Strain Identity of the Ectomycorrhizal Fungus Laccaria bicolor Is More Important than Richness in Regulating Plant and Fungal Performance under Nutrient Rich Conditions.

Christina Hazard,David Johnson,Fatou T Mbow,Laura Kruitbos,Hazel Davidson,Andy F S Taylor

doi:10.3389/fmicb.2017.01874

Abstract

Effects of biodiversity on productivity are more likely to be expressed when there is greater potential for niche complementarity. In soil, chemically complex pools of nutrient resources should provide more opportunities for niche complementarity than chemically simple pools. Ectomycorrhizal (ECM) fungal genotypes can exhibit substantial variation in nutrient acquisition traits and are key components of soil biodiversity. Here, we tested the hypothesis that increasing the chemical complexity and forms of soil nutrients would enhance the effects of intraspecific ECM diversity on host plant and fungal productivity. In pure culture, we found substantial variation in growth of strains of the ECM fungus Laccaria bicolor on a range of inorganic and organic forms of nutrients. Subsequent experiments examined the effects of intraspecific identity and richness using Scots pine (Pinus sylvestris) seedlings colonized with different strains of L. bicolor growing on substrates supplemented with either inorganic or organic forms of nitrogen and phosphorus. Intraspecific identity effects on plant productivity were only found under the inorganic nutrient amendment, whereas intraspecific identity affected fungal productivity to a similar extent under both nutrient treatments. Overall, there were no significant effects of intraspecific richness on plant and fungal productivity. Our findings suggest soil nutrient composition does not interact strongly with ECM intraspecific richness, at least under experimental conditions where mineral nutrients were not limiting. Under these conditions, intraspecific identity of ECM fungi becomes more important than richness in modulating plant and fungal performance.

Highlights

Research on biodiversity-ecosystem function relationships has tended to focus on species diversity (Loreau et al, 2001; Tilman et al, 2014) with much less emphasis on within-species diversity (Hughes et al, 2008)
After 28 days, growth on glutamic acid and glycine was greater in comparison to ammonium nitrate (P-value < 0.001), and LbD had significantly less biomass in comparison to LbA and LbC (Figure 1)
We demonstrated intraspecific variation in organic N source utilization by L. bicolor strains in pure culture, but these findings were not consistent with the effects on plant and fungal productivity when in symbiosis

Summary

Introduction

Research on biodiversity-ecosystem function relationships has tended to focus on species diversity (Loreau et al, 2001; Tilman et al, 2014) with much less emphasis on within-species diversity (Hughes et al, 2008). Intraspecific diversity has been shown to have wide-ranging effects on numerous ecosystem processes in a myriad of systems (Hughes et al, 2008; Johnson et al, 2012). Little is known about the nature of the biodiversity-ecosystem function relationship with respect to forest ecosystems and intraspecific diversity of soil microorganisms. A key group of forest soil microorganisms are the ectomycorrhizal (ECM) fungi, which compose a significant proportion of the soil microbial biomass (Högberg and Högberg, 2002), and colonize the majority of the fine root systems of trees in boreal and temperate biomes (Smith and Read, 2008). Ectomycorrhizal fungi have important functional roles in forest ecosystems, for biogeochemical cycling and nutrient acquisition to trees (Smith and Read, 2008). The roots of an individual Populus tremula tree were found to support between 182 and 207 species of ECM fungi, and 23 ITS genotypes of Cenococcum geophilum (Bahram et al, 2010)

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