Plant Nutrition(Ch. 37)

Physiological adaptationDogs pee on trees…Why don’t trees pee on dogs?

NH3

animal waste

plant nutrient

Nutritional needs• Autotrophic does not

mean autonomous– plants need…

• sun as an energy source

• inorganic compounds as raw materials

– water (H2O)

– CO2

– minerals

Macronutrients• Plants require these nutrients in relatively

large amounts– C, O, H, N, P, K, Ca, Mg, S

For what & from where?

C macromolecule synthesis CO2

O macromolecule synthesis CO2

H macromolecule synthesis & proton pumps H2O

N protein & nucleic acid synthesis soil

P nucleic acids, ATP, phospholipids soil

K stomate control, water balance soil

Ca cell wall & membrane structure, regulation soil

Mg chlorophyll soil

S proteins, enzymes soil

to make all plant proteins

establish a strong root system in young plants, growth

Flowers, absorption of water, strong roots, root crops (ie. carrots)

Cell walls, nutrient and soil conditioner

Local Long Island soil issues

Granite

Acid soils bind upmineral ionspH by adding lime

Quartz silica based soils- low in P- can be acid

Micronutrients• Plants require in very small amounts

– Cl, Fe, Mn, Bo, Zi, Ni, Mb– primarily cofactors for enzyme function

Nutrient deficiencies• Lack of essential nutrients

– exhibit specific symptoms• dependent on

function of nutrient• dependent on

solubility of nutrient

• Mineral deficiency symptoms depend not only on the role of the nutrient but also on its mobility within the plant. If a nutrient moves about freely, symptoms will show up first in older organs because young, growing tissues have more “drawing power” for nutrients in short supply. For example, magnesium is relatively mobile and is shunted preferentially to young leaves. Therefore, a plant starved for magnesium will show signs of chlorosis first in its older leaves. The mechanism for preferential routing is the source–to–sink translocation in phloem as minerals move along with the sugars to the growing tissues. In contrast, a deficiency of a mineral that is relatively immobile will affect young parts of the plant first. Older tissues may have adequate amounts, which they are able to retain during periods of short supply. For example, iron does not move freely within a plant, and an iron deficiency will cause yellowing of young leaves before any effect on older leaves is visible.

• Deficiencies of nitrogen, phosphorus, and potassium are most common. Shortages of micronutrients are less common and tend to occur in certain geographic regions because of differences in soil composition. The symptoms of a mineral deficiency are often distinctive enough for a plant physiologist or farmer to diagnose its cause

Magnesium deficiency• Symptoms

– chlorosis = yellowing of leaves– Why? What is magnesium’s function?

Take 2 fertilizer pellets

& call me in the morning

Chlorophyll

Why does magnesium deficiency cause chlorosis?

The chlorosis shows up in older leaves first, because plant moves Mg+ to newer leaves. Why?

The role of soils• Plants are dependent on soil quality

– texture / structure• relative amounts of various sizes of soil particles

– composition• organic & inorganic chemical components• fertility

Agronomistsreally dig dirt!

Importance of organic matter• Topsoil

– most important to plant growth– rich in organic matter

• humus– decomposing organic material

» breakdown of dead organisms, feces, fallen leaves & other organic refuse by bacteria & fungi

– improves soil texture– reservoir of minerals

– organisms• 1 tsp. of topsoil has ~5 billion bacteria

living with fungi, algae, protists, insects, earthworms, nematodes

So don’t rakeyour lawn or

bag your leaves

Soil health as a global issueNot taking care of soil health has far-reaching, damaging consequences

– 1920’s Dust Bowl– lack of soil conservation

• growing the same crop year after year (wheat)

• grazing by cattle• bare ground exposed to

wind erosion in winter• drought

Soil health as a global issue

• Soil conservation & sustainable agriculture– maintaining healthy environment– sustainable production of food supply– economically viable farming industry

contour plowing crop rotation

“A sustainable agriculture does not deplete soils or people.” – Wendell Berry

cover crops

Fertilizers• “Organic” fertilizers

– manure, compost, fishmeal• “Chemical” fertilizers

– commercially manufactured– N-P-K (ex. 15-10-5)

• 15% nitrogen• 10% phosphorus • 5% potassium

What are thepolitical, economic,

environmentalissues?

Your next Current event!

Nitrogen uptake• Nitrates

– plants can only take up nitrate (NO3-)

• Nitrogen cycle by bacteria– trace path of nitrogen fixation!

What will the plant use N for?

root

Soybean root nodules• N fixation by Rhizobium bacteria

– symbiotic relationship with bean family (legumes)

Increasing soil fertility• Cover crops

– growing a field of plants just to plow them under• usually a legume crop• taking care of soil’s health

– puts nitrogen back in soil

erosion control, too

A farmer… outstandingin his field?

Plow it under?Why would you

that?

2006-2007

Some plant oddities…

Parasitic plants

• tap into host plant vascular systemIndian pipe

Mistletoe

Plants of peat bogs• High acid environment

– most minerals & nutrients bound up & are not available to plants

• must find alternative sources of nutrients

Carnivorous plants

Are they really carnivores?

Pitcher plantVenus fly trapSundew

Pitcher plant

Uses of peat

Any Questions??

Review Questions

1. The inorganic compound that contributes most of the mass to a plant’s organic matter is *A. H2O.B. CO2.C. NO3

2.D. O2.E. C6H12O6.

2. You are conducting an experiment on plant growth. You take a plant fresh from the soil and it weighs 5 kg. Then you dry the plant overnight and determine the dry weight to be 1 kg. Of this dry weight, how much would you expect to be made up of inorganic minerals?A. 50 gramsB. 500 gramsC. 1 kgD. 4 kg E. 5 kg

• we can rule out C, D , and E and because the dry weight of any plant is going to be mostly cellulose ( a polymer of glucose) we can pretty much be assured half of the dry weight is not going to be from inorganic minerals and ions. The only choice that makes any sense at all is 50grams. No calculations needed

This figure shows the results of a study to determine the effect of soil air spaces on plant growth. Use these data to answer the following question.

3. The best explanation for the shape of this growth response curve is that

A. the plant requires air in the soil for photosynthesis. B. the roots are able to absorb more nitrogen (N2) in high

levels of air.C. most of the decrease in weight at low air levels is due

to transpiration from the leaves.D. increased soil air produces more root mass in the soil

but does not affect the top stems and leaves.E. the roots require oxygen for respiration and growth.

4. Carnivorous plants have evolved mechanisms that trap and digest small animals. The products of this digestion are used to supplement the plant's supply ofA. energy.B. carbohydrates.C. lipids and steroids.D. minerals. E. water.

• Are some essential elements more important than others? Explain.

No, because even though macronutrients are required in greater amounts, all essential elements are necessary for the plant to complete its life cycle.

• Can a single leaf be used to diagnose all of a plant’s mineral deficiencies? Explain.

a. No, because deficiencies of nutrients that are more mobile show up first in older leaves, whereas deficiencies in nutrients that are less mobile show up first in younger leaves.