1 . Lack of Freshwat er or Hi gh Sali ni t y Condi t i on

1 . Lack of Freshwat er or Hi gh Sali ni t y Condi t i on

Mang ro ves are surro unded by salt water, and the trees have to abso rb salt water instead o f freshwater. Thus mang ro ves have develo ped vario us mec hanisms to reg ulate the salt c o nc entratio n in the plant. These mec hanisms inc lude extrac tio n o f freshwater fro m salty water, blo c king o ut the salt at the ro o t level,

g etting rid o f exc ess salt o n their leaves, salt sec reting leaves and sto rag e o f salt and absc issio n. In o rder to be able to abso rb any water at all fro m the salty brine, their plant c ells maintain a very hig h

o smo tic pressure. In o ther wo rds, the salt c o nc entratio n inside the c ell is hig her than that o f seawater.

A c o mplic ated ultrafiltratio n mec hanism in the mang ro ve ro o ts allo ws the diffusio n o f water to wards the hig her salt c o nc entratio n within the c ells, but prevents any intake o f salt.

Variatio n o f salt c o nc entratio n influenc es the distributio n o f mang ro ve spec ie s in the mang ro ve fo rest. Ce rtain spe c ie s o f mang ro ve s e xc lude salt fro m the ir syste ms, o the rs ac tually e xc re te the salt the y take in via the ir le ave s, ro o ts, o r b ranc he s. So me mang ro ve plants c an also sto re wate r ( salt suc c ule nc e ) in o rde r to dilute hig h salt c o nc e ntratio ns. In additio n, the y c an she d le ave s impre g nate d with salt, and so me have salt g lands and salt hairs fo r the purpo se s o f e xc re ting e xc e ss salt. Sinc e the diffe re nt spe c ie s have varying

de g re e s o f suc c e ss in c o ping with the e xc e ssive salt le ve ls. The pro g re ssive ly hig he r c o nc e ntratio ns o f salt mo ving inland, influe nc e the distrib utio n o f spe c ie s in the mang ro ve fo re st.

Mang ro ve plants in a nursery

4 6 Mang ro ves – Func tio ns and Threats

In salt exc luding mang ro ve spec ies the mang ro ve ro o t system is so effec tive in filtering o ut salt that a thirsty traveller c o uld drink fresh water fro m a c ut ro o t, tho ug h the tree itself stands in saline so il.