Answer to Question 1
Answer: Chemical-weathering processes form soils, as indicated by the mineral additions, subtractions, and transformations that define soil horizons. Mineral dissolution and downward flushing of dissolved ions and fine-grained weathering products are characteristic of A and E horizons, where water enters the soil from rain or snowmelt and biologic activity forms acids and organic compounds that enhance mineral weathering. The B horizon contains colorful oxide and hydroxide minerals and clays that physically wash down from overlying horizons, precipitate from ions dissolved in the overlying horizons, or form in place by weathering reactions. Calcite precipitates in arid-region B horizons when water evaporates.
Answer to Question 2
Answer: The effects of climate and vegetation on soil formation are strongly interconnected. This relationship exists because climate determines the type and abundance of vegetation. Soil-horizon properties change between the Upper Great Lakes and the east slope of the Rocky Mountains. Rainfall decreases westward across this region and, as a result, forests in the east give way to grasslands and desert shrubs farther west. The different vegetation types determine the thickness and richness of organic matter in the A horizon. Dense mats of fine roots generate thick, organic-rich A horizons in grassland soils. Forest soils have O horizons of leaf and needle litter. There is very little organic matter in most desert soils, simply because vegetation is scarce.
A theoretical photosynthetic response curve.
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