Growth response of drought-stressed Pinus sylvestris seedlings to single- and multi-species inoculation with ectomycorrhizal fungi.

Tabea Kipfer,Jaboury Ghazoul,Simon Egli,Thomas Wohlgemuth,Marcel G A Van Der Heijden,Kurt O Reinhart

doi:10.1371/journal.pone.0035275

Abstract

Many trees species form symbiotic associations with ectomycorrhizal (ECM) fungi, which improve nutrient and water acquisition of their host. Until now it is unclear whether the species richness of ECM fungi is beneficial for tree seedling performance, be it during moist conditions or drought. We performed a pot experiment using Pinus sylvestris seedlings inoculated with four selected ECM fungi (Cenococcum geophilum, Paxillus involutus, Rhizopogon roseolus and Suillus granulatus) to investigate (i) whether these four ECM fungi, in monoculture or in species mixtures, affect growth of P. sylvestris seedlings, and (ii) whether this effect can be attributed to species number per se or to species identity. Two different watering regimes (moist vs. dry) were applied to examine the context-dependency of the results. Additionally, we assessed the activity of eight extracellular enzymes in the root tips. Shoot growth was enhanced in the presence of S. granulatus, but not by any other ECM fungal species. The positive effect of S. granulatus on shoot growth was more pronounced under moist (threefold increase) than under dry conditions (twofold increase), indicating that the investigated ECM fungi did not provide additional support during drought stress. The activity of secreted extracellular enzymes was higher in S. granulatus than in any other species. In conclusion, our findings suggest that ECM fungal species composition may affect seedling performance in terms of aboveground biomass.

Highlights

Tree roots are usually colonized by a wide range of microbes, including those fungi that form ectomycorrhizas (ECM)
The presence of S. granulatus caused an increase in shoot biomass from 105 6 9 mg to 312 6 7 mg, whereas under dry conditions, shoot biomass increased from 82 6 11 mg to 157 6 6 mg
The positive relationship between species number and shoot biomass depicted in Figure 1A can be explained by the fact that with increasing species number, a higher proportion of samples are containing the growth-promoting species S. granulatus

Summary

Introduction

Tree roots are usually colonized by a wide range of microbes, including those fungi that form ectomycorrhizas (ECM). Shifts in community composition and decreases in species number have been found as a consequence of anthropogenic nitrogen deposition [2], elevated CO2 [3,4], drought [5] and disturbances such as forest fire [6]. After forest fires in the dry inner-alpine valleys of the Central Alps, a reduction in ECM fungal species number and changes in fungal species composition were found [7]. It is hypothesized that ECM fungi may play a crucial role for P. sylvestris tree regeneration, especially under adverse climatic conditions, given that this tree species obligately depends on fungal symbionts [9,10]. The consequences of a reduction in ECM fungal species richness and changes in ECM community composition for tree performance, are poorly explored

Methods

Results

Conclusion