Mycorrhizal Role in Net Primary Priduction and Nutrient Cytcling in Abies Amabilis Ecosystems in Western Washington

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Abstract
The potential contribution of mycorrhizal fungi (as sporocarps and mycorrhizal sheaths) to total ecosystem biomass and turnover and nutrient distribution and turnover was examined in a 23—yr—old and a 180—yr—old Pacific silver fir (Abies amabillis) stand in western Washington. While mycorrhizal fungi contributed roughly 1% a total ecosystem biomass in both stands, the percentage of net primary production (NPP) in the mycorrhizal fungal component was roughly 14% in the younger stand and 15% in the mature stand. Mycorrhizal fungi plus conifer fine roots contributed °45% of NPP in the young stand and °75% in the mature stand. Sclerotia production (2700 kg°ha—1°yr—1) contributed the largest proportion of total mycorrhizal fungal production in both stands followed by mycorrhizal sheath production (°350 kg°ha—1°yr—1 and 430 kg°ha—1°yr—1 in the young and mature stands, respectively). Potentially, 27 kg°ha—1°yr—1 of N is cycled through sporocarps in the young stands and 41 kg°ha—1°yr—1 in the mature stand. Annually, fine roots (including mycorrhizae) cycle at least 60, 10, 20, 30 and 10 kg°ha—1°yr—1 of N, P, K, Ca, and Mg, respectively, in the young stand. In contrast, 110, 20, 20, 30 and 10 kg°ha—1°yr—1 of N, P, K, Ca and Mg, respectively, are cycled through fine roots in the mature stand.