Main stem

Abstract: During 2009 the Amazon basin was hit by a heavy flooding with a magnitude and duration few times observed in several decades. Torrential rain in northern and eastern Amazonia during the austral summer of 2008–2009 swelled the Amazon River and its tributaries. By July 2009, water levels of the Rio Negro, a major Amazon tributary, reached at Manaus harbor a new record, the highest mark of the last 107 years. During the 2008–2009 hydrological year, the rainy season on northern and northwestern Amazonia started prematurely, and was followed by a longer-than-normal rainy season. An anomalously southward migration of the ITCZ during May–June 2009, due to the warmer than normal surface waters in the tropical South Atlantic, was responsible for abundant rainfall in large regions of eastern Amazonia and Northeast Brazil from May to July 2009. We also compared the flood of 2009 with other major events recorded in 1989 and 1999. The hydrological consequences of this pattern were earlier than normal floods in Amazon northern tributaries, which peak discharges at their confluences with the main stem almost coincided with the peaks of southern tributaries. Since the time displacement of the contribution to the main stem of northern and southern Amazon tributaries is fundamental for damping flood waves in the main stem, the simultaneous combinations of peak discharges of tributaries resulted in an extreme flood.

Abstract: Documented increases in global atmospheric CO2 concentration have stimulated interest in the direct effects of CO2 on plant growth and yield as well as the interactive effects of CO2 with other major climatic variables. This study was conducted to determine the effects and interactions of CO2 cocentration and air temperature on the development, growth, total nonstructural carbohydrate (TNC), and final seed yield of soybean [Glycine max. (L.) Merr., cv. Bragg] grown season-long in naturally lit, controlled-environment chambers. Day/night air temperatures of 26/19, 31/24, and 36/29 degrees C were maintained in CO2 treatments of 330 and 660 micromole CO2 mol-1 air. Both CO2 enrichment and increasing air temperature decreased main stem plastochron interval, while increasing air temperature increased final main stem node number. Leaf area and above-ground biomass increased with CO2 enrichment and with temperature from 26/19 degrees C to 31/24 degrees C. The nonlinear increase with temperature in leaf area, aboveground biomass, and plastochron interval was attributed to the highest temperature treatment being near or above the optimum for soybean growth and development. Seed yield increased with CO2 enrichment due mainly to an increase in seed number rather than weight per seed. Individual seed weight decreased, while seed number increased with increasing temperature. Leaflet TNC displayed large diurnal variations, while stem TNC was relatively stable throughout the day. Stem TNC was less affected by CO2 than by temperature treatment and decreased with increasing temperature. These results indicate that the response of soybean to elevated CO2 concentration is highly temperature dependent.