Past freeze-thaw events onPinusseeds increase seedling herbivory

Tomato Defenses Under Stress: The Impact of Salinity on Direct Defenses Against Insect Herbivores

Abiotic stressors, such as salt stress, can reduce crop productivity, and when combined with biotic pressures, such as insect herbivory, can exacerbate yield losses. However, salinity-induced changes to plant quality and defenses can in turn affect insect herbivores feeding on plants. This study investigates how salinity stress in tomato plants (Solanum Lycopersicum cv. Better Boy) impacts the behavior and performance of a devastating insect pest, the tomato fruitworm caterpillar (Helicoverpa zea). Through choice assays and performance experiments, we demonstrate that salt-stressed tomato plants are poor hosts for H. zea, negatively affecting caterpillar feeding preferences and growth rates. While changes in plant nutritional quality were observed, the primary factor influencing insect performance appears to be direct ionic toxicity, which significantly impairs multiple life history parameters of H. zea including survival, pupation, adult emergence, and fecundity. Plant defense responses show complex interactions between salt stress and herbivory, with two proteinase inhibitor genes - PIN2 and AspPI, showing a higher induced response to insect herbivory under salt conditions. However, plant defenses do not seem to be the main driver of reduced caterpillar performance on salt-treated plants. Furthermore, we report reduced oviposition by H. zea moths on salt-treated plants, which was correlated with altered volatile emissions. Our findings reveal that H. zea exhibits optimal host selection behaviours for both larval feeding and adult oviposition decisions, which likely contribute to its success as an agricultural pest. This research provides insights into the complex interactions between abiotic stress, plant physiology, and insect behaviour, with potential implications for pest management strategies in saline agricultural environments.

Extreme cold reduces seedling establishment, but native species appear more susceptible than non-native species

PREMISE

Extreme-cold events are increasingly recognized as one of the most damaging aspects of climate change in northern temperate ecosystems. However, little data exists describing how native and non-native species may respond to these extreme events, especially as seeds. We used a greenhouse experiment to test how extreme cold reduces seedling establishment in seven woody species common to eastern North America. We hypothesized that the effects of extreme cold depend on provenance (native vs. non-native) and chilling period.

METHODS

Following chilling periods of 80, 100, or 120 days, seeds experienced a false-spring with temperatures at 15°C for one week; half of the seeds in each dormancy treatment group experienced a two-day extreme-cold event (-13.9°C) while the rest returned to mild winter temperatures (4°C).

RESULTS

Extreme-cold events universally decreased seedling establishment, but non-native species had four times greater survival in the extreme-cold treatment (mean ± s.e.: 0.108 ± 0.024) compared to native species (0.024 ± 0.018). Furthermore, native seeds were increasingly susceptible to extreme-cold damage following a 120-day chilling period, whereas non-native seeds were able to resist extreme cold equally following all chilling periods.

CONCLUSIONS

These results suggest that in eastern North America, cold resistance could be a trait facilitating the success of non-native species. The introduction of non-native species may synergize with climate change to alter community composition, which could have important consequences for forest biodiversity in the Anthropocene.

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

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.

Extreme cold consistently reduces seedling growth but has species-specific effects on browse tolerance in summer

PREMISE OF THE STUDY

Extreme weather events can injure plants, causing decreased survival. However, we may underestimate the ecological importance of extreme events if they have strong sublethal effects that manifest after several months. We tested the hypothesis that late-winter extreme-cold events decrease the ability of woody plants to grow and tolerate stem removal in summer.

METHODS

Seedlings from four temperate tree species (Abies balsamea, Pinus resinosa, P. strobus, Quercus rubra) were acclimated to winter conditions in growth chambers, and experienced 1 week of warm temperatures before being exposed to one of three 24-h extreme-cold events (minimum temperature: 8°C control, -8°C, or -16°C). Seedlings were then transferred to a greenhouse where we monitored survival and growth. Three months after the extreme-cold event, we mimicked an herbivore attack by removing either 25% or 75% of new stem growth from seedlings of two species (P. resinosa, Q. rubra).

KEY RESULTS

While extreme cold had no immediate effect on seedling survival, the coldest temperature treatment reduced stem growth 51% relative to controls. Stem removal decreased P. resinosa survival in the -16°C treatment, but stem removal treatment had no effect on P. resinosa survival in the intermediate -8°C treatment or 8°C control. Stem removal did not alter Q. rubra survival.

CONCLUSIONS

Ephemeral late-winter cold temperatures can have unappreciated effects on growing-season seedling dynamics, including growth and herbivory. For predicting how extreme-cold events might alter large-scale patterns of tree distribution, seedlings should be monitored throughout the growing season following extreme late-winter frosts.