Feeding enhances photosynthetic efficiency in the carnivorous pitcher plant Nepenthes talangensis

Comprehensive approaches for assessing extinction risk of endangered tropical pitcher plant Nepenthes talangensis

It has been 23 years since the conservation status of highland tropical pitcher plant Nepenthes talangensis was assessed in 2000. A number of existing threats (anthropogenic and environmental) may be increasing the risk of extinction for the species. A better understanding of the ecology and conservation needs of the species is required to manage the wild populations. Specifically, better information related to population distributions, ecological requirements, priority conservation areas, the impact of future climate on suitable habitat, and current population structure is needed to properly assess extinction risks. A better understanding of the requirements of the species in its natural habitat would benefit for successfully securing the species at Botanic Gardens. We have identified 14 new occurrence records of N. talangensis in Mount Talang. Study on the ecological requirement using Random Forest (RF) and Artificial Neural Network (ANN) suggested that elevation, canopy cover, soil pH, and slope are four important variables. The population of N. talangensis was dominated by juvenile and mature (sterile) individuals, we found only a few mature males (7 individuals) and females (4 individuals) in the sampled areas. Our modelling of current conditions predicted that there were 1,076 ha of suitable habitat to very highly suitable habitat in Mount Talang, which is 14.7% of the total area. Those predicted habitats ranged in elevation from 1,740-2,558 m. Suitable habitat in 2100 was predicted to decrease in extent and be at higher elevation in the less extreme climate change scenario (SSP 1-2.6) and extreme climate change scenario (SSP 5-8.5). We projected larger habitat loss in the SSP 5-8.5 compared to the SSP 1-2.6 climate change scenario.. We proposed the category CR B1ab(iii,v), C2a(ii) as the new conservation status of N. talangensis. The status is a higher category of threat compared to the current status of the species (EN C2b, ver 2.3). Nepenthes talangensis seedlings and cuttings established in a Botanic Garden have relatively high survival rate at about 83.4%. Sixty percent of the seeds germinated in growth media successfully grew to become seedlings.

Photosynthetic electron transport in pitcher plants (Nepenthes mirabilis)

Pitcher plants (Nepenthes sp.) are insectivorous angiosperm plants with modified leaves known as pitchers best known as acting as traps for insects. Pitcher plants are typically found under boggy conditions under both forest cover and open areas with very poor nutrient status, particularly N-status. The pitchers have low photosynthetic activity. The Chl a content of the pitcher tissue of both Nepenthes mirabilis (green and red) varieties was very low. Chl b/a ratios of the green variety phyllodes (lamina) and pitchers were ≈ 0.24 to 0.29. In the red variety, the mature phyllodes had a Chl b/a ratio ≈ 0.28 but both the pitchers and the young phyllodes had Chl b/a ratios of nearly 0.5. Photosynthetic electron transport (ETR) was measured using PAM technology. Phyllodes of both varieties showed photoinhibition at supra-optimal irradiances [Nepenthes mirabilis (green variety), E_opt ≈ 200-250 µmol photon m^-2 s^-1; red variety, E_opt ≈ 100-150 µmol photon m^-2 s^-1]. Pitchers had low optimum irradiances (E_opt ≈ 40-90 µmol photon m^-2 s^-1). Maximum ETR (ETR_max) of phyllodes of both varieties was low (ETR_max ≈ 50 µmol e^- g^-1 Chl a s^-1); ETR_max was higher for pitchers on a Chl a basis (ETR_max ≈ 80-100 µmol e^- g^-1 Chl a s^-1); a consequence of their low Chl a content on a surface area basis. ETR_max of cut disks of phyllodes did not respond strongly to incubation in NH₄⁺, glutamate or aspartate as N-sources but did respond positively to added urea.

Optimization of Propagation of the Polish Strain of Aldrovanda vesiculosa in Tissue Culture

Aldrovanda vesiculosa is a rare and critically endangered carnivorous plant species. Its populations have declined worldwide, so there is a need to protect the species from extinction. The research was conducted to establish an effective method of in vitro propagation of the species in order to obtain plants for reintroduction in the wild. The procedures included disinfection, multiplication, and acclimatization of plants. Contamination-free in vitro cultures were established using shoots and turions, which were disinfected with 0.25% sodium hypochlorite. The shoots were first defoliated. The explants regenerated better in liquid 1/5 MS medium than in solidified one. The optimum medium for the multiplication phase contained MS macro- and microelements diluted to 1/10. Plants cultivated in that medium were of good quality, long, and branched. The advantageous effect of medium was also confirmed by the content of photosynthetic pigments in the plant material. The content of chlorophyll a was highest in plants cultivated in 1/5 or 1/10 MS medium. The plants obtained were acclimatized to ex vitro conditions and reintroduced in the wild.

Alternative oxidase (AOX) in the carnivorous pitcher plants of the genus Nepenthes: what is it good for?

BACKGROUND AND AIMS

The carnivorous pitcher plants of the genus Nepenthes have evolved modified leaves that act as pitcher traps. The traps are specialized for prey attraction, capture, digestion and nutrient uptake but not for photosynthetic assimilation.

METHODS

In this study, we used antibodies against different photosynthetic (D1, Lhcb2, Lhcb4, RbcL) and respiratory-related (AOX, COXII) proteins for semi-quantification of these proteins in the assimilation part of the leaves and the pitcher traps of different Nepenthes species and hybrids. Different functional zones of the trap and the traps from different ontogenetic stages were investigated. The pitcher traps of the distantly related species Sarracenia purpurea ssp. venosa were used as an outgroup. In addition, chlorophyll fluorescence and infrared gas analysis were used for measurements of the net rate of photosynthesis (AN) and respiration in the dark (RD).

KEY RESULTS

The pitcher traps contained the same or lower abundance of photosynthesis-related proteins in accordance with their low AN in comparison to the assimilation part of the leaves. Surprisingly, all traps contained a high amount of alternative oxidase (AOX) and low amount of cytochrome c oxidase subunit II (COX II) than in the assimilation part of the leaves. Thermal imaging did not confirm the role of AOX in pitcher thermogenesis.

CONCLUSIONS

The pitcher traps contain a high amount of AOX enzyme. The possible role of AOX in specialized pitcher tissue is discussed based on knowledge of the role and function of AOX in non-carnivorous plants. The roles of AOX in prey attraction, balance between light and dark reactions of photosynthesis, homeostasis of reactive oxygen species, digestive physiology and nutrient assimilation are discussed.

First record of functional underground traps in a pitcher plant: Nepenthespudica (Nepenthaceae), a new species from North Kalimantan, Borneo

Nepenthespudica, a new species from North Kalimantan, Indonesia, is described and illustrated. The species belongs to the N.hirsuta group (sensu Cheek and Jebb 1999) but exhibits some characters that are unique within the group or even within the genus. Above all, it produces underground, achlorophyllous shoots with well-developed, ventricose lower pitchers that form in soil cavities or directly in the soil. No lower pitchers are formed above ground. The main part of its prey are ants, besides other litter- and soil-inhabiting species of invertebrates. A number of infaunal species were found in both aerial and underground pitchers, mainly Diptera and nematodes. Nepenthespudica is known only from a few neighbouring localities in the Mentarang Hulu district of North Kalimantan, where it grows on ridgetops at an elevation of 1100-1300 m. Its discovery underlines the natural richness of Borneo's rainforest and the necessity to preserve this important ecosystem with its enormous and still undiscovered biodiversity.

Recent ecophysiological, biochemical and evolutional insights into plant carnivory

BACKGROUND

Carnivorous plants are an ecological group of approx. 810 vascular species which capture and digest animal prey, absorb prey-derived nutrients and utilize them to enhance their growth and development. Extant carnivorous plants have evolved in at least ten independent lineages, and their adaptive traits represent an example of structural and functional convergence. Plant carnivory is a result of complex adaptations to mostly nutrient-poor, wet and sunny habitats when the benefits of carnivory exceed the costs. With a boost in interest and extensive research in recent years, many aspects of these adaptations have been clarified (at least partly), but many remain unknown.

SCOPE

We provide some of the most recent insights into substantial ecophysiological, biochemical and evolutional particulars of plant carnivory from the functional viewpoint. We focus on those processes and traits in carnivorous plants associated with their ecological characterization, mineral nutrition, cost-benefit relationships, functioning of digestive enzymes and regulation of the hunting cycle in traps. We elucidate mechanisms by which uptake of prey-derived nutrients leads to stimulation of photosynthesis and root nutrient uptake.

CONCLUSIONS

Utilization of prey-derived mineral (mainly N and P) and organic nutrients is highly beneficial for plants and increases the photosynthetic rate in leaves as a prerequisite for faster plant growth. Whole-genome and tandem gene duplications brought gene material for diversification into carnivorous functions and enabled recruitment of defence-related genes. Possible mechanisms for the evolution of digestive enzymes are summarized, and a comprehensive picture on the biochemistry and regulation of prey decomposition and prey-derived nutrient uptake is provided.

Enzyme activities in two sister-species of carnivorous pitcher plants (Nepenthes) with contrasting nutrient sequestration strategies

The carnivorous pitcher plants of the genus Nepenthes usually attract, capture and digest arthropod prey to obtain mineral nutrients. But few members of the genus have evolved specialized nutrient sequestration strategies to acquire nitrogen from the faeces and urine of mutualistic mammals, which they attract. Because the plants obtain significant amounts of nitrogen in a more available form, we hypothesized that they have relaxed the production of digestive enzymes. If so, species that digest mammal faeces should show fewer digestive enzymes than closely related species that rely on arthropods. We tested this hypothesis by comparing digestive enzymes in 1) Nepenthes hemsleyana, whose pitchers serve as roosts for the mutualistic woolly bat Kerivoula hardwickii, which also defecate inside the pitchers, and 2) the close relative Nepenthes rafflesiana, a typical arthropod capturing species. To investigate the dynamics of aspartic proteases (nepenthesin I and II) and type III and IV chitinases in both species, we conducted qPCR, western blotting, mass spectrometry, and enzyme activity measurements. We found that mRNA in pitcher tissue and enzyme abundance in the digestive fluid is upregulated in both species in response to faeces and insect feeding. Contrary to our initial hypothesis, the final nepenthesin proteolytic activity in the digestive fluid is higher in response to faeces addition than to insect prey irrespective of Nepenthes species. This indicates that faeces can mimic arthropod prey triggering the production of digestive enzymes and N. hemsleyana retained capacity for production of them.

Biochemical and mesophyll diffusional limits to photosynthesis are determined by prey and root nutrient uptake in the carnivorous pitcher plant Nepenthes × ventrata

BACKGROUND AND AIMS

Carnivorous plants can enhance photosynthetic efficiency in response to prey nutrient uptake, but the underlying mechanisms of increased photosynthesis are largely unknown. Here we investigated photosynthesis in the pitcher plant Nepenthes × ventrata in response to different prey-derived and root mineral nutrition to reveal photosynthetic constrains.

METHODS

Nutrient-stressed plants were irrigated with full inorganic solution or fed with four different insects: wasps, ants, beetles or flies. Full dissection of photosynthetic traits was achieved by means of gas exchange, chlorophyll fluorescence and immunodetection of photosynthesis-related proteins. Leaf biochemical and anatomical parameters together with mineral composition, nitrogen and carbon isotopic discrimination of leaves and insects were also analysed.

KEY RESULTS

Mesophyll diffusion was the major photosynthetic limitation for nutrient-stressed Nepenthes × ventrata, while biochemistry was the major photosynthetic limitation after nutrient application. The better nutrient status of insect-fed and root-fertilized treatments increased chlorophyll, pigment-protein complexes and Rubisco content. As a result, both photochemical and carboxylation potential were enhanced, increasing carbon assimilation. Different nutrient application affected growth, and root-fertilized treatment led to the investment of more biomass in leaves instead of pitchers.

CONCLUSIONS

The study resolved a 35-year-old hypothesis that carnivorous plants increase photosynthetic assimilation via the investment of prey-derived nitrogen in the photosynthetic apparatus. The equilibrium between biochemical and mesophyll limitations of photosynthesis is strongly affected by the nutrient treatment.

The function of secondary metabolites in plant carnivory

BACKGROUND

Carnivorous plants are an ideal model system for evaluating the role of secondary metabolites in plant ecology and evolution. Carnivory is a striking example of convergent evolution to attract, capture and digest prey for nutrients to enhance growth and reproduction and has evolved independently at least ten times. Though the roles of many traits in plant carnivory have been well studied, the role of secondary metabolites in the carnivorous habit is considerably less understood.

SCOPE

This review provides the first synthesis of research in which secondary plant metabolites have been demonstrated to have a functional role in plant carnivory. From these studies we identify key metabolites for plant carnivory and their functional role, and highlight biochemical similarities across taxa. From this synthesis we provide new research directions for integrating secondary metabolites into understanding of the ecology and evolution of plant carnivory.

CONCLUSIONS

Carnivorous plants use secondary metabolites to facilitate prey attraction, capture, digestion and assimilation. We found ~170 metabolites for which a functional role in carnivory has been demonstrated. Of these, 26 compounds are present across genera that independently evolved a carnivorous habit, suggesting convergent evolution. Some secondary metabolites have been co-opted from other processes, such as defence or pollinator attraction. Secondary metabolites in carnivorous plants provide a potentially powerful model system for exploring the role of metabolites in plant evolution. They also show promise for elucidating how the generation of novel compounds, as well as the co-option of pre-existing metabolites, provides a strategy for plants to occupy different environments.

Nepenthes pitchers are CO2-enriched cavities, emit CO2 to attract preys

Carnivorous plants of the genus Nepenthes supplement their nutrient deficiency by capturing arthropods or by mutualistic interactions, through their leaf-evolved biological traps (pitchers). Though there are numerous studies on these traps, mostly on their prey capture mechanisms, the gas composition inside them remains unknown. Here we show that, Nepenthes unopened pitchers are CO2-enriched 'cavities', when open they emit CO2, and the CO2 gradient around open pitchers acts as a cue attracting preys towards them. CO2 contents in near mature, unopened Nepenthes pitchers were in the range 2500-5000 ppm. Gas collected from inside open N. khasiana pitchers showed CO2 at 476.75 ± 59.83 ppm. CO2-enriched air-streaming through N. khasiana pitchers (at 619.83 ± 4.53 ppm) attracted (captured) substantially higher number of aerial preys compared to air-streamed pitchers (CO2 at 412.76 ± 4.51 ppm). High levels of CO2 dissolved in acidic Nepenthes pitcher fluids were also detected. We demonstrate respiration as the source of elevated CO2 within Nepenthes pitchers. Most unique features of Nepenthes pitchers, viz., high growth rate, enhanced carbohydrate levels, declined protein levels, low photosynthetic capacity, high respiration rate and evolved stomata, are influenced by the CO2-enriched environment within them.

A carnivorous sundew plant prefers protein over chitin as a source of nitrogen from its traps

Carnivorous plants have evolved in nutrient-poor wetland habitats. They capture arthropod prey, which is an additional source of plant growth limiting nutrients. One of them is nitrogen, which occurs in the form of chitin and proteins in prey carcasses. In this study, the nutritional value of chitin and protein and their digestion traits in the carnivorous sundew Drosera capensis L. were estimated using stable nitrogen isotope abundance. Plants fed on chitin derived 49% of the leaf nitrogen from chitin, while those fed on the protein bovine serum albumin (BSA) derived 70% of its leaf nitrogen from this. Moreover, leaf nitrogen content doubled in protein-fed in comparison to chitin-fed plants indicating that the proteins were digested more effectively in comparison to chitin and resulted in significantly higher chlorophyll contents. The surplus chlorophyll and absorbed nitrogen from the protein digestion were incorporated into photosynthetic proteins - the light harvesting antennae of photosystem II. The incorporation of insect nitrogen into the plant photosynthetic apparatus may explain the increased rate of photosynthesis and plant growth after feeding. This general response in many genera of carnivorous plants has been reported in many previous studies.

A novel insight into the cost-benefit model for the evolution of botanical carnivory

BACKGROUND

The cost-benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (AN) in the microsites inhabited by carnivorous plants.

SCOPE

This review summarizes results from the classical interpretation of the cost-benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost-benefit model.

CONCLUSIONS

Traps of carnivorous plants have lower AN than leaves, and the leaves have higher AN after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, RD) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted.

Abundance of cysteine endopeptidase dionain in digestive fluid of Venus flytrap (Dionaea muscipula Ellis) is regulated by different stimuli from prey through jasmonates

The trap of the carnivorous plant Venus flytrap (Dionaea muscipula) catches prey by very rapid closure of its modified leaves. After the rapid closure secures the prey, repeated mechanical stimulation of trigger hairs by struggling prey and the generation of action potentials (APs) result in secretion of digestive fluid. Once the prey's movement stops, the secretion is maintained by chemical stimuli released from digested prey. We investigated the effect of mechanical and chemical stimulation (NH₄Cl, KH₂PO₄, further N(Cl) and P(K) stimulation) on enzyme activities in digestive fluid. Activities of β-D-glucosidases and N-acetyl-β-D-glucosaminidases were not detected. Acid phosphatase activity was higher in N(Cl) stimulated traps while proteolytic activity was higher in both chemically induced traps in comparison to mechanical stimulation. This is in accordance with higher abundance of recently described enzyme cysteine endopeptidase dionain in digestive fluid of chemically induced traps. Mechanical stimulation induced high levels of cis-12-oxophytodienoic acid (cis-OPDA) but jasmonic acid (JA) and its isoleucine conjugate (JA-Ile) accumulated to higher level after chemical stimulation. The concentration of indole-3-acetic acid (IAA), salicylic acid (SA) and abscisic acid (ABA) did not change significantly. The external application of JA bypassed the mechanical and chemical stimulation and induced a high abundance of dionain and proteolytic activity in digestive fluid. These results document the role of jasmonates in regulation of proteolytic activity in response to different stimuli from captured prey. The double trigger mechanism in protein digestion is proposed.

Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis

BACKROUND AND AIMS: It has been suggested that the rate of net photosynthesis (AN) of carnivorous plants increases in response to prey capture and nutrient uptake; however, data confirming the benefit from carnivory in terms of increased AN are scarce and unclear. The principal aim of our study was to investigate the photosynthetic benefit from prey capture in the carnivorous sundew Drosera capensis.

METHODS

Prey attraction experiments were performed, with measurements and visualization of enzyme activities, elemental analysis and pigment quantification together with simultaneous measurements of gas exchange and chlorophyll a fluorescence in D. capensis in response to feeding with fruit flies (Drosophila melanogaster).

KEY RESULTS

Red coloration of tentacles did not act as a signal to attract fruit flies onto the traps. Phosphatase, phophodiesterase and protease activities were induced 24 h after prey capture. These activities are consistent with the depletion of phosphorus and nitrogen from digested prey and a significant increase in their content in leaf tissue after 10 weeks. Mechanical stimulation of tentacle glands alone was not sufficient to induce proteolytic activity. Activities of β-D-glucosidases and N-acetyl-β-D-glucosaminidases in the tentacle mucilage were not detected. The uptake of phosphorus from prey was more efficient than that of nitrogen and caused the foliar N:P ratio to decrease; the contents of other elements (K, Ca, Mg) decreased slightly in fed plants. Increased foliar N and P contents resulted in a significant increase in the aboveground plant biomass, the number of leaves and chlorophyll content as well as AN, maximum quantum yield (Fv/Fm) and effective photochemical quantum yield of photosystem II (ΦPSII).

CONCLUSIONS

According to the stoichiometric relationships among different nutrients, the growth of unfed D. capensis plants was P-limited. This P-limitation was markedly alleviated by feeding on fruit flies and resulted in improved plant nutrient status and photosynthetic performance. This study supports the original cost/benefit model proposed by T. Givnish almost 30 years ago and underlines the importance of plant carnivory for increasing phosphorus, and thereby photosynthesis.

Venus Flytrap Seedlings Show Growth-Related Prey Size Specificity

Venus flytrap (Dionaea muscipula) has had a conservation status of vulnerable since the 1970s. Little research has focussed on the ecology and even less has examined its juvenile stages. For the first time, reliance on invertebrate prey for growth was assessed in seedling Venus flytrap by systematic elimination of invertebrates from the growing environment. Prey were experimentally removed from a subset of Venus flytrap seedlings within a laboratory environment. The amount of growth was measured by measuring trap midrib length as a function of overall growth as well as prey spectrum. There was significantly lower growth in prey-eliminated plants than those utilising prey. This finding, although initially unsurprising, is actually contrary to the consensus that seedlings (traps < 5 mm) do not catch prey. Furthermore, flytrap was shown to have prey specificity at its different growth stages; the dominant prey size for seedlings did not trigger mature traps. Seedlings are capturing and utilising prey for nutrients to increase their overall trap size. These novel findings show Venus flytrap to have a much more complex evolutionary ecology than previously thought.

Disproportional plastome-wide increase of substitution rates and relaxed purifying selection in genes of carnivorous Lentibulariaceae

Carnivorous Lentibulariaceae exhibit the most sophisticated implementation of the carnivorous syndrome in plants. Their unusual lifestyle coincides with distinct genomic peculiarities such as the smallest angiosperm nuclear genomes and extremely high nucleotide substitution rates across all genomic compartments. Here, we report the complete plastid genomes from each of the three genera Pinguicula, Utricularia, and Genlisea, and investigate plastome-wide changes in their molecular evolution as the carnivorous syndrome unfolds. We observe a size reduction by up to 9% mostly due to the independent loss of genes for the plastid NAD(P)H dehydrogenase and altered proportions of plastid repeat DNA, as well as a significant plastome-wide increase of substitution rates and microstructural changes. Protein-coding genes across all gene classes show a disproportional elevation of nonsynonymous substitutions, particularly in Utricularia and Genlisea. Significant relaxation of purifying selection relative to noncarnivores occurs in the plastid-encoded fraction of the photosynthesis ATP synthase complex, the photosystem I, and in several other photosynthesis and metabolic genes. Shifts in selective regimes also affect housekeeping genes including the plastid-encoded polymerase, for which evidence for relaxed purifying selection was found once during the transition to carnivory, and a second time during the diversification of the family. Lentibulariaceae significantly exhibit enhanced rates of nucleotide substitution in most of the 130 noncoding regions. Various factors may underlie the observed patterns of relaxation of purifying selection and substitution rate increases, such as reduced net photosynthesis rates, alternative paths of nutrient uptake (including organic carbon), and impaired DNA repair mechanisms.

Capture mechanism in Palaeotropical pitcher plants (Nepenthaceae) is constrained by climate

BACKGROUND AND AIMS

Nepenthes (Nepenthaceae, approx. 120 species) are carnivorous pitcher plants with a centre of diversity comprising the Philippines, Borneo, Sumatra and Sulawesi. Nepenthes pitchers use three main mechanisms for capturing prey: epicuticular waxes inside the pitcher; a wettable peristome (a collar-shaped structure around the opening); and viscoelastic fluid. Previous studies have provided evidence suggesting that the first mechanism may be more suited to seasonal climates, whereas the latter two might be more suited to perhumid environments. In this study, this idea was tested using climate envelope modelling.

METHODS

A total of 94 species, comprising 1978 populations, were grouped by prey capture mechanism (large peristome, small peristome, waxy, waxless, viscoelastic, non-viscoelastic, 'wet' syndrome and 'dry' syndrome). Nineteen bioclimatic variables were used to model habitat suitability at approx. 1 km resolution for each group, using Maxent, a presence-only species distribution modelling program.

KEY RESULTS

Prey capture groups putatively associated with perhumid conditions (large peristome, waxless, viscoelastic and 'wet' syndrome) had more restricted areas of probable habitat suitability than those associated putatively with less humid conditions (small peristome, waxy, non-viscoelastic and'dry' syndrome). Overall, the viscoelastic group showed the most restricted area of modelled suitable habitat.

CONCLUSIONS

The current study is the first to demonstrate that the prey capture mechanism in a carnivorous plant is constrained by climate. Nepenthes species employing peristome-based and viscoelastic fluid-based capture are largely restricted to perhumid regions; in contrast, the wax-based mechanism allows successful capture in both perhumid and more seasonal areas. Possible reasons for the maintenance of peristome-based and viscoelastic fluid-based capture mechanisms in Nepenthes are discussed in relation to the costs and benefits associated with a given prey capture strategy.

Strategy of nitrogen acquisition and utilization by carnivorous Dionaea muscipula

Plant carnivory represents an exceptional means to acquire N. Snap traps of Dionaea muscipula serve two functions, and provide both N and photosynthate. Using (13)C/(15)N-labelled insect powder, we performed feeding experiments with Dionaea plants that differed in physiological state and N status (spring vs. autumn plants). We measured the effects of (15)N uptake on light-saturated photosynthesis (A(max)), dark respiration (R(D)) and growth. Depending on N status, insect capture briefly altered the dynamics of R(D)/A(max), reflecting high energy demand during insect digestion and nutrient uptake, followed by enhanced photosynthesis and growth. Organic N acquired from insect prey was immediately redistributed, in order to support swift renewal of traps and thereby enhance probability of prey capture. Respiratory costs associated with permanent maintenance of the photosynthetic machinery were thereby minimized. Dionaea's strategy of N utilization is commensurate with the random capture of large prey, occasionally transferring a high load of organic nutrients to the plant. Our results suggest that physiological adaptations to unpredictable resource availability are essential for Dionaea's success with regards to a carnivorous life style.

A novel type of nutritional ant-plant interaction: ant partners of carnivorous pitcher plants prevent nutrient export by dipteran pitcher infauna

Many plants combat herbivore and pathogen attack indirectly by attracting predators of their herbivores. Here we describe a novel type of insect–plant interaction where a carnivorous plant uses such an indirect defence to prevent nutrient loss to kleptoparasites. The ant Camponotus schmitzi is an obligate inhabitant of the carnivorous pitcher plant Nepenthes bicalcarata in Borneo. It has recently been suggested that this ant–plant interaction is a nutritional mutualism, but the detailed mechanisms and the origin of the ant-derived nutrient supply have remained unexplained. We confirm that N. bicalcarata host plant leaves naturally have an elevated ¹⁵N/¹⁴N stable isotope abundance ratio (δ¹⁵N) when colonised by C. schmitzi. This indicates that a higher proportion of the plants’ nitrogen is insect-derived when C. schmitzi ants are present (ca. 100%, vs. 77% in uncolonised plants) and that more nitrogen is available to them. We demonstrated direct flux of nutrients from the ants to the host plant in a ¹⁵N pulse-chase experiment. As C. schmitzi ants only feed on nectar and pitcher contents of their host, the elevated foliar δ¹⁵N cannot be explained by classic ant-feeding (myrmecotrophy) but must originate from a higher efficiency of the pitcher traps. We discovered that C. schmitzi ants not only increase the pitchers' capture efficiency by keeping the pitchers’ trapping surfaces clean, but they also reduce nutrient loss from the pitchers by predating dipteran pitcher inhabitants (infauna). Consequently, nutrients the pitchers would have otherwise lost via emerging flies become available as ant colony waste. The plants’ prey is therefore conserved by the ants. The interaction between C. schmitzi, N. bicalcarata and dipteran pitcher infauna represents a new type of mutualism where animals mitigate the damage by nutrient thieves to a plant.

A carnivorous plant fed by its ant symbiont: a unique multi-faceted nutritional mutualism

Scarcity of essential nutrients has led plants to evolve alternative nutritional strategies, such as myrmecotrophy (ant-waste-derived nutrition) and carnivory (invertebrate predation). The carnivorous plant Nepenthes bicalcarata grows in the Bornean peatswamp forests and is believed to have a mutualistic relationship with its symbiotic ant Camponotus schmitzi. However, the benefits provided by the ant have not been quantified. We tested the hypothesis of a nutritional mutualism, using foliar isotopic and reflectance analyses and by comparing fitness-related traits between ant-inhabited and uninhabited plants. Plants inhabited by C. schmitzi produced more leaves of greater area and nitrogen content than unoccupied plants. The ants were estimated to provide a 200% increase in foliar nitrogen to adult plants. Inhabited plants also produced more and larger pitchers containing higher prey biomass. C. schmitzi-occupied pitchers differed qualitatively in containing C. schmitzi wastes and captured large ants and flying insects. Pitcher abortion rates were lower in inhabited plants partly because of herbivore deterrence as herbivory-aborted buds decreased with ant occupation rate. Lower abortion was also attributed to ant nutritional service. The ants had higher δ(15)N values than any tested prey, and foliar δ(15)N increased with ant occupation rate, confirming their predatory behaviour and demonstrating their direct contribution to the plant-recycled N. We estimated that N. bicalcarata derives on average 42% of its foliar N from C. schmitzi wastes, (76% in highly-occupied plants). According to the Structure Independent Pigment Index, plants without C. schmitzi were nutrient stressed compared to both occupied plants, and pitcher-lacking plants. This attests to the physiological cost of pitcher production and poor nutrient assimilation in the absence of the symbiont. Hence C. schmitzi contributes crucially to the nutrition of N. bicalcarata, via protection of assimilatory organs, enhancement of prey capture, and myrmecotrophy. This combination of carnivory and myrmecotrophy represents an outstanding strategy of nutrient sequestration.

Nutritional benefit from leaf litter utilization in the pitcher plant Nepenthes ampullaria

The pitcher plant Nepenthes ampullaria has an unusual growth pattern, which differs markedly from other species in the carnivorous genus Nepenthes. Its pitchers have a reflexed lid and sit above the soil surface in a tighly packed 'carpet'. They contain a significant amount of plant-derived materials, suggesting that this species is partially herbivorous. We tested the hypothesis that the plant benefits from leaf litter utilization by increased photosynthetic efficiency sensu stricto cost/benefit model. Stable nitrogen isotope abundance indicated that N. ampullaria derived around 41.7 ± 5.5% of lamina and 54.8 ± 7.0% of pitcher nitrogen from leaf litter. The concentrations of nitrogen and assimilation pigments, and the rate of net photosynthesis (A(N)), increased in the lamina as a result of feeding, but did not increase in the trap. However, maximal (F(v) /F(m)) and effective photochemical quantum yield of photosystem II (Φ(PSII)) were unaffected. Our data indicate that N. ampullaria benefits from leaf litter utilization and our study provides the first experimental evidence that the unique nitrogen sequestration strategy of N. ampullaria provides benefits in term of photosynthesis and growth.

Electrical signaling and photosynthesis: can they co-exist together?

Mechanical irritation of trigger hairs and subsequent generation of action potentials have significant impact on photosynthesis and respiration in carnivorous Venus flytrap (Dionaea muscipula). Action potential-mediated inhibition of photosynthesis and stimulation of respiration is confined only to the trap and was not recorded in adjacent photosynthetic lamina. We showed that the main primary target of electrical signals on assimilation is in the dark enzymatic reaction of photosynthesis. Without doubt, the electrical signaling is costly, and the possible co-existence of such type of signals and photosynthesis in plant cell is discussed.

Spatio-temporal changes of photosynthesis in carnivorous plants in response to prey capture, retention and digestion

Carnivorous plants have evolved modified leaves into the traps which assist in nutrient uptake from captured prey. It is known that the traps of carnivorous plants have usually lower photosynthetic rates than assimilation leaves as a result of adaptation to carnivory. However a few recent studies have indicated that photosynthesis and respiration undergo spatio-temporal changes during prey capture and retention, especially in the genera with active trapping mechanisms. This study describes the spatio-temporal changes of effective quantum yield of photochemical energy conversion in photosystem II (Ф PSII) in response to ant-derived formic acid during its capture and digestion.

The carnivorous syndrome in Nepenthes pitcher plants: current state of knowledge and potential future directions

Nepenthes is the largest genus of pitcher plants, with its centre of diversity in SE Asia. The plants grow in substrates that are deficient in N and offset this deficiency by trapping animal prey, primarily arthropods. Recent research has provided new insights into the function of the pitchers, particularly with regard to prey tapping and retention. Species examined to date use combinations of wettable peristomes, wax layers and viscoelastic fluid to trap and retain prey. In many respects, this has redefined our understanding of the functioning of Nepenthes pitchers. In addition, recent research has shown that several Nepenthes species target specific groups of prey animals, or are even evolving away from a strictly carnivorous mode of operation. Future research into nutrient sequestration strategies and mechanisms of prey attraction would no doubt further enhance our knowledge of the ecology of this remarkable genus.

Trap geometry in three giant montane pitcher plant species from Borneo is a function of tree shrew body size

*Three Bornean pitcher plant species, Nepenthes lowii, N. rajah and N. macrophylla, produce modified pitchers that 'capture' tree shrew faeces for nutritional benefit. Tree shrews (Tupaia montana) feed on exudates produced by glands on the inner surfaces of the pitcher lids and defecate into the pitchers. *Here, we tested the hypothesis that pitcher geometry in these species is related to tree shrew body size by comparing the pitcher characteristics with those of five other 'typical' (arthropod-trapping) Nepenthes species. *We found that only pitchers with large orifices and lids that are concave, elongated and oriented approximately at right angles to the orifice capture faeces. The distance from the tree shrews' food source (that is, the lid nectar glands) to the front of the pitcher orifice precisely matches the head plus body length of T. montana in the faeces-trapping species, and is a function of orifice size and the angle of lid reflexion. *Substantial changes to nutrient acquisition strategies in carnivorous plants may occur through simple modifications to trap geometry. This extraordinary plant-animal interaction adds to a growing body of evidence that Nepenthes represents a candidate model for adaptive radiation with regard to nitrogen sequestration strategies.

Ion fluxes across the pitcher walls of three Bornean Nepenthes pitcher plant species: flux rates and gland distribution patterns reflect nitrogen sequestration strategies

Nepenthes pitcher plant species differ in their prey capture strategies, prey capture rates, and pitcher longevity. In this study, it is investigated whether or not interspecific differences in nutrient sequestration strategy are reflected in the physiology and microstructure of the pitchers themselves. Using a non-invasive technique (MIFE), ion fluxes in pitchers of Nepenthes ampullaria Jack, Nepenthes bicalcarata Hook.f., and Nepenthes rafflesiana Jack were measured. Scanning electron microscopy was also used to characterize the distribution of glandular and other structures on the inner pitcher walls. The results demonstrate that nutrient sequestration strategy is indeed mirrored in pitcher physiology and microstructure. Species producing long-lived pitchers with low prey capture rates (N. ampullaria, N. bicalcarata) showed lower rates of NH(4)(+) uptake than N. rafflesiana, a species producing short-lived pitchers with high capture rates. Crucially, species dependent upon aquatic commensals (N. ampullaria, N. bicalcarata) actively manipulated H(+) fluxes to maintain less acid pitcher fluid than found in 'typical' species; in addition, these species lacked the lunate cells and epicuticular waxes characteristic of 'typical' insectivorous congeners. An unexpected finding was that ion fluxes occurred in the wax-covered, non-glandular zones in N. rafflesiana. The only candidates for active transport of aqueous ions in these zones appear to be the epidermal cells lying beneath the lunate cells, as these are the only sites not visibly coated with epicuticular waxes.

Dark respiration of leaves and traps of terrestrial carnivorous plants: are there greater energetic costs in traps?

In this study, O2-based dark respiration rate (RD) in leaf and trap cuttings was compared in 9 terrestrial carnivorous plant species of 5 genera to decide whether traps represent a greater energetic (maintanence) cost than leaves or photosynthetic parts of traps. RD values of cut strips of traps or leaves of terrestrial carnivorous plants submerged in water ranged between 2.2 and 8.4 nmol g−1 s−1 (per unit dry weight) in pitcher traps of the genera Sarracenia, Nepenthes, and Cephalotus, while between 7.2 and 25 nmol g−1 DW s−1 in fly-paper or snapping traps or leaves of Dionaea and Drosera. No clear relationship between RD values of traps (or pitcher walls) and leaves (or pitcher wings or petioles) was found. However, RD values of separated Drosera prolifera tentacles exceeded those of leaf lamina 7.3 times.

Trap closure and prey retention in Venus flytrap (Dionaea muscipula) temporarily reduces photosynthesis and stimulates respiration

BACKGROUND AND AIMS

The carnivorous plant Venus flytrap (Dionaea muscipula) produces a rosette of leaves: each leaf is divided into a lower part called the lamina and an upper part, the trap, with sensory trigger hairs on the adaxial surface. The trap catches prey by very rapid closure, within a fraction of a second of the trigger hairs being touched twice. Generation of action potentials plays an important role in closure. Because electrical signals are involved in reduction of the photosynthetic rate in different plant species, we hypothesized that trap closure and subsequent movement of prey in the trap will result in transient downregulation of photosynthesis, thus representing the energetic costs of carnivory associated with an active trapping mechanism, which has not been previously described.

METHODS

Traps were enclosed in a gas exchange cuvette and the trigger hairs irritated with thin wire, thus simulating insect capture and retention. Respiration rate was measured in darkness (RD). In the light, net photosynthetic rate (AN), stomatal conductance (gs) and intercellular CO2 concentration (ci) were measured, combined with chlorophyll fluorescence imaging. Responses were monitored in the lamina and trap separately.

KEY RESULTS

Irritation of trigger hairs resulted in decreased AN and increased RD, not only immediately after trap closure but also during the subsequent period when prey retention was simulated in the closed trap. Stomatal conductance remained stable, indicating no stomatal limitation of AN, so ci increased. At the same time, the effective quantum yield of photosystem II (PSII) decreased transiently. The response was confined mainly to the digestive zone of the trap and was not observed in the lamina. Stopping mechanical irritation resulted in recovery of AN, RD and PSII.

CONCLUSIONS

We put forward the first experimental evidence for energetic demands and carbon costs during insect trapping and retention in carnivorous plants, providing a new insight into the cost/benefit model of carnivory.