Differential effects of type and quantity of leaf damage on growth, reproduction and defence of lima bean (Phaseolus lunatus L.)

A dataset of functional traits for compound pinnate leaves of plants in the Huangshui River Valley of Qinghai Province, China

Background

Here, we present data collected from the Qinghai-Tibet Plateau that describes the variation of leaf functional traits across 32 plant species and could be used to investigate plant community functioning and predict the impact of climate change on biogeochemical cycles. The sampling area is located in Huangshui River Valley, in the southeast of Qinghai Province, China (36° 19' to 36° 53' N, 100° 59' to 102° 48' E). The area contains an alpine meadow typical of the Qinghai-Tibet Plateau.

New information

This dataset includes field survey data on the functional properties of compound leaves from herbaceous species in the Huangshui River Basin of Qinghai Province, China, at altitudes from 1800 m to 4000 m in the summer of 2021. Data were collected from 326 plots, including 646 data points of compound leaf plants, spanning 32 compound leaf plant species belonging to 14 genera and four families. The study species were chosen from 47 families, 165 genera and 336 species present in the plots and all compound leaf plants were chosen within each plot. We picked the parts containing leaves, petioles and rachis from the study plants and separated the leaves from the plants. The cut compound leaf part was a leaflet, while the petiole and rachis were linear elements. The dataset includes information about the leaflet trait variation (i.e. leaflet area, leaflet dry mass, specific leaflet area and leaflet nitrogen content per unit dry mass) and linear elements' biomass and nitrogen content per unit dry mass (i.e. both petiole and rachis) of 646 compound leaves. This dataset can be used to analyse the evolution of leaf traits and the basic functioning of ecosystems. Moreover, the dataset provides an important basis for studying the species distribution and protection of biodiversity of the Qinghai-Tibet Plateau and evaluating ecosystem services. These data also support the high-quality development of the Yellow River Basin and have empirical and practical value for alpine biodiversity protection and ecosystem management.

Early damage enhances compensatory responses to herbivory in wild lima bean

Damage by herbivores can induce various defensive responses. Induced resistance comprises traits that can reduced the damage, while compensatory responses reduce the negative effects of damage on plant fitness. Timing of damage may be essential in determining the patterns of induced defenses. Here, we tested how timing and frequency of leaf damage affect compensatory responses in wild lima bean plants in terms of growth and seed output, as well as their effects on induced resistance to seed beetles. To this end, we applied mechanical damage to plants at different ontogenetical stages, at one time point (juvenile stage only) or two time points (seedling and juvenile stage or juvenile and reproductive stage). We found that plants damaged at the seedling/juvenile stage showed higher compensatory growth, and seed output compared to plants damaged only at the juvenile stage or juvenile/reproductive stage. Seeds from plants damaged at the juvenile and juvenile/reproductive stages had fewer beetles than seeds from undamaged plants, however this was driven by a density dependent effect of seed abundance rather than a direct effect of damage treatments. We did not find differences in parasitism rate by parasitoid wasps on seed beetles among plant treatments. Our results show that damage at the seedling stage triggers compensatory responses which implies that tolerance to herbivory is enhanced or primed by early damage. Herbivory often occurs at several time points throughout plant development and this study illustrates that, for a full understanding of the factors associated with plant induced responses in a dynamic biotic environment, it is important to determine the multitrophic consequences of damage at more than one ontogenetical stage.

Effects of amount and recurrence of leaf herbivory on the induction of direct and indirect defences in wild cotton

The induction of defences in response to herbivory is a key mechanism of plant resistance. While a number of studies have investigated the time course and magnitude of plant induction in response to a single event of herbivory, few have looked at the effects of recurrent herbivory. Furthermore, studies measuring the effects of the total amount and recurrence of herbivory on both direct and indirect plant defences are lacking. To address this gap, here we asked whether insect leaf herbivory induced changes in the amount and concentration of extrafloral nectar (an indirect defence) and concentration of leaf phenolic compounds (a direct defence) in wild cotton (Gossypium hirsutum). We conducted a greenhouse experiment where we tested single event or recurrent herbivory effects on defence induction by applying mechanical leaf damage and caterpillar (Spodoptera frugiperda) regurgitant. Single events of 25% and 50% leaf damage did not significantly influence extrafloral nectar production or concentration. Extrafloral nectar traits did, however, increase significantly relative to controls when plants were exposed to recurrent herbivory (two episodes of 25% damage). In contrast, phenolic compounds increased significantly in response to single events of  leaf damage but not to recurrent damage. In addition, we found. that local induction of extrafloral nectar production was stronger than systemic induction, whereas the reverse pattern was observed for phenolics. Together, these results reveal seemingly inverse patterns of induction of direct and indirect defences in response to herbivory in wild cotton.

Compensation to simulated insect leaf herbivory in wild cotton (Gossypium hirsutum): responses to multiple levels of damage and associated traits

Identifying the mechanisms of compensation to insect herbivory remains a major challenge in plant biology and evolutionary ecology. Most previous studies have addressed plant compensatory responses to one or two levels of insect herbivory, and the underlying traits mediating such responses remain elusive in many cases. We evaluated responses associated with compensation to multiple intensities of leaf damage (0% control, 10%, 25%, 50%, 75% of leaf area removed) by means of mechanical removal of foliar tissue and application of a caterpillar (Spodoptera exigua) oral secretions in 3-month-old wild cotton plants (Gossypium hirsutum). Four weeks post-treatment, we measured plant growth and multiple traits associated with compensation, namely: changes in above- and belowground, biomass and the concentration of nutrients (nitrogen and phosphorus) and non-structural carbon reserves (starch and soluble sugars) in roots, stems and leaves. We found that wild cotton fully compensated in terms of growth and biomass allocation when leaf damage was low (10%), whereas moderate (25%) to high leaf damage in some cases led to under-compensation. Nonetheless, high levels of leaf removal (50% and 75%) in most cases did not cause further reductions in height and allocation to leaf and stem biomass relative to low and moderate damage. There were significant positive effects of leaf damage on P concentration in leaves and stems, but not roots, as well as a negative effect on soluble sugars in roots. These results indicate that wild cotton fully compensated for a low level of leaf damage but under-compensated under moderate to high leaf damage, but can nonetheless sustain growth despite increasing losses to herbivory. Such responses were possibly mediated by a re-allocation of carbohydrate reserves from roots to shoots.

Timing and mode of simulated ungulate herbivory alter aspen defense strategies

Timing of herbivory or selection of specific plant tissues (mode of herbivory) by different ungulate herbivore species are likely to have important influences on plant defense strategies. In this study, we devised two different modes of simulated herbivory, representing a selective ungulate feeding strategy (defoliation: leaf tissue removal only) and a bulk feeding strategy (clipping: leaves, twigs and meristems taken together). We applied these contrasting herbivory treatments to juvenile aspen suckers (Populus tremuloides Michx.) regenerating underneath aspen stands in early summer (June), late summer (August) or at both times to determine the effects of herbivory mode, timing and frequency on regenerating aspen. In response to the simulated herbivory treatments, we measured traits related to three plant defense strategies: tolerance (aboveground biomass and stem diameter), resistance (foliar phenolic glycosides) and vertical escape (sucker height and average leader length). There was no evidence that mode, timing or frequency of simulated herbivory induced or repressed phenolic glycoside production. Early summer herbivory was more detrimental than late summer herbivory on aspen tolerance and escape. Repeat herbivory in late summer did not amplify the negative effects of early summer herbivory. Clipping and defoliation tended to have similar effects on tolerance but clipping was more detrimental than defoliation on vertical escape. These results suggest that different ungulate herbivore species may have disparate impacts on the plant communities by selecting different tissues of the same plant, or browsing the plant at different times in the growing season.

Cascading effects of combining synthetic herbivore-induced plant volatiles with companion plants to manipulate natural enemies in an agro-ecosystem

BACKGROUND

Whether tactics to manipulate natural enemies in agro-ecosystems enhance their ecosystem function and services remains debatable. We conducted field experiments in 2015-2016 to test the hypothesis that attraction of natural enemies to herbivore-induced plant volatiles (HIPVs), alone or in combination with companion plants, increases crop productivity. Our treatments consisted of bean plants alone or baited with methyl salicylate (MeSA; an HIPV), or combined with coriander (a companion plant), or with both MeSA and coriander. Numbers of arthropods were visually sampled in each treatment. Sentinel aphids were used to measure ecosystem function (i.e. predation). Plant damage and biomass, and the number and weight of pods and seeds, were measured as a proxy for ecosystem services.

RESULTS

MeSA and coriander, when alone or combined, increased the abundance of insect predators from six families, reduced herbivore (e.g. spider mite and thrips) populations, and increased aphid predation. MeSA and coriander also reduced damage by spider mites. MeSA with or without coriander did not, however, increase crop biomass or any yield parameters.

CONCLUSIONS

MeSA alone or combined with coriander attracted different predator communities, altered pest communities, and reduced damage; however, these results did not cascade down to improve crop productivity. © 2018 Society of Chemical Industry.

Friend or Foe-Light Availability Determines the Relationship between Mycorrhizal Fungi, Rhizobia and Lima Bean (Phaseolus lunatus L.)

Plant associations with root microbes represent some of the most important symbioses on earth. While often critically promoting plant fitness, nitrogen-fixing rhizobia and arbuscular mycorrhizal fungi (AMF) also demand significant carbohydrate allocation in exchange for key nutrients. Though plants may often compensate for carbon loss, constraints may arise under light limitation when plants cannot extensively increase photosynthesis. Under such conditions, costs for maintaining symbioses may outweigh benefits, turning mutualist microbes into parasites, resulting in reduced plant growth and reproduction. In natural systems plants commonly grow with different symbionts simultaneously which again may interact with each other. This might add complexity to the responses of such multipartite relationships. We experimented with lima bean (Phaseolus lunatus), which efficiently forms associations with both types of root symbionts. We applied full light and low-light to each of four treatments of microbial inoculation. After an incubation period of 14 weeks, we quantified vegetative aboveground and belowground biomass and number and viability of seeds to determine effects of combined inoculant and light treatment on plant fitness. Under light-limited conditions, vegetative and reproductive traits were inhibited in AMF and rhizobia inoculated lima bean plants relative to controls (un-colonized plants). Strikingly, reductions in seed production were most critical in combined treatments with rhizobia x AMF. Our findings suggest microbial root symbionts create additive costs resulting in decreased plant fitness under light-limited conditions.

Specificity of induced defenses, growth, and reproduction in lima bean (Phaseolus lunatus) in response to multispecies herbivory

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PREMISE OF THE STUDY

Following herbivore attack, plants can either reduce damage by inducing defenses or mitigate herbivory effects through compensatory growth and reproduction. It is increasingly recognized that such induced defenses in plants are herbivore-specific, but less is known about the specificity of compensatory responses. Damage by multiple herbivores may also lead to synergistic effects on induction and plant fitness that differ from those caused by a single herbivore species. Although largely unstudied, the order of arrival and damage by different herbivore species might also play an important role in the impacts of herbivory on plants.•

METHODS

We investigated the specificity of defense induction (phenolics) and effects on growth (number of stems and leaves) and reproduction (number of seeds, seed mass, and germination rate) from feeding by two generalist leaf-chewing herbivores (Spodoptera eridania and Diabrotica balteata) on Phaseolus lunatus plants and evaluated whether simultaneous attack by both herbivores and their order of arrival influenced such dynamics.•

KEY RESULTS

Herbivory increased levels of leaf phenolics, but such effects were not herbivore-specific. In contrast, herbivory enhanced seed germination in an herbivore-specific manner. For all variables measured, the combined effects of both herbivore species did not differ from their individual effects. Finally, the order of herbivore arrival did not influence defense induction, plant growth, or seed number but did influence seed mass and germination.•

CONCLUSIONS

Overall, this study highlights novel aspects of the specificity of plant responses induced by damage from multiple species of herbivores and uniquely associates such effects with plant lifetime fitness.