Tillväxt hos husmossa (Hylocomium splendens) i boreal skog och växthus : effekter av ökad vattentillgång

Abstract: Hylocomium splendens (Glittering wood-moss) is a common species in the Nordic countries and can be found in many different types of boreal forests. It usually forms dense moss carpets on the forest floor. The shoots grow in segments and new segments form annually on the previous years growth. The size of the segments is probably regulated in a high extent by local micro environmental conditions. Previous experiments suggest increased growth of H. splendens following water treatment compared to untreated shoots. The purpose of this study was to investigate how length and biomass growth of H. splendens is affected by water supply, relative humidity and nutrient addition in field- and greenhouse experiments. The field study was carried out in Hallen, Jämtlands län, Sweden, in forests dominated by spruce, during July up to October of 2001. Moss growth was compared in watered and non watered plots. The greenhouse study was done to study how the growth in length and biomass of moss segments was affected by different water- and nutrient regimes under controlled conditions. Watering, with distilled water, took place three times a week under three different regimes. Nutrients were added to half of the plots. To study if the growth of the moss segments is affected by the humidity gradient due to the distance to small water courses, samples were collected from two humidity gradients in Krokom community, Jämtlands län, Sweden. Water additions in the field study had a positive effect on the length and biomass growth of the current years segments, but the increase was not statistically significant. Although the differences are small they show that the watering had a positive effect on the growth in spite of a very rainy summer and autumn. The biomass for the last years segments was significantly larger in the none-treated plots than in the watered ones. The water regimes of the greenhouse experiment showed significantly larger current year segments with increased water supply. The last year's segments had a corresponding decrease in growth with increased water supply. Nutrient addition had no significant effect on moss growth. The moss growth showed a great variation between the patches along the gradients. However, there was no clear tendency that the distance from water (the gradient of humidity) should be an important factor for growth. Both the field study in Hallen and the greenhouse experiment showed that increased water supply generates a greater growth of the current years segments, while the growth of the last years segments decrease. This indicates that the moss allocates more resources to the current years segments when the water supply is good. The nutrient addition treatment showed no effect on growth during the greenhouse study; probably the experimental time was too short. For the gradient studies there are no results that clearly can be due to gradients of relative humidity. Other factors than the distance from the water probably have greater influences on the growth: for example the topography, ground conditions, temperature and density of the forest.