Jahresgang der Blatt-Wasserpotentiale von Pflanzen in der Krautschicht eines Kalkbuchenwaldes

Abstract

Summary In the years 1982 and 1983 the water potential (Θ L ) in the leaves of six understorey plant species was investigated in a beech forest on limestone. The seasonal course of Θ L was compared to the seasonal courses of climatic factors (photosynthetic active radiation, PAR; air temperature, T a ; saturation deficit of the air, SD; precipitation), and relationships were discussed. In spring a high PAR is accompanied by relative low T a - and SD-values. In both years precipitation was high during the spring. In the summer 1982 the PAR reached only 1 to 2 %, in summer 1983 3 to 5 % of the PAR above the canopy. Especially in the summer 1983 T a and SD were high. From July to October 1982 the precipitation was low with 54 mm rain; 36 mm fell during the three thunderstorms in July and August. Form July till October 1983 the precipitation reached only 70% of the rain which fell during the same time in 1982. But in contrast to 1982 the distribution of the precipitation was more even. The spring geophytes Allium ursinum and Arum maculatum during their short vegetation period always had high leaf water potentials because of high soil water saturation, high precipitation and relative low SD. In summer 1982 as a result of the long dry period, the Θ L in Asarum europaeum and Mercurialis perennis decreased with minimum values of −2.0MPa (A. europaeum) and less than −3.0MPa (M. perennis). In summer 1983 Θ L decreased as low as −2.5 MPa in M. perennis and −1.5MPa in A. europaeum. The water potential in the leaves of the grasses Hordelymus europaeus and Melica uniflora decreased in the summer 1983 to similar values. The higher Θ L in the summer 1983 with contrasts to the values in 1982 is caused by the more even distribution of rain.