Isotopic evidence indicates saprotrophy in post-fire Morchella in Oregon and Alaska

Abstract

We assessed the nutritional strategy of true morels (genus Morchella) collected in 2003 and 2004 in Oregon and Alaska, 1 or 2 y after forest fires. We hypothesized that the patterns of stable isotopes (δ¹³C and δ¹⁵N) in the sporocarps would match those of saprotrophic fungi and that radiocarbon (Δ¹⁴C) analyses would indicate that Morchella was assimilating old carbon not current-year photosynthate. We compared radiocarbon and stable isotopes in Morchella with values from concurrently collected foliage, the ectomycorrhizal Geopyxis carbonaria (Alb. & Schwein.) Sacc., the saprotrophic Plicaria endocarpoides (Berk.) Rifai, and with literature to determine isotopic values for ectomycorrhizal or saprotrophic fungi. Geopyxis, Plicaria and Morchella, respectively, were 3‰, 5‰ and 6‰ higher in ¹³C than foliage and 5‰, 7‰ and 7‰ higher in ¹⁵N. High ¹⁵N enrichment in Morchella indicated that recent litter was not the primary source for Morchella nitrogen, and similar ¹³C and ¹⁵N enrichments to Plicaria suggest that Morchella assimilates its carbon and nitrogen from the same source pool as this saprotrophic fungus. From radiocarbon analyses Morchella averaged 11 ± 6 y old (n = 19), Plicaria averaged 17 ± 5 y old (n = 3), foliage averaged 1 ± 2 y old (n = 8) and Geopyxis (n = 1) resembled foliage in Δ¹⁴C. We conclude that morels fruiting in post-fire environments in our study assimilated old carbon and were saprotrophic.

Citation

Hobbie, Erik A.; Rice, Samuel F.; Weber, Nancy S.; Smith, Jane E. 2016. Isotopic evidence indicates saprotrophy in post-fire Morchella in Oregon and Alaska. Mycologia. 108(4): 638-645.