Lecture 13: Agricultural productivity and light interception 1 Flashcards
most animal products derive from
cultivated plants
-most of our protein is from plants (even that from animals as e.g. cattle eat grass)
of fats & oils come from plants
2/3
what 3 crops account for nearly all cereal crop production
Wheat, rice and maize
light interception is affected by:
- 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
crop photosynthesis is ___ related to light intercepted
linearly
more light intercepted by crops, more they grow, increased biomass
what does LAI (or L) stand for?
LEAF AREA INDEX
-total leaf area pair unit ground area (m^2 leaf per m^2 ground area)
exception to grasses with photosynthesis
other photosynthetic parts (Stems, leaf sheaths) are included in LAI
how does like penetrate the canopies (light attenuation in canopies)
- top canopy receives most direct sunlight
- each leaf layer absorbs about 80% of incident radiation
- undergrowth plants receive significantly less light
what is the light compensation point:
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
do shade / sun plants have LOWER light compensation points?
SHADE
do crops have optimum LAI
YES
- too many plants result in self-shading
- above optimum leaves are unproductive
Leaf Area Duration (D)
a measure of the persistence of the assimilatory surface (LAI) over time - how long the LAI (L) lasts
Leaf area duration and yield are __ correlated
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
leaf orientation types:
- erectophile
- plagiophile
- planophile
erectophile:
leaf angle > 60 degrees
-cereals, grasses
plagiophile:
leaf angle = 30-60 degrees
-sugar beet, rape, tobacco
planophile:
- <30 degrees
- clover, cucumber, bean, sunflower
distribution of leaf area index within a canopy: ryegrass vs white clover
ryegrass:
-LAI low in top strata. Light can penetrate deeply into canopy
White Clover:
-top layers contain a high proportion of LAI
effect of leaf orientation on photosynthesis (in rice)
canopies with vertically orientated leaves have better light penetration & higher rates of photosynthesis per unit ground area
Matsushima (1964) Leaf angle study on rice
- 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
Advantages of vertically-orientated leaves (i.e. rice)
- increased grain yield
- crop growth rate also increases
how do we change canopy architecture (i.e. in wheat) to increase light capture & photosynthesis
select for more erect leaves
improving light penetration into the canopy (Soybean)
- soybean canopy is very dense
- pale green varieties of soybean mean less chlorophyll allows greater light penetration into lower layers of canopy
leaf architecture can /cannot be optimal throughout crop growth?
CANNOT
- soon after sowing, developing canopy, light saturated photosynthesis low LAI
- later on, closed canopy. Light saturated & light-limited photosynthesis - higher LAI
