Mission 2007 - Hydrocarbon Potential Evaluation Team

Nutrient cycling

Arctic ecosystems receive a higher proportion of nutrients input from precipitation and nitrogen fixation than do temperate systems, because chemical weathering is inhibited by low temperature and permafrost. Mosses and lichens have a major influence on nutrient cycling in tundra and other northern ecosystems through their role in nitrogen fixation, and the ability of mccosses to aumulate and retain elements from precipitation. Retention of precipitation by bryophytes is also likely to redice losses by leaching of nutrients already existing in the soil. The general role of mosses and lichens in nitrogen fixation bases on that the cyanobacteria growing on their stems and roots help transfer the nitrogen nutrients to the mosses and lichens themselves and also to the other plants, enriching the nitrogen content of the whole vegetation.

Bryophytes act as efficient filters of nutrients arriving in precipitation, throughfall or litter and from the soil by absorbing them directly into their tissues, or retaining them externally in solution in capillary spaces. The annual growth increment of the moss layer at an Alaskan taiga site was found to contain nutrients in excess of inputs from throughfall. The mosses, and also the lichens, help increase the nirtogen concentration in the soil. Their absorption from the soil retains large amount of phosphorous and potassium in their cytoplasm. Mosses alone account for 75% of the annual accumulation of phosphorous in an Alaskan black spruce (Picea mariana) forest. Other nutrients such as calcium and magnesium are also intensively retained in the tissues of mosses and lichens.

Nutrient immobilization in slowly decomposing bryophyte phytomass may thus have a major influence in restricting recycling, and therefore in controlling ecosystem development and productivity. In mires, absorption of nitrogen and other elements by Sphagnum reduces availability to other plants. Bryophytes therefore may increase the pools of nutrients in the Alaskan ecosystems, but reduce availability to other organisms.