Disturbance, nutrient availability and plant growth in phenol-rich plant communities

• Main Author: Berglund, Linda
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2004
• Subjects: Not in use; please see Agris categories; Subarctic; Tundra
• Online Access: https://pub.epsilon.slu.se/638/; https://pub.epsilon.slu.se/638/1/AVHandling.Linda.pdf

Disturbances, such as fire, usually result in a higher N and nutrient availability. However, little is known regarding the role of fire-produced charcoal and other disturbance-induced effects on nutrient availability and the consequences for plant growth and ecosystem development. Late-successional boreal forests and subarctic forest-tundra ecotones are dominated by plants with high tissue-levels of phenolic compounds and have large quantities of N locked up in thick humus-layers. Factorial experiments were set up in both field and laboratory, manipulating amount of phenol-rich litter, charcoal and glycine. Nitrogen mineralization, nitrification, soluble P and phenolic compounds were measured by ionic and non-ionic resin capsules. Nitrogen-fixation was measured by acetylene reduction assays. Removal of phenol-rich litter with the charcoal-layer intact in a recently burned stand increased growth and nutrient uptake by tree seedlings, with birch (Betula pendula) being the most responsive species. Litter and charcoal may function synergistically thus influencing seedling establishment after fire, especially in early-successional species like birch. Nitrification-rates increased with addition of activated carbon (AC) (as a surrogate for fire-produced charcoal) in laboratory incubations of boreal and subarctic soils and phenolic accumulation on non-ionic resin-capsules was reduced by AC amendments. Nitrogen-fixation rates were found to increase linearly with time since fire. This increase was likely a function of the degree of colonization by cyanobacteria and site factors such as light, moisture and available N. Nitrogen addition rates of 4 Kg N ha -1 yr-1 eliminated Nfixation in late succession sites. The findings suggest that N-fixation in boreal forests becomes more important in late secondary succession were available N are low in spite of higher total N. Subarctic birch-forests had higher soluble P and phenol concentrations compared to heath tundra. In contrast, there were no differences in available NH4 + or NO3 -. The addition of glycine greatly enhanced N-mineralization rates in birch forests and heath tundra, suggesting severe N-limitation. Anthropogenic disturbances resulting in the loss of birch would greatly reduce positive influences from birch and increase soil-erosion and nutrient losses, creating both reduced N and P availability. I conclude that a drastically altered disturbance regime in boreal and subarctic regions, both decreased (e.g. reduction of fire) and increased (e.g land-use), may have profound long-term effects on ecosystem processes.