Abstract

Globally, forest die-off from global-change-type drought events (hotter droughts) are of increasing concern, with effects reported from every forested continent. While implications of global-change-type drought events have been explored for above-ground vegetation, below-ground organisms have received less attention, despite their essential contributions to plant growth, survival, and ecosystem function. We investigated rhizosphere fungal communities in soils beneath trees affected by a global-change-type drought in a Mediterranean climate-type ecosystem in southwestern Australia, quantifying how fungal richness, composition and functional groups varied along a drought impact gradient. Following a forest die-off three years previously, we collected soils beneath dead and alive trees within forest exhibiting high, minimal and relatively unaffected levels of forest die-off. Rhizosphere fungal DNA was extracted from soils, amplified and subjected to high throughput sequencing. Fungal community composition varied significantly (P < 0.001) along the drought impact gradient with less richness in drought affected stands. There was some evidence of community differentiation between dead versus alive trees (P = 0.09), and no difference in rarefied richness and diversity. When considered by functional group, die-off-impacted plots had more arbuscular mycorrhizal fungi (AM) and saprotrophs, and fewer ectomycorrhizal fungi (ECM), compared with living trees from the unaffected plots. Further, within die-off plots, dead versus alive tree rhizosphere samples contained more AM, saprotrophs and pathogens, and fewer ECM. Disruptions to rhizosphere fungal communities, such as altered functional groups, can have implications for ecosystem persistence and function, particularly in regions projected to experience increased global-change-type drought events.

Highlights

  • Drought and heat-induced forest die-off is garnering increasing concern and prominence, with effects reported from every forested continent (Allen et al 2010, Cobb et al 2017, Ruthrof et al 2018)

  • Our study has revealed rhizosphere soil beneath forest trees affected by a global-change-type drought was characterised by significantly different fungal community composition and abundance of key functional groups, namely higher levels of arbuscular mycorrhizal fungi (AM) fungi, saprotrophs, and fewer ectomycorrhizal fungi (ECM) fungi in drought-affected plots

  • Soil beneath trees affected by drought had different fungal community composition and changes in the abundance of key functional groups, namely higher levels of AM and saprotrophs, and fewer ECM mycorrhizal fungi

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Summary

Introduction

Drought and heat-induced forest die-off is garnering increasing concern and prominence, with effects reported from every forested continent (Allen et al 2010, Cobb et al 2017, Ruthrof et al 2018). Consequences of forest die-off events may be cross-scale and complex, including substantial direct changes to forest structure (Matusick et al 2016), composition (Allen and Breshears 1998) and function (Royer et al 2011, Lindenmayer et al 2012) and indirectly through interactions with other disturbance agents, including fire (Enright et al 2015, Ruthrof et al 2016) and pests (Jactel et al 2012). Common effects include changes to the carbon cycle (Hicke et al 2012), nutrient and water balances (Adams et al 2012), near-ground radiation (Royer et al 2010), and potential fire behaviour (Ruthrof et al 2016). The implications of global-changetype drought events have been investigated for aboveground vegetation, below-ground organisms have received much less attention, despite their essential contributions to diversity and ecosystem processes (Bardgett et al 1999, van der Heijden et al 2008)

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