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Does freezing set the latitudinal limit
of mangrove forests? Stuart, Stephanie*,1, Choat,
Brendan1, Holbrook, Michele1, Ball, Marilyn2,
1 Harvard University, Canbridge2 ABSTRACT- Coastal wetlands are dominated
by mangrove forests in the tropics, and by salt marshes at higher latitudes.
This world-wide transition from woody to herbaceous vegetation has long been
attributed to temperature, but fundamental mechanisms excluding woody plants
from tidal habitats at high latitudes are unknown. One possibility is that
freeze-thaw events could reduce the capacity for water transport to leaves
and stems. Dissolved gases excluded from developing ice crystals may form
bubbles that expand on thawing, causing conduits to become embolised, blocking water flow.
Mangroves could be particularly vulnerable to this type of freezing injury
because their xylem sap is subject to large negative pressures, or tensions,
even when transpiration is low, due to soil salinity. Tension is an important
determinant of bubble expansion; the more negative the pressure, the greater
the probability that a bubble will nucleate an embolism. Here we show that
constraints on water transport caused by interactions between xylem tension,
conduit diameter, and freezing temperatures impose latitudinal limits on the
distribution of halophytic trees. Key words: Mangrove, Freeze-Induced
Embolism, Avicennia, Rhizophora * Presenting Author |
