Lesson 32 Mineral Cycling - Alaska Geobotany Center

Summary
Aspects of nutrient cycling
– Gaseous (e.g., Carbon and Nitrogen cycles) and sedimentary cycles (e.g., Potassium
cycle).
– Nutrients are compartmentalized into (a) rocks and soils, (b) soil solution, ( c) the
atmosphere, and (d) biomass.
– Transfer into or out of the system can be via meteorologic, geologic, or biologic
events.
– Time scales of cycles can require minutes, decades, or millennia to revolve. Biological
cycling within systems is much more rapid than abiotic cycling.
– Abiotic factors include fire, earth movement, and aspects of the hydrologic cycle
(deposition, leaching, evapotranspiration, runoff, infiltration).
– Biotic factors include litter production, organic matter accumulation, decomposition,
ingestion and digestion, gas flux, root exudation, and retrieval of nutrients from deep
soil layers through roots.
– Stability of systems often depend on a variety of homeostatic mechanisms to retain
nutrients in the sytem, including resorption (ability to withdraw nutrients from plant
parts that senesce to avoid loss of nutrients in litterfall), high nutrient use efficiency
(high rate of production per unit of nutrient), large storage pools within the system
(such as large standing crop of trees), and immobilization of nutrients (e.g., in
decomposer microorganisms, and plants to prevent leaching.
– The carbon and nitrogen cycles are tightly linked because plant tissues have high
demand for nitrogen. Production is often limited by the availability of nitrogen.
– Acid rain affects mineral cycles through lower soil water pH, which leaches nutrients
from the soil. Nitrogen saturation occurs from enhanced inputs of N in rain water and
dry deposition and leads to stream eutrophication.
– Increases in greenhouses gases including CO 2
, NH 4
,N 2
O, and water vapor are of
major concern because of possible effects on global climate.