Effect of Nitrogen Addition to the Soil on Atlantic Forest Tree Seedlings

The input of large amounts of fertilizers in agricultural areas may result in nitrogen (N) leakage to nearby forest fragments, which can impact the physiology and growth of trees. The current study aimed to assess the effects of soil N addition on seedlings of four tree species in the Brazilian Atlantic Forest: Croton floribundus and Astronium graveolens (pioneer), Guarea kunthiana and Aspidosperma polyneuron (non-pioneer). The experiment was carried out in a greenhouse condition with three treatments: reference (soil without addition of nutrients), N addition (N: soil with addition of ammoniacal-N), and complete (C: soil with addition of ammoniacal-N and other macro and micronutrients). Croton floribundus seedlings presented higher shoot growth with N addition, mainly in treatment C, and only this treatment increased net photosynthesis. There was great variation in the metabolic responses induced by treatments N and C, with accumulation of nitrate in the leaves and xylem sap only in seedlings in treatment N. In A. graveolens, there was a decrease in transpiration in response to treatments N and C. However, water use efficiency, leaf area, and dry mass increased only in seedlings subjected to treatment C. Regarding metabolic parameters, A. graveolens was little responsive to the treatments. In G. kunthiana seedlings, the treatments decreased net photosynthesis and increased leaf total N. Only treatment N led to decreased stem dry mass and increased nitrate contents in leaves and xylem sap. Aspidosperma polyneuron exhibited no change in growth, but there was an accumulation of N compounds in the leaves for both treatments N and C, which suggests that this species could be a good bioindicator of N addition to the soil. Although influencing different parameters, the results indicate that soil N addition affects the performance of both pioneer and non-pioneer species. Finally, the implications of these results for biomonitoring of N availability in the soil of forest fragments are discussed.