Abstract
Rhodospatha oblongata (Araceae) is an aroid vine which reaches maturity at trees canopies. The beginning of R. oblongata’s ascension towards the canopy occurs when one of the branches reaches the stem of a host, being able to reach eight to ten meters in height. Throughout this ascendant path R. oblongata develops two types of aerial roots: the anchor roots, which is shorter and adhered to the host, never reaching the soil; and the feeder roots, which is long, also adheres to the host but connects the vine to the forest soil. Both roots are here compared in morpho-physiological aspects related to the efficiency of axial hydraulic conductivity. Two hypotheses are tested: i) both roots present distinct xylem hydraulic conductivity; ii) hydraulic conductivity of both roots vary with plant size. The characterization of the roots was based on crescent R. oblongata individuals divided in five size classes. Thirty specimens of each anchor and feeder roots were analyzed along plant size increase. Both roots gradually increase in number and external diameter while the R. oblongata vertically ascends to reach plant canopies. The stele of both roots increase in diameter, in order to accommodate xylem vessels that became larger. The increase in these morpho-anatomical parameters has a positive influence on the xylem hydraulic conductivity, that also increases along the ascendant way of R. oblongata. Comparative measurements show that in general anchor roots present smaller morpho-anatomical structures and lower hydraulic conductivity in comparison to feeder roots. Xylem diameter distribution is unimodal for anchor roots, but bimodal for feeder ones. While all feeder roots present a great concentration of vessels around 60 mm of diameter, the second peak occurs at xylem diameter values that increase with plant size. These modifications optimize the root water transport while the vegetative body of R. oblongata increases in size, connecting its leaves at canopies to the soil water with elevated hydraulic efficiency
Highlights
Aroid vines that begin their life cycle as terrestrial plants and later ascend up to the canopy may undergo profound external morphological modifications of the vegetative body, a growth type classified as allomorphic by Ray (1990)
Two aerial root types are developed during the ascendant phase: anchor roots that attach the vine to the host trunk and feeder roots that descend and establish a connection with the soil (Croat, 1988)
Anatomy and physiology The influence of root size on the respective hydraulic conductivity of these root types was evaluated for 30 anchor roots and 30 feeder roots
Summary
Aroid vines that begin their life cycle as terrestrial plants and later ascend up to the canopy may undergo profound external morphological modifications of the vegetative body, a growth type classified as allomorphic by Ray (1990) As they grow toward the canopy, they gradually develop shorter and thicker internodes that support larger leaves. Two aerial root types are developed during the ascendant phase: anchor roots that attach the vine to the host trunk and feeder roots that descend and establish a connection with the soil (Croat, 1988) Both types present size increase in external and stele diameter, as well as xylem vessel diameters, along plant growth, potentially improving hydraulic conductivity to larger leaves
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