Crescimento de pimentão em diferentes arranjos espaciais

The objective of this work was to evaluate the growth of green pepper cv. Atlantis under different spatial arrangements. Three spacing arrangements between double and simple planting rows (1.5x0.5 m, 1.6x0.4 m and 1.7x0.3 m) and four spacing distances between plants in the rows (0.2, 0.3, 0.4 and 0.5 m) combined in factorial scheme were evaluated. A randomized block design in split-plots divided in time with three replicates was used. The growth assessment was done in nine occasions, 14 days apart, and the first one was performed 14 days after transplanting (DAT). Leaf area (LA), leaf area index (LAI), dry masses of leaves (LDM), stem (SDM), fruit (FrDM) and total shoot (TDM); absolute growth rate (AGR), rates of net assimilation (NAR) and relative growth (RGR); and leaf area (LAR) and leaf mass (LWR) ratios were evaluated until 126 DAT. The changes in LA, RGR, LWR and LAR did not depend on row spacing, but spacing influenced LDM, SDM, FrDM and TDM, LAI and AGR. The increase in spacing reduces LAI and LAR, and increases LA, LDM, SDM, FrDM, TDM, AGR and NAR, but does not influence RGR and LWR.O objetivo deste trabalho foi avaliar o crescimento do pimentão cv. Atlantis sob diferentes arranjos espaciais. Foram avaliados três arranjos de espaçamentos entre fileiras duplas e fileiras simples de plantio (1,5x0,5, 1,6x0,4 e 1,7x0,3 m), e quatro espaçamentos entre plantas nas fileiras (0,2, 0,3, 0,4 e 0,5 m), combinados em esquema fatorial. Utilizou-se o delineamento de blocos ao acaso, com três repetições e parcelas subdivididas no tempo. A avaliação de crescimento foi realizada em nove épocas espaçadas em 14 dias, com a primeira avaliação realizada 14 dias após o transplantio (DAT). Até os 126 DAT, foram avaliados: área foliar (AF); índice de área foliar (IAF); massas secas de folhas (MSF), do caule (MSC), de frutos (MSFr) e do total da parte aérea (MST); taxa de crescimento absoluto (TCA), assimilatória líquida (TAL) e de crescimento relativo (TCR); e as razões de área foliar (RAF) e de massa foliar (RMF). As alterações em AF, TCR, RMF e RAF foram independentes do espaçamento entre fileiras que, no entanto, influenciou MSF, MSC, MSFr e MST, IAF e TCA. O aumento do espaçamento entre plantas reduz o IAF e a RAF e aumenta a AF, MSF, MSC, MSFr, MST, TCA e TAL, mas não influencia a TCR e RMF

Effects of temperature at constant air dew point on leaf carboxylation efficiency and CO 2 compensation point of different leaf types

The effect of temperature on photosynthesis at constant water-vapor pressure in the air was investigated using two sclerophyll species, Arbutus unedo and Quercus suber , and one mesophytic species, Spinacia oleracea . Photosynthesis and transpiration were measured over a range of temperatures, 20–39° C. The external concentration of CO 2 was varied from 340 μbar to near CO 2 compensation. The initial slope (carboxylation efficiency, CE) of the photosynthetic response to intercellular CO 2 concentration, the CO 2 compensation point (Γ), and the extrapolated rate of CO 2 released into CO 2 -free air ( R i ) were calculated. At an external CO 2 concentration of 320–340 μbar CO 2 , photosynthesis decreased with temperature in all species. The effect of temperature on Γ was similar in all species. While CE in S. oleracea changed little with temperature, CE decreased by 50% in Q. suber as temperature increased from 25 to 34° C. Arbutus unedo also exhibited a decrease in CE at higher temperatures but not as marked as Q. suber . The absolut value of R i increased with temperature in S. oleracea , while changing little or decreasing in the sclerophylls. Variations in Γ and R i of the sclerophyll species are not consistent with greater increase of respiration with temperature in the light in these species compared with S. oleracea .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47470/1/425_2004_Article_BF00397389.pd

Dynamics of competition between wild oats (Avena fatua L.) and winter cereals

This study examined the effects of competition on the growth of Avena fatua, winter wheat and winter barley. Plants were sampled at frequent intervals from replacement series experiments at two contrasting sites in the U.K. A. fatua was much slower to establish than the two cereals, but thereafter exhibited a faster rate of growth. In monoculture, it took a considerable time for A. fatua to reach a size equal to that of the cereals, but by the end of the experiments it was the largest of the three species. The change-over from cereal dominance in mixtures to A. fatua dominance was rapid, and in three cases coincided with cereal flag leaf emergence. In the fourth case, it appeared to coincide with the start of canopy height extension. At one site the order of competitiveness at anthesis was A. fatua = barley > wheat, and at the other site the order was A. fatua > wheat > barley. In order to explain and predict differences between years and sites, more studies are required on morphological development in relation to abiotic variables