0The News:
- In a breakthrough research, scientists in India have discovered a high concentration of carbon dioxide (CO2), is used to trap insects and small mammals, in a genus of carnivorous plants.
- Researchers found the leaf-evolved biological traps of the plant Nepenthes to be CO2-enriched cavities, and that CO2 emission from pitchers act as sensory cues attracting insects towards these traps.
- This is the first time that high CO2 content has been detected in carnivorous plants, though CO2 emitting devices are widely used by man as traps against mosquitoes, flies and other insects.
Methodology:
- In the study, CO2 was demonstrated as an insect attractant emitted by Nepenthes, genus of carnivorous plants, which consists of approximately 160 species distributed in the Madagascar-South East Asia-North Australia-New Guinea region.
- CO2 contents in near mature, unopened Nepenthes pitchers were found to be in the range 2500-5000 ppm.
About The Research:
- The research was conducted by India’s Jawaharlal Nehru Tropical Botanic Garden and Research Institute and National Centre for Earth Sciences. The findings have been published in the journal Scientific Reports.
- The study showed that Indian pitcher plant, Nepenthes khasiana, as more CO2-enriched air-streamed through the pitchers, they attracted (captured) substantially higher number of insects.
- The study demonstrated respiration of pitcher tissues as the factor contributing to the high CO2 within the ‘closed cavities’ of Nepenthes traps.
Characteristic of nepenthes pitcher plant:
- Nepenthes and most other carnivorous plants grow in wet, sunny and nutrient-poor habitats. In order to supplement this nutrient deficiency, the species evolved mechanisms to capture arthropods (insects, ants etc.) and involve in mutuality interactions with small mammals (tree shrews, rats, bats etc.), through their leaf-evolved prey traps called pitchers.
- Nepenthes pitchers are influenced by the high content of CO2 entrapped within them.
- Nepenthes pitchers are natural model systems mimicking an anticipated elevated CO2 scenario on Earth. With their adaptations, Nepenthes (and other carnivorous plants) survive and they remain as one of unique life forms on the surface of Earth.
- Carnivorous plants follow a photosynthetic pathway, with high CO2 levels which enhance respiration rates.
- Unlike most plant leaf structures, high growth rate and unique physiological functions (prey attraction, capture, digestion, absorption of nutrients) of Nepenthes pitchers demand more energy, prompting higher respiration rates in the trap tissues, resulting in the release of more of CO2.
How pitchers use Co2?
- Nepenthes pitchers are modified leaves in which their upper surface curls around and fuses to form the inner side of the pitcher.
- The tendrils of aerial pitchers are usually coiled in the middle, and once in contact with other objects for long enough, they curl around them, forming anchor points for pitchers.
- In this way, Nepenthes tendrils help to support the growing stem of the plant.
- As it matures, the pitcher ‘inflates’ and gets partially filled with an acidic enzymatic fluid. Pitchers also have a flap (operculum), which initially ‘hermetically seals’ the growing trap, and once mature breaks open for prey capture.
- In most Nepenthes species, a lid covers the pitcher opening and protects it from rain, preventing dilution of the pitcher fluid.
- Large Nepenthes pitchers are capable of trapping rodents, lizards, and birds. Once open, Nepenthes pitchers involve in prey capture from a few weeks up to nine months depending on the species.
Why are insects attracted towards Co2?
- CO2 is a sensory cue and most insects pay special attention to ‘subtle variations’ or ‘gradients’ of CO2 in the form of plumes arising from individual point sources. Insects have well developed CO2 receptors, which can detect these variations (even small variations) as a means of locating their food.
- The study demonstrated CO2 as an insect attractant emitted by Nepenthes prey traps and revealed a new prey capture mechanism within them.
Link with climate change:
- CO2 (high) and CO, CH4 and N2O (ambient) found in Nepenthes pitchers are greenhouse gases. Global CO2 levels are predicted to go up to 800 ppm by 2100 and further onto even higher levels.
- This elevation of CO2 levels on Earth surface has prompted several simulation studies towards understanding its effects on various features of plants. Nepenthes prey traps with elevated CO2 contents (3000-5000 ppm) are simulating this futuristic scenario in their ‘closed cavities’ (before trap opening).
- As in other CO2-enrichment experiments, high carbohydrate and low protein contents were detected in Nepenthes pitchers. Carbohydrate accumulation is a major acclimation response to elevated CO2. High carbohydrate contents in pitchers, transformed into nectar by nectaries, act as a major ‘lure’ in prey capture.
This evidence also infers Nepenthes pitchers as ideal examples reflecting the effects of an anticipated high CO2 level on Earth’s surface on the characteristic features of plants.
