Fotossíntese e teores de carboidratos em espécies arbóreas crescendo em áreas de pastagens abandonadas na Amazônia Central

Abstract

The conversion of areas of the Amazon forest to other forms of land use account for more than 700 thousand km2. Of these, about 60% correspond to areas of low productivity pastures, usually used for some years and then abandoned. Abandonment occurs because of lack of sustainability of the pastures front of low natural fertility of soils from. In these areas it is common to observe pioneer tree species in abundance beginning the process of forest succession. Therefore considering the importance of the photosynthetic process of tropical trees, this study proposed to investigate ecophysiological characteristics of pioneer species growing in succession relating to carbon sequestration in abandoned pastures in central Amazonia. The variables comprise measurements of the response curve of photosynthesis to elevated CO2 controlled, determinations of the carbohydrate level in leaves and roots, pigment contents, specific leaf area and leaf water potential and nutritional status in plant-soil in five pioneer species (Vismia japurensis; Vismia cayennensis; Laetia procera; Goupia glabra; Bellucia dichotoma) observed along a chronosequence of four (4) classes of abandonment. The study was conducted in barns located in the experimental area of the Dynamic Biology Project of Forest Fragments – DBPFF (02º34’S, 60º07’W). As responses of the photosynthetic potential (Apot) showed a variation from 10.76 to 37.78 (μmol m-2 s-1) throughout the different ages of the barns, V. cayennensis and G. glabra did not show a significant pattern across different ages, but V. japurensis; L. procera, and B. dichotoma showed significant effects. But also varied in the Vc-max and Jmax from 135.33 to 32.22 and from 113.09 to 55.37 (μmol m-2 s-1) in V. Japurensis had observed a negative interaction between the parameters along the successional chronosequence, the ratio of stomatal conductance (gs) B. dichotoma was the only species that showed a significant difference between the different classes of abandonment. The species used different strategies in the capture of light energy, thus obtaining an efficient acquisition of CO2 and thus a more effective production of assimilates, since concentrations of starch in leaves and roots showed the highest concentrations among the first stages between successional species, but G. glabra did not show a pattern along the chronosequence, in addition, the levels of soluble sugars in leaves and roots did not show a significant variation between different classes of abandonment. The concentrations of photosynthetic pigments were observed among species elevated ratios of Chl a:b, and Chl a + b: Cx+c between the first classes of abandonment. The leaf water potential (Ψw) showed a range between -1.1 to -2.5 (MPa) at different ages and species of abandonment the lowest values were observed between the classes (0-4 years), ranging between -1 6, and -2.4 (MPa) in different species. As for specific leaf area (IEF) showed a variation between 43 and 211 (cm2 g-1) along the succession chronosequence, and V. japurensis showed a smaller effect on the different classes of abandonment. In relation to leaf nutritional status of the species, there were dry all requirements and/or different strategies In the accumulation of mineral elements in leaf tissue, showing a wide variation in nutrient levels at various stages of abandonment, which somehow characterizes the balance and nutrient cycling in soil-plant system in the Amazon. The results showed a correlation between the nutrient concentrations in surface soil layers with different classes of abandonment. It was concluded that these species have good conditions for sustainability and that the five species shown to be capable of regeneration in areas of abandoned pastures in Central Amazonia.