PLANT ADAPTATIONS TO THE ENVIRONMENT II:
THERMAL, MOISTURE, AND NUTRIENT ENVIRONMENTS.
Chapter 7
PLANTS AND THE THERMAL ENVIRONMENT
Plants are constantly absorbing short-wave and long-wave radiation from the surrounding environment.
THERMAL ENERGY BALANCE
Plants maintain a thermal balance through evaporation and convection.
Leaf size, shape and the stomatal opening/closing control influence these processes.
The energy absorbed by plants per unit of time is referred to as the plant’s net radiation balance, Rn.
Plants absorb and reflect solar radiation, and absorb short-wave radiation and emit long-wave radiation.
The difference between the two is the net radiation balance.
Rn = M + S + (C + λE)
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Less than 5% of the absorbed radiation is used in photosynthesis and stored in chemical bonds,
M.
Energy is also used in heating the plant tissues and raising the temperature of the boundary
layer, S.
Convection (C) and evaporation (E) dissipate energy into the environment; evaporation includes
transpiration and direct evaporation.
λ = latent heat of vaporization; energy required to transform one unit of liquid water to vapor.
Transpiration and evaporation occur in plants: evapotranspiration.
Evaporation occurs from the surface of leaves.
Heat is dissipated by evaporation and transpiration.
Air temperature directly affects evaporation and transpiration.
Transpiration is the result of stomatal conductance and vapor pressure deficit.
Convection depends on the temperature difference between the plant and the surrounding air.
Factors influencing heat loss by convection:
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Difference between leaf and air temperatures.
Conductance of the boundary layer.
Wind removes the warm air of the boundary layer and increases the difference between the leaf and the
atmosphere; the boundary layer conductance increases with the movement of air.
The size and shape of the leaf affects the conductance of the boundary layer.
The ratio of surface to volume affects heat convection.
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Small, lobed leaves are more effective at heat exchange than are larger, less lobed leaves.
Plants must replace the water lost in evapotranspiration.
Air temperature and wind velocity impose limits on the ability of plants to dissipate excess heat energy.
Water lost must be replaced; therefore, precipitation patterns have a direct effect on the plant’s energy
balance.
THERMAL EFFECTS ON PHOTOSYNTHESIS AND RESPIRATION
Photosynthesis and photorespiration are sensitive to temperature changes, and respond directly to
variations in temperature.
High temperatures favor oxygenation over carboxylation.
Carboxylation occurs during the dark phase, Calvin cycle, of photosynthesis and is the direct result of the
activity of rubisco.
Rubisco activase is an enzyme required to change rubisco from the inactive to the active form in order
to carry out carboxylation.
Rubisco activity is sensitive to temperature:
“The temperature-dependent association of rubisco activase with the thylakoid membrane was due to a
conformational change in the rubisco activase itself, not to heat-induced alterations in the thylakoid
membrane……During a sudden and unexpected exposure of plants to heat stress, rubisco activase is
likely to manifest a second role as a chaperone in association with thylakoid-bound ribosomes, possibly
protecting, as a first aid, the thylakoid associated protein synthesis machinery against heat inactivation.”
Rubisco activase: an enzyme with a temperature-dependent dual function? Rokka A, Zhang L, Aro EM. Plant J. 2001
Feb;25(4):463-71. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11260502&dopt=Abstract
The net photosynthetic rate is the difference between the rate of carbon uptake in photosynthesis and
the rate of carbon lost in respiration.
The net photosynthetic rate varies in plants depending on the environment in which the plant lives.
Plants living in cooler climate have a lower maximum (T max) and minimum temperature (Tmim) in which
photosynthesis approaches zero. Their temperature optimum is lower, T opt
Biochemical and physiological adaptations allow the plant to shift its optimum uptake of carbon through
photosynthesis toward the prevailing temperature of the environment. This process can also be observed
during the seasonal shifts of temperature: acclimation.
PEP carboxylase is found in CAM and C4 plants, and is absent in C3 plants.
C3 and C4 show consistent differences in their photosynthetic response to temperature.
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There is no photorespiration during the initial carbon fixation by PEP carboxylase in C4 plants.
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The Topt of PEP carboxylase is higher than rubisco and high temperatures have little effect on C 4
plants.
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The Topt for the C3 pathway approaches that of rubisco. The T opt for C4 corresponds to the range
of temperatures in which the activity of both enzymes, rubisco and PEP carboxylase, is relatively
high.
Additional information about the influence of temperature in the activity of rubisco:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11260502&dopt=Ab
stract
http://www.pnas.org/cgi/content/full/97/24/12937
TEMPERATURE AND PLANT GROWTH
Plants require certain amount of photosynthetic activity accumulated over time to reach certain point of
development: maximum growth, flowering, ripening of seeds, etc.
Plants require a number of degree-days of growth (photosynthetic activity) to reach maturity or bloom.
The rates of photosynthesis vary with the time of the day and the season. It stops above and below
certain temperatures, Tmax and Tmin. The optimum temperature occurs between these two values.
The index of degree-days is used to relate growth to variations of temperature in a single season.
The index of degree-days is the sum of the departures in temperatures above some minimum or base
temperature.
The minimum temperature is selected as the temperature at which photosynthesis approaches zero.
The mean daily temperature reflects growth and carbon accumulation.
Taken from http://ohioline.osu.edu/agf-fact/0101.html
Ohio University Extension, Department of Horticulture and Crop Science .
Formula: GDD = (T High plus T Low) divided by 2, minus 50
The following adjustments are necessary: 1) temperatures below 50 degrees F are set at 50
degrees F, and 2) temperatures above 86 degrees F are set at 86 degrees F. This method of
calculating GDD is often referred to as the (86,50) system.
Examples of GDD Calculations:
For High = 80 degrees F, Low = 60 degrees F:
GDD = 80 plus 60 divided by 2 minus 50 = 20;
For High = 60 degrees F, Low = 40 degrees F:
GDD = 60 plus 50(40) divided by 2 minus 50 = 5;
For High = 90 degrees F, Low = 70 degrees F:
GDD = 86(90) plus 70 divided by 2 minus 50 =
28
Growing Degree Days or heat units are calculated for each day starting the day after planting.
Check this site for a good explanation of “degree-days”:
http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html
EXTREME TEMPERATURES AND PLANT SURVIVAL
Freezing temperatures can result in the formation of intra- and extracellular ice as well as phase change
in membrane lipids.
Factors associated with the ability of cells to withstand freezing temperatures:
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Increased solute concentrations.
Unsaturated lipids (soluble fats) increase.
Lipid concentration increases.
Amino acids are removed from proteins: depolimerization.
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Cell membrane becomes more permeable.
Small cell size
Abscisic acid.
Abscisic acid accumulates in the leaves with dehydration. Through its effects on second messengers
such calcium ions, potassium ion channels open in the guard cells causing a massive lost of potassium.
This loss of ions from the guard cells, causes water to leave the cells and the subsequent loss of turgor of
the guard cells closes the stomata.
Critical minimum temperature: 0° to 10°C and -15° to -40°C.
In region where the temperature falls between -15° to -40°C, the dominant vegetation consists of broadleaf deciduous plants.
These plants lower their freezing point by supercooling, the lowering of the freezing point by increasing
solute concentration.
Cells can lower the freezing point by no more than 3°C by increasing solute concentrations.
30 genes were found in Larix kaempferi that increase the supercooling capability to -60ºC. See abstract at
http://jxb.oxfordjournals.org/content/58/13/3731.abstract?sid=61b647e7-b477-4b7
Water in the cell wall and middle lamella freezes first with dropping temperature and releases heat (heat
of fusion or specific heat of melting), which is absorbed by the adjacent cells and helps them to remain
liquid. Then, water moves out of the cells attracted to the ice crystals.
Tolerance to freezing is not uniformly distributed through a plant.
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Roots, bulbs and rhizomes are the most sensitive to freezing (-10 to -30°C).
Terminal buds are less resistant than lateral buds.
Woody stems are more resistant than buds and leaves.
Changes in the ultrastructure of the cells have been observed: multiple small vacuoles, increase in the
number of vesicles, etc. For more details see: http://aob.oxfordjournals.org/cgi/content/full/90/5/637
Annals of Botany 90: 637-645, 2002, Marzanna Stefanowska, Mieczys aw Kura and Alina Kacperska
Hairs insulate by trapping air and heat.
The growth habit also helps in surviving freezing temperatures: the interior temperature of cushion and
rosette plants may be 20°C higher than the surrounding air.
A high temperature of 45°C disrupts metabolic processes.
Heat shock proteins are involved but their role is not well understood.
Cacti can maintain protein synthesis as fast as proteins breakdown and, in this way, avoid ammonia
poisoning.
Morphological and nactic movements allow plants to adjust to high temperatures, e.g. folding of leaves,
spines, narrow leaves, photosynthesis carried out in the stem, changing the orientation of leaves to a
parallel position to sun rays.
PROCESSES OTHER THAN SURVIVAL AND GROWTH
Temperature affects germination, reproduction, flower formation, flower unfolding, and ripening of fruits.
Temperatures between –3 and +13°C are needed by certain annuals and biennials to flower normally in
the spring.
PLANT RESPONSE TO WATER
Open stomata allow CO2 into the leaves for photosynthesis, but also allow the water to escape,
transpiration.
WATER UPTAKE AND THE SOIL-PLANT-ATMOSPHERE CONTINUUM
A water potential gradient exists between the soil, and the tissues of the roots, the stem and branches,
the leaves, and the atmosphere.
This water potential gradient is responsible for the movement of water from the soil through the plant into
the atmosphere.
The units used to describe the water potential are megapascals, MPas.
Water flows from areas of high water potential (ψ) to areas of low water potential. This is called osmotic
potential.
The soil has the highest water potential and the atmosphere the lowest.
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Ψatmosphere < ψleaf < ψstem < ψroots < ψsoil
The movement of water across a membrane is called osmosis.
The osmotic potential of the cells (concentration of solutes in the cytoplasm), the matric potential or
tendency of water molecules to adhere to soil particles, and the pull of gravity or gravitational potential, all
influence the total water potential in the body of the plant.
As plants lose water through transpiration, the solute in the cells becomes more concentrated, the water
pressure drops in the cells, and water moves in from the areas of higher concentration.
As water moves from the soil into the roots, the water potential of the soil drops and becomes more
negative.
The tendency of water to adhere to surfaces is called matric potential.
As the water content of the soil drops, the remaining water adheres more tightly to soil particles and the
matric potential drops.
Cohesion between the water molecules also plays a role increasing surface tension in the soil pores
between the clay particles and creating menisci (sing. meniscus). Adhesion to clay particles and the
formation of menisci can increase the matric potential significantly and make it unavailable to plant roots.
The texture of the soil affects the matric potential. Clay provides more surface than do sand and
maintains a more negative matric potential.
As the soil water potential drops, it becomes more difficult for the plant to maintain its water potential and
eventually it cannot absorb more water.
At this point, the stomata close to prevent the loss of water through transpiration but this also prevents the
entry of CO2 into the leaves and disrupts photosynthesis.
The value of the leaf water potential at which the stomata close varies with the species, and depends on
the biochemistry, physiology and morphology of the species.
Water must overcome the pull of gravity in order to move up the vascular tissue of the plant.
The gravitational potential is a factor of the height of the plant from a reference point. It is positive above
the reference point and negative below. It is important in the movement of water in tall trees.
The gravitational potential, ψg, increases by 0.01 MPa m-1 above the ground.
RESPONSE TO SHORT-TERM MOISTURE STRESS
The closing of the stomata prevents the loss of heat by transpiration but the plant continues to intercept
radiation and its internal temperature rises.
An increase in internal temperature results in heat stress that interferes with protein synthesis and if
prolonged, with chlorophyll synthesis.
The plant may respond by curling its leaves, wilting, and dropping the leaves prematurely. The oldest
leaves are shed first. If the drought continues, the tender twigs and branches die back.
Some plants under water-stress reduce their osmotic potential by accumulating ions of Ca 2+, Mg2+, K+ and
Na2+, and amino acids, sugars and sugar alcohols. The lower water potential of the leaves maintains the
potential gradient from plant to soil.
Conifers and evergreens may experience a browning and a dieback during the winter months due to
water stress. If the temperature is high enough for water in the vascular tissue to liquefy, the trees lose
their water by transpiration but the water cannot be replaced because the ground is frozen. Dehydration
of the foliage occurs.
PLANT RESPONSES TO LONG-TERM VARIATIONS IN WATER AVAILABILITY
Individual plants growing under dry conditions have thicker leaves than members of the same species
growing under moist conditions.
The leaves are thicker because more layers of mesophyll are produced. There is more mesophyll per unit
of area.
More mesophyll layers increase photosynthesis but reduce the surface area that absorbs radiation and
loses water through transpiration.
Root production increases under dry conditions by shifting the allocation of carbon from leaves to roots.
Individuals growing under contrasting environmental condition show responses that compensate for the
shortage of an essential resource.
INTERPSECIFIC VARIATION IN ADAPTATIONS TO MESIC AND XERIC ENVIRONMENTS.
Xerophytes have greater water use efficiency than mesophytes, that is, a greater rate of carbon uptake
per unit of water transpired.
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Water use efficiency: rate of carbon uptake per unit of water transpired.
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Photosynthesis/transpiration
C4 have higher water use efficiency than C3 plants.
C4 plants maintain a very low concentration of CO2 within the mesophyll of the cells by having a great rate
of carboxylation. This causes a steep gradient of CO2 concentration between the inside of the leaf and the
outside air.
The steeper CO2 gradient allows C4 to maintain a higher rate of photosynthesis than C3 plants for a given
stomatal conductance.
The ratio of root mass (g) to leaf is (cm 2) increase with decreasing water availability.
Species adapted to high and low resource availability show responses that compensate for the shortage
of an essential resource:
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Under xeric condition, there is a lower stomatal conductance and lower rate of net photosynthesis
than those species living in mesic environments.
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Lower stomatal conductance, however, results in greater water use efficiency.
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Lower allocation of carbon to production of leaves results in greater root production that increases
the plant’s access to soil water.
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Reduced leaf surface area and reduced photosynthesis results in less carbon uptake and
reduced growth.
There is a trade off between higher rates of photosynthesis and growth when water is available and
survival, growth and reproduction when water is consistently in short supply.
LINK BETWEEN PLANT WATER AND ENERGY BALANCE
Plants dissipate heat through the loss of water by transpiration.
If the water potential in the soil declines, the ability to absorb water also declines.
Under mesic conditions, transpiration is the preferred means for heat dissipation.
Plants also dissipate heat by convection.
In xeric environments, plants dissipate most its heat by convection.
Leaf size decreases gradually as conditions change from mesic to xeric.
PLANTS RESPONSE TO FLOODING
Too much water around the roots causes the death of root tips due to lack of oxygen.
Root death follows due to poor absorption. Detritus is added to the vascular tissue and the xylem clogs.
High water table causes plants to develop horizontal root systems that grow along the oxygenated soil
zone.
PLANT ADAPTATIONS TO FLOODING
Aerenchyma is a specialized tissue that contains air spaces that facilitate gas exchange and transport of
air from shoots to roots.
The porosity of plants adapted to flooding could be as great as 60%. Plants living in mesic or xeric
environments usually have a porosity of 2-7% space by volume.
Pneumatophores are adaptations to permanently flooded environments. They probably help in providing
oxygen to roots.
Aerenchyma formation: Without oxygen...
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Roots shift for aerobic to anaerobic respiration.
Uptake of ions is inhibited
The concentration oxygen, potassium, nitrogen, and phosphorus decreases.
Ethylene is produced and accumulates.
Ethylene is insoluble and does not diffuse out of the roots and oxygen uptake is prevented.
Ethylene causes cells next to the cortex to break and separate to form interconnected gasfilled chambers, aerenchyma tissue.
Stem and lenticel hypertrophy
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Hypertrophy is the enlargement of an organ without an increase in the number of constituent
cells. An example of this is buttressing or butt swell which is an increase in the diameter at
the base of the stem.
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The role of this seems to be to increase air space which allows for increased movement of
gases.
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Besides that, the wide base provides extra support for shallow rooted structures on a soggy
substrate.
PLANT ADAPTATIONS TO SALINITY
Salts originate from the weathering of rocks, irrigation and floods, human and animal additions and
fertilizers.
As salinity increases, plants have more difficulty in extracting water from the soil.
In salty environments either soil or water, the water potential is lower than that of the cells or water tends
to leave the cells. Eventually the cells dehydrate and plasmolyze.
High concentration of organic ions may be toxic, e.g. high Al3+ is suspected to interfere with Mg2+ uptake.
“Salt toxicity comprises osmotic and ionic components both of which can severely affect root and shoot growth.
Uptake of Na+ across the plasma membrane is very fast resulting in physiological effects on extracellular as well as
intracellular sites. Sodium reduces binding of Ca++ to the plasma membrane, inhibits influx while increasing efflux of
Ca++, and depletes the internal stores of Ca++ from endomembranes. These changes in the cell Ca++ homeostasis are
suggested here to be the primary responses to salt stress that are perceived by root cells. Salt would almost instantly
reduce the amount of Ca++ being transferred to the leaf cells, with Ca++ activity dropping and Na+ activity rising in the
apoplasm of leaf cells.”
Plant, Cell and Environment (1992) 15, 625-632. The role of calcium in salt toxicity. Z. RENGEL. Department of
Plant Science, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, SA 5064,Australia.
http://www.blackwell-synergy.com/doi/pdf/10.1111/j.13653040.1992.tb01004.x#search=%22salt%20toxicity%20plants%22
Halophytes are plants adapted to salty environments.
Soils with more than 0.2% salt content are considered salty. These soils are common in desert regions.
1. The endodermis is the first effective barrier to too much salt in the environments of halophytes. Their
cortex contains a large amount of salt but their leaves have much less salt.
2. Some plants have specialized organs to dispose of excess salt. These plants do not have very
effective barrier to salt absorption and the excess salt must be eliminated by other means.
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Salt-excreting glands selectively remove slat from the vascular tissue of the leaves.
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Other plants accumulate salt in the leaf tissues and then shed the leaves.
A few halophytes are obligate and require salt in their environment to grow best, e.g. mangroves grow
best in low salinity; Salicornia grows best in moderate salinity and growth decreases in low and high
salinity.
Some non-halophytes are resistant to salt spray but others are particularly sensitive.
Fleshy leaves are often found in halophytes: storage of water, e. g. Salicornia or pickelweed.
Additional information: http://www.shef.ac.uk/aps/mbiolsci/jeni/dissertation.pdf
http://www.botgard.ucla.edu/html/botanytextbooks/lifeforms/halophytes/fulltextonly.html
PLANTS AND NUTRIENTS
All plants require at least 16 nutrients for growth. Some plants require additional elements.
Macronutrients are those elements that are needed in large amounts.
There are 9 macronutrients: C, H, O, K, P, S, N, Ca, and Mg.
C, H, and O form the bulk of the body of the plant and they are derived mostly from H 2O and CO2.
Nutrients are released in to the soil by weathering processes and absorbed by plant roots and
incorporated into their tissues.
There is a nutrient cycle from the soil to the plant and back to the soil.
NUTRIENT UPTAKE AND PLANT PROCESSES
Availability of nutrients and demand affects the nutrient uptake by plants.
Nutrient uptake is mediated by enzymes.
As the concentration of nutrients increase, the absorption rate increases. Eventually the plant reaches a
maximum uptake rate and any further increase in concentration does not affect the uptake rate.
The Michaelis-Menten equation relates these to factors:
V = (Vmax X Cext)/Km + Cext)
V = rate of nutrient uptake
Vmax = saturation uptake rate; all enzyme molecules are bound to substrate.
Cext = external concentration
Km = value of Cext at which V is half of Vmax; 50% of the active sites are bound to substrate.
Nutrients are the substrate. At low concentrations of nutrients, the enzyme exists in an equilibrium
between both the free form of the enzyme and the enzyme–substrate complex; the nutrient substrate is
the limiting factor; increasing nutrient concentration also increases enzyme substrate complex at the
expense of the free enzyme, shifting the binding equilibrium to the right. Since the rate of the reaction
depends on the concentration enzyme-substrate complex, the rate is sensitive to small changes in
nutrient concentration. However, at very high nutrient concentration, the enzyme is entirely saturated with
substrate (nutrient), and exists only in the enzyme-substrate complex form. Under these conditions, the
rate is insensitive to small changes in nutrient concentration.
The nutrient concentrations of plant tissues have a direct relationship to key processes related to plant
growth, survival and reproduction.
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Example: over 50% of the total nitrogen in leaf tissues affects photosynthesis, including the
synthesis of rubisco and chlorophyll.
PLANT ADAPTATIONS TO VARIATIONS IN NUTRIENT AVAILABILITY
1. Root growth versus shoot growth
There is an increase allocation of carbon to root production with declining nutrient availability.
The allocation of carbon to roots varies between species living in nutrient rich or nutrient poor habitats.
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Species living in nutrient rich habitats continue to increase its growth rate as nutrient availability
increases.
Species living in nutrient poor habitats declines after a short increase in growth as the nutrient
concentration increases.
Species living in a moderated nutrient environment increase its growth up to a point and reaches
a plateau.
Growth response was measured as the accumulation of dry weight over the period of the
experiment.
2. Leaf longevity
Experiments have shown that species with short-lived leaves tend to have higher leaf nitrogen
concentrations than those species having longer-lived leaves.
Species with short-lived leaves tend to have a higher rate of photosynthesis than those with longer-lived
leaves: an inverse relationship between leaf life span and photosynthetic rate.
There is a cost in producing a leaf in carbon and essential nutrients.
Long-lived leaves are found in nutrient poor habitats, so when a leaf is produced it lasts long because
there is slow nutrient uptake due to the low availability of nutrients. If leaves are shed often in a low
nutrient environment, the plant will lose more nutrients than it can take from the soil resulting in a net loss
and eventually in death.
3. Influence on nutrient availability
Roots take up nutrients in soil solution as water is absorbed.
Active transport of nutrient also occurs.
As nutrients are taken from the soil, a zone of nutrient depletion is formed around the roots. Nutrients flow
into this zone of nutrient depletion from the surrounding areas as a result of the diffusion gradient
established by the root uptake.
As leaves become old, senescent, nutrients are removed and transported to perennial part of the plant to
be reused. This process is called nutrient retranslocation.
Mutualistic relationships between plants and mycorrhizae and nitrogen-fixing bacteria increase nutrient
availability to plants.
Rhizobium bacteria are the nitrogen-fixing bacteria associated with the roots of plants. Rhizobium
depends on the carbon provided by the plant as a source of energy, and in turn they provide the plant
with nitrogen.
Cyanobacteria, blue-green algae, are the nitrogen-fixing organisms found in aquatic environments.
These mutualistic associations are most beneficial in environments with low-nutrient availability. In
environment with high nutrient availability it represents a cost since the plant must provide photosynthates
to support the bacteria and mycorrhizal fungi with little benefit.
CALCICOLES AND CALCIFUGES
Soil acidity affect nutrient uptake because acidity affects the solubility of minerals.
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Calcicole plants are those that prefer a basic or alkaline soil; soils rich in calcium slats.
Calcifuge plants are those that prefer an acid soil. Calcifuge means lime-hating; low in calcium
salts.
Neutrophilus plants are those that tolerate either condition.
Low pH is associated to calcium deficiency.
Highly acidic soils contain high amounts of aluminum and iron, which are toxic to many plants.
Free aluminum accumulates on the surface of the root and in the root cortex. it interacts with phosphorus
to form highly insoluble compounds.
PLANTS OF SERPENTINE AND TOXIC SOILS.
Serpentine is a magnesium-iron silicate, (Mg, Fe)2SiO4.
 It also contains Ca, Al, Na and Ti.
 It may contain chromite, FeCr2O4 and garnierite, (Mg, Ni)SiO3 • nH2O
 Si, Mg and Fe are the major constituents; Al is low.
 Concentration of Ca and heavy metals is low but plays an important role in the soil.
Heavy metals such as iron, nickel, chromium, cesium, zinc and cobalt are toxic to plants, causing
chlorosis and stunted growth.
They interfere with nutrient uptake and root growth and penetration.
High concentrations of heavy metals (Ni, Cr, Co), and Mg, a low Ca/Mg ratio and low fertility characterize
serpentine soils; they are low in Ca, P, Na, and Al.
Serpentine soils contain a flora tolerant of these conditions.
"Plants can be strikingly different on serpentine soils for several reasons. Minerals that contain high
levels of nickel and chromium are relatively common in serpentine soils and can cause toxicity in plants.
Although some serpentine soils can be deep, most are shallow, restricting water holding capacity and
rooting depths. Additionally, serpentine soils have nutrient deficiencies and imbalances. Important
nutrients like potassium, phosphorous, nitrogen, and molybdenum have been found to be in very low
amounts in most serpentine soils. Overall, the most consistent restriction for plant growth appears to be
the extraordinary low level of calcium compared to magnesium. Although both are necessary
macronutrients—and plants can be selective in absorption of specific minerals—calcium and magnesium
in plant available forms are similar chemically and can “compete” for adsorption. Calcium deficiencies
result. Some serpentine endemics have adapted by having an ability to accumulate calcium and exclude
excess magnesium. Others isolate and store toxic heavy metals." Frank Rauchschwalbe, 4/30/04.
http://w.w.w.ucce.ucdavis.edu/counties/cetuolumne/
Serpentine soils have a high proportion of endemic and ecotype species.
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Endemics are species restricted to a particular habitat or geographical region.
Ecotypes are ecological races well adapted to a local set of conditions
These types tolerate Ni and Cr in their tissues at levels highly toxic to other plants.
Some plants have developed mechanisms that exclude heavy metals from the plant.
A few species grow only in the presence of certain heavy metals and are indicators of the presence of
those metals in the soil.
The selective influence of heavy metals...
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Favors tolerant seedlings from the surrounding area.
Continue selection against susceptible genotypes despite gene flow from the surrounding
population.
Selection for the ability to survive in physically harsh, largely xeric, nutrient-poor environment.