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I had thought photosynthesis and respiration where pretty much Oxygen and Carbon neutral per calorie.
If, as the project plans, crops are cultivated within the settlers' habitat, Do found that they would produce unsafe levels of oxygen that would exceed fire safety thresholds, requiring continuous introduction of nitrogen to reduce the oxygen level.
Says that a closed system of plants grown to provide calories for human will end up with more oxygen.
Where does the imbalance come from? Where does the extra Carbon go?
If oxygen and respiration were carbon and oxygen neutral, there wouldn't be free oxygen at all. Plants would just respire all the oxygen they produce.
The extra carbon goes into the plants themselves. It isn't just what they use for energy, it is also what they are made of.
See also this question:
Are plants really oxygen neutral?
Plants are oxygen neutral when we take into account the decomposition of the plant, i.e. take the long-term view where the carbon making up the plant gets back to being CO2.
'The Martian': What Would It Take to Grow Food on Mars?
NASA has laid out plans to send people to Mars in the 2030s, but don't expect these Red Planet visitors to landscape the rocky sphere with fresh produce the way astronaut and botanist Mark Watney does in "The Martian."
(Spoiler alert) In the movie, when Watney (played by Matt Damon) gets stranded on Mars, he plants potatoes in a greenhouse using Martian soil and his own "metabolic waste." And it works: He's able to stay alive for more than a year living largely on potatoes.
Though "The Martian," which hit theaters last Friday (Oct. 2), is fairly realistic, growing food on Mars wouldn't play out exactly as described on the big screen. And it would take hundreds of years before the Red Planet could be farmed without protective greenhouses, according to Paul Sokoloff, a botanist at the Canadian Museum of Nature. [7 Most Mars-Like Places on Earth]
Martian agriculture challenges
Martian soil is devoid of the nutrients found in Earth's soil, and it is also fine, meaning water would likely seep through it much more quickly than it would on Earth. Using human poop or other fertilizers could provide a quick boost of nutrients, such as nitrogen, and may also change the texture of the soil so it would cling to water longer, said Sokoloff, who was a crewmember last year at the Mars Desert Research Station in Hanksville, Utah.Earthly soil gets its nitrogen from the atmosphere, though atmospheric nitrogen is in a form that is not easy for plants to use. To transform nitrogen into a better "food" for plants, bacteria "fix" it.
"On Earth, a lot of nitrogen in our soil is fixed by bacteria that reside in the roots of various plants, like legumes," Sokoloff told Live Science. "In the long term, you would want a way to fix nitrogen to the soil there."
Martian soil is also laced with nasty chemicals called perchlorates, which would have to be chemically removed for plants to grow there, Sokoloff said.
And then there's gravity. Mars has about one-third the gravity of Earth. Though experiments have shown that some plants can grow relatively normally in microgravity on the International Space Station (ISS), there's really no way to mimic the "gravity-lite" of the Red Planet.
"Plants use gravity as a way of orienting themselves, so some plant species may or may not be confused," Sokoloff said.
For instance, willow seedlings taken up to the ISS grew twisted because, in microgravity, they never developed their orienting "root-shoot axis," Sokoloff said.
A 2014 study in the journal PLOS ONE showed that tomatoes, wheat, cress and mustard leaves grew particularly well, and even flowered and produced seeds, in simulated Martian soil for 50 days, without any fertilizers. In fact, these hardy plants grew even better in Martian soil or "regolith" than in nutrient-poor river soil from Earth. [7 Theories on the Origin of Life]
To determine what food ingredients to actually bring to Mars, scientists must balance trade-offs among the nutritional density of a crop, the resources required to grow them and the germination time. Scientists may be growing lettuce on the ISS as a demonstration, but "man cannot live on lettuce alone," Sokoloff said.
Instead, people have suggested crops such as radishes and strawberries as better Martian snacks, he said. (Number crunchers have determined it would actually require less fuel to simply send over premade foods, rather than the ingredients for farming, for initial short-term visits, Sokoloff said.)
Simulating Martian conditions
Before the Martian farming project gets going, humans would need to know a lot more about how plants will grow. That's part of the reasoning behind simulations of the Martian environment, such as the Mars Desert Research Station.
Scientists there have grown everything from native desert plants to barley and hops in the station's simulated Martian soil. The soil, called Johnson Space Center Simulant I, is produced using Earthling rocks and soil based on Martian soil samples from 1970s-era Viking landers.
And researchers at the University of Guelph in Canada are growing plants in low-pressure, or hypobaric chambers to mimic the thin atmosphere of Mars. The team exposes plants to a host of rough conditions &mdash including varying levels of carbon dioxide, pressure, heat, light, nutrition and humidity &mdash to see which plants are hardy enough to survive Martian conditions outside a self-contained, air-controlled greenhouse, The Star peported.
Greening the Red Planet?
Growing plants out in the Martian elements, and not in a temperature- and air-controlled greenhouse, would be much more challenging, Sokoloff said.
"Some people have said we should make Mars more like Earth," Sokoloff said. "That's not something to be taken lightly. It's in the realm of science fiction, for sure."
And even if people decided it's ethically acceptable to "terraform" Mars, it would be hundreds of years before the thin Martian atmosphere could be transformed into an oxygen-rich cradle for life.
To build up that atmosphere, explorers would need to seed Martian soil chock-full of oxygen-producing cyanobacteria, lichens and microbes, and it would take hundreds of years for them to produce enough oxygen and nitrogen for an atmosphere. That's still not too shabby, considering it took hundreds of millions of years for Earth's oxygen levels to stabilize. (People could conceivably eat the cyanobacteria in the meantime, though the tiny organisms are not noted for their tastiness, Sokoloff said.)
While the microbes were busy creating an atmosphere, solar wind would constantly be blowing that atmosphere away, because Mars lacks a magnetosphere (a magnetic field to shield the planet from solar radiation), he said.
Even if people could figure out how to generate atmosphere faster than it dissipated, Martian winters can be a bone-chilling minus 207 degrees Fahrenheit (minus 133 degrees Celsius). It's possible that people could tailor an atmosphere with greenhouse gases that trap heat, but Mars is simply farther from the sun than Earth is, so it would still likely be colder than our planet on average, Sokoloff said.
The process of making of food by green plants in the presence of sunlight and chlorophyll is known as photosynthesis. Photosynthesis is the combination of two words- Photo + Synthesis. ‘Photo’ means light and ‘Synthesis’ means to make.
Process of food making in green plants:
Green plants make their food themselves. Green leaves make food from Carbon dioxide and water in the presence of sunlight and chlorophyll.
Leaves have several tiny pore-like structures on the lower surface. These pores are called stomata. Leaves absorb carbon dioxide from air, through these pores. Water is transported to leaves through very thin pipelines from the roots. These pipelines are present throughout the plant, i.e. from roots to branches and leaves. These pipelines are known as Xylem. Xylem is a type of tissue. You will learn about tissues in your higher classes. Chlorophyll is a green pigment that is found in green leaves. Chlorophyll absorbs sunlight and gives energy. Chlotrophyll is inside chloroplast. Chloroplast is the site of photosynthesis. At the end of photosynthesis, carbohydrate and oxygen are formed. Carbohydrate is used as food and oxygen is emitted out to the atmosphere. This whole process of making food by plants is called photosynthesis.
The reaction that takes place in the process of photosynthesis can be written as:
Carbohydrate is ultimately converted into starch and stored in leaves. From leaves, starch is transported to different parts of a plant. Starch is a type of carbohydrate.
Leaves are known as the kitchen or food factory of plants because photosynthesis takes place in leaves. Leaves look green because of the presence of chlorophyll.
Besides leaves, photosynthesis also takes place in other green parts of the plant, such as in green stems. Chlorophyll is necessary for photosynthesis, hence photosynthesis takes place only in green plants.
The leaves of plants that grow in desert areas are modified in spine like structure or scales to reduce the loss of water in the course of transpiration. In such plants photosynthesis takes place in green stems. Stem is modified into thick spongy leaf-like structures in such plants.
Photosynthesis helps to maintain a balance between oxygen and carbon dioxide in the atmosphere as it absorbs carbon dioxide and releases oxygen.
Sunlight is necessary for photosynthesis. Thus sun is the ultimate source of energy for all living organism.
Our earth is the unique planet, where photosynthesis takes place. In the absence of photosynthesis life would not be possible on earth.
Necessary Factors for Photosynthesis:
Photosynthesis in Algae
Green patches in ponds or near the stagnant water can be seen easily. These green patches are living organism called algae. Algae are plants. Often algae grow near shallow waterlogged areas such as near tube-wells, taps, etc. One may slip over it. Algae look green because of presence of Chlorophyll. Algae prepare their own food by the process of photosynthesis.
Questions 1: What is photosynthesis?
Answer: The process of making food in green plants in the presence of sunlight is known as photosynthesis.
Questions 2: What are the essentials factors for the photosynthesis?
Answer: Carbon dioxide, water, chlorophyll and sunlight are essentials factors for photosynthesis to take place.
Question 3: What is chlorophyll?
Answer: Chlorophyll is the green pigment present in green leaves.
Question 4: Why do leaves look green?
Answer: Leaves look green because of the presence of chlorophyll, which is a green pigment.
Questions 5: What is the function of chlorophyll?
Answer: Chlorophyll absorbs the sunlight for photosynthesis.
Question 6: What are the final products made after photosynthesis?
Answer: Carbohydrate and oxygen are the final products after photosynthesis.
Questions 7: What are stomata?
Answer: The small pores present on the lower surface of leaf, are called stomata.
Questions 8: What is function of stomata?
Answer: Stomata absorb carbon dioxide from air for photosynthesis. Stomata facilitates exchange of gases and transpiration.
Question 9: What is the ultimate source of energy?
Answer: Sun is the ultimate source of energy.
Question 10: How water is transported to the leaves?
Answer: Water is transported to the leaves through pipe like structures from the roots of plant. These pipe-like structures are present from root to leaves through branches throughout.
Invention of modern day hydroponics
In the 19 th century, a German botanist at the University of Wurzburg, Julius Sachs , dedicated his career to understanding the essential elements that plants need to survive. By examining differences between plants grown in soil and those grown in water, Sachs found that plants did not need to grow in soil but only needed the nutrients that are derived from microorganisms that live in the soil. In 1860, Sachs published the “nutrient solution” formula for growing plants in water, which set the foundation for modern day hydroponic technology (Figure 1).
Figure 1: Nutrient Solution. Plants obtain 3 nutrients from the air–carbon, hydrogen, and oxygen–and 13 nutrients from supplemented water: nitrogen, phosphorous, potassium, calcium, magnesium, sulfur, iron, manganese, copper, zinc, boron, chlorine, and molybdate.
In 1937, an American scientist, Dr. W.E. Gericke described how this method of growing plants could be used for agricultural purposes to produce large amounts of crops. Gericke and others demonstrated that the fluid dynamics of water changed the architecture of plant roots , which allowed them to uptake nutrients more efficiently than plants grown in soil, causing them to grow larger in a shorter amount of time. Since then, scientists have optimized the nutrient solution, a total of 13 macronutrients and micronutrients , that are added to water for hydroponic farming (Figure 1).
Hydroponic systems today are very sophisticated there are systems that will monitor the level of nutrients pH, and temperature of the water, and even the amount of light the plants are receiving. There are three main types of hydroponic systems: a nutrient film technique, an Ebb and Flow System, and a Wick system (Figure 2). A nutrient film hydroponic technique involves plants being grown in a grow tray that it slightly angled and positioned above a reservoir filled with the water-nutrient mix. This allows a thin stream of water to flow across plant roots, allowing the plants to have sufficient water, nutrients and aeration, and then drained back into the reservoir. The nutrient film technique is the most common hydroponic system used today. Plenty and Bowery , two of the largest hydroponic farms in the US, use nutrient film techniques to grow lettuce, spinach and other leafy greens. The Ebb and Flow technique allows plants to be flooded with the nutrient-rich water, and after the plant roots uptake nutrients, water is actively drained back into a reservoir to be reused. Finally, a hydroponic wick system is the simplest of all, as nutrients are passively given to the plant from a wick or piece of string running up to the plant from the water reservoir. In this system, plants are grown in an inert growing medium such as sand, rock, wool or clay balls that help anchor the plant roots. These different systems are interchangeable, but some systems may be better for growing different types of plants.
Figure 2: The three most common techniques for hydroponic farming. In all approaches, water is fortified with a nutrient solution is stored in a nutrient reservoir. The water is then actively pumped to the grow tray (panels A and B) or it is passively passed to the grow tray (panel C) through a wick. The plant roots grow thicker than those of plants grown in soil, which allow them to uptake nutrients more effectively.
The advantages of using any of these hydroponic systems are manifold. First, since there is no soil, there is no need to worry about having a plot of land, weeds, pathogens living in dirt, or treating the crops with pesticides. Water is also greatly conserved due to the nutrient reservoir because the same water can be reused over and over. Moreover, as most of these hydroponics farms are indoors, food can be produced all year round and even in the middle of a large city, like New York City. Given all of these benefits, we may begin to see more hydroponic farms sprouting up across the US and around the world because this method of farming holds much promise to revolutionize agriculture by using less water and other resources.
NEXT STAGE - FOOD
More space is needed for non algae foods because you need head room for the crops. But still, with the crops they use in BIOS-3 such as dwarf wheat - not a huge amount of clearance is needed. With the BIOS-3 experiments they had a total of 237 cubic meters set aside for growing crops. But it is clear the experiment wasn't set out to be optimized for volume as they only grew the crops in a single level.
So that's only a little more growing area per person than was needed for the algae. It's clear from the photographs that they weren't optimizing for volume, as there is lots of spare headroom above the plants and just one layer of crops in the room. If those 13 square meters per person are all that you need to illuminate, then that makes it 7.8 kW total power for the lighting for a crew of six.
There seems plenty of space for three or four layers if you had them in trays. The wheat was used to make bread. So, that growing area of 237 cubic meters is very much an over estimate.
"Wheat plants of various ages showing the "conveyor" approach that was used in the Bios experiments, Young wheat plants are in the foreground, with more mature plants toward the back. The aisle between benches is narrow (to leave as much space as possible for the crops). The post, with some environmental sensors attached, further obstructs the aisle. Crew members planted various herbs and other special plants in the corner and next to the wall to the left, space that would otherwise be wasted." photo from here
I can't find an estimate of the total volume needed for the crops themselves if it was used in a space station with minimal overhead space above the crop. But it looks as if you could easily fit them within a third of the space.
Raising giant insects to unravel ancient oxygen
The giant dragonflies of ancient Earth with wingspans of up to 70 centimeters (28 inches) are generally attributed to higher oxygen atmospheric levels in the atmosphere in the past. New experiments in raising modern insects in various oxygen-enriched atmospheres have confirmed that dragonflies grow bigger with more oxygen, or hyperoxia.
However, not all insects were larger when oxygen was higher in the past. For instance, the largest cockroaches ever are skittering around today. The question becomes how and why do different groups respond to changes in atmospheric oxygen.
The secrets to why these changes happened may be in the hollow tracheal tubes insects use to breathe. Getting a better handle on those changes in modern insects could make it possible to use fossilized insects as proxies for ancient oxygen levels.
"Our main interest is in how paleo-oxygen levels would have influenced the evolution of insects," said John VandenBrooks of Arizona State University in Tempe. To do that they decided to look at the plasticity of modern insects raised in different oxygen concentrations. The team raised cockroaches, dragonflies, grasshoppers, meal worms, beetles and other insects in atmospheres containing different amounts of oxygen to see if there were any effects.
One result was that dragonflies grew faster into bigger adults in hyperoxia. However, cockroaches grew slower and did not become larger adults. In all, ten out of twelve kinds of insects studied decreased in size in lower oxygen atmospheres. But there were varied responses when they were placed into an enriched oxygen atmosphere. VandenBrooks is presenting the results of the work Nov. 1 at the annual meeting of the Geological Society of America in Denver.
"The dragonflies were the most challenging of the insects to raise," said VandenBrooks because, among other things, there is no such thing as dragonfly chow. As juveniles they need to hunt live prey and in fact undergraduate students Elyse Muñoz and Michael Weed working with Dr. VandenBrooks had to resort to hand feeding the dragonflies daily.
"Dragonflies are notoriously difficult to rear," said VandenBrooks. "We are one of the only groups to successfully rear them to adulthood under laboratory conditions."
Once they had worked that out, however, they raised three sets of 75 dragonflies in atmospheres containing 12 percent (the lowest oxygen has been in the past), 21 percent (like modern Earth's atmosphere) and 31 percent oxygen (the highest oxygen has been).
Cockroaches, as anyone who has fought them at home knows, are much easier to rear. That enabled the researchers to raise seven groups of 100 roaches in seven different atmospheres ranging from 12 percent to 40 percent oxygen mimicking the range of paleo-oxygen levels. Cockroaches took about twice as long to develop in high oxygen levels.
"It is the exact opposite of what we expected," said VandenBrooks. One possibility is that the hyperoxic reared roaches stayed in their larval stage longer, perhaps waiting for their environment to change to a lower, maybe less stressful oxygen level.
This surprising result prompted the researchers to take a closer look at the breathing apparatus of roaches -- their tracheal tubes. These are essentially hollow tubes in an insect's body that allow gaseous oxygen to enter directly into the insect tissues.
VandenBrooks and his team took their hyperoxic reared roaches to Argonne National Lab's x-ray synchrontron imaging facility to get a closer look at the tracheal tubes. The x-ray synchrontron is particularly good at resolving the edges where things of different phases meet -- like solids on liquids or gas on solids. That's just what the inside of a tracheal tube is.
What they found was that the tracheal tubes of hyperoxic reared roaches were smaller than those in lower oxygen atmospheres. That decrease in tube size with no increase in the overall body size would allow the roaches to possibly invest more in tissues used for other vital functions other than breathing -- like eating or reproducing. The roaches reared in hypoxia (lower oxygen) would have to trade off their investment in these other tissues in order to breathe.
The next step, said VandenBrooks, will be to look closely at the tracheal tubes of insects fossilized in amber to see what they might say about oxygen levels at various times in the past. These might possibly serve as a proxy for paleo-oxygen levels.
"There have been a lot of hypotheses about the impact of oxygen on evolution of animals, but nobody has really tested them," said VandenBrooks. "So we have used a two-pronged approach: 1) study modern insects in varying oxygen levels and 2) study fossil insects and understand changes in the past in light of these results."
Materials provided by Geological Society of America. Note: Content may be edited for style and length.
Abiotic factors are the non-living components of the ecosystem, including its chemical and physical factors. Abiotic factors influence other abiotic factors. In addition, they have profound impacts on the variety and abundance of life in an ecosystem, whether on land or in water. Without abiotic factors, living organisms wouldn’t be able to eat, grow, and reproduce. Below is a list of some of the most significant abiotic factors.
- Sunlight: As the world’s biggest source of energy, sunlight plays an essential role in most ecosystems. It provides the energy that plants use to produce food, and it affects temperature. Organisms must adapt depending on how much access they have to sunlight.
- Oxygen: Oxygen is essential to the majority of life forms on Earth. The reason? They need oxygen in order to breathe and to release energy from food. In this way, oxygen drives the metabolism of most organisms.
- Temperature: The average temperature, range of temperature, and extremes of temperature in both air and water are all important in how organisms live and survive in an ecosystem. Temperature also affects an organism’s metabolism, and species have evolved to thrive in the typical temperature range in their ecosystem.
- Wind: Wind can exert many effects on an ecosystem. It moves other abiotic factors, like soil and water. It disperses seeds and spreads fire. Wind affects temperature as well as evaporation from soil, air, surface waters, and plants, changing humidity levels.
- Water: Water is essential for all life. In terrestrial (land) ecosystems where water is scarce, such as deserts, organisms develop traits and behaviors that help them survive by harvesting and storing water efficiently. This can sometimes create a water source for other species as well. In ecosystems like rainforests where the abundance of water depletes soil nutrients, many plants have special traits that let them collect nutrients before water washes them away. Water also contains nutrients, gases, and food sources that aquatic and marine species depend on, and it facilitates movement and other life functions.
- Ocean currents: Ocean currents involve the movement of water, which in turn facilitates movement of biotic and abiotic factors like organisms and nutrients. Currents also affects water temperature and climate. They play an important role in the survival and behavior of organisms that live in water, since currents can influence things like food availability, reproduction, and species migration.
- Nutrients: Soil and water contain inorganic nutrients that organisms require to eat and grow. For example, minerals like phosphorous, potassium, and nitrogen found in soil are important for plant growth. Water contains many dissolved nutrients, and soil runoff can carry nutrients to aquatic and marine environments.
What About Soil?
Composed of both biotic and abiotic components, soil is an interesting case. Soil filters and stores water and anchors the roots of plants. It contains nutrient minerals and gases, as well as millions of microorganisms like bacteria, fungi, and single-celled organisms called archaea. These are important decomposers, the planet’s indispensable recyclers.
Plant sugars are crucial players in the oxidative challenge during abiotic stress: extending the traditional concept
Plants suffering from abiotic stress are commonly facing an enhanced accumulation of reactive oxygen species (ROS) with damaging as well as signalling effects at organellar and cellular levels. The outcome of an environmental challenge highly depends on the delicate balance between ROS production and scavenging by both enzymatic and metabolic antioxidants. However, this traditional classification is in need of renewal and reform, as it is becoming increasingly clear that soluble sugars such as disaccharides, raffinose family oligosaccharides and fructans--next to their associated metabolic enzymes--are strongly related to stress-induced ROS accumulation in plants. Therefore, this review aims at extending the current concept of antioxidants functioning during abiotic stress, with special focus on the emanate role of sugars as true ROS scavengers. Examples are given based on their cellular location, as different organelles seem to exploit distinct mechanisms. Moreover, the vacuole comes into the picture as important player in the ROS signalling network of plants. Elucidating the interplay between the mechanisms controlling ROS signalling during abiotic stress will facilitate the development of strategies to enhance crop tolerance to stressful environmental conditions.
Keywords: antioxidants oxidative stress reactive oxygen species vacuole.
The Rhône River Basin
Jean-Michel Olivier , . Jean-Paul Bravard , in Rivers of Europe , 2009
Aquatic plant diversity in the Rhône and tributaries results mostly from the high number of abandoned channels. These channels are shaped by river dynamics, and are consequently highly diverse in terms of sinuosity, hydraulic capacity, and distance from the river. This geomorphological complexity combined with hydrology dictates (1) the frequency and duration of floods, (2) the net effect of floods (erosion versus deposition), and (3) the discharge of groundwater exfiltrating in these channels ( Bornette et al. 1998 ). The Upper Rhône and several of its tributaries (e.g. Ain, Doubs, Ardèche, Isère, Drôme) are piedmont rivers, characterized by a coarse bedload, and a relatively high slope. In such situations, flood duration is low (usually a few days), and floods cause increases in flow velocity that damage plant communities and erode fine sediment, particularly cut-off channels with low sinuosity and hydraulic capacity. In more sinuous channels, floods have no or a silting effect, depending on the frequency of connections between the river and the channels. Groundwater discharge is usually low in sinuous channels that are frequently clogged with fine sediment. Groundwater discharge can be quite high in others, depending on the channel slope and substrate grain-size. This groundwater comes either from nutrient-rich river seepage or from more nutrient-poor hillslope aquifers. Oligotrophic cut-off channels are abundant along the Ain and in some places along the Rhône. In most situations, the high human activity in the catchment leads to fairly high (e.g. Upper Rhône, Isère) or very high nutrient-content of the water (Saône, Doubs, lower Rhône). Highest species richness is observed in cut-off channels with intermediate nutrient levels and the lowest species richness occurs in nutrient-rich cut-off channels. Oligotrophic communities have low richness but a high proportion of rare species. Among the most abundant species that occur in cut-off channels of the Rhône river and its tributaries are eutrophic species (Lemna minor, Ceratophyllum demersum, Spirodela polyrhiza, Myriophyllum spicatum) and species intolerant to flood scouring (Phragmites australis, Nuphar lutea, Nymphea alba) ( Bornette et al. 2001 ). Some relatively rare species mainly occur along the Saône (Stratiotes aloides, Hydrocharis morsus-ranae, Nymphoides peltata). A few species including Callitriche platycarpa, Elodea canadensis, Berula erecta, and Phalaris arundinacea occur in flood-disturbed cut-off channels (e.g. the Ain and French upper-Rhône). Many species related to intermediate and low trophic levels occur along the Ain River (Potamogeton coloratus, Chara major, Luronium natans, Baldellia ranunculoïdes, Hydrocotyle vulgaris, Cladium mariscus, Schoenoplectus nigricans).
In an exhaustive study of aquatic vegetation in all cut-off channels of the Rhône from Lake Léman to the sea, Henry and Amoros (unpublished data, 1998) showed that species richness is high (67 strictly aquatic species and 46 helophyte species) but not uniformly distributed. Cut-off channels along the French Upper Rhône have a relatively low proportion of eutrophic species due to oligotrophic groundwater from karstic origins and inputs from the Ain. From Lyon to the confluence with the Isère, aquatic species that colonize cut-off channels are mainly eutrophic. Downstream from the Isère confluence, the proportion of eutrophic species decreases slightly, and some channels have oligotrophic species. Species richness increases significantly below the confluence with the Drome River with a high proportion of oligotrophic species in cut-off channels. Further downstream, cut-off channels of the Rhône again become highly eutrophic. Some mesotrophic species occur exclusively in cut-off channels upstream from Lyon, such as Hippuris vulgaris, Hottonia palustris, C. platycarpa, and Potamogeton natans. Some species occur both in the upper river and downstream of the Isère confluence (e.g. Groenlandia densa, Sparganium emersum) or the Drôme River (e.g. P. coloratus, Sagittaria sagittifolia, Juncus articulatus). Finally, some species are found only in the eutrophic lower river, (Spirodela polyrhiza, Vallisneria spiralis, Lemna gibba). The main non-native aquatic plant species are Egeria densa, E. canadensis, E. nuttallii, Lagarosiphon major, Ludwigia peploides and L. grandiflora, Myriophyllum aquaticum.
Plants require more than just water and sunlight to grow. They also require many nutrients found in the soil. One of the most important nutrients required for plant growth is nitrogen. Nitrogen is used to build plant proteins and nucleic acids, including DNA.
Nitrogen is found naturally in the atmosphere and in the soil. Even though there is an abundance of nitrogen available, the most common form of nitrogen (N2) cannot be used by plants. Nitrogen can be combined chemically with oxygen or hydrogen to form types of nitrogen compounds that plants can use. These nitrogen compounds can be added to the soil in the form of ammonium (NH4 + ) and nitrate (NO3 - ) fertilizers. Plants grow well when fertilizer containing nitrogen is added to the soil, but this method can be expensive and has to be repeated each time the nitrogen in the soil is used up.
Figure 1. Adding fertilizers containing nitrogen to the soil can help plants grow well.
In this experiment, you will compare plants grown without nitrogen fertilizer to plants grown with nitrogen fertilizer. You will observe the effects of nitrogen on the health of the plants by measuring the increase in biomass (the total mass, or weight, of each plant) during the experiment.