11 - Plant nutrition and soils

96% of plants are mad eof which element

hydrogen

carbon

oxygen

Macronutrient:

required in rel. large amounts

Micronutrient:

required in rel. small amounts

1. Which elements are typically addressed as the seven macronutrients?

Calcium, Magnesium, Nitrogen, Phophorus, Potassium, Silicon, Sulfur

1. Which three macronutrients are commonly most limiting for plant growth (so that they get advertised most broadly on bags of fertilizers for example in the garden store)?

Nitrogen, Phophorus, Potassium

1. Two macronutrients are crucial components of ATP and NAPD. Which ones?

Nitrogen, Phosphorus

why is nitrogen is essential

amino acids

chlorophylls

nucleic acids

energy coreency (atp ot nadp)

1. In which ecosystems are soils typically limited in nitrogen?

Dunes, On new volcanic islands, Soils after the melt of glaciers

Atmosphere as the main global repository of this limiting nutrient -  

nitrogen         

Bedrock as the main global repository of this limiting nutrient - 

phosphorus               

Erosion and continental uplift as the main mechanisms to move this limiting nutrient through its global cycle -  

phosphorus         

Involvement of unicellular organisms as the main mechanism to move this limiting nutrient through its global cycle -  

nitrogen         

Mainly abiotically driven cycle - 

    nitrogen         

Mainly biotically driven cycle -    

  phosphorus   

Abiotically Driven –

A process that occurs due to non-living physical or chemical factors

Biotically Driven –

A process that is caused or influenced by living organisms.

why is phosphrus imp in plants

nucleic acids

atp and nadp

Phosphorus cycle source

bedrock

bioavailability in soils: highly reactive P precipitates and mostly is bio-unavailable

is phosphorus cycle geological or biogenic

geological

is nitrogen cycle geological or biogenic

biogenic

what is Potassium imp 4 rsns

Important in the process of sugar and starch production

Increases size and quality of fruits

Increases plant disease resistance, assists in enzyme activation and photosynthesis

Opening and closing of stomata

Which typically limiting macronutrient is hardly ever in solution and generally present as an anion?

Phosphorus

Which macronutrient is present in the atmosphere but inaccessible from this pool to all living organisms but some bacteria

Nitrogen

1. What limiting macronutrient is especially hard for plant roots to take up?

Phosphorus

Typical nutrient cations

K +, NH4 +, Mg2+, Ca2+, Zn+, Mn2+, Fe2+, Cu+

Typical nutrient anions

NO3 - , H2PO4 - , HPO4 - , SO4 - , BO3 - , MoO4 -

what is p mostly present as

anion

Cation Exchange

(Anions react with positively charged dissolved molecules and precipitate

which soil has high cec

clay and humus

which soil has low cec

sand

cec

Cation Exchange Capacity

Which two soil components have especially many negatively charged sites on their surface?

Humus and clay 

1. What influences CEC?

Soil type

Retention of nutrients with cec

more cec = more reteniton for nutrients

Cation Exchange Capacity CEC of soils

Clay and humus: negatively charged sites → binding sites for cations

H+: strongest affinity to negatively charged soil sites

Plant roots can only take up dissolved minerals (in soil solution)

Soil pore size vs. nutrient leaching

The smaller the pore size, the more likely adhesion and cohesion will tie water to pores

The more water is tied to the soil, the less likely nutrients will leach from the soil

Soil pore size and retention

small pore = more retention of nutrients

Which of the following soil particles have the smallest pore size?

Clay

1. In the following list, which soil particle has the smallest diameter?

clay

1. Soils rich in clay can retain cations more effectively than sandy soils

true

1. The smaller the pore size, the larger the chance for a dissolved nutrient to get washed from soils

false

In highly acidic soils, the likelihood of cations being leached is lower than in less acidic soils

false

If nutrients are dissolved in the soil water, they can leach when it rains

true

1. Hydrogen ions have a higher affinity to negatively soil sites than nutrient cations

true

Some nutrients are more bio-available under acidic conditions, while other are more bio-available under basic condition

true

1. Which soil component is typically dark or even black?

humus

Humus is of abiotic origin

false

how are anion exchanged

no equivalence to cation

→ Anions react with positively charged dissolved molecules and precipitate (fall out of solution)

→ as solids: almost always bio-inaccessible!

P: especially reactive and thus problematic to access for plants!

soil pH and nutrients

high ph = more nutrients

low ph = less nutrinet

soil pH: cation exchange

Soil H+ displaces mineral cations from clay/humus particles

in low ph h+ takes up cec instead of nutrients

Humus charcteristics

Nutrient rich

High CEC

Light & fluffy

High H2O holding capacity

• The more organic contents (black soil) →

higher soil fertility

Cation uptake by root hairs

To uptake a nutrient, it must be dissolved and hence present in the soil water solution

Bound cations? → plants simulate cation exchange = ‘force’ cations off negatively charged soil sites → force cations into solution

needs energy burned

Cation vs anion uptake

Cations: through cation exchange

Anions: from soil water solution if dissolved

Rhizobacteria

fix atmospheric N ≈ source of biogenic N

Mycorrhiza

better access to dissolved nutrients (esp. P)

is Mycorrhiza fungi or bacteria

fungi

is rhizobacteria fungi or bacteria

bacteria

1. Where do symbiotic rhizobium bacteria commonly live?

In roots 

1. To take up nutrients, plants need to respire some previously fixed carbon
   

true

Nutrients released from soil particles dissolve in the water solution located btw soil particles and root hairs

true

Root hairs take up dissolved nutrients through specific channels

true

1. For which two limiting macronutrients do plants use biotic helpers to more effectively access them?

N,  P

2. Nitrogen is only bio-accessible to plants through symbiotic rhizobia

False 

1. What is mycorrhiza?

Association between roots and fungi

Symbiosis between plants and fungi

This word comes from old Greek and means ‘fungus’ and ‘root’

1. Which plant-based food contains especially large amounts of protein?

beans

1. The benefits gained from the plant-mycorrhiza interaction are free for plants

false

1. Besides helping plants to take up phosphorus and nitrogen, what other benefits do symbiotic mycorrhizal fungi have on their plant hosts?

Better growth, Better resistance against pathogens, Better water uptake, enhanced reproduction