Succession Flashcards
Dirt
No vegetation, no structure, compacts easily, inorganic fertilizer required to grow plants
F:B ratio:
Low to no bacteria, < 45 μg/g; Low to no fungi, < 5 μg/g; F:B < 0.01
Nutient Cycling:
No Predators; no nutrient cycling, plants lack soluble nutrients; inorganic fertilizer used to supply soluble nutrients, but any excess is rapidly leached
Bare Soil
No vegetation, poor soil structure, compacts easily, loss of nutrients through anaerobic conditions
F:B ratio:
Bacteria > 450 μg/g soil
Fungi < 23 μg/g, typically mostly disease causing fungi
F:B ≈ 0.05
Nutrient Cycling:
Protozoa: Ciliates indicate anaerobic conditions
Nematodes: Rare
Plants suffer lack of available nutrients: strictly nitrate
Weeds
r-selected, little effort put into building soil, limited root depth, uses strictly nitrate, compaction is common.
Towards the end of this stage of succession, tap root plants appear.
F:B ratio:
Bacteria > 450 μg/g soil
Fungi < 45 μg/g, typically mostly disease fungi
F:B ≈ 0.1
Nutrient Cycling:
Protozoa: Ciliates often present, nutrient pulses typical
Nematodes: Rare, bacterial-feeders
Functioning food web is barely present, soluble nutrients pulse high, low, high, low
Early Successional
Wetlands, Brassicas, e.g. Cole, Kale, Mustards.
Limited root depth, structure poor, strong tap rooted plants provide foods to break compaction
F:B ratio:
Bacteria > 135 - 270 μg/g soil Actinobacteria very important to protect roots from mycorrhizal colonization
Fungi 32 - 90 μg/g, but may be mostly disease causing fungi; typically not mycorrhizal
F:B ≈ 0.3
Nutrient Cycling:
Protozoa: Flagellates and amoebae ≈ 10,000 /g soil so nutrient cycling functions normally
Nematodes: Bacterial feeders present; nitrate high but measurable ammonium usually present
Vegetables & Early Successional Grasses
Bromus, Bermuda grasses, Root- crops, lettuce, greens, etc.
Need both nitrate and ammonium, compaction not well tolerated
F:B ratio:
Bacteria 135 - 450 μg/g soil
Fungi 68 - 225 μg/g soil, and for most species, mycorrhizal colonization (VAM) is required
F:B ≈ 0.5
Nutrient Cycling:
Protozoa: Constant number of flagellates and amoebae 10,000 - 50,000 /g soil in growing season;
Nematodes: Bacterial feeders, fungal feeders and predatory nematodes present
Mid-Successional
Turf such as ryegrass; vegetables, annual crops and flowers.
Use predominantly nitrate but need ammonium.
F:B ratio:
Bacteria 135 - 1350 μg/g soil
Fungi 101 - 1012 μg/g, mycorrhizal colonization (VAM) required
F:B ≈ 0.75
Nutrient Cycling:
Protozoa: Constant number of flagellates and amoebae > 50,000 /g soil in growing season
Nematodes: Bacterial feeders, fungal feeders and predatory nematodes present
Productive pastures, row crops
Lawns with no weeds, requiring no fertilizers; Corn, wheat, barley, etc.
Need equal balance of nitrate and ammonium.
F:B ratio:
Bacteria 135 - 1350 μg/g soil
Fungi 135 - 1350 μg/g soil, mycorrhizal colonization (VAM) required
F:B ≈ 1.0
The higher the balanced biomass of both F and B, higher yields, deeper roots grow, higher retention of nutrients, higher organic matter sequestered
Nutrient Cycling:
Protozoa: Constant number of flagellates and amoebae > 50,000 /g soil in growing season;
Nematodes: Bacterial feeders, fungal feeders and predatory nematodes necessary
Shrubs, bushes, vines
Require more ammonium than nitrate; therefore fungal activity must be greater than bacterial activity
F:B ratio:
Bacteria 135 - 1350 μg/g soil
Fungi 270 - 6750 μg/g soil, mycorrhizal colonization (VAM/Ecto/Ericoid) required
F:B ≈ 2.0 - 5.0
Nutrient Cycling:
Protozoa: Constant number of flagellates and amoebae > 50,000 /g soil in growing season
Nematodes: Fungal and predatory nematodes, along with microarthropods, should start to rival bacterial feeder numbers
Deciduous trees
Require mostly ammonium; nitrate can be harmful and encourages disease fungi
F:B ratio:
Bacteria 135 - 900 μg/g soil
Fungi 675 - 9000 μg/g soil, mycorrhizal colonization (VAM) required
F:B ≈ 5 - 10
Nutrient Cycling:
Protozoa: Constant #s of flagellates and amoebae > 10,000/g soil in growing season
Nematodes: Fungal and predatory nematodes should equal bacterial feeder numbers, unless their function is replaced by microarthropods
Conifer/Evergreen trees
Just before the growing season begins, most of the weight of a gram of soil will be fungal; Require strictly ammonium; nitrate will harm the trees
F:B ratio:
Bacteria 135 - 450+ μg/g soil
Fungi 1350 - 45000+ μg/g, mycorrhizal colonization (Ecto) required
F:B > 10
Fungal biomass seasonally consumed by predators to provide the nutrients plants require, but fungal re-growth occurs in the dormant season
Nutrient Cycling:
Protozoa: Not as important in a fungal dominated system; > 10,000 /g soil in growing season.
Nematodes: Fungal and predatory nematodes should exceed bacterial feeder numbers unless their function is replaced by microarthropods
