Forest mosses sensitively indicate nitrogen deposition in boreal background areas

Area of Science:

• Ecology
• Environmental Science
• Biomonitoring

Background:

• Mosses absorb nitrogen (N) from precipitation, making them sensitive bioindicators of N deposition.
• Boreal forests in Finland experience low N deposition loads, making them ideal for studying subtle N impacts.

Purpose of the Study:

• To investigate the relationship between nitrogen deposition and nitrogen concentration in common terrestrial moss species.
• To evaluate the effectiveness of different nitrogen forms and deposition monitoring methods (bulk deposition vs. throughfall) in predicting moss N content.
• To assess the nitrogen saturation status of boreal mosses under low N deposition scenarios.

Main Methods:

• Collected mosses (Pleurozium schreberi, Hylocomium splendens, Dicranum spp.) from coniferous forests and open areas.
• Monitored in situ nitrogen deposition as bulk deposition (BD) and stand throughfall (TF), analyzing ammonium, nitrate, dissolved organic N, and total N.
• Used regression analysis to correlate moss N concentration (mossN%) with various N deposition parameters.

Main Results:

• Moss N concentration showed positive relationships with N deposition, with higher concentrations inside forests.
• Inorganic N in bulk deposition best predicted moss N in open areas, while dissolved organic N in throughfall was key within forests.
• Mosses appeared near N saturation at deposition levels of 3-5 kg N ha⁻¹ yr⁻¹, indicated by asymptotic curves and ammonium accumulation.

Conclusions:

• Moss N concentration is a reliable indicator of N deposition in boreal ecosystems.
• Open site measurements of moss N are preferable for monitoring to avoid confounding factors like tree canopy absorption and litter leachate.
• The study provides valuable data on the sensitivity of boreal mosses to low N deposition and their response to different N forms.