Root condensed tannins vary over time, but are unrelated to leaf tannins.

Margarete A Dettlaff,James F Cahill,Nadir Erbilgin,Valerie Marshall

doi:10.1093/aobpla/ply044

Abstract

Although the negative effects of root herbivores on plant fitness are expected to be similar to those of above-ground herbivores, the study of below-ground plant defences is limited compared to the rich literature on above-ground defences. Current theory predicts that concentrations of defensive chemicals above- and below-ground should be correlated, as the evolutionary drivers that shape plant defence are similar across the whole plant. We conducted a field study to measure root condensed tannin concentrations in Populus tremuloides, and determine how they related to leaf condensed tannin concentrations, tree position within the stand (edge vs. interior), tree size, and time of year. Overall, root tannin concentrations were substantially lower than leaf tannin concentrations. At individual sampling periods, root and leaf tannin concentrations were uncorrelated with each other, and did not vary with stand position or size. Across the growing season both root and leaf tannin concentrations did show similar trends, with both highest in the early summer, and declining through mid-summer and fall. These results suggest that the mechanisms that influence leaf and root tannin levels in aspen are independent within individual stems, possibly due to different evolutionary pressures experienced by the different tissue types or in response to localized (roots vs. foliage) stressors. However, across individual stems, the similar patterns in chemical defence over time, independent of plant size or stand position indicate that larger scale processes can have consistent effects across individuals within a population, such as the relative investment in defence of tissues in the spring versus the fall. Overall, we conclude that using theories based on above-ground defence to predict below-ground defences may not be possible without further studies examining below-ground defence.

Highlights

The question of how plants defend above-ground tissues has received substantial research attention (Agrawal and Fishbein 2006; Chen 2008; Mithöfer and Boland 2012; Fürstenberg-Hägg et al 2013), grounded in a well-developed body of theory (Loomis 1932; McKey 1979; Rhoades 1979; Bryant et al 1983)
Dettlaff et al – Aspen root chemistry related to season, but not leaf chemistry below-ground defence may require new or modified theory is poorly understood, in the context of below-ground chemical defences (Rasmann and Agrawal 2008)
This study focuses on the relationship between leaf and root tannins in naturally occurring aspen, so the frequent approach of using an artificially created common garden with propagated clones would not be feasible, despite the advantage of controlling for genetic relatedness between individuals

Summary

Introduction

The question of how plants defend above-ground tissues has received substantial research attention (Agrawal and Fishbein 2006; Chen 2008; Mithöfer and Boland 2012; Fürstenberg-Hägg et al 2013), grounded in a well-developed body of theory (Loomis 1932; McKey 1979; Rhoades 1979; Bryant et al 1983). Dettlaff et al – Aspen root chemistry related to season, but not leaf chemistry below-ground defence may require new or modified theory is poorly understood, in the context of below-ground chemical defences (Rasmann and Agrawal 2008). This is a striking gap, as the few studies that have compared the effects of above- and belowground herbivory on plants indicate that they can have equivalent fitness consequences for the entire plant (Blossey and Hunt-Joshi 2003; Wurst et al 2008), and are vulnerable to stress (Kaplan et al 2008). Whether root and shoot defensive chemistry changes in concert or independently in response to these basic ecological factors is unclear (Wurst et al 2008)

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Discussion

Conclusion