European aspen with high compared to low constitutive tannin defenses grow taller in response to anthropogenic nitrogen enrichment

Franziska Bandau,Benedicte Riber Albrectsen,Kathryn M Robinson,Michael J Gundale

doi:10.1016/j.foreco.2021.118985

Franziska Bandau, Benedicte Riber Albrectsen + Show 2 more

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https://doi.org/10.1016/j.foreco.2021.118985

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Abstract

Boreal forests receive nitrogen-(N)-enrichment via atmospheric deposition and industrial fertilization. While it is known that N-enrichment can intensify interactions with natural antagonists, it remains poorly understood how genetic variability in plant defense chemistry can affect biotic interactions and height growth in N-enriched environments. We grew replicates of five low- and high-tannin Populus tremula genotypes, respectively, under three N-treatments (ambient, 15, and 150 kg N ha−1 yr−1). We assessed shoot blight occurrence (i.e. symptoms caused by Venturia fungi) during four growing seasons, and tree height growth during the same period. Damage by Venturia spp. increased with N-addition during all years, likely due to enhanced foliar quality. Low–tannin plants showed higher incidences of Venturia infection than high-tannin plants, regardless of the N-input-level. Height responded to an N-by-tannin-group interaction, which occurred because high-tannin plants grew taller than low-tannin plants at the high N-treatment, but not under the other N-levels. This pattern indicates that innate resource investment into tannin production yields a positive effect on growth under N-enriched conditions. Given that N-deposition is increasing globally, our research suggests that further studies are needed to investigate how N-enrichment interacts with plant defense traits globally. Moreover, our research suggests that N-deposition may provide an advantage for well-defended, high-tannin plants; and further, that genetic diversity in plant defense may be a key mechanism by which plant populations respond to this change.

Highlights

During the past century, humans have greatly altered the supply of nitrogen (N) to terrestrial ecosystems (Galloway et al, 2008)
During the four-year observation period, we found that Venturia infection frequencies significantly increased with N-addition (Table 1, Table 1 Final model terms retained in log linear analyses that evaluated the effect of nitrogen (N), constitutive tannin level, and their interaction on the incidence of Venturia shoot blight in a Populus tremula common garden
We found a significant positive relationship between foliar condensed tannin concentrations measured near the beginning of the study (i.e. 2013), and height growth measured at the end of the study period (Fig. 3b)

Summary

Introduction

Humans have greatly altered the supply of nitrogen (N) to terrestrial ecosystems (Galloway et al, 2008). A number of tree species within this genus are valuable timber species due to their rapid regen eration and growth rates, and short rotation period, serving as a source for wood and paper products (Holeski et al, 2009). Because of their fast growth and ability to resprout after coppicing, Populus spp. and their hybrids are increasingly managed for bioenergy (Lasch et al, 2010; Nikula et al, 2010; Derba-Maceluch et al, 2020). Susceptibility to Venturia spp. has been shown to vary among Populus genotypes (Holeski et al, 2009; Albrectsen et al, 2010; Grady et al, 2015), and has been suggested to be influenced by a tree’s constitutive foliar condensed tannin (CT) content (Holeski et al, 2009)

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