Crescimento de crambe na presença ou ausência de competição interespecífica

RESUMOCrambe (Crambe abyssinica) has a cropping cycle of around 90 days, being suitable as an alternative to the second grain crop planted after soybean is harvested in the Center West region of Brazil. It is necessary to understand the growth and development dynamics of crambe plants in order to allow correct management of the production factors. This study aimed to describe the growth and development parameters of crambe plants under presence or absence of interspecific competition. The experiment was installed in the fall-winter 2011 in an Oxisoil, in completely randomized blocks design with three replications. Treatments comprised crambe plants growing either in presence or absence of interspecific simulated competition, throughout the cropping cycle. Plants were collected for the growth analysis every 15 days from harvest until 75 days after emergence. Growth parameters leaf area (AF), dry mass of stems/culms (MSC), leaves (MSF) and total (MST) dry mass, leaf area index (IAF), absolute (TCA) and relative (TCR) growth rates, net assimilation rate (TAL), specific leaf area (AFE), leaf area duration (DAF), leaf area ratio (RAF) and leaf mass ratio (RMF) were determined for the crop plants, subjected or not to competition, as well as for the simulated competitor. Crambe is a low competitive crop, being the competition more severe until 60-70 days after emergence. Besides, crop performance under field conditions was properly described by the net assimilation rate (TAL), which is also affected by the leaf area duration (DAF) and leaf mass ratio (RMF).

Low soil temperature reduces the positive effects of high nutrient supply on the growth and biomass of white birch seedlings in ambient and elevated carbon dioxide concentrations

To investigate the interactive effects of soil temperature (Tsoil) and nutrient supply on the responses of growth and biomass of white birch ( Betula papyrifera Marsh.) to atmospheric carbon dioxide concentration ([CO2]), seedlings were grown under two [CO2] (360 and 720 µmol·mol–1), three Tsoil (5, 15, and 25 °C initially, increased to 7, 17, and 27 °C one month later), and three nutrient regimes (Low: N–P–K = 4:1.8:3.3 mg·L–1; Intermediate: N–P–K = 80:35:66 mg·L–1; and High: N–P–K = 160:70:132 mg·L–1) for 4 months. Low Tsoil reduced leaf and total biomass at high nutrient supply and root biomass at intermediate and high nutrient supply. There were significant three-factor interactive effects on root collar diameter (RCD), stem biomass, and leaf mass ratio. Low Tsoil reduced RCD at high nutrient supply and stem biomass at intermediate and high nutrient supply in elevated [CO2] while intermediate and high Tsoil enhanced them. Values of leaf mass ratio were lowest at low Tsoil and low nutrient supply in elevated [CO2]. The effect of Tsoil was generally insignificant at low nutrient supply, but the responses of growth and biomass remained significantly higher under high than low nutrient supply at all Tsoil.