Pollinator Reward Research Articles

Impacts of increased temperatures on floral rewards and pollinator interactions: a meta-analysis

Flowering plants produce pollinator rewards such as nectar and pollen, whose quantity and quality usually depend on the whole-plant state under specific environmental conditions. Increasing aridity and temperature linked to climate change may force plants to allocate fewer resources to these traits, potentially disrupting plant-pollinator interactions. In this study, for the first time, both quantitative review (vote-counting procedure) and meta-analytic approach were used to assess the implications of increased temperatures linked to global warming on floral rewards, including nectar (sugar concentration, content, and volume) and pollen (germination and viability), as well as on pollinator visits. Furthermore, we explored whether observed effects of warming are related either to temperature range, plant type (wild vs crop), or study approach (greenhouse vs field experiments). We also assessed the correlations between elevated temperatures and the characteristics that were affected by the temperature range. The results of the vote-counting technique showed that higher temperatures led to a decrease in floral rewards but did not affect the number of pollinator visits. Concurrently, meta-analysis detected adverse effects of warming on pollen germination and viability. Warming effects depended on the plant type for pollen germination and viability, on study approach for nectar sugar concentration and pollen germination, and on temperature range for pollen germination and pollinator visits. Additionally, we found that pollen germination and pollinator visits significantly decreased as temperature range increased. Our results showed that global warming affects floral rewards in both wild and crop plants, providing insights into the effects of changing climatic conditions on plant-pollinator interactions and pollination services.

A Case Study of Florivory: Rewards for Pollinators of Bombax ceiba (Linn.), In and Around Gondia District (Maharashtra) India

Bombax ceiba is a deciduous tree also known as Red Silk Cotton or Semal or Katesawar. In India it belongs to Bombacaceae (Baobab family). Identification can be easily made when it is in full bloom with most enchantingly beautiful huge blood red flowers in the month of March and April. B.

An evolutionary disruption of the buzz pollination syndrome in neotropical montane plants.

Under pollinator limitations, specialized pollination syndromes may evolve toward contrasting responses: a generalized syndrome with increased pollinator attraction, pollinator reward, and pollen transfer capacity; or the selfing syndrome with increased self-pollen deposition, but reduced pollinator attraction and pollen transfer capacity. The buzz-pollination syndrome is specialized to explore female vibrating bees as pollinators. However, vibrating bees become less-active pollinators at montane areas of the Atlantic Forest (AF) domain. This study investigated whether the specialized buzz-pollination syndrome would evolve toward an alternative floral syndrome in montane areas of the AF domain, considering a generalized and the selfing syndromes as alternative responses. We utilized a lineage within the buzz-pollinated Miconia as study system, contrasting floral traits between montane AF-endemic and non-endemic species. We measured and validated floral traits that were proxies for pollinator attraction, reward access, pollen transfer capacity, and self-pollen deposition. We inferred the evolution of floral trait via phylogenetic comparative methods. AF-endemic species have selectively evolved greater reward access and more frequently had generalist pollination. Nonetheless, AF-endemic species also have selectively evolved toward lower pollen transfer capacity and greater self pollination. These patterns indicated a complex evolutionary process that has jointly favored a generalized and the selfing syndromes. The buzz pollination syndrome can undergo an evolutionary disruption in montane areas of the AF domain. This floral syndrome is likely more labile than often assumed, allowing buzz-pollinated plants to reproduce in environments where vibrating bees are less-reliable pollinators.

Floral scents of the protogynous aroid Spathiphyllum cannifolium: Investigating the chemistry and timing of emission at female and male phases

AbstractSpathiphyllum is a Neotropical aroid genus whose inflorescences are composed of protogynous bisexual flowers that emit strong perfumes. These scents serve as both attractants and rewards for male euglossine pollinators. We investigated the inflorescence scent of S. cannifolium, asking whether inflorescence at female and male phases differ in scent traits. For this, we collected scent samples from inflorescence at the two phases using dynamic headspace methods and analyzed them by a gas chromatograph coupled to a mass spectrometer (GC‐MS). The inflorescence scent of S. cannifolium consisted of 26 compounds, with benzyl acetate as major component (ca. 80% of the scent bouquet). We found no quantitative or qualitative differences between scents of inflorescences at female and male phases, nor in the emission time. However, when considering the timing of scent emission among individuals, we observed two general plant groups. Some individuals emitted more scent at 06:00, while others emitted more scent at 09:00, independent of the sexual phase. The similarity of floral scents between the sexes might promote floral constancy by male euglossine pollinators and consequently alternate pollinator flow between inflorescences at female and male phases. The occurrence of the two general patterns of scent emission can be interpreted as a way to ensure the pollination service. Since plants emit scents in the morning, even outside the peak emission period, this would enable these plants to attract pollinators that are active at different times than the peak emission of floral scents. This way, it would ensure the flow of pollen, even if it occurs at a low frequency.

Shining a light on UV-fluorescent floral nectar after 50 years

Nature is aglow with numerous captivating examples of UV-fluorescence in the animal kingdom. Despite a putative role as a visual signal, exploration of UV-fluorescence in plants and its role in plant-animal interactions is lagging in comparison. Almost 50 years ago, UV-fluorescence of floral nectar, a crucial reward for pollinators, was reported for 23 flowering plant species. Since this intriguing discovery, UV-fluorescent nectar has only seldom been addressed in the scientific literature and has not been scrutinized in a phylogenetic or ecological context. Here, we report the prevalence of vibrant UV-fluorescent floral nectar across the family Cleomaceae, including the first photographic documentation in vivo colour for flowering plants. Though Cleomaceae flowers are morphologically diverse varying in colour, nectary prominence, and nectar volume, UV-fluorescent floral nectar may be a ubiquitous characteristic of the family. Fluorescence spectra show that the identity and number of fluorescent compounds in floral nectar may differ among Cleomaceae species. As Cleomaceae pollinators range from insects to bats and birds, we suggest that the UV-fluorescent floral nectar not only functions as a visual cue for the diurnal pollinators but also for the nocturnal/crepuscular pollinators in low light settings.

Convergence and molecular evolution of floral fragrance after independent transitions to self-fertilization

Studying the independent evolution of similar traits provides valuable insights into the ecological and genetic factors driving phenotypic evolution.1 The transition from outcrossing to self-fertilization is common in plant evolution2 and is often associated with a reduction in floral attractive features such as display size, chemical signals, and pollinator rewards.3 These changes are believed to result from the reallocation of the resources used for building attractive flowers, as the need to attract pollinators decreases.2,3 We investigated the similarities in the evolution of flower fragrance following independent transitions to self-fertilization in Capsella.4,5,6,7,8,9 We identified several compounds that exhibited similar changes in different selfer lineages, such that the flower scent composition reflects mating systems rather than evolutionary history within this genus. We further demonstrate that the repeated loss of β-ocimene emission, one of the compounds most strongly affected by these transitions, was caused by mutations in different genes. In one of the Capsella selfing lineages, the loss of its emission was associated with a mutation altering subcellular localization of the ortholog of TERPENE SYNTHASE 2. This mutation appears to have been fixed early after the transition to selfing through the capture of variants segregating in the ancestral outcrossing population. The large extent of convergence in the independent evolution of flower scent, together with the evolutionary history and molecular consequences of a causal mutation, suggests that the emission of specific volatiles evolved as a response to changes in ecological pressures rather than resource limitation.

Strawberry varieties differ in pollinator-relevant floral traits.

A rising global population will need more food, increasing demand for insect pollination services. However, general insect declines conflict with this demand. One way to mitigate this conflict is to grow crop flowers that are easier for insects to find and more rewarding to those that visit them. This study quantifies variation in the pollinator-relevant traits of nectar and pollen production, flower size and flower shape in commercial strawberry, finding significant variation between varieties in all traits. Bumblebees could learn to distinguish between the extremes of variation in flower shape, but this learning is very slow, indicating that this variation is at the limit of that which can be detected by bumblebees. Bee preferences for nectar of differing sugar concentrations at field-realistic volumes were consistent with previous observations at larger volumes, suggesting that it is valid to translate lab findings to the field. This study builds on our knowledge of the range of pollinator reward present in a single cultivated species and of the impact of field-realistic levels of variation in floral traits on bumblebee preferences.

Multifunctionality of angiosperm floral bracts: a review.

Floral bracts (bracteoles, cataphylls) are leaf-like organs that subtend flowers or inflorescences but are of non-floral origin; they occur in a wide diversity of species, representing multiple independent origins, and exhibit great variation in form and function. Although much attention has been paid to bracts over the past 150 years, our understanding of their adaptive significance remains remarkably incomplete. This is because most studies of bract function and evolution focus on only one or a few selective factors. It is widely recognised that bracts experience selection mediated by pollinators, particularly for enhancing pollinator attraction through strong visual, olfactory, or echo-acoustic contrast with the background and through signalling the presence of pollinator rewards, either honestly (providing rewards for pollinators), or deceptively (attraction without reward or even trapping pollinators). However, studies in recent decades have demonstrated that bract evolution is also affected by agents other than pollinators. Bracts can protect flowers, fruits, or seeds from herbivores by displaying warning signals, camouflaging conspicuous reproductive organs, or by providing physical barriers or toxic chemicals. Reviews of published studies show that bracts can also promote seed dispersal and ameliorate the effects of abiotic stressors, such as low temperature, strong ultraviolet radiation, heavy rain, drought, and/or mechanical abrasion, on reproductive organs or for the plants' pollinators. In addition, green bracts and greening of colourful bracts after pollination promote photosynthetic activity, providing substantial carbon (photosynthates) for fruit or seed development, especially late in a plant's life cycle or season, when leaves have started to senesce. A further layer of complexity derives from the fact that the agents of selection driving the evolution of bracts vary between species and even between different developmental stages within a species, and selection by one agent can be reinforced or opposed by other agents. In summary, our survey of the literature reveals that bracts are multifunctional and subject to multiple agents of selection. To understand fully the functional and evolutionary significance of bracts, it is necessary to consider multiple selection agents throughout the life of the plant, using integrative approaches to data collection and analysis.

Negative Effects of Pollen Drought Stress on Floral Volatiles, Floral Nectar, Pollinator Behavior, and Seed Production in Ocimum basilicum Plants

Ocimum basilicum is an aromatic plant belonging to the family of Lamiaceae. Many biotic and abiotic factors particularly drought stress influences its reproduction. Drought stress can harm the pollen grains of O. basilicum plants and disrupt the production of floral volatiles, reduce floral rewards for pollinators, decrease pollinator activity, and ultimately result in a decline in the seed set. These detrimental impacts highlight the importance of sufficient pollen availability for the successful reproduction and survival of plant species. The reproduction in plants is significantly impacted by drought stress, as it can directly or indirectly alter the attraction of pollinators. In this study, the effect of drought stress in O. basilicum plants was investigated by comparing drought- with no drought-stressed plants in order to examine various elements including: (1) nectar quantity and quality (2) pollen production (3) flower volatile emissions (4) pollinator visitation rates from both domesticated and wild species, and (5) the plant’s' reproductive outcomes, which contributes to the knowledge of the relationship between drought stress and pollination on O. basilicum. The planting was done in two different locations within the Saran division of Bihar state in India, first one is Chapra town and second one is Siwan town, in June 2019. The result indicated that plants with drought conditions, in contrast to drought free plants, produced a reduced quantity of pollen and had a decrease of the number of flowers and the volume of nectar produced per flower. Furthermore, drought affected plants produced nectar with a lower percentage of sucrose in relation to the total sugar content. Bees visiting rate was low compared to control plants and plants emitted more Z-3-hexenol, C4H8O, C5H10O, and Isovaleraldehyde. Moreover, this study utilized HPLC analysis to investigate the impact of drought stress on the floral nectar of O. basilicum plants. The findings revealed significant changes in nectar composition, highlighting the susceptibility of plantpollinator interactions and seed production to environmental stress factors.

Chemical composition of guarana flowers and nectar and their ecological significance

The plant species Paullinia cupana Kunth (Sapindaceae), commonly known as guarana, originates from the central Amazonian Basin and has a long history of local use for its stimulant properties. It is currently commercialized worldwide for its health beneficial properties. The seeds chemical composition has been extensively studied over the years. However, the chemistry of guarana flowers, particularly the nectar content, have been barely investigated. From an ecological perspective, floral nectar and pollen are the primary food rewards for pollinators. In the present study, we investigated the chemical composition of nectar and whole pistillate, and staminate guarana flowers harvested separately. Although guarana is well known for its high concentration of caffeine in its seeds, to the best of our knowledge, this is the first report of caffeine and other methylxanthines as the main constituents of the nectar. The significant difference between guarana floral chemistry, which is more diverse and complex, and nectar chemical profile, which primarily contains methylxanthines, suggests that the presence of these compounds in guarana nectar may have an impact on plant-pollinator interactions, which can affect the fitness of both plants and flower visitors

Pollination strategies of deceptive orchids – a review

Orchids can be classified in terms of their pollination into rewarding species, which produce nectar in their flowers that serves as a reward for pollinators and deceptive species, whose flowers do not contain nectar and save energy for other purposes. This paper concentrates on the latter. Deceptive orchids attempt to deceive their pollinators by being similar to some non-orchid rewarding species, but not providing a reward. Each of these strategies has its advantages and disadvantages in terms of their effect on future fitness of a plant and/or population and subsequently its survival as a species. In summary, the literature indicates that deceptive strategies may lower reproductive success, but may be compensated for in that they cost less in terms of energy. This should be taken into consideration when developing management strategies for these species, which is often done by non-orchid specialists. This article is intended for such non-specialist audience and includes a description of the main types of deceptive strategies used by orchids, as well as examples of the most typical species.

While Prosopanche (Hydnoraceae) flowers gently heat: mutualistic pollination relationships among the perianth-bearing Piperales

Abstract Flowers of most Piperales do not reward pollinators. However, a few mutualistic pollination relationships have been proposed among the perianth-bearing species. To test the hypothesis of a mutualistic relationship between Prosopanche and beetle pollinators, we studied the pollination biology of three species (P. americana, P. bonacinae, P. panguanensis). For all three species, we recorded flower visitors and flower volatile organic compounds (VOCSs). In addition, for P. americana we investigated flower phases, thermogenesis, visitors’ behaviour, and viability of transported pollen. Using a behavioural experiment, we identified the role of flower heat and fragrance in pollinator attraction. We recorded Neopocadius nitiduloides and Lasiodactylus sp. sap beetles (Nitidulidae) as main pollinators and Hydnorobius hydnorae and H. helleri weevils (Belidae) as occasional pollinators. Thermogenic female flowers heat up to 8°C above the ambient temperature. Flowers only trap the small-sized sap beetles. Methyl-3-methyl-2-butenoate dominated the VOC profile. This was a powerful attractant for sap beetles in controlled bioassays. We conclude that pollination in Prosopanche is mutualistic. This was observed through a pollinator-size-based access limit to the stigmatic chamber and a strong olfactory attractant. Mutualism in Prosopanche therefore contrasts with that of most perianth-bearing Piperales, suggesting it is a novel pollination relationship in early-diverging angiosperms.

The role of within-plant variation in nectar production: an experimental approach.

Nectar, a plant reward for pollinators, can be energetically expensive. Hence, a higher investment in nectar production can lead to reduced allocation to other vital functions and/or increased geitonogamous pollination. One possible strategy employed by plants to reduce these costs is to offer variable amounts of nectar among flowers within a plant, to manipulate pollinator behaviour. Using artificial flowers, we tested this hypothesis by examining how pollinator visitation responds to inter- and intra-plant variation in nectar production, assessing how these responses impact the energetic cost per visit. We conducted a 2 × 2 factorial experiment using artificial flowers, with two levels of nectar investment (high and low sugar concentration) and two degrees of intra-plant variation in nectar concentration (coefficient of variation 0 and 20 %). The experimental plants were exposed to visits (number and type) from a captive Bombus impatiens colony, and we recorded the total visitation rate, distinguishing geitonogamous from exogamous visits. Additionally, we calculated two estimators of the energetic cost per visit and examined whether flowers with higher nectar concentrations (richer flowers) attracted more bumblebees. Plants in the variable nectar production treatment (coefficient of variation 20 %) had a greater proportion of flowers visited by pollinators, with higher rates of total, geitonogamous and exogamous visitation, compared with plants with invariable nectar production. When assuming no nectar reabsorption, variable plants incurred a lower cost per visit compared with invariable plants. Moreover, highly rewarding flowers on variable plants had higher rates of pollination visits compared with flowers with few rewards. Intra-plant variation in nectar concentration can represent a mechanism for pollinator manipulation, enabling plants to decrease the energetic costs of the interaction while still ensuring consistent pollinator visitation. However, our findings did not provide support for the hypothesis that intra-plant variation in nectar concentration acts as a mechanism to avoid geitonogamy. Additionally, our results confirmed the hypothesis that increased visitation to variable plants is dependent on the presence of flowers with nectar concentration above the mean.

Floral nectar reabsorption and a sugar concentration gradient in two long-spurred Habenaria species (Orchidaceae)

BackgroundFloral nectar is the most common reward flowers offered to pollinators. The quality and quantity of nectar produced by a plant species provide a key to understanding its interactions with pollinators and predicting rates of reproductive success. However, nectar secretion is a dynamic process with a production period accompanied or followed by reabsorption and reabsorption remains an understudied topic. In this study, we compared nectar volume and sugar concentration in the flowers of two long-spurred orchid species, Habenaria limprichtii and H. davidii (Orchidaceae). We also compared sugar concentration gradients within their spurs and rates of reabsorption of water and sugars.ResultsBoth species produced diluted nectar with sugar concentrations from 17 to 24%. Analyses of nectar production dynamics showed that as flowers of both species wilted almost all sugar was reabsorbed while the original water was retained in their spurs. We established a nectar sugar concentration gradient for both species, with differences in sugar concentrations at their spur’s terminus and at their spur’s entrance (sinus). Sugar concentration gradient levels were 1.1% in H. limprichtii and 2.8% in H. davidii, both decreasing as flowers aged.ConclusionWe provided evidence for the reabsorption of sugars but not water occurred in wilted flowers of both Habenaria species. Their sugar concentration gradients vanished as flowers aged suggesting a slow process of sugar diffusion from the nectary at the spur’s terminus where the nectar gland is located. The processes of nectar secretion/reabsorption in conjunction with the dilution and hydration of sugar rewards for moth pollinators warrant further study.

Patterns and drivers of heat production in the plant genus Amorphophallus.

Thermogenesis - the ability to generate metabolic heat - is much more common in animals than in plants, but it has been documented in several plant families, most prominently the Araceae. Metabolic heat is produced in floral organs during the flowering time (anthesis), with the hypothesised primary functions being to increase scent volatilisation for pollinator attraction, and/or to provide a heat reward for invertebrate pollinators. Despite in-depth studies on the thermogenesis of single species, no attempts have yet been made to examine plant thermogenesis across an entire clade. Here, we apply time-series clustering algorithms to 119 measurements of the full thermogenic patterns in inflorescences of 80 Amorphophallus species. We infer a new time-calibrated phylogeny of this genus and use phylogenetic comparative methods to investigate the evolutionary determinants of thermogenesis. We find striking phenotypic variation across the phylogeny, with heat production in multiple clades reaching up to 15°C, and in one case 21.7°C above ambient temperature. Our results show that the thermogenic capacity is phylogenetically conserved and is also associated with inflorescence thickness. Our study paves the way for further investigations of the eco-evolutionary benefits of thermogenesis in plants.

Decoding the black essence of Melianthus nectar.

This article is a Commentary on Magner et al. (2023), 239: 2026–2040.

A common protocol for reliable comparison of pollen fatty acid profiles: highlighting pitfalls and proposing a methodology for ecological research

IntroductionPollen is an important tissue in plants that plays a vital role in plant reproduction as it carries male gametes and occasionally also serves as a pollinator reward. There has been an increasing interest in pollen chemistry due to the impact of chemical variation on pollinator choices and well-being, especially in bees. The pollen fat content and lipid-to-protein ratio have been shown to play a crucial role in regulating pollen intake, and some bee species avoid overconsumption of fatty acids while specific pollen fatty acid ratios are essential for bee cognition. Therefore, knowledge of the fatty acid composition of plant pollen is crucial for understanding plant-pollinator interactions. However, existing methods for fatty acid analyses are not always specific to pollen fatty acids, and non-pollen-derived fatty acids can easily contaminate samples, making comparison between different methods impossible. Hence, the objectives of our study were to highlight the common mistakes and pitfalls made during pollen fatty acid extraction and analysis and propose a common protocol for reliable comparisons of pollen samples.MethodsThe proposed method, developed in two different labs using different gas chromatograph/mass spectrometers and gas chromatograph/flame ionization detectors, involved manually homogenizing pollen, extracting it with chloroform:methanol (2:1), and analyzing it using gas chromatography (GC) and mass spectrometry (MS) and a flame ionization detector (FID) for identification and quantification.ResultsWe found that many fatty acids were present in plastic materials and many solvents commonly used in the labs, cautioning against the use of plastic and recommending blank samples to determine the level of contamination. We also suggest adding an internal standard and checking the MS and FID’s saturation limit before starting pollen homogenization.DiscussionOur proposed method generated reliable fatty acid profiles of pollen from two different plant species analyzed in the two labs, and we hope it serves as a blueprint for achieving a common methodology for characterizing and comparing pollen fatty acid profiles in ecological research.

Reproductive challenges related to a complex sexual system in Euphorbia rosescens, a rare endemic herb

AbstractWhen the sexual system of a rare plant species is complex, characterizing floral development, plant morphology, and subpopulation structure is essential for assessing reproductive potential. Availability of pollinator rewards and positioning of sexual morphs within inflorescences relates to outcrossing potential. We studied the complex sexual system of the recently discovered Euphorbia rosescens E.L. Bridges & Orzell, a rare species occurring in a single Florida county. Euphorbia rosescens has both monomorphic subpopulations of female plants and mixed subpopulations with male and andromonoecious plants. Most data on cyathia sex, inflorescence architecture, floral visitors, and fruit set came from one female subpopulation and one mixed subpopulation. Cyathia longevity, flowering phase, nectar secretion, pollen production, and viability were measured in female, male, and hermaphrodite cyathia. Female plants had fewer inflorescence levels and cyathia and significantly smaller cyathia than male and andromonoecious plants. Andromonoecious plants were larger and produced more cyathia relative to male plants. Within mixed populations, sex switching occurred in both directions between male and andromonoecious plants. Female plants did not switch sexes. Proximal to distal inflorescence levels transitioned from hermaphrodite to male cyathia on andromonoecious plants. Nectar secretion corresponded to initiation of staminate flowering, but in female cyathia stigmas were receptive approximately a day before nectar secretion. Pollen production and viability were similar in male and hermaphrodite cyathia. Fruit maturation was minimal, primarily observed on andromonoecious plants. Nectar availability, pollen rewards, trimorphic inequalities in inflorescence display, and low fruit set suggest high geitonogamy, thus limiting outcrossing potential for this species.

Secondary Metabolites in Nectar-Mediated Plant-Pollinator Relationships.

In recent years, our understanding of the complex chemistry of floral nectar and its ecological implications for plant-pollinator relationships has certainly increased. Nectar is no longer considered merely a reward for pollinators but rather a plant interface for complex interactions with insects and other organisms. A particular class of compounds, i.e., nectar secondary compounds (NSCs), has contributed to this new perspective, framing nectar in a more comprehensive ecological context. The aim of this review is to draft an overview of our current knowledge of NSCs, including emerging aspects such as non-protein amino acids and biogenic amines, whose presence in nectar was highlighted quite recently. After considering the implications of the different classes of NSCs in the pollination scenario, we discuss hypotheses regarding the evolution of such complex nectar profiles and provide cues for future research on plant-pollinator relationships.

Impacts of soil nutrition on floral traits, pollinator attraction, and fitness in cucumbers (Cucumis sativus L.)

Annual plants allocate soil nutrients to floral display and pollinator rewards to ensure pollination success in a single season. Nitrogen and phosphorus are critical soil nutrients whose levels are altered by intensive land use that may affect plants’ fitness via pollinator attractiveness through floral display and rewards. In a controlled greenhouse study, we studied in cucumbers (Cucumis sativus) how changes in soil nitrogen and phosphorus influence floral traits, including nectar and pollen reward composition. We evaluated how these traits affect bumble bee (Bombus impatiens, an important cucumber pollinator) visitation and ultimately fruit yield. While increasing nitrogen and phosphorus increased growth and floral display, excess nitrogen created an asymptotic or negative effect, which was mitigated by increasing phosphorus. Male floral traits exhibited higher plasticity in responses to changes in soil nutrients than female flowers. At 4:1 nitrogen:phosphorus ratios, male flowers presented increased nectar volume and pollen number resulting in increased bumble bee visitation. Interestingly, other pollinator rewards remained consistent across all soil treatments: male and female nectar sugar composition, female nectar volume, and pollen protein and lipid concentrations. Therefore, although cucumber pollination success was buffered in conditions of nutrient stress, highly skewed nitrogen:phosphorus soil ratios reduced plant fitness via reduced numbers of flowers and reward quantity, pollinator attraction, and ultimately yield.