ii Flashcards
biota
all the living organisms in an area
types of biota
plants, animals, bacteria, fungus, etc.
bacteria
single-celled organisms
can be photosynthetic or not photosynthetic
non-photosynthetic bacteria
some feed on dead organic matter, and some feed on living organisms
fungi
are single-celled or multi-celled
none are photosynthetic
some feed on living organisms and on dead organic matter
many species of soil biota …
are decomposers
how much biota is in 1 m^2 [39 in x 39 in] of soil in a forest?
200000 inverterbrate animals [e.g. insects and worms] from 200 species
1 gram [1/28] of soil has how many species of what?
1 million different species of bacteria
soil texture
consists of mineral particles less than 2 mm [1/12 “] in diameter
larger particles such as stones …
are “in” the soil, but are not “the” soil itself just like living organisms, dead organic matter, and water
mineral particles from largest to smallest
sand (.05 - 2 mm) -> silt (.002 - .05 mm) -> clay (<.002 mm)
loam
consists of equal amounts of all three textures (40% sand, 40% sand, 20% clay)
the ____ the texture of the soil, the ____ it’s surface area
finer; greater
cation exchange capacity
the amount of cations that can be absorbed and released by a standard weight of soil
H+ Abundance
H20 + CO2 -> H2CO3 -> HCO3 + H+
relationship between cations and hydrogen ions
cations are released from the soil when hydrogen ions are present in the soil. since hydrogen ions are active, they push the cations off the soil
CEC increases as
the soil texture becomes finer
CEC is highest for
organic soils because they have humus particles
humus particles
tiny clay-sized particles of broken down organic matter which also have negative charges on their surface, so they absorb and release cations
soil water types
pore water, unavailable water, available water
pore water
fills pores between mineral grains but drains away due to gravity within a few days
unavailable water
water that adheres directly to the soil particles - so strongly that it can’t be removed by a plant
available water
water that coheres to unavailable water, and is held loosely enough that plants can remove it and use it
when is available water most abundant
right after rain, but progressively smaller amounts available for up to 2 weeks
usable vs. available water
the plant can use both pore water and available water
pore water is highest …
for sandy soils
unavailable water is highest …
for clay soils
available water is highest for …
a loam texture
clay holds _____ more tightly than it holds ____
water molecules; cations
a loam texture has the highest ___ ___ and second highest ___
available water; CEC
best soil for plant growth
loam texture
nutrients
the chemical elements needed for plants to complete their life cycle
macronutrients
are needed in large amounts as each makes up more than .1% of a plant’s dry weight
top 9 macronutrients from largest to smallest
carbon, oxygen, hydrogen, nitrogen, potassium, calcium, magnesium, phosphorous, sulfur
micronutrients
essential but each is less than .1% of a plant’s dry weight
most abundant macronutrient
carbon
is the only macronutrient absorbed mainly by the leaves
copper
can be absorbed in small amounts from rain or dust that falls on the leaf
transport
nutrients absorbed by leaves travel in the phloem
veins in a leaf
contain xylem and phloem
xylem conducts water from the branch out to the edge of the leaf
phloem conducts carbohydrates from the leaf towards the branch
most nutrients enter plants by
first dissolving into soil water and then entering roots
two paths of entry
between cells (apoplastic) or within cells (symplastic)
Casparian Strip
a waxy, water repellent layer near the outside of the roots
where does nutrients go after entry
casparian strip
relationships between amount of each plant nutrient and plant growth rates
deficiency range, critical range, luxury range, toxicity range
deficiency range
growth changes rapidly with small changes in that nutrient
critical range
small growth responses to large changes in that nutrient
luxury range
plant growth doesn’t respond to changed nutrient levels
toxicity range
excessive nutrients reduce growth rates
at low abundances of a nutrient …
it will be taken up rapidly by the plant using selective methods at the casparian strip
stoichiometry
the ratio of pairs of nutrients for plants
optimal or sub-optimal
sub-optimal ratios
the plant will change its growth patterns to try an change the ratio
ex: C:N
ratio of C:N too high
the plant will produce many roots to absorb N, at the expense of shoots from which it would absorb C through photosynthesis
ratio of C:N too low
N is too abundant
the plants will grow few roots making it susceptible to drought
nitrogen in plants and soils
plants need nitrogen to create chlorophyll, DNA, and proteins
the 4th most abundant element by weight
usually the most limiting nutrient to growth
organic matter and inorganic compounds …
both contain nitrogen that can be used by plants
atmosphere is ___ elemental N2, but …
78%; plants cannot biologically use it
symbiosis
when 2 species live close to each other and help each other
occurs between many nitrogen-fixing bacteria and plants
2 major forms of symbiosis between bacteria and plants
- bacteria in root nodules on plants, especially legumes and alder trees
- free-living bacteria can form loose associations with plants whose roots leak nutrients
nitrogen deficiency
leaves turn pale green and then yellow due to chlorosis (chlorophyll death), because they do not have enough Nitrogen to make the chlorophyll
stunts plants
phosphorous in plants
8th most abundant nutrients in plants by weight
2nd most likely nutrient whose limited availability is causing limitations in plant growth
phosphorous in soils
usually found in forms that plants cannot use and thus accumulate in the soil (except old tropical soils)
biological phosphorous absorption
mycorrhizae are fungi that are symbiotic with plant roots. all coniferous plants and 80% of flowering plants have a symbiotic relationship with a species of MR
MR symbioses
all involve the strands of fungus extending from the soil to the root
MR relationship with plants
provide many nutrients to the plant root, especially important for phosphorous
excrete an enzyme that releases phosphorous from strong chemical bonds in the soils and then into the plant
MR relationship with water in plants
MR strands can grow 4 in. in one day (roots only 1 in/day)
MR provides water to plants, especially during droughts, speeding up plant recovery
phosphorous deficiency
is only noticeable when very severe
leaves (esp in veins) turn purple
plants get stunted
WWW
the wood-wide web reflects the connections between trees
WWW fungus
connects trees of the same and different species by sharing phosphorous and water
WWW bacteria
connects trees of the same and different species by sharing nitrogen
mother trees
old trees that have been in the forest for a long time and thus have many fungal and bacterial connections
connect many living trees
helps new trees become established by having fungal and bacterial partners that then reach and help the new tree establish
