Innumerable types of ecoystems exist, with the composition and dynamics of each particular ecosystem type depending on climate, soils, successional history, fire, human activity, and many other factors. Just as soils influence the ecosystems they are part of, so do various factors in those ecosystems influence the properties and development of the soils contained therein.
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| Wetland north of Sutter Buttes, Sacramento Valley, CA, USA. | Meadow outside of Zion National Park, UT, USA | Montane meadow, central Sierra Nevada mountains, CA, USA, at an elevation of about 2200 m |
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| Open chapparal community, Santa Cruz Island, CA, USA. | Fir and canyon maple, small canyon, Zion National Park, UT, USA. | Grass-oak savanna, Anoka sand plain, MN, USA. |
quantity - amount deposited over a period of time
quality
- chemistry - types of compounds present: lignin, protein, cellulose, etc.
- biodegradability - C:N ratios, types of constituents present
where added - soil surface, uppermost few inches, throughout the solum
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| Soil formed under prairie vegetation | Soil formed under mixed coniferous/deciduous forest vegetation |
seasonal distribution of additions - continuous, annual, longer cycles
effects of organic materials (sloughed root materials, excreted organic acids) released in the rhizosphere
- effects on microbes
- degradation of minerals
- pH effects
Throughfall Stemflow Throughfall Stemflow Throughfall Stemflow mm mm g OC m-2 yr-1 g OC m-2 yr-1 µg Hg m-2 yr-1 µg Hg m-2 yr-1 Open Air Precip 677 -- 1.21 -- 5.70 -- Black Spruce 604 0.5 8.39 0.08 17.96 0.05 Aspen 572 16.3 6.81 0.81 7.63 0.83 Balsam Fir 575 14.0 14.01 0.53 17.57 0.98
Organisms involved
Ecological distribution: see table 1.
Ecosystem type Fungi Bacteria Microfauna (kg / ha) (kg / ha) (kg / ha) Tundra 20 - 80 3 - 9 8 - 36 Desert 135 4 7 Grassland 4000 3000 226 Temperate deciduous forest 890 - 1290 1 - 265 83 - 786 Coniferous forest 836 - 4620 1 - 110 84 - 786 Subtropical and tropical broadleaf forest 4500 1100 84
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Lowering of redox potential:
reduction, solubilization, and mobilization of Fe, Mn formation of mottles, gleyed horizons, iron pans, concretions reduction of sulfates and nitrates formation of sulfides emission of hydrogen sulfide, methane, reduced nitrate forms |
| Heavily mottled soil horizon. |
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| Filled insect burrow (possibly a cicada-like insect) in paleosol horizon, eastern Washington state, USA. | Paleosol horizon composed mainly of numerous filled insect burrows similar to the one in the picture to the left. This particular morphological feature is an excellent indicator of buried paleosols in this region of eastern Washington state, USA. |
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| Ant mound from central Wyoming. Approximately 0.3 m tall, 1 m diameter. Numerous mounds were observed in this area. | The large sloping dark mass in the right center of the image is a filled-in crotovina, probably from a mouse or other small rodent. Note its effects on the movement of water and subsequent leaching/staining of the horizon beneath. |
compaction - affects aeration and water movement, seed emergenceearthworms - a special case - important in:
- redistribution of organic matter
- formation of macropores
- formation of soil structure
- ants and termites perform many of these functions in tropical and arid soils
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| Many savanna areas are maintained by fire, sometimes managed by local human populations; alteration of the fire regime often allows other plant communities to invade and become established. Controlled burn site, Cedar Creek Natural History Area near East Bethel, MN, USA. |
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| Soil developed in a shell mound or midden, Santa Cruz Island, CA, USA. White coarse fragments are shell fragments; black soil material between is enriched in organic matter derived from food residues and other human refuse. |
Jenny's model: s = f(cl, o, r, p, t, ...)
In order to "solve" this function for one factor, all other factors must remain constant. This situation is called a "biofunction". Finding such sites may be difficult if not impossible, but we may approximate this condition in some places.
Can we find a case where this is true for vegetation?
Let's examine soils from the prairie - forest boundary in western Minnesota. They have:
- very similar glacial till parent materials
- formed over the same time period
- essentially the same topography and relief (more or less)
- the same macroclimate. The different structures of these two communities provides different microclimates, but this may be considered to be a part of, or at least caused by, the biofactor
Consequently, at least for the purposes of our discussion, we may assume that only the biological factor is different and that all other factors have remained more or less constant.
A comparison of some morphological features and chemical properties is given below:
Table 2. Comparison of properties between prairie and forest soils.
(Please note that these are general trends that are not true in all cases.)
Prairie Soils Forest Soils O Horizon Thin, if present Thick to thin, composed of leaf litter A Horizon Thick, dark, high base saturation Thin, light in color (if present), lower base saturation E Horizon Generally absent; sometimes present, particularly in sodic soils Generally present. Lighter in color, lower in clay content B Horizon Generally a cambic B or absent; argillics uncommon Displays accumulation of clays or Fe and Al sesquioxides if soil is sufficiently well-developed Clay Content Generally even throughout. May display some evidence of lessivage, but usually minimal Highest in B horizon, which generally becomes argillic if sufficiently developed. Lower in A and E horizons pH Neutral or slightly acid Neutral to moderately acid. May be very acid under coniferous vegetation Organic Matter Content of A Horizon Generally higher content, distributed to greater depth Generally lower content; mainly present at the surface in the O and thin A horizons
What factors have produced differences in these soils?
What specific interactions have influenced the development of these soils?
Ugolini, F. C., and R. L. Edmonds, 1983. Soil Biology. Chapter 7, pp. 193 - 231. In: Wilding, L. P., N. E. Smeck, and G. F. Hall (eds.) Pedogenesis and Soil Taxonomy: I. Concepts and Interactions. Elsevier, New York.