Sensitivity of understorey vegetation to nitrogen and sulphur deposition in a spruce stand

Abstract

The response of understorey vegetation to addition of nitrogen and sulphur was examined in a 60-year-old Norway spruce ( Picea abies Karst.) stand in southern Finland. The understorey vegetation was studied on experimental plots receiving nitrogen (25 kg N ha −1) and sulphur (30 kg S ha −1) as ammonium sulphate once a year for 4 years. The dominant moss species on the site were Pleurozium schreberi (Mitt.) and Dicranum polysetum (Sw.). The biomass of the dominant moss species was decreased significantly by sulphur and nitrogen deposition during the study period. Due to the addition of nitrogen and sulphur, the biomass of P. schreberi was decreased by 60% and the biomass of D. polysetum by 78%. Over a 4-year study period the responses of vascular plants to addition of nitrogen and sulphur were not significant. Forest-floor mosses seemed to be more sensitive to nitrogen and sulphur deposition than vascular plants. Since bryophytes lack a cuticle and absorb water very rapidly after rain, they are exposed more to the direct effects of acid deposition than other plants. Thus, mosses may indicate changes in forest vegetation due to acid deposition.