Fertilizer and fungicide use increases the abundance of less beneficial ectomycorrhizal species in a seedling nursery

Abstract

Ectomycorrhizal (ECM) associations are critical to the establishment and growth of Pinus radiata D. Don seedlings. However, the effect of fertilizer and fungicide applications on the benefits seedlings receive from ECM associations is not clear. We determined if changes to relative ECM taxa abundance on nine-month-old P. radiata seedlings (due to exposure to various combinations of fertilizer and fungicide) were correlated with seedling growth and performance. Rhizopogon rubescens was the most abundant ECM taxa on the seedlings, followed by Wilcoxina mikolae, Hebeloma sp., Tuber sp. and Thelephora terrestris. Increased fertilizer and fungicide application rates substantially decreased the relative abundance of R. rubescens and increased the presence of Hebeloma sp. and W. mikolae. The relative abundance of R. rubescens was positively correlated with foliar concentrations of several nutrients while correlations with the four other dominant ECM taxa were negative in most cases. These correlations were observed across all treatments, regardless of the amounts of fertilizer or fungicide used. Given the effects of fertilizer and fungicide on the relative abundance of R. rubescens, increased chemical use appeared to have offsetting negative effects by encouraging mycorrhization with ECM taxa which provided few significant benefits for the seedlings.