Environmental drivers of ectomycorrhizal communities in Europe's temperate oak forests

Abstract

Ectomycorrhizal fungi are major ecological players in temperate forests, but they are rarely used in measures of forest condition because large-scale, high-resolution, standardized and replicated belowground data are scarce. We carried out an analysis of ectomycorrhizas at 22 intensively monitored long-term oak plots, across nine European countries, covering complex natural and anthropogenic environmental gradients. We found that at large scales, mycorrhizal richness and evenness declined with decreasing soil pH and root density, and with increasing atmospheric nitrogen deposition. Shifts in mycorrhizas with different functional traits were detected; mycorrhizas with structures specialized for long-distance transport related differently to most environmental variables than those without. The dominant oak-specialist Lactarius quietus, with limited soil exploration abilities, responds positively to increasing nitrogen inputs and decreasing pH. In contrast, Tricholoma, Cortinarius and Piloderma species, with medium-distance soil exploration abilities, show a consistently negative response. We also determined nitrogen critical loads for moderate (9.5-13.5 kg N/ha/year) and drastic (17 kg N/ha/year) changes in belowground mycorrhizal root communities in temperate oak forests. Overall, we generated the first baseline data for ectomycorrhizal fungi in the oak forests sampled, identified nitrogen pollution as one of their major drivers at large scales and revealed fungi that individually and/or in combination with others can be used as belowground indicators of environmental characteristics.

Monitoring ectomycorrhizal fungi at large scales for science, forest management, fungal conservation and environmental policy

“…Boletaceae, Geastraceae), but they are also increasingly focused on acquiring information about fungal communities in the context of a range of ecosystem processes (for instance how N deposition will affect ecosystem function via impacts on fungal communities), rather than only on rare and/or declining species. Clear demonstrations of changes in mycorrhizal communities with increasing N deposition analogous to the changes that have been reported for other organisms Emmett et al 2011) are emerging from analyses of ICP Forests mycorrhizal data (Cox et al 2010b;Suz et al 2014). There are also some hints as to which traits are likely to respond, e.g.…”

“…Moreover, these functional traits that define each exploration type can confer different capabilities with regard to storing carbon and taking up and translocating nutrients (Courty et al 2010;Hobbie and Agerer 2010). We have seen that mycorrhizal communities in temperate oak forests respond differently to environmental variables depending on their soil exploration type (Suz et al 2014). Because the effects of changes in the presence and proportions of different ECM functional groups across Europe may affect the resilience of forests to environmental change, they need more investigation.…”

“…2) have been carried out in 12 Scots pine (Pinus sylvestris) ICP Forest Level II plots in Britain and Germany (Cox et al 2010b) and 22 oak level II plots (Quercus robur and/or Quercus petraea) across nine countries (Suz et al 2014). Over 3,000 soil cores have been examined and over 10,000 mycorrhizas analysed using DNA-based techniques that identified 112 mycorrhizal fungi in pine and ca.…”

“…The vast European forest monitoring network (www.icpforests.org) is an ideal study platform because its intensively monitored long-term forest plots have tremendous potential for developing and scaling up forest mycorrhizal research and biomonitoring (Cox 2010;Cox et al 2010a, b;Suz et al 2014). In April 2014, a multidisciplinary workshop focused on how the network can be used to investigate mycorrhizal diversity and ecology at large scales (www3.imperial.ac.uk/ e c o s y s t e m s a n d e n v i r o n m e n t / e v e n t s / w o r k s h o p s / nercimpactworkshops/macroecologyofmicrobes).…”

“…In April 2014, a multidisciplinary workshop focused on how the network can be used to investigate mycorrhizal diversity and ecology at large scales (www3.imperial.ac.uk/ e c o s y s t e m s a n d e n v i r o n m e n t / e v e n t s / w o r k s h o p s / nercimpactworkshops/macroecologyofmicrobes). Presentations and discussions assessed the state-of-the-art, findings from ECM communities in a pine study across England and Germany (Cox et al 2010b), a study of oak plots across Europe (Suz et al 2014) and from an ongoing Europe-wide analysis of ECM fungi in spruce, pine and beech plots carried out in plots belonging to this network and using its rich in situ environmental data (listed below). The complementary needs and resources of the monitoring, nature conservation, scientific and forest management communities were discussed.…”