Metabolismo do carbono e nitrogênio em plantas de arroz irrigado sob atmosfera enriquecida com CO2

Abstract

Since industrial era to present day, CO2 concentration in atmosphere has increased, directly impacting crops development. Plants can mitigate these impacts through photosynthetic conversion of atmospheric CO2 into carbohydrates or other organic compounds, but the potential for this conversion and plant responses to climate change remains uncertain. In this sense, carbon and nitrogen metabolism studies in plants under CO2 enriched atmosphere are necessary in order to understand plants behavior in this climate change scenario. Thus, present work aimed to characterize the effect of increase CO2 atmospheric concentration under gas exchanges, carbon and nitrogen metabolism and irrigated rice plants production of cultivar IRGA 424 RI. Therefore, two studies were conducted, from of irrigated rice plants cultivation open top chambers (OTC'S) with two CO2 concentrations, 400 (ambient) and 700ppm (high). Evaluations occurred in vegetative (V5 and V11) and reproductive stages (R2 and R7). In relation to gas exchanges, plants cultivated under high CO2 presented an increase in CO2 net assimilation rate, greater efficiency in water use and higher intercellular CO2 concentration in at least three of four phenological stages evaluated. For stomatal conductance, chlorophyll index, nitrogen balance index, nitrogen percentage in leaves and 1000-grain weight were found the lowest values for this treatment. Second study showed changes in enzymatic activity related to nitrogen metabolism, increasing activity of glutamine synthetase enzymes and nitrate reductase in leaves and roots under high CO2, as well as higher nitrate, starch, water soluble polysaccharides and total soluble sugars content in leaves in the first phenological stage evaluated. In roots, inverse was observed for nitrate and starch content in V5, obtaining lowest values for high CO2 treatment. Thus, high CO2 increases photosynthetic rate, nitrogen consumption and water use efficiency and reduces stomatal conductance, altering carbohydrates allocation and intensifying glutamine synthetase activity in V11 and nitrate reductase in all periods evaluated in leaves.