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1. Dispensing a Synthetic Green Leaf Volatile to Two Plant Species in a Common Garden Differentially Alters Physiological Responses and Herbivory

   https://doi.org/10.3390/agronomy11050958  

   Freundlich, Grace E.; Shields, Maria; Frost, Christopher J. (May 2021, Agronomy)

   null (Ed.)

   Herbivore-induced plant volatile (HIPV)-mediated eavesdropping by plants is a well-documented, inducible phenomenon that has practical agronomic applications for enhancing plant defense and pest management. However, as with any inducible phenomenon, responding to volatile cues may incur physiological and ecological costs that limit plant productivity. In a common garden experiment, we tested the hypothesis that exposure to a single HIPV would decrease herbivore damage at the cost of reduced plant growth and reproduction. Lima bean (Phaseolus lunatus) and pepper (Capsicum annuum) plants were exposed to a persistent, low dose (~10 ng/h) of the green leaf volatile cis-3-hexenyl acetate (z3HAC), which is a HIPV and damage-associated volatile. z3HAC-treated pepper plants were shorter, had less aboveground and belowground biomass, and produced fewer flowers and fruits relative to controls, while z3HAC-treated lima bean plants were taller and produced more leaves and flowers than did controls. Natural herbivory was reduced in z3HAC-exposed lima bean plants, but not in pepper. Cyanogenic potential, a putative direct defense mechanism in lima bean, was lower in young z3HAC-exposed leaves, suggesting a growth–defense tradeoff from z3HAC exposure alone. Plant species-specific responses to an identical volatile cue have important implications for agronomic costs and benefits of volatile-mediated interplant communication under field conditions. 

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2. Quantitative effects of soil salinity on the symbiosis of wild lima bean (Phaseolus lunatus L.) and Bradyrhizobium in Costa Rica

   https://doi.org/DOI:10.5073/JABFQ.2018.091.039  

   Ballhorn, D.J.; Wolfe, E.R.; Tyler, Jess; Ronan, W.; Sands-Gouner, S; Shaw, C..; Balkan, M.A. (January 2018, Journal of applied botany and food quality)

   Global climate change and local anthropogenic activities are increasing soil salinization with permanent negative effects on agricultural and ecosystem productivity. While salt stress is known to affect plant performance, its effects on the association with key microbial plant symbionts, such as legume-associated nitrogen-fixing rhizobia, are less understood. In this field study conducted in Costa Rica (Puntarenas), we used sympatrically-occurring wild lima bean (Phaseolus lunatus L.) and Bradyrhizobium to quantify biomass production of unfertilized rhizobial (R+) and fertilized rhizobia-free (R-) plants at different levels of experimentally manipulated salinity in native soil. In response to salt stress, nodulation was significantly reduced even at slightly increased salt levels. Plants growing at soil salinity levels of 2, 4, 6, and 8 mS/cm showed a mean reduction of nodules by 60.22, 76.52, 83.98, and 92.5% compared to the controls. Similarly, we also observed a significant decline in plant biomass at elevated salinity. However, biomass accumulation of R- plants was significantly less impacted compared to R+ plants, suggesting that the plant-microbe symbiosis is more salt-sensitive than the plant host itself. We suggest that the search for more salt-tolerant, crop plant-compatible rhizobial strains may provide a sustainable approach to maintain agricultural productivity on low to moderately saline soils. 

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3. Plant defenses interact with insect enteric bacteria by initiating a leaky gut syndrome

   Charles J Mason, Swayamjit Ray (June 2019, Proceedings of the National Academy of Sciences of the United States of America)

   Plants produce suites of defenses that can collectively deter and reduce herbivory. Many defenses target the insect digestive system, with some altering the protective peritrophic matrix (PM) and causing increased permeability. The PM is responsible for multiple digestive functions, including reducing infections from potential pathogenic microbes. In our study, we developed axenic and gnotobiotic methods for fall armyworm (Spodoptera frugiperda) and tested how particular members present in the gut community influence interactions with plant defenses that can alter PM permeability. We observed interactions between gut bacteria with plant resistance. Axenic insects grew more but displayed lower immune-based responses compared with those possessing Enterococcus, Klebsiella, and Enterobacter isolates from field-collected larvae. While gut bacteria reduced performance of larvae fed on plants, none of the isolates produced mortality when injected directly into the hemocoel. Our results strongly suggest that plant physical and chemical defenses not only act directly upon the insect, but also have some interplay with the herbivore’s microbiome. Combined direct and indirect, microbe-mediated assaults by maize defenses on the fall armyworm on the insect digestive and immune system reduced growth and elevated mortality in these insects. These results imply that plant–insect interactions should be considered in the context of potential mediation by the insect gut microbiome. 

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4. A Continuum From Positive to Negative Interactions Drives Plant Species' Performance in a Diverse Community

   https://doi.org/10.1111/ele.70059  

   Buche, Lisa; Shoemaker, Lauren G; Hallett, Lauren M; Bartomeus, Ignasi; Vesk, Peter; Weiss‐Lehman, Christopher; Mayfield, Margaret; Godoy, Oscar (January 2025, Ecology Letters)

   ABSTRACT With many species interacting in nature, determining which interactions describe community dynamics is nontrivial. By applying a computational modeling approach to an extensive field survey, we assessed the importance of interactions from plants (both inter‐ and intra‐specific), pollinators and insect herbivores on plant performance (i.e., viable seed production). We compared the inclusion of interaction effects as aggregate guild‐level terms versus terms specific to taxonomic groups. We found that a continuum from positive to negative interactions, containing mostly guild‐level effects and a few strong taxonomic‐specific effects, was sufficient to describe plant performance. While interactions with herbivores and intraspecific plants varied from weakly negative to weakly positive, heterospecific plants mainly promoted competition and pollinators facilitated plants. The consistency of these empirical findings over 3 years suggests that including the guild‐level effects and a few taxonomic‐specific groups rather than all pairwise and high‐order interactions, can be sufficient for accurately describing species variation in plant performance across natural communities. 

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5. Heat waves induce milkweed resistance to a specialist herbivore via increased toxicity and reduced nutrient content

   https://doi.org/10.1111/pce.15040  

   López‐Goldar, Xosé; Mollema, Alyssa; Sivak‐Schwennesen, Caz; Havko, Nathan; Howe, Gregg; Agrawal, Anurag A; Wetzel, William C (December 2024, Plant, Cell & Environment)

   Abstract Over the last decade, a large effort has been made to understand how extreme climate events disrupt species interactions. Yet, it is unclear how these events affect plants and herbivores directly, via metabolic changes, and indirectly, via their subsequent altered interaction. We exposed common milkweed (Asclepias syriaca) and monarch caterpillars (Danaus plexippus) to control (26:14°C, day:night) or heat wave (HW) conditions (36:24°C, day:night) for 4 days and then moved each organism to a new control or HW partner to disentangle the direct and indirect effects of heat exposure on each organism. We found that the HW directly benefited plants in terms of growth and defence expression (increased latex exudation and total cardenolides) and insect her'bivores through faster larval development. Conversely, indirect HW effects caused both plant latex and total cardenolides to decrease after subsequent herbivory. Nonetheless, increasing trends of more toxic cardenolides and lower leaf nutritional quality after herbivory by HW caterpillars likely led to reduced plant damage compared to controls. Our findings reveal that indirect impacts of HWs may play a greater role in shaping plant‐herbivore interactions via changes in key physiological traits, providing valuable understanding of how ecological interactions may proceed in a changing world. 

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