Great Basin Bristlecone Pine Volatiles as a Climate Change Signal Across Environmental Gradients

Curtis A Gray,Michael J Jenkins,Justin B Runyon

doi:10.3389/ffgc.2019.00010

Abstract

Alpine treeline species, like Great Basin bristlecone pine (GBBP) (Pinus longaeva Bailey), have received attention for their potential as indicators of climate change. Most studies have focused on climate-induced changes to treeline position, but climate effects on the physiology and stress of treeline plants remain poorly understood. Volatile organic compounds (VOCs) could provide insights into plant responses to climate change since the quantity and blends of VOCs released by plants exhibit variation in response to the environment, and can convey detailed information about the status of the emitting plant. We collected and analyzed GBBP VOCs and within-needle chemistry along elevational gradients (lower treeline, upper treeline, and midway in between) near the northern and southern geographic limits of GBBP. Random Forest analysis distinguished elevation classes using VOCs with 83% accuracy and identified the compounds most important for classification. Ordination revealed that elevation, temperature, heat load index, and relative humidity were significantly correlated with VOCs. Within-needle chemistry provided less predictive value in classifying elevation class (73% accuracy) and was correlated only with elevation and heat load index. These findings suggest that GBBP VOCs are highly sensitive to the environment and could be used to assess and predict tree status and responses to environmental change. The potential effects of climate- and elevation-induced changes in GBBP chemistry on abiotic and biotic interactions are discussed.

Highlights

Treeline species that live in harsh, high-elevation environments are susceptible to climate change and can serve as early signals of change (Körner, 1998, 2012)
Gas chromatography–mass spectrometry (GC-mass spectrometer (MS)) analysis identified 42 volatile compounds emitted by Great Basin bristlecone pine (GBBP) trees (21 select compounds based on mean decrease in accuracy (MDA) are shown in Table 1; all compounds are shown in Supplementary Table 1)
Volatile organic compounds (VOCs) across elevations differed quantitatively and not qualitatively, each tree emitted an identical suite of VOCs, but elevation strongly affected the quantities of the compounds that were emitted

Summary

Introduction

Treeline species that live in harsh, high-elevation environments are susceptible to climate change and can serve as early signals of change (Körner, 1998, 2012). This is thought to be because trees growing near the treeline are at, or near, their survival limits and so should be highly sensitive to environmental change and respond earlier than the rest of the forest (Smith et al, 2009; Körner, 2012). Climate effects on the physiology of treeline plants have received much less attention and remains largely unknown, despite the fact that understanding the impacts of environmental variability on plant physiology could help predict how treelines will change

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Conclusion