Ectomycorrhizal and Dark Septate Fungal Associations of Pinyon Pine Are Differentially Affected by Experimental Drought and Warming.

Catherine Gehring,Sanna Sevanto,Danielle E M Ulrich,Adair Patterson,Cheryl R Kuske

doi:10.3389/fpls.2020.582574

Abstract

Changing climates can cause shifts in temperature and precipitation, resulting in warming and drought in some regions. Although each of these factors has been shown to detrimentally affect forest ecosystems worldwide, information on the impacts of the combined effects of warming and drought is lacking. Forest trees rely on mutualistic root-associated fungi that contribute significantly to plant health and protection against climate stresses. We used a six-year, ecosystem-scale temperature and precipitation manipulation experiment targeted to simulate the climate in 2100 in the Southwestern United States to quantify the effects of drought, warming and combined drought and warming on the root colonization (abundance), species composition and diversity of ectomycorrhizal fungi (EMF), and dark septate fungal endophytes in a widespread woodland tree, pinyon pine (Pinus edulis E.). Our results show that pinyon shoot growth after 6 years of these treatments was reduced more by drought than warming. The combined drought and warming treatment reduced the abundance and diversity of EMF more than either treatment alone. Individual ectomycorrhizal fungal taxa, including the drought tolerant Cenococcum geophilum, were present in all treatments but the combined drought and warming treatment. The combined drought and warming treatment also reduced the abundance of dark septate endophytes (DSE), but did not affect their diversity or species composition. The current year shoot growth of the trees correlated positively with ectomycorrhizal fungal diversity, highlighting the importance of diversity in mutualistic relationships to plant growth. Our results suggest that EMF may be more important than DSE to aboveground growth in P. edulis, but also more susceptible to the negative effects of combined climate stressors.

Highlights

Changes in climate, including the combined effects of increased drought and warming temperatures, are significantly affecting temperate forest ecosystems
To examine the effects of drought and warming on ectomycorrhizal fungi (EMF) and dark septate endophytes (DSE) in P. edulis, roots were sampled from trees that had been under ambient, drought (~50% reduction in precipitation), warming and a combination of drought and warming treatments for 6 years at the Los Alamos Survival-Mortality (SUMO) experiment located in Los Alamos County, New Mexico (35.49°N, 106.18°W, 2175 m a.s.l)
Our results indicate that EMF are more sensitive than DSE, with the former showing declines in both abundance and diversity

Summary

Introduction

Changes in climate, including the combined effects of increased drought and warming temperatures, are significantly affecting temperate forest ecosystems Intraspecific differences among trees in morphological and physiological traits can be substantial enough to alter predictions of future plant distributions (Ikeda et al, 2017) Microbial plant mutualists, such as root-associated fungi, significantly affect plant responses to climate change (reviewed by Kivlin et al, 2013; Mohan et al, 2014; Bennett and Classen, 2020). Many dominant temperate tree species form associations with ectomycorrhizal fungi (EMF), a diverse assemblage of ascomycete and basidiomycete fungi that improve host plant access to soil nutrients and water and provide protection from some pathogens in exchange for fixed carbon (Smith and Read, 2008) These fungi may buffer plants against climate change, but their activities and buffering ability can be affected by hot and dry conditions. It is important to understand how root-colonizing fungi respond to environmental changes and to link those responses to the growth and survival of their plant hosts

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