo granítico São Sepé (CGSS) é discutida a partir de informações de campo, geológicas e estruturais, complementadas com a avaliação dos sistemas tectônicos regionais integrando sensores remotos (MDE-SRTM e imagem ASTER) e mapas aeromagnetométricos, e com a investigação detalhada de texturas e estruturas. O CGSS, localizado no oeste do Escudo Sul-riograndense (Bloco São Gabriel), representa os níveis epizonais (250-160 MPa) de uma coluna vertical de magma-mush com atividade moderada, controlada por zonas de falha pré-existentes N30-35°E e N55-60°W, cuja atividade foi vinculada aos eventos pós-colisionais da Orogênese Dom Feliciano (640-620 Ma). Sua formação ocorreu no final do Neoproterozóico (570-560 Ma), durante evento tectônico transtensivo ao longo de zonas de falha N15-20°E, responsável pelo soerguimento regional e expressivo magmatismo ácido, que é reflexo de orogenias mais jovens ocorridas a norte. É um pluton composto de dimensão moderada (473 km²), consistindo de monzogranitos centrais e sienogranitos na borda, que exibem grande variedade de texturas. A expansão do sistema magmático com acúmulo de voláteis no final de sua formação, como registrado pela cúpula granítica e ampla margem resfriada félsica, teria promovido a reativação do sistema de falhas NW-SE. Isto permite inferir o papel, mesmo reduzido, de mecanismos de alojamento via o soerguimento do teto.  De acordo com o modelo proposto, a construção do CGSS decorre de episódios progressivos e cíclicos de recarga com magma máfico na base de uma soleira sienogranítica precursora, o que é registrado por feições diversificadas de hibridismo nos monzogranitos. Isto acarretou a estratificação do magma residente, que inicia a cristalizar separadamente: monzogranitos hibridizados na base, e sienogranitos a partir de líquidos magmáticos residuais coletados no topo, cuja cristalização foi sucessivamente postergada com a concentração de voláteis (H2 O e F). Episódios subsequentes de recarga máfica, em uma intrusão mais fria e parcialmente solidificada, promoveram o reaquecimento e a consequente maturidade textural e erosão termal das fácies cristalizadas; a remobilização de mushes cristalinos, com reintrusão e co-mingling de magmas hibridizados; e o maior subresfriamento termal no polo máfico. Tais feições apontam para o acúmulo de magmas sienograníticos altamente móveis, que sustentaram uma das câmaras magmáticas alimentadoras do vulcanismo coevo (Formação Acampamento Velho)

Monitoramento da ocorrência da ferrugem asiática da soja no extremo Sul do Brasil no período 2003-2005.

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