Nutrient supply from soil and sky

Learning goals:

* Understand what nutrients are, their basic functions, and their origins in ecosystems

* Be able to describe what makes up a soil, how it forms, and why it is important for nutrient and water supply

All organisms require nutrients, specific chemical elements for metabolism and growth
Organisms absorb these elements from the environment or get them in their food
The ultimate source of mineral nutrients is the Earths crust and atmosphere
Biogeochemistry is the study of the physical, chemical, and biological factors that influence the movements and transformations of elements.

Nutrient requirements
All organisms share similarities in their nutrient requirements, but the sources may differ considerably
All organisms are composed primarily of C, H, and O; Amounts and specific nutrients needed vary according to the organism’s mode of energy acquisition, mobility, and thermal physiology- influences the ratios of nutrients (e.g. C:N)
All plants require a core set of nutrients; macronutrients required in greater amounts than micronutrients

Plants and microorganisms take up nutrients in simple, soluble forms from the environment. Animals mostly get nutrients in food in the form of complex molecules. Some of these are broken down and new molecules are synthesized. Other molecules are absorbed intact, such as some amino acids which can not be synthesized.

Nutrient Origins

Nutrients enter ecosystems through the chemical breakdown of minerals in rocks or through fixation of gases (C & N) in the atmosphere
Nutrients may be cycled within an ecosystem, repeatedly passing through organisms and the soil or water

Mineral sources of nutrients:
Minerals - solid substances with characteristic chemical properties.
Rocks are collections of different minerals.
Elements are released from rock minerals by mechanical and chemical weathering
Weathering of rock results in formation of soil: a mix of mineral particles, solid organic matter (primarily decomposing plant matter), water containing dissolved organic matter, minerals, and gases (the soil solution), and organisms
Soil texture refers to the size of soil particles: Sand, silt, and clay
Cation exchange capacity - the ability of a soil to hold and exchange cations (positively charged ions); related to amount and types of clay particles present. Important component of soil fertility

soil texture also influences water holding capacity
Parent material - the rock or mineral material that was broken down by weathering to form a soil. Includes bedrock, loess, and till
Over time, soil formation involves weathering, accumulation of organic matter, and chemical alteration and leaching of dissolved organic matter and fine mineral particles to deeper layers, resulting in formation of horizons. Soils that have weathered for long periods of time (e.g. in the tropical lowlands) are low in rock based nutrients and acidic.

Atmospheric sources of nutrients (C and N)
C fixed by autotrophs in photo- and chemosynthesis
Nitrogen fixation - the process of converting N2 into a biologically useful form
Biological fixation uses the enzyme nitrogenase, which only occurs in certain bacteria
Both free-living and symbiotic N2-fixation occur; example of the latter includes legumes with nodules to house the fixing bacteria

The atmosphere also contains fine dust and suspended solid, liquid, and gaseous particles known as aerosols.
This particulate matter falls to Earth by gravity or with precipitation = atmospheric deposition
Anthropogenic emissions of pollutant aerosols and gases can detrimentally impact ecosystems