Observations of mycorrhizal inoculation of pin and scarlet oak production in containers

Abstract

Over the course of the last century mycorrhizal symbiosis has come to be recognized as highly beneficial for the host plant. Increased growth, water relations, nutrient acquisition, amelioration of the effects of metal toxicity, and increased resistance to pathogens are all benefits attributed to plants colonized by mycorrhizal fungi. A large body of literature exists that indicates that mycorrhizal inoculation programs are useful for improving the performance of forest tree seedlings. Commercial mycorrhizal products, many containing the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch (Pt), have emerged from this research and are now being marketed for landscape tree growers. In this study, two experiments were conducted to determine the best protocol for inoculation of landscape trees, and to determine if mycorrhizal inoculation is beneficial to trees growing in modern landscape tree container production systems. The first experiment evaluated mycorrhizal inoculation programs utilizing two inocula types employing various substrates for landscape tree production in containers. Quercus palustris Muenchh. (pin oak) and Q. coccinea Muenchh. (scarlet oak) grown in pine bark, sterilized pine bark, sterilized mineral soil, and sterilized vermiculite-based substrates were inoculated with Pt commercial spore inoculum or Pt vegetative inoculum. The vegetative inoculum was unsuccessful at forming mycorrhizae even though the Pt continued to live in the planting substrates. A higher proportion of pin oak was colonized than scarlet oak in all substrates, and vermiculite was a superior environment for mycorrhizal formation than the other three substrates. The second experiment examined the effectiveness of an indigenous mycorrhizal fungus, Scleroderma bovista Fr., to increase growth and resistance to drought stress of scarlet oak grown in containers in the pot-in-pot growing system. Scleroderma bovista did not affect tree growth, and mycorrhizal trees in containers proved to be more susceptible to drought stress than nonmycorrhizal trees. Leaf water potential was more negative for mycorrhizal trees, and conductance was lower for mycorrhizal trees after a 10 day dry down period. A commercial Pt product was also used as an inoculum in this study and again proved completely ineffective at colonizing scarlet oak in pine bark substrate.