Lecture 12

Question 1

___ is the staple food of over half the worlds population

Answer 1

Rice

-grown in waterlogged soils (paddy fields)

Question 2

soil when its waterlogged =

Answer 2

changes redox state

-soil saturated with water quickly runs out of of available O2 (O2 moves slower in water than gas)

Question 3

redox in normal soils =

Answer 3

O2 decreases with depth

CO2 increases with depth

Question 4

redox reactions in soil are ___ driven

Answer 4

biologically

Question 5

anthropogenic methane % release

Answer 5

63%

-paddy fields issue, global warming

Question 6

rice paddy fields and global warming

Answer 6

contribute >10% of global methane emissions, and have increasing contributions to N2O fluxes too

Question 7

paddy fields crop yields

Answer 7

good as no limitation by water, rice has little competition from weed and nutrients made available as they’re in water

Question 8

N2O and Ch4 related to CO2

Answer 8

N2O is 296X greater than equal mass of CO22
CH4 is 20X greater
(global warming potential)

Question 9

temperate agricultural crop rooting depths

Answer 9

• most in top 20cm of soil
• shallow roots
• effected easily by weather (droughts), utilisation of nitrate lacking as they cant reach it
• Fan et al 2016

Question 10

root penetration through depths

Answer 10

hard for roots to penetrate below 30cm (where ploughing occurs)

• earthworms help, but hard work for them too
• therefore large soil underexploited = nutrient losses

Question 11

Clarke et al 2017 did what to wheat

Answer 11

• breed it with wild relative

- select genotypes for deeper roots, significantly increase root depths

Question 12

annual vs perennial root

Answer 12

annual grow only one season, so shorter, dont compete with perennial root systems
-grow perennial first, then annual to release nutrients?

Question 13

use of herbal leys in rotations =

Answer 13

use diverse herbal leys in crop rotations including deep rooting species and nitrogen fixing legumes that have potential to improve soil structure and nutrient status of arable soils

Question 14

deeper roots and carbon

Answer 14

deeper roots lock carbon organic matter into soil

-clay contents seem to be higher deeper into soil

Question 15

phosphorous deposition in soil

Answer 15

• majority in topsoil,
• more roots then more uptaken
• root hair lengths more phosphorous uptaken

Question 16

over __ of plant species form mycorrhizal associations to assist in uptake of _ & _

Answer 16

80%

P and N

Question 17

how do the plants that dont form mycorhiza cope and examples

Answer 17

cabbage, cauliflower, turnips, sugar beet

• root hairs to increase P capture (as P goes up, root hairs drop, negative feedback)
• adding fertiliser requires more fertiliser to be added?
• fine root hairs!

Question 18

phosphorous ending up in grain

Answer 18

• normally >50%
• many cereal crops put most of P in above ground biomass
• issue w that is can be (88% in wheat) stored in phytate or phytic acid which is not reasily digested ends up in manure (hard to break down in soil)

Question 19

strategies for improving P efficiency in cropping systems

Answer 19

1) greater use of crop species with cluster roots (in environments w large amounts of P but low P availiability)
2) potential of native sp with p-effiicent traits for use in crops
3) breeding of greater P-use efficiency in existing crops
4) better understanding of molecular basis of P-efficient traits
5) intercropping & crop rotations to provide benefits of P-efficient crops to less efficient ones

Question 20

P and Fe often availibility in soil

Answer 20

often in plentiful quanitties but bound to the soil and not v accesible to plants

Question 21

proteoid roots

Answer 21

• good for phosphorous uptake
• hugely branched, overlapping
• but generate chemical alteration in soil in intesne patches where they then mine out nutrients

Question 22

plants that form cluster roots often have

Answer 22

N fixing symbiosis (e.g. rhizobium nodules) but rarely have mycorrhiza

Question 23

cluster roots are __ at high P supply

Answer 23

suppressed

Question 24

cluster root growth

Answer 24

v quickly, 3 weeks whole structure has formed and completely lifestyle
-release burst of organic acid at fullest growth to compete w bacteria

Question 25

proteoid root production is stimulated by __

Answer 25

P limitation but also by limitations of some other elements (Fe)

Question 26

burst of organic acid by cluster roots effect on pH

Answer 26

lower pH, i.e. free up iron

Question 27

Cyperaceae:

Answer 27

• Davies et al 1973
• major family in Monocotyledonidae Sedges
• over 70spp. in uk, some v common & widespread
• form Dauciform roots
• -hairy structures, v long root hairs produced at v high freq
• sensitive to phosphorous
• release exudates like cluster roots

Question 28

proteoid roots found in

Answer 28

Proteaceae

Question 29

potential to breed crops for greater nutrient use efficiency:

Answer 29

• root hairs
• root branching
• root branching angle
• root fineness
• specialised roots for “mining” P & Fe from soils
• crop rotations
• intercropping plants w different rooting traits
• use of perennial deep rooting intercrops
• breeding to create mycorrhizal associations
• management to promote mycorrhiza
• microbial inoculants to increase nutrient use
• reduced nutrient demand - selection for reduced phytate accumulation in grains