Agriculture Reference
In-Depth Information
zophora
species produce lateral roots from the base of the stems which form arch
and re-arch before reaching substratum. Prop roots in
Rhizophora
species produce
numerous thin unbranched roots at different heights. At ground level, they pro-
duce innumerable fibrous roots which help in absorption of water and nutrients.
Avicennia and Sonneratia
possess specialized finger like respiratory roots called
pneumatophores with lenticels for passive diffusion of oxygen. Oxygen may pass
through non-lenticellular part of the pneumatophores as well. Knee roots found in
Bruguiera, Ceriops, Lumnitzera
, etc., are lateral roots that bend upwards and come
above the ground where they make knee-like curve before entering into soil again
(Dagar et al.
1991
). Lenticels are common on the knee roots and they are also con-
sidered to help in gas exchange.
2.2 Physiological Adaptations
Existence of high osmotic and diffusion pressure deficit (DPD) of cell sap, ultra-
filtration mechanism of ions and salt-secreting glands are some of the physiological
adaptations. Salt tolerance-related physiological adaptations are dealt subsequently
in this chapter.
2.3 Anatomical Adaptations
Leaves have thick-walled epidermis with thick layer of cuticle and adequate tis-
sue. Palisade tissue is well developed; water stomata are present in some cases, for
example
Aegiceras corniculatum
; Mucillage cells occur in some species such as
Sonneratia, Rhizophora
, etc. The aerial roots on reaching the ground show short
elongation zone and almost non-existent secondary growth. Like in aquatic plants,
there are no root hairs in true mangroves and the endodermis acts as an effective
absorbing layer (Tomlinson
1986
). Mangrove woods exhibit unique anatomical
features that enable the plants to withstand the high osmotic potential and the tran-
spiration caused by high temperature (Tomlinson
1986
). A number of vessels run
through the wood and helps in developing high tension in the xylem (Scholander
et al.
1964
,
1965
; Tomlinson
1986
).
2.4 Reproductive Strategies
Four methods of reproduction in mangroves have been described by Bhosale and
Mulik (
1991
). These are:
1. Vivipary
2. Cryptovivipary
