Nutrient Cycling in Forest Stands

What is the definition of a stand

an area of forest relatively uniform in history of site and uniform species

What are atmospheric inputs to nutrient cycling of forest stands

NH4+ and NO3- in rain, dust, sometimes insects on a local importance, and unfixed N2 gas

what is the Haber process

the process for the manufacture of N Fertilizer originally used as explosives, also fixes N and is now one of the main fixed N sources globally

Why is the atmospheric input of N2 complicated

most of the atmosphere is nitrogen but N2 is not immediately available for plant uptake since it has to be fixed to a usable form such as NH4+ or NO3-. There are soil and root-associated bacteria that can do this and lightning can do it too

what are the overland flow inputs in the nutrient cycling of forest stands

convex vs concave landforms since water flowing downhill carries nutrients and soil, animal movements can also be important on a local level

what are the outputs of nutrient cycling in forest stands

leaching, erosion and overland flow (is most likely to happen on steep slopes and animals affect on a local level), and volatilization

what is volatilization

loss in gas form that fire is usually the cause

what is leaching

water movement through the soil can leach nutrients from the soil and carry them into groundwater

what helps guard against leaching

a high CEC in the soil

what is the internal cycling of nutrients aboveground

plants grow using nutrients taken from the soil, some of these components are captured by the herbivores (herbivory) and sometimes later by predators, then ultimately all these nutrients become part of the soils organic matter (litterfall) and are recycled by the soil into plant nutrients

what is the internal cycling of nutrients belowground

mineralization of soil organic matter to release nutrients, immobilization of OM decay taken from soil, weathering adds mineral fractions, CEC and AEC exchange nutrients, and uptake by plant roots and associated mycorrhizal

what is AEC

anion exchange capacity that is used under some conditions some soil solids have a positive surface charge so they can also exchange anions with soil solutions

when comparing between nutrient cycling underground and nitrogen cycling underground what is no longer a contributor for nitrogen cycling

weathering

what are the differences between the internal underground nutrient cycling and the nitrogen cycle

N released is not related to the weathering of soil minerals, N fixation by soil and root bacteria can be important input, and atmospheric deposition and volitation are important inputs and outputs

N fixation requires what?

requires a lot of energy and can only be done by certain bacteria under low oxygen conditions and microsites in soil and nodules in some plants provide these condition

Give highlights to Phosphorus (P) cycling

weathering of soil minerals, atmospheric input and output is negligible except sometimes from incoming dust and P exists in many complec organic an dinorganic forms that are hard for unassisted rotos to uptake

what are mycorrhizal associations

fungi associated with plant roots, in what generally is taken to be a mutually beneficial relationship

describe what benefits plants and fungi obtain from mycorrhizal associations

the fungal partner gets easily available energy from the plant and the plant gets help capturing immobile nutrients like P which occurs in two ways

what are the two ways fungi help with P capturing

1) the thin strands of fungal hyphae can explore a greater volume of soil so that P has a shorter distance to diffuse the to the fungal strands and 2) the fungi are often able to break down (mineralize) soil OM making P locked up in organic forms available for uptake

what are the two varieties of fungal associations

Ectomycorrhizae (form sleeves of hyphae around the roots and common in conifers, birches, and oaks) and Arbuscular mycorrhizae (hyphae penetrate into the cells of roots to create exchange within the cells that are common to maples, ash and aspen)

in general what is the pattern of mycorrhizal fungi associations and tree species association

most mycorrhical fungi associate with several tree species and most tree species associate with several mycorrhizal species (but not true for all such as suilus pictus are only associated with white pine)

what are hyphae

fungal strands