Strategies for the use of excessive nitrogen in soil by Atlantic Forest species under the influence of high temperature

Abstract

Despite the anthropic deposition of N soluble compounds and the warming of the atmosphere have already been proven in the vicinity of urban remnants of Atlantic Forest in São Paulo, little is known about the effects of these environmental disturbances on the biogeochemical processes in soil and on N metabolism of their native species. Thus, the present study was proposed with the aims of: 1) To verify whether the bioavailability of NH4+ and NO3- in soil and soluble N concentrations in the roots and leaves of young plants of a liana spceies, a pioneer tree species and a non-pioneer tree species increase when they are cultivated in pots containing superficial soil from an urban fragment of Atlantic Forest, after nitrogen addition; 2) To verify whether the activity level of nitrate reductase, glutamine synthetase and glutamate dehydrogenase, the concentrations of amino acids and chlorophylls in roots and/or leaves differ among the aforementioned species; 3) To verify whether the proportions between NH4+ and NO3- in the soil and whether the strategies of using these soluble N forms by the three species are altered by the increase in air temperature. Three independent experiments will be carried out (one for each species) in a growth chamber, subdivided into two autonomous environments, called Chamber 1 and Chamber 2; The plants will be kept in a thermoperiod of 26oC day/19oC night in Chamber 1 and in a thermoperiod of 30oC day/23oC night in Chamber 2. The other meteorological variables will not vary between both chambers. Each experiment will be initiated with 96 plants per chamber, being 48 plants cultivated in urban forest soil without addition of N and 48 plants cultivated in the same soil with addition of N, composing 4 replicates entirely randomized by treatment, with 12 plants each. Three potted plants will be removed per replicate of treatment after 7, 14, 21 and 28 days of experiment. Roots and leaves of them will be gathered in order to obtain 4 composed samples of both organs per treatment, every 7 days. At the beginning of each experiment, 12 additional seedlings of the 2 soil treatments will form groups of plants T0. The composed samples of roots and leaves will be analyzed for determining the activity of the enzymes nitrate reductase, glutamine synthetase and glutamate dehydrogenase and concentrations of chlorophylls A and B, free amino acids and concentrations of N-NH4 and N-NO3. The soil used for growth of the 3 seedlings per treatment replicate will also be joined after 7, 14, 21 and 28 days of experiment to compose 4 samples per treatment and per week for analysis of the concentrations of NH4+ and NO3-. The data will be subjected to analysis of variance with three factors (factor 1: temperature; factor 2: soil treatment; factor 3: Time). Associations will be established between variables in plants and soil. (AU)