Soil pH influences availability of soil nutrients.

Fine roots and root hairs “mine” the soil for nutrients. Mycorrhizal hyphae do this even better. 4. Roots and mineral nutrient acquisition

Roots Provide large surface area for nutrient uptake - Root hairs

Why are fine structures like hyphae and root hairs particularly effective at nutrient absorption? For a given volume (or mass) of roots, what size root presents the most surface area?

Surface area of a cylinder SA = circumference x length SA =  x diam x length SA =  x 2r x length Volume = area x length Vol =  x r 2 x length SA/Vol = (  x 2r x length)/(  x r 2 x length) SA/Vol = 2/r As the radius decreases, the surface area per volume increases.

Minirhizotron photos of yellow birch roots in the Hubbard Brook Experimental Forest (New Hampshire) in April (left) and June (right). 0.3 mm in diameter.

Fig. 5.7 Depletion zones - regions of lower nutrient concentration -develop around roots

A depletion zone of low concentration forms near the root when the rate of nutrient uptake exceeds the rate of diffusion

Mycorrhizae “fungus - root” Symbiosis with fungi Nutrient Uptake and Mycorrhiza

Roots and Mycorrhiza – an old symbiosis Mutual benefit Carbohydrates for the fungus P, Zn, Cu, water, N for plant Different types 1. Vesicular-arbuscular mycorrhiza – VA-mycorrhiza 2. Ectomycorrhiza Other types ericoid orchid endomycorrhiza

1. Vesicular arbuscular mycorrhiza (AM) Glomales (130 species – infects plant species) Found on roots of herbaceous angiosperms, most trees, mosses, ferns… not present on Cruciferae, Chenopodiaceae, Proteaceae small biomass compared to roots

Vesicular Arbuscular Mycorrhiza Inside root Intercellular mycelium Intracellular arbuscule tree-like haustorium Vesicle with reserves Outside root Spores (multinucleate) Hyphae thick runners filamentous hyphae Form extensive network of hyphae even connecting different plants

AM Arbuscule of Glomus mosseae – branching provides large surface area

Outside of root network of hyphae and spores

2. Ectomycorrhiza (EM) Ascomycetes and Basiodiomycetes – form large fruiting bodies 5000 species interact with 2000 plant species Interaction with trees: angiosperms and all Pinaceae

Ectomycorrhiza Inside root Intercellular hyphae Does not enter cells Outside root Thick layer of hyphae around root Fungal sheath Lateral roots become stunted Hyphae Mass about equal to root mass Forms extensive network of hyphae even connecting different plants

Ectomycorrhizal root tip

Mantle Hyphae Hartig Net

Why mycorrhiza? Roots and root hairs cannot enter the smallest pores

Why mycorrhiza? Root hair Smallest hyphae Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th diameter of root hair Increased surface area Surface area/volume of a cylinder: SA/vol ≈ 2/radius

Inoculated with mycorrhizae Not inoculated with mycorrhizae Why mycorrhiza? Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th of root hair Increased surface area Extension beyond depletion zone

Why mycorrhiza? Roots and root hairs cannot enter the smallest pores Hyphae is 1/10 th of root hair Increased surface area Extension beyond depletion zone Breakdown of organic matter C – C – NH 2 --> C – C + NH 3

Summary on mycorrhizae Symbiosis with mycorrhiza allows greater soil exploration, and increases uptake of nutrients (P, Zn, Cu, N, water) Great SA per mass for hyphae vs. roots Mycorrhiza gets carbon from plant Two main groups of mycorrhiza – Ectomycorrhiza and VA-mycorrhiza

For us more on nitrogen nutrition Why is N so important for plant growth? What percentage of the mass of plant tissues is N? What kinds of compounds is N found in? Why is there a strong relationship between the N concentration of leaves and photosynthesis?

Nitrogen - the most limiting soil nutrient Evidence - factorial fertilization experiments (N, P, K, etc.) show largest growth response to N. 1.Required in greatest amount of all soil nutrients 2. A component of proteins (enzymes, structural proteins, chlorophyll, nucleic acids) 3. The primary photosynthetic enzyme, Rubisco, accounts for a 25 to 50% of leaf N. Photosynthetic capacity is strongly correlated with leaf N concentration. 4. Availability in most soils is low 5. Plants spend a lot of energy on N acquisition - growing roots, supporting symbionts, uptake into roots, biochemical assimilation into amino acids, etc.

The inorganic forms of nitrogen in soils. 1.NH 4 +, ammonium ion. A cation that is bound to clays. 2.NO 3 -, nitrate ion. An anion that is not bound to clays. Nutrient “mobility” in soils refers to the rate of diffusion, which is influenced by nutrient ion interactions with soil particles. Would you expect NH 4 + or NO 3 - to diffuse more rapidly? Would you expect a more pronounced depletion zone for NH 4 + or NO 3 - ?

The Nitrogen Cycle

1. Emissions to atmosphere Dead organisms and tissues Pathways of N loss from ecosystems 2.