Lecture 13: Agricultural productivity and light interception 1

Question 1

most animal products derive from

Answer 1

cultivated plants

-most of our protein is from plants (even that from animals as e.g. cattle eat grass)

Question 2

of fats & oils come from plants

Answer 2

2/3

Question 3

what 3 crops account for nearly all cereal crop production

Answer 3

Wheat, rice and maize

Question 4

light interception is affected by:

Answer 4

• the number of leaves (LAI)
• leaf duration - the longer leaves last the more light they will intercept
• leaf orientation (size, shape, vertical separation)
• heliotropism (leaf movements)
• structures other than leaves - awns, stems, ears

Question 5

crop photosynthesis is ___ related to light intercepted

Answer 5

linearly

more light intercepted by crops, more they grow, increased biomass

Question 6

what does LAI (or L) stand for?

Answer 6

LEAF AREA INDEX

-total leaf area pair unit ground area (m^2 leaf per m^2 ground area)

Question 7

exception to grasses with photosynthesis

Answer 7

other photosynthetic parts (Stems, leaf sheaths) are included in LAI

Question 8

how does like penetrate the canopies (light attenuation in canopies)

Answer 8

• top canopy receives most direct sunlight
• each leaf layer absorbs about 80% of incident radiation
• undergrowth plants receive significantly less light

Question 9

what is the light compensation point:

Answer 9

level at which light absorbed is not sustainable for photosynthesis

• 10‐20 μmol.m‐2.s‐1 in a sun leaf
• 2‐6 μmol.m‐2.s‐1 in a shade leaf

Question 10

do shade / sun plants have LOWER light compensation points?

Answer 10

SHADE

Question 11

do crops have optimum LAI

Answer 11

YES

• too many plants result in self-shading
• above optimum leaves are unproductive

Question 12

Leaf Area Duration (D)

Answer 12

a measure of the persistence of the assimilatory surface (LAI) over time - how long the LAI (L) lasts

Question 13

Leaf area duration and yield are __ correlated

Answer 13

linearly

• grain yield increases as leaf area duration increases
• The more leaves there are, and the longer they are deployed, the more light is intercepted

Question 14

leaf orientation types:

Answer 14

• erectophile
• plagiophile
• planophile

Question 15

erectophile:

Answer 15

leaf angle > 60 degrees

-cereals, grasses

Question 16

plagiophile:

Answer 16

leaf angle = 30-60 degrees

-sugar beet, rape, tobacco

Question 17

planophile:

Answer 17

• <30 degrees

- clover, cucumber, bean, sunflower

Question 18

distribution of leaf area index within a canopy: ryegrass vs white clover

Answer 18

ryegrass:
-LAI low in top strata. Light can penetrate deeply into canopy
White Clover:
-top layers contain a high proportion of LAI

Question 19

effect of leaf orientation on photosynthesis (in rice)

Answer 19

canopies with vertically orientated leaves have better light penetration & higher rates of photosynthesis per unit ground area

Question 20

Matsushima (1964) Leaf angle study on rice

Answer 20

• used paper clips to drop leaf angle in rice

- assimilation rate per unit ground area same in widely spaced plants, but decreased by 35% in closely spaced plants

Question 21

Advantages of vertically-orientated leaves (i.e. rice)

Answer 21

• increased grain yield

- crop growth rate also increases

Question 22

how do we change canopy architecture (i.e. in wheat) to increase light capture & photosynthesis

Answer 22

select for more erect leaves

Question 23

improving light penetration into the canopy (Soybean)

Answer 23

• soybean canopy is very dense

- pale green varieties of soybean mean less chlorophyll allows greater light penetration into lower layers of canopy

Question 24

leaf architecture can /cannot be optimal throughout crop growth?

Answer 24

CANNOT

• soon after sowing, developing canopy, light saturated photosynthesis low LAI
• later on, closed canopy. Light saturated & light-limited photosynthesis - higher LAI

Question 25

low LAI compared to high LAI

Answer 25

low = few leaves in a area 
high = lots of leaves (dense)