question: how come plants survive if they are submerged in a backyard pond but if a plant is given too much water it can drown?
comment: Different plants like different conditions. They’re not all the same. Some trees only grow on ridge tops while others only grow in bottomlands or riparian zones close to water. Obviously pond plants prefer being in water. You can’t plant a water lily in your yard.
passages: Most plants have the ability to close their stomata at the start of water stress, at least partially, to restrict rates of transpiration. They use signals or hormones sent up from the roots and through the transpiration stream. Since roots are the parts responsible for water searching and uptake, they can detect the condition of dry soil. The signals sent are an early warning system - before the water stress gets too severe, the plant will go into water-economy mode.
   BULLET::::- Drainage: In soils of bad drainage the water delivered through rain or irrigation may pool and stagnate. As a result, prevail anaerobic conditions and plant roots suffocate. Stagnant water also favors plant-attacking water molds. In soils of excess drainage, on the other hand, plants don't get to absorb adequate water and nutrients are washed from the porous medium to end up in groundwater reserves.
   The distinction between aquatic and terrestrial plants is often blurred because many terrestrial plants are able to tolerate periodic submersion and many aquatic species have both submersed and emersed forms. There are relatively few obligate submersed aquatic plants (species that cannot tolerate emersion for even relatively short periods), but some examples include members of Hydrocharitaceae and Cabombaceae, "Ceratophyllum", and "Aldrovanda", and most macroalgae (e.g. "Chara" and "Nitella"). Most aquatic plants can, or prefer to, grow in the emersed form, and most only flower in that form. Many terrestrial plants can tolerate extended periods of inundation, and this is often part of the natural habitat of the plant where flooding is common. These plants (termed helophytes) tolerate extended periods of waterlogging around the roots and even complete submersion under flood waters. Growth rates of helophytes decrease significantly during these periods of complete submersion and if water levels do not recede the plant will ultimately decline and perish.
   Waterlogging reduces the supply of oxygen to the roots and can kill a plant within days. Plants cannot avoid waterlogging, but many species overcome the lack of oxygen in the soil by transporting oxygen to the root from tissues that are not submerged. Species that are tolerant of waterlogging develop specialised roots near the soil surface and aerenchyma to allow the diffusion of oxygen from the shoot to the root. Roots that are not killed outright may also switch to less oxygen-hungry forms of cellular respiration. Species that are frequently submerged have evolved more elaborate mechanisms that maintain root oxygen levels, such as the aerial roots seen in mangrove forests.
   There are many factors which affect water availability, which is the major limiting factor of seed germination, seedling survival, and plant growth. These factors include infrequent raining, intense sunlight and very warm weather leading to faster water evaporation. An extreme environmental pH and high salt content of water also disrupt plants' water uptake.
  
  Section::::Types.
   The principal factor controlling the distribution of aquatic plants is the depth and duration of flooding. However, other factors may also control their distribution, abundance, and growth form, including nutrients, disturbance from waves, grazing, and salinity.
  
  Section::::Evolution.
   BULLET::::- Elodeids: stem plants that complete their entire lifecycle submerged, or with only their flowers above the waterline
  
  BULLET::::- Isoetids: rosette plants that complete their entire lifecycle submerged
  
  BULLET::::- Helophytes: plants rooted in the bottom, but with leaves above the waterline
  
  BULLET::::- Nymphaeids: plants rooted in the bottom, but with leaves floating on the water surface
  
  BULLET::::- Pleuston: vascular plants that float freely in the water
  
  Section::::Functions of macrophytes in aquatic system.
   If the plant shows dehydration tolerance, the environmental factor enters the plant tissues but the tissues survive, by e.g. maintaining turgor and osmotic adjustment.
  
  Section::::Mechanisms of Drought Resistance.:Escape.
  
  Dehydration escape involves e.g. early maturing or seed dormancy, where the plant uses previous optimal conditions to develop vigor.
  
  Dehydration Recovery refers to some plant species being able to recuperate after brief drought periods.
   Most crops require specific soil moisture conditions, and do not grow well in wet, mucky soil. Even in soil that is not mucky the roots of most plants do not grow much deeper than the water table. Early in the growing season when water is in ample supply, plants are small and do not require as much water. During this time, the plants do not need to develop their roots to reach the water. As the plants grow and use more water water becomes more scarce. During this time, the water table begins to fall. Plants then need to develop roots to reach the water. During periods of dryness the water table can fall faster than the rate at which plants grow roots to reach it, which condition can gravely stress the plants.
   "Potamogeton pectinatus" is one of the aquatic plant agents in the model. It is an annual growth plant that absorbs nutrients from the soil and reproduces through root tubers and rhizomes. Reproduction of the plant is not impacted by water flow, but can be influenced by animals, other plants, and humans. The plant can grow up to two meters tall, which is a limiting condition because it can only grow in certain water depths, and most of its biomass is found at the top of the plant in order to capture the most sunlight possible. The second plant agent in the model is "Chara aspera", also a rooted aquatic plant. One major difference in the two plants is that the latter reproduces through the use of very small seeds called oospores and bulbills which are spread via the flow of water. "Chara aspera" only grows up to 20 cm and requires very good light conditions as well as good water quality, all of which are limiting factors on the growth of the plant. "Chara aspera" has a higher growth rate than "Potamogeton pectinatus" but has a much shorter life span. The model also considered environmental and animal agents. Environmental agents considered included water flow, light penetration, and water depth. Flow conditions, although not of high importance to "Potamogeton pectinatus", directly impact the seed dispersal of "Chara aspera". Flow conditions affect the direction as well as the distance the seeds will be distributed. Light penetration strongly influences "Chara aspera" as it requires high water quality. Extinction coefficient (EC) is a measure of light penetration in water. As EC increases, the growth rate of "Chara aspera" decreases. Finally, depth is important to both species of plants. As water depth increases, the light penetration decreases making it difficult for either species to survive beyond certain depths.
   In non-tropical areas, it is easily grown in containers given enough water in a bright sunny location. It readily roots from cuttings.
  
  Section::::Invasiveness.
   However, for many terminally overwatered houseplants, the initial symptoms of waterlogging can resemble those due to drought. This is particularly true for flood-sensitive plants that show drooping of their leaves due to epinasty (rather than wilting).
  
  Section::::Plants.:concentration.
   About 15 million km2 of the land surface is covered by crop-land, and about 16% of this area is equipped for irrigation (Siebert "et al." 2005). Thus, in many parts of the world, including the United States, plants may frequently encounter dehydration stress. Rainfall is very seasonal and periodic drought occurs regularly. The effect of drought is more prominent in sandy soils with low water holding capacity. On such soils some plants may experience dehydration stress after only a few days without water.
   Mesophytes are plants living in lands of temperate zone, which grow in well-watered soil. They can easily compensate the water lost by transpiration through absorbing water from the soil. To prevent excessive transpiration they have developed a waterproof external covering called cuticle.
  
  Section::::In animals.
   These microecosystems with limited water volume are often only of temporary duration and hence colonized by organisms which possess a drought-resistant spore stage in the lifecycle, or by organisms which do not need to live in water continuously. The ecosystem conditions applying at a typical pond edge can be quite different from those further from shore. Extremely space-limited water ecosystems can be found in, for example, the water collected in bromeliad leaf bases and the "pitchers" of "Nepenthes".
  
  Section::::Some examples.:Soil microecosystems.
   Section::::Recovery efforts.
   "Chamaegigas intrepidus" is one of approximately 330 desiccant-tolerant vascular plants, 90% of which are found growing on inselbergs. It is one of the rare desiccant-tolerant vascular plants that is not a fern or monocotyledon. The basal leaves can survive complete drying for 4.5 months, with more than 50% of them reviving after receiving moisture—so the plants simply resume growing once the pools fill again after a dry spell. New floating leaves, which do not survive drying as well as the basal leaves, can reach the water surface as soon as 2–4 days after the pool refills, with flowers appearing as early as 4 days after breaking dormancy.
   The ability of plants to access water depends on the structure of their roots and on the water potential of the root cells. When soil water content is low, plants can alter their water potential to maintain a flow of water into the roots and up to the leaves (Soil plant atmosphere continuum). This remarkable mechanism allows plants to lift water as high as 120 m by harnessing the gradient created by transpiration from the leaves.
   Too much or too little water can damage plants. If there is too little water then tissues will dehydrate and the plant may die. If the soil becomes waterlogged then the soil will become anoxic (low in oxygen), which can kill the roots of the plant.
   BULLET::::- Submerged plants are those that live almost completely under the water, sometimes with leaves or flowers that grow to the surface such as with the water lily. These plants are placed in a pond or container usually below the water surface. Some of these plants are called oxygenators because they create oxygen for the fish that live in a pond. Examples of submerged plants are:
  
  BULLET::::- Water lily (Hardy and Tropical)
  
  BULLET::::- Hornwort ("Ceratophyllum demersum")
   Section::::Nutrient distribution.:Absorption.
  
  Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure. It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is usually due to high temperatures, high humidity, darkness or drought.
  
  Section::::Nutrient distribution.:Conduction.
   Hydrochory is seed dispersal by water. Seeds can disperse by rain or ice or be submerged in water. Seeds dispersed by water need to have the ability to float and resist water damage. They often have hairs to assist with enlargement and floating. More features that cause floating are air space, lightweight tissues and corky tissues. Hydrochory syndromes are most common in aquatic plants.
  
  Section::::Types and functions.:Zoochory.
  
  Zoochory is the dispersal of seeds by animals and can be further divided into three classes.
   The hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Traditional methods favor the use of plastic buckets and large containers with the plant contained in a net pot suspended from the centre of the lid and the roots suspended in the nutrient solution.
   Thompson Reservoir is classified as mesotrophic. There are low densities of A. formosa in the spring and low densities of C. hirundinella and M. granulata in summer. Due to the extreme water fluctuations from reservoir operations, macrophytes are scarce. 
  
  Section::::Recreation.
   Section::::In Hydroponics.:Principles of Operation.
  
  The fundamental principle of hydroponics relies on fertilized and aerated water which provides both nutrition and oxygen to a plant's 
  
  root zone. It often involves relatively sophisticated mechanization processes which can be daunting to casual hobbyists. Nutrient solutions must usually be below the temperature at which pathogen growth can begin, yet not so cool that root activity is suppressed. Active aeration of the fertilizer solution is common, since root systems themselves remove oxygen, creating conditions which also can promote pathogenic bacteria and water-borne molds.
  
presuppositions: All plants can survive in a pond. Plants that survive if submerged in a backyard pond are the same plants that drown when given too much water.
corrections: Only specific plants can thrive in a pond. Plants that survive if submerged in a backyard pond are different from the plants that drown when given too much water.
raw_presuppositions: All plants can survive in a pond. Plants that survive if submerged in a backyard pond are the same plants that drown when given too much water.
raw_corrections: Only specific plants can thrive in a pond. Plants that survive if submerged in a backyard pond are different from the plants that drown when given too much water.