Carnivorous plant ecology

Carnivorous plants trap and utilize animals in order to improve their supply with mineral nutrients. One strategy for prey capture is the use of adhesive traps, i.e., leaves that produce sticky substances. Sticky shoots are widespread in the plant kingdom and serve to protect the plant, especially flowers and seeds. In some taxa, mechanisms have been developed to absorb nutrients from the decaying carcasses of animals killed by the glue. In carnivorous plants sensu stricto, additional digestive enzymes are secreted into the glue to accelerate degradation of prey organisms. The glues are secreted by glands that are remarkably uniform throughout all taxa producing adhesive traps. They follow the general scheme of plant glandular organs: the glands consist of a stalk, a neck equipped with a suberin layer that separates the gland from the rest of the plant, and the glandular cells producing sticky secretions. This glue always forms droplets at the tip of the glandular hairs. In most genera, these glands produce only glue whereas enzymes for prey digestion are secreted by a second type of gland. Two types of glue can be distinguished, polysaccharide mucilage in Droseraceae, Lentibulariaceae and their relatives, and terpenoid resins in Roridulaceae. On the ultrastructural level, mucilage is produced by the Golgi apparatus. Resins can be expected to be produced by the endoplasmic reticulum and by leucoplasts. Adhesive traps are suitable not only for the capture of small animals but also for the collection of organic particles like pollen grains. The glue may contain toxic compounds but the prey usually dies from suffocation by clogging of its tracheae. In Pinguicula and Drosera, the performance of the traps is improved by a slow movement, i.e., the folding of the leaf around the prey animal upon stimulation. In some species of Nepenthes, a pitcher with smooth walls is filled with a sticky digestive fluid. Some organisms, however, have developed strategies to survive on the deadly traps. Several species of Hemiptera are able to walk on the sticky traps and nourish on the prey; their faeces are absorbed by the plant. In Roridula, this relationship is highly specialized and essential for both the plant and the insect. Mutualistic fungi and bacteria are common in many adhesive traps where they degrade and dissolve the plant’s prey. The traps of Drosera, on the other hand, are virtually sterile. In spite of the extensive literature on adhesive traps, numerous questions still remain. Only a small percentage of “sticky” plants have actually been tested for carnivory. The properties and composition of their glues are widely unknown. In advanced adhesive traps, the mechanisms regulating secretion and absorption are poorly understood. Thereby, some glues may be applicable for human as they are non-toxic, quite stable under environmental conditions, and partly exhibit mildly antibiotic properties. Some carnivorous plants with adhesive traps have been used by humans for the capture of insects as well as for food processing.

Much of the focus of Darwin’s bicentenary has been on the origin of species by natural selection, emerging evolutionary thought and the key scientists with whom he corresponded. His botanical contributions to science have occupied a lesser role in the celebrations, and female correspondents an even more ephemeral position in the so-called ‘Darwin enterprise’. It has been suggested that there is a need to draw the curtains behind which these women stand and give them a ‘present voice’. This paper considers the work of two American women botanists who contributed, through correspondence networks, to the insectivorous plant studies of Darwin, his botanical contemporaries and subsequent plant studies.

In most species of the Genlisea–Utricularia sister lineage, the organs arising directly after germination comprise a single leaf-like structure, followed by a bladder-trap/stolon, with the lack of an embryonic primary root considered a synapomorphic character. Previous anatomical work suggests that the most common recent ancestor of Utricularia possessed an embryo comprising storage tissue and a meristematic apical region minus lateral organs. Studies of embryogenesis across the Utricularia lineage suggest that multiple primary organs have only evolved in the viviparous Utricularia nelumbifolia, Utricularia reniformis, and Utricularia humboldtii within the derived Iperua/Orchidioides clade. All three of these species are specialized for growth as “aquatic epiphytes” in the tanks of bromeliads, with recent phylogenetic evidence suggesting the possibility that multiple primary organs may have evolved twice independently within this clade. The primary organs of viviparous Utricularia a...

The carnivorous plant Drosophyllum lusitanicum inhabits heathland and ruderal sites in Portugal, Spain and Morocco. In the literature, various theories have been discussed concerning the ability of Drosophyllum to survive the annual dry period in summer. In August 2004, we examined: (1) the microclimate, (2) soil parameters and (3) the physiological conditions of the plants on two sites in Portugal and Spain. First, during the day, plants are exposed to very high air and soil temperatures and very low air humidity. The climatic extremes are not significantly softened by the population, only the wind speed is drastically decreased. During the night, on the other hand, very high air humidity and dew formation could be observed. The harsh climate is accompanied by stressful soil conditions. Second, the soil is completely dry, poor in fine earth, calcium and nutrients and more or less acid. Third, in spite of these climatic and edaphic extremes, all plants were green, produced trapping mucilage and caught numerous animals. Far from being affected by these conditions, Drosophyllum showed even better growth and reproduction on more extreme sites. We analysed the root system and found living fine roots missing. The osmotic value of the plants is rather low and water storage organs are absent. Therefore we conclude that in summer Drosophyllum is nourished by the dew at night.

Abstract: A new ELF (enzyme labelled fluorescence) assay was applied to detect phosphatase activity in glandular structures of 47 carnivorous plant species, especially Lentibulariaceae, in order to understand their digestive activities. We address the following questions: (1) Are phosphatases produced by the plants and/or by inhabitants of the traps? (2) Which type of hairs/glands is involved in the production of phosphatases? (3) Is this phosphatase production a common feature among carnivorous plants or is it restricted to evolutionarily advanced species? Our results showed activity of the phosphatases in glandular structures of the majority of the plants tested, both from the greenhouse and from sterile culture. In addition, extracellular phosphatases can also be produced by trap inhabitants. In Utricularia, activity of phosphatase was detected in internal glands of 27 species from both primitive and advanced sections and different ecological groups. Further positive reactions were found in Genlisea, Pinguicula, Aldrovanda, Dionaea, Drosera, Drosophyllum, Nepenthes, and Cephalotus. In Utricularia and Genlisea, enzymatic secretion was independent of stimulation by prey. Byblis and Roridula are usually considered as “proto-carnivores”, lacking digestive enzymes. However, we found high activity of phosphatases in both species. Thus, they should be classified as true carnivores. We suggest that the inflorescence of Byblis and some Pinguicula species might also be an additional “carnivorous organ”, which can trap a prey, digest it, and finally absorb available nutrients.

Micronesia encompasses about 2,100 islands scattered over some 12 million sq km of the central Pacific between Hawaii and the Philippines. Only about 125 of these small islands are inhabited. The total land area of Micronesia is less than 3,200 sq km, about the size of the state of Rhode Island. The largest island is Guam, with an area of

Prey derived N is predicted to become less important for carnivorous plants as N availability increases. We tested this prediction along a latitudinal N deposition gradient in Sweden. Using natural abundance stable isotope techniques we measured in-situ the contribution of prey N to the N budget of Drosera rotundifolia.

Aquatic carnivorous plants of the genus Utricularia capture and utilise a wide range of small aquatic organisms. Most of the literature focuses on animals as prey. In this study, we investigate the occurrence of algae inside the traps of four species of bladderwort. We observed that algae of 45 genera form up to 80% of the total prey; algae were found frequently in traps without animal prey. The majority are coccal and trichal algae of the families Desmidiaceae and Zygnemataceae. The percentage of algae increases significantly with decreasing electric conductivity of the water (r S = −0.417; P = 0,000). Thus, algae are the most frequent prey in extremely soft waters. The percentage of algae did not differ significantly, not within the investigated Utricularia species or within the various study sites. However, the taxonomic composition of the algal prey showed highly significant differences between different sites. More than 90% of the trapped algae were killed and degraded by the bladders. The recent data allow for two alternative hypotheses: either algal prey supplements animal prey in oligotrophic waters, or the unprofitable trapping of algae is rather an additional stress factor for Utricularia and contributes to its limited distribution in some peat bogs.

Abstract: A new ELF (enzyme labelled fluorescence) assay was applied to detect phosphatase activity in glandular structures of 47 carnivorous plant species, especially Lentibulariaceae, in order to understand their digestive activities. We address the following questions: (1) Are phosphatases produced by the plants and/or by inhabitants of the traps? (2) Which type of hairs/glands is involved in the production of phosphatases? (3) Is this phosphatase production a common feature among carnivorous plants or is it restricted to evolutionarily advanced species? Our results showed activity of the phosphatases in glandular structures of the majority of the plants tested, both from the greenhouse and from sterile culture. In addition, extracellular phosphatases can also be produced by trap inhabitants. In Utricularia, activity of phosphatase was detected in internal glands of 27 species from both primitive and advanced sections and different ecological groups. Further positive reactions were found in Genlisea, Pinguicula, Aldrovanda, Dionaea, Drosera, Drosophyllum, Nepenthes, and Cephalotus. In Utricularia and Genlisea, enzymatic secretion was independent of stimulation by prey. Byblis and Roridula are usually considered as “proto-carnivores”, lacking digestive enzymes. However, we found high activity of phosphatases in both species. Thus, they should be classified as true carnivores. We suggest that the inflorescence of Byblis and some Pinguicula species might also be an additional “carnivorous organ”, which can trap a prey, digest it, and finally absorb available nutrients.

The hypothesis that carnivorous plants are less responsive to prey at high soil nutrient levels than at lower levels (Givnish et al. 1984) is tested on four plant species (Drosera rotundifolia, Pinguicula alpina, P. villosa and P. vulgaris) from a subarctic environment. The response, measured in terms of seven characteristics (winter bud weight, winter bud nitrogen and phosphorus content, flowering frequency, total seed weight, seed number and weight per seed), was analysed. Although all species responded to prey supply the response varied depending on the characteristic and species concerned. In 5 cases (out of 28 tests) the hypothesis was supported, whereas in 1 case it was refuted, i.e. the response to prey was higher for plants supplied with soil nutrients. In the remaining three-quarters of the tests, responses to prey were not significantly different between the two nutrient levels. Thus, the hypothesis that the response to prey diminishes as soil nutrient availability increases was not supported by our findings. A modification of the model presented by Givnish et al. (1984) is therefore suggested. This modified model measures the cost of carnivory as loss in growth rate and assumes that responses to prey remain unchanged as the soil nutrient content increases. Although the distribution of carnivorous plants is still predicted to be limited mainly to wet and sunny but nutrient-poor sites, the modified model also allows for their occurrence in richer habitats, provided competition is low.

Leaves of the carnivorous Drosera rotundifolia (sundew) exhibit variation in leaf pigment composition. Data obtained from UK ombotrophic bogs with a wide range of N deposition, along with the manipulation of the light environment, is used to address the significance of light radiation and N availability in driving differences in D. rotundifolia leaf pigmentation.