Zur Stickstoffernährung von Urtica dioica L. auf Böden unterschiedlichen Wasserhaushaltes

Abstract

Summary The influences of soil water and nitrogen supply on growth and nitrogen nutrition of Urtica dioica L. was determined of four sites during a vegetation period from April to October 1983. The nitrogen supply of the four soils investigated varied between 124 and 264 kg/ha. Depending on season and stage of ontogenesis, Urtica dioica takes up varying amounts out of this nitrogen pool. Despite higher amounts of plant available mineral nitrogen in the soils at the dry and sunny sites, Urtica dioica shows a minor exploitation of the nitrogen supply there. This is most likely due to deficiency of plant available water. On these soils, height growth is limited to about 110 cm. This may also be caused by a higher allocation of nitrogen into flowers and fruits instead of vegetative plant parts. On soils high in both plant available water and nitrogen, Urtica dioica reaches a shoot length of 190 cm in the penumbra of deciduous forests. At all sites investigated, Urtica dioica loses many of its leaves during summer, which is probably due to light deficiency in the deep shade of a closed canopy, but may also be a genetically fixed property of this species for the redeployment of nitrogen. It is shown that the nitrogen demand of closed stands of Urtica dioica can change significantly even at neighbouring sites which differ in irradiation, but have the same soil characteristics. The nitrogen supply out of the rhizomes into the areal shoots of Urtica dioica contributes 20—40% of the total demand during the main growth period from April to June. Loss of nitrogen due to self-thinning makes it difficult to estimate precise values.