Ecophysiological responses of species of secondary succession, growing on abandoned pastures in central Amazon

The catle ranch is the main land use responsible for deforestation in the Amazon. Due to low soil fertility and low use of productive technology, pastures may become unsustainable, and then abandoned, giving way to a typical secondary vegetation. To try to understand the strategies adopted by most common tree species in abandoned pastures we analysed certain characteristics related to ecophysiological and successional chronosequence of secondary vegetation in different periods of precipitation. Were studied secondary forests with ages between 0-19 years, located in the area of the Biological Dynamics of Forest Fragments (PDBFF). Were determined the chemical characteristics of the soil as well as leaf nutrient levels, specific leaf area, leaf water potential and parameters involved in gas exchange and chlorophyll fluorescence. Concentrations of N, P and K increased, while Ca and Mg in the soil decreased with age of the stand. Foliar concentrations of some nutrients, as well as the efficiency of use, varied both between species as a function of the stand’s age. The response of photosynthetic rate showed higher values for early successional species and lower for late successional species. The highest values of Amax were observed for the genus Vismia. Variables Amax, gs, Rd and E values decreased with the age of the stand for most species, except for Goupia glabra. The performance index of species increased with the age of the stand, especially for Belluciagrossularioides and Laetia procera. Plants of younger stands dissipated more energy as fluorescence than did those of older stands. The leaf hydric potential showed little variation between species and also the ages of the stands. Both index values of chlorophyll content and the values of specific leaf area, had increase with age of stands for all species. The analysis of the variables set suggests that species differ as regards the position within the successional group and that, despite the improvement in nutritional conditions depending on the age of stands, their efficiency in usage has been limited. Increases in the amounts of specific leaf area photosynthetic rates and reductions in power dissipation depending on the age of stands, suggest that may have occurred modifications relating to the plasticity of plants over time, changes which also typically are associated with changes in availability irradiance.