Ectomycorrhizal fungal exoenzyme activity differs on spruce seedlings planted in forests versus clearcuts
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Ectomycorrhizal (ECM) fungal community structure and potential exoenzymatic activity change after clearcut harvesting, but functional complementarity and redundancy among those ECM fungal species remaining support growth of regenerating seedlings.
Ectomycorrhizal (ECM) fungal community composition is altered by forest harvesting, but it is not clear if this shift in structure influences ECM fungal physiological function at the community level. In this study, we characterized activities of extracellular enzymes in the ectomycorrhizospheres of Picea engelmannii seedlings grown in forest and clearcut plots. These exoenzymes are critical for the breakdown of large organic molecules, from which nutrients are subsequently absorbed and translocated by ECM fungi to host plants. We found that ectomycorrhizae on seedlings planted in forests had different exoenzyme activity profiles than those on seedlings planted in clearcuts. Specifically, the activities of glucuronidase, laccase, and acid phosphatase were higher on forest seedlings (P ≤ 0.006). These differences may have been partly driven by soil properties. Total carbon, total nitrogen (N), extractable phosphorus, extractable ammonium-N, and mineralizable N were higher, while pH was lower in forest plots (P ≤ 0.01). However, we also found that enzyme activity only shifted where community composition also changed. Functional complementarity can be inferred within ECM fungal communities in both forests and clearcuts because ectomycorrhizae formed by different species in the same environment had distinct enzyme profiles (P < 0.0001). However, ectomycorrhizae of Thelephora terrestris exhibited high levels of N- and P-mobilizing exoenzyme activities. Seedling biomass did not differ between forest and clearcut environments, so the high abundance of T. terrestris ectomycorrhizae in the clearcuts may have sustained nutrient acquisition by clearcut seedlings even in soils with lower N and P and with reduced ECM fungal species richness.
KeywordsExoenzyme assay Ectomycorrhizal physiology Functional complementarity and redundancy Picea engelmannii Bioassay seedling Clearcut harvesting
This research was supported by a Discovery Grant from the Natural Sciences and Engineering Research Council of Canada and by the Forest Investment Account of the Forest Science Program of the British Columbia (BC) Ministry of Forests, Lands and Natural Resource Operations (MFLNRO) awarded to MJ. JW acknowledges support from the University of British Columbia, Okanagan Campus and the Province of British Columbia for scholarships. We thank Alan Vyse for access to information about the Sicamous Creek field site, MaryAnn Olson, Fawn Ross, and Brendan Twieg for help in the field, and Natasha Lukey and Ayla Fortin for help in the field and lab. Finally, we are immensely grateful to the BC MFLNRO for establishment and long-term maintenance of the Sicamous Creek Silvicultural System Research Project (http://www.for.gov.bc.ca/rsi/research/sicamous/index.htm).
Conflict of interest
The authors declare that they have no conflict of interest.
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