Abstract. Numerous studies have shown that ectomycorrhizal fungi can profoundly affect conifer performance by facilitating nutrient and water uptake, maintaining soil structure, and protecting roots from pathogens and environmental extremes. However, fertilizing and irrigating practices in seedling production nurseries are very different than field conditions at harsh outplanting sites. More information is needed on the ability of specific mycorrhizal fungi to establish at the nursery and improve seedling performance in the outplanted environment. This study was conducted to test the ability of a specific ectomycorrhizal fungus, Rhizopogon rubescens, inoculated onto the root systems of plug-1 ponderosa pine (Pinus ponderosa) seedlings grown in fumigated and nonfumigated bare-root nursery beds to influence conifer establishment on two harsh, dry sites in southwest Oregon, U.S. After outplanting, survival of Rhizopogon-inoculated seedlings were significantly higher than noninoculated seedlings at both field sites (p < 0.05). Survival averaged 93% for Rhizopogon-inoculated seedlings and 37% for noninoculated seedlings at the Central Point site. Survival averaged 71% for Rhizopogon-inoculated seedlings and 41% for noninoculated seedlings at the Applegate site. Field survival did not differ significantly for ponderosa pine seedlings grown in fumigated compared to nonfumigated beds. Seedling height did not differ significantly between Rhizopogon-inoculated and noninoculated ponderosa pine seedlings or fumigated and nonfumigated beds in the nursery or outplanting sites. Foliar analysis at the Applegate site indicated significantly higher phosphorous contents for Rhizopogon-inoculated seedlings. Results from this study indicate that Rhizopogon inoculated plug-1 ponderosa pine survive at a much higher rate on dry, harsh sites in southwest Oregon. Poor survival by noninoculated pine seedlings grown in both fumigated and nonfumigated beds and outplanted on harsh sites indicate that field survival should be considered one of the more important criteria for selection of Rhizopogon species suitable for nursery inoculation.
Commercial production of tree seedlings often includes various biocidal soil treatments for disease control. Such treatments can be effective in eliminating or reducing disease organisms in the soil, but may also eliminate non-targeted beneficial soil organisms, such as mycorrhizal fungi, that improve seedling performance, both in the nursery as well as the outplanted environment. The arbuscular mycorrhizal fungal (AMF) relationship has been verified for some important western coniferous species such as Calocedrus decurrens (Torr.) Florin (incense cedar), Sequoia sempervirens, (D.Don) Endl(coastal redwood) and Thuja plicata J. Donne ex D. Don (western red cedar).
This study was designed to determine the response of Calocedrus decurrens after soil fumigation with and without the addition of phosphorous fertilizer and a commercial mycorrhizal inoculant containing Glomus intraradices. Calocedrus seedling performance was monitored in both the nursery and outplanted environments.
At the nursery, non mycorrhizal seedlings had significantly less foliar phosphorous levels and uneven growth even when phosphorous fertilizers were applied. Mycorrhizal inoculation at the nursery significantly improved height growth and improved seedling uniformity on treated plots. Seedlings from the nursery beds were then outplanted on two reforestation sites. Mycorrhizal inoculation at the nursery improved survival and growth of seedlings at the outplanted site.
This brief animation shows how mycorrhizae work and how mycorrhizal fungi attach to roots, explore the soil and absorb vital nutrients for plants.