Interação entre a alta concentração de dióxido de Carbono e fertirrigação com nitrato e amônio em plantas de tabaco (Nicotiana tabacum L.)

Abstract

The initial stimulation of photosynthesis in elevated CO2 concentration (e[CO2]) is often followed by a photosynthesis decline, known as CO2 acclimation. This phenomenon is typically promoted by a decreases Rubisco content, an accumulation starch and reduction in plant nitrogen (N) levels. Changes in N levels under e [CO2] can be particularly affected if plants are fertilized with nitrate (NO3 -) or ammonium (NH4 + ), as N sources. The NO3 -assimilation consumes around 25% of energy produced by an expanded leaf, whereas NH4 + needs a lower energetic requirement to be incorporated into organic compounds. These energetic needs are extremely relevant, once depending on the absorbed ion, associated to environmental condition, the cell energetic metabolism can be impacted in different ways. Thus, under e[CO2], the increase in photosynthesys would require amplification and flexibility of the energy production systems to meet metabolic demand mainly during NO3 -assimilation. In this contexto, some studies have pointed out the possibility of NH4 + be a better N source to be absorpted and assimilated in C3 plants under e [CO2]. However, high NH4 + levels in plant tissues may be toxic, causing some physiological and morphological changes. Although plant N relations is an important for food crops productivity and nutritional value worldwide, most studies do not compare plant performance supplied with different N sources. Therefore, this study aims go beyond of treating N as a single entity — so-called total N soil or total N plant — because the specific N compounds formed from inorganic N available in soil subsequently become strongly engaged in all aspects plant metabolism and determine plant responses to atmospheric e[CO2]. For this, the suitability of different criteria to assess the plant N metabolism was analyzed and discussed through of the experiment results with e[CO2] and fertigation with NO3 -and NH4 + ratio in tobacco (Nicotiana tabacum) plants. The results showed that plants that received only NO3 -as source of N had low growth performance when exposed to [CO2] of 760 μmol.mol -1 . On the other hand, in fertirrigated plants with only NH4 + , the increase [CO2] positively favored the gas exchanges and availability of carbon skeletons. This was essential for maintenance of metabolic pathways responsible for N assimilation and distribution for growing tissues. These data show that the physiological performance of tobacco plants exposed to high [CO2] depends on metabolic implications inherent to the inorganic N source being absorbed and assimilated.