1. Transport in Plants

2. Why does over-watering kill a plant?
Transport in plants
H2O & minerals
transport in xylem
transpiration
evaporation, adhesion & cohesion
negative pressure
Sugars
transport in phloem
bulk flow
Calvin cycle in leaves loads sucrose into phloem
positive pressure
Gas exchange
photosynthesis
CO2 in; O2 out
stomates
respiration
O2 in; CO2 out
roots exchange gases within air spaces in soil
Why does over-watering kill a plant?

3. Ascent of xylem fluid
Transpiration pull generated by leaf

4. Water & mineral absorption
Water absorption from soil
osmosis
aquaporins
Mineral absorption
active transport
proton pumps
active transport of H+
aquaporin
root hair
proton pumps
H2O

5. Mycorrhizae increase absorption
Symbiotic relationship between fungi & plant
symbiotic fungi greatly increases surface area for absorption of water & minerals
increases volume of soil reached by plant
increases transport to host plant

6. Pressure flow in phloem
Mass flow hypothesis
“source to sink” flow
direction of transport in phloem is dependent on plant’s needs
phloem loading
active transport of sucrose into phloem
increased sucrose concentration decreases H2O potential
water flows in from xylem cells
increase in pressure due to increase in H2O causes flow
can flow 1m/hr
In contrast to the unidirectional transport of xylem sap from roots to leaves, the direction that phloem sap travels is variable. However, sieve tubes always carry sugars from a sugar source to a sugar sink. A sugar source is a plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch. Mature leaves are the primary sugar sources. A sugar sink is an organ that is a net consumer or storer of sugar. Growing roots, buds, stems, and fruits are sugar sinks. A storage organ, such as a tuber or a bulb, may be a source or a sink, depending on the season. When stockpiling carbohydrates in the summer, it is a sugar sink. After breaking dormancy in the spring, it is a source as its starch is broken down to sugar, which is carried to the growing tips of the plant.
A sugar sink usually receives sugar from the nearest sources. Upper leaves on a branch may send sugar to the growing shoot tip, whereas lower leaves export sugar to roots. A growing fruit may monopolize sugar sources around it. For each sieve tube, the direction of transport depends on the locations of the source and sink connected by that tube. Therefore, neighboring tubes may carry sap in opposite directions. Direction of flow may also vary by season or developmental stage of the plant.
On a plant… What’s a source…What’s a sink?

7. Plant Nutrition

8. Physiological adaptation
Dogs pee on trees…Why don’t trees pee on dogs?
NH3
plant nutrient
animal waste

9. Nutritional needs Autotrophic does not mean autonomous plants need…
sun as an energy source
inorganic compounds as raw materials
water (H2O)
CO2
minerals

10. Macronutrients
Plants require these nutrients in relatively large amounts
C, O, H, N, P, K, Ca, Mg, S

11. 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

12. Take 2 fertilizer pellets & call me in the morning
Magnesium deficiency
Symptoms
chlorosis = yellowing of leaves
Why? What is magnesium’s function?

13. Chlorophyll Why does magnesium deficiency cause chlorosis?
The chlorosis shows up in older leaves first, because plant moves Mg+ to newer leaves. Why?

14. Agronomists really dig dirt!
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

15. Importance of organic matter
So don’t rake your lawn or bag your leaves
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

16. Soil health as a global issue
Not 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

17. Soil health as a global issue
Soil conservation & sustainable agriculture
maintaining healthy environment
sustainable production of food supply
economically viable farming industry
“A sustainable agriculture does not deplete soils or people.”
– Wendell Berry
contour plowing
cover crops
crop rotation

18. What are the political, economic, environmental issues?
Fertilizers
“Organic” fertilizers
manure, compost, fishmeal
“Chemical” fertilizers
commercially manufactured
N-P-K (ex )
15% nitrogen
10% phosphorus
5% potassium
What are the political, economic, environmental issues?

19. What will the plant use N for?
Nitrogen uptake
Nitrates
plants can only take up nitrate (NO3-)
Nitrogen cycle by bacteria
trace path of nitrogen fixation!
root
What will the plant use N for?

20. Soybean root nodules N fixation by Rhizobium bacteria
symbiotic relationship with bean family (legumes)

21. Increasing soil fertility
Plow it under?
Why would you that?
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
A farmer… outstanding in his field?
erosion control, too

22. Some plant oddities…

23. Parasitic plants tap into host plant vascular system Indian pipe
Mistletoe

24. Plants of peat bogs High acid environment
most minerals & nutrients bound up & are not available to plants
must find alternative sources of nutrients

25. Carnivorous plants Are they really carnivores? Sundew Venus fly trap
Pitcher plant
Are they really carnivores?

26. Pitcher plant

27. Uses of peat