Response of Quercus petraea seedlings to nitrogen fertilization

In view of increasing concern about long-term effects of N deposition on forest ecosystem, decline of oak stands in many central European countries, and poor documentation of nutrient budgets of oak stands, a pot experiment was performed on N-fertilized oak seedlings (Quercus petraea Liebl.) to study impact on biomass, morphology and nutrition. Seedlings were treated at equivalent N amounts with ammonium sulfate, calcium nitrate, a mineral multi-nutrient fertilizer (N, P, K, Mg) and a slow release organic fertilizer (N, P, K, Mg, Ca) and grown in an acidic soil low in nutrients and a calcareous soil with high nutrient supply. All N-fertilization types increased biomass production, number of leaves and leaf area; however, total mass produced per leaf mass declined. Multi-nutrient fertilized oak seedlings were able to maintain the highest leaf area by means of lowest amounts of fine roots. Each N addition increased N foliar contents. Nitrogen-induced growth caused dilution effects indicated by suboptimal N levels of both foliage and fine roots. Nitrogen fine-root contents were a better indicator of N inputs than foliar contents. All fertilization types increased N storage of the plants. In the acidic soil, the highest N storage per seedling (multi-nutrient fertilizer) was coupled with the highest total biomass production, while the organic fertilizer treatment, which induced maximum total dry matter gain on the calcareous soil, represented the lowest N storage of all N treatments. Differences of N partitioning (leaves, shoot, coarse roots, fine roots) were small. Plant uptake of added N was estimated up to 61%. N/P ratios of all treated seedlings exceeded the harmonious range and it is concluded that further N input will cause severe N-induced nutritional imbalance for base cations on substrates with low nutrient supply as well. In general, effects of N additions to the oak seedlings were more pronounced on the substrate with lower nutrient supply. (C) 2001 Elsevier Science B.V. All rights reserved.