Generalist herbivore response to volatile chemical induction varies along a gradient in soil salinization

Brian M Connolly,Jocelyn M Marsack

doi:10.1038/s41598-022-05764-0

Brian M Connolly, Jocelyn M Marsack

Open Access

https://doi.org/10.1038/s41598-022-05764-0

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Abstract

Elevated soil salinity directly modifies plant physiology and indirectly alters the biotic interactions that shape plant performance. However, it is unclear how soil salinization interacts with plant defenses to alter patterns of leaf consumption or herbivore survival, development, and performance. In this study, we carried out laboratory feeding trials and a common garden experiment to investigate how gradients in soil salinization interact with plant induction status (modified via exogenous application of methyl jasmonate [MeJA]) to influence feeding consumption and performance of the generalist herbivore Spodoptera exigua on tomato (Solanum lycoperscium) plants. Our results showed that S. exigua consumed less leaf tissue from tomatoes treated with ≥ 50 mM NaCl; at these higher salinity treatments, these herbivores were less likely to pupate and died more quickly. Treatment with MeJA only reduced leaf consumption in the 0 mM NaCl treatment. Our common garden study demonstrated that natural populations of leaf chewing herbivores were less likely to damage tomatoes treated with > 50 mM NaCl solutions. Treatment with MeJA in the common garden reduced damage from natural populations of herbivores, but only for salt treatments at the 50 mM NaCl concentration level and we did observe variation in herbivore damage between cohorts in common garden trials. These results suggest that both soil salinization and volatile jasmonate signals may generate complementary shifts in decreased plant quality for herbivores. Overall, our study concludes that soil salinization could be a potential driver in spatial patterns of variation in both herbivory and herbivore demography.

Highlights

Elevated soil salinity directly modifies plant physiology and indirectly alters the biotic interactions that shape plant performance
Our understanding of the effects of anthropogenic inputs can have on plant–herbivore interactions is developing, see Tao et al (2013)[20] and Forieri et al (2016)[21], but we still lack a clear understanding of how anthropogenic chemical inputs influence herbivory[21] and modify induced defenses
Chemical induction via methyl jasmonate reduced the amount of leaf tissue consumed by S. exigua, but only for plants that received the control salinization solution (Fig. 1A, Table 1)

Summary

Introduction

Elevated soil salinity directly modifies plant physiology and indirectly alters the biotic interactions that shape plant performance. Dombrowski (2003)[31] demonstrated that greater soil salinity upregulates proteinase inhibitors (i.e., enzymes that limit herbivore digestion and survival) in Solanum lycopersicum (tomato) seedlings, suggesting greater soil salinity may mimic the effect of defense signaling associated with herbivory or VOC signals from wounded neighboring plants, see Forieri et al (2016)[21] and Younginger et al (2009)[32] It is still unclear how gradients in soil salinization interact with induction by volatile chemicals to modify leaf herbivory and generalist herbivore survival. We used laboratory feeding trials and a common garden experiment to examine how gradients in soil salinization interact with plant induction status (modified via MeJA spray) to influence feeding consumption and performance of the generalist lepidopteran herbivore Spodoptera exigua on tomato (Solanum lycoperscium) plants. We aim to gain insight into how gradients in soil salinization affect patterns of leaf consumption and herbivore survival in the presence and absence of volatile plant hormones associated with imminent herbivory

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