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Plant Structure and Function I - E col 182 – 4-14-2005 Downloaded at 9:00 pm on 4-13 The Angiosperms: Flowering Plants A number of synapomorphies , or shared derived traits, characterize the angiosperms: They have double fertilization (upcoming figure). They produce triploid endosperm.
Downloaded at 9:00 pm on 4-13
Plants bridge the steep potential energy gradient
between the soil and the air & use it as a mechanism for
water and solute transport
- The soil is not an endless supply of water!
y = ys +yp
Figure 36.4 Apoplast and Symplast – routes of water movement from the soil into the plant
When water is withheld – the pressure potential of the cells declines (hours to days) and rates of cell expansion are reduced (long-term).
-Rates of photosynthesis declines (stomata close- short).
-New leaves are smaller, with smaller cells (long).
-Profound change in patterns of allocation (long).
EVEN THE WIDEST VESSELS IN RING-POROUS TREES ARE SUFFICIENTLY NARROW TO PREVENT BREAKING OF A WATER COLUMN….(Sperry 1995)
Other mechanisms besides vessel diameter alone are important in determining drought stress tolerance
DIFFERENCES IN CONDUIT DIAMETER CAN AFFECT THE POTENTIAL FOR GAS EMBOLISMS FORMING FROM GAS MOVING OUT OF SOLUTION
Constraints on water transport when embolism occurs; differences in phenology and distribution
Vessels confined to spring wood (uniform distribution)
Emboli zed vessels cannot be re-filled; water transport is dependent upon new spring wood construction (which tent to have large vessels)
Vessels occur uniformly throughout the annular ring; re-filling can occur over the winter.
Think about this figure as a general example of how soils and plants interact in all different ecosystems
Mesic species with the ability to recover each night operate close to the xylem tensions that cause 100% cavitation
Xeric species that do not have that opportunity to recover operate with a much larger safety margin
Variation within and between species associated with variation in PSN capacity, leaf N content, leaf morphology/ontogeny
Variation between species associated with adaptation to aridity
Range of leaf conductance
Productivity (g m-2 y-1)
N uptake (g m-2 y-1)
Tight coupling of nutrient cycling in an ecosystem and the functional diversity of dominant plant species
Relative conducting abilities of aboveground and belowground structures – surface area characteristics
Biomass is often used as a proxy of this allocation of energy to function (both surface exchange capacity and rates of exchange)
Compensatory changes in each exchange surface result in different patterns of growth
The physiological underpinnings of these two strategies are quite different but as a result of physiological trade-offs, these strategies may be highly correlated
Because of these trade-offs, there are not “competitively superior species” for all environments