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

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.