Ejw. Visser et al., FLOODING-INDUCED ADVENTITIOUS ROOTING IN RUMEX - MORPHOLOGY AND DEVELOPMENT IN AN ECOLOGICAL PERSPECTIVE, Acta botanica neerlandica, 45(1), 1996, pp. 17-28
The formation of aerenchymatous adventitious roots is a morphological
acclimation to soil flooding in many wetland plants. The large air spa
ces in these roots facilitate the diffusion of gases between shoot and
root. This study investigated adventitious root formation in species
of the genus Rumex, and related the differences between species to the
natural habitat of the species. Large differences in both the number
and the morphology of the adventitious roots were found between closel
y related species. R. hydrolapathum, a species of almost permanently w
aterlogged soils, showed only a slow growth of adventitious roots, but
these roots were extremely porous and very thick. R. palustris, which
is flooded very frequently but not permanently, developed a large num
ber of adventitious roots with a high content of aerenchyma. On the ot
her hand, adventitious rooting in R. thypsiflorus and R. acetosa, whic
h are species of dry and seldom flooded habitats, was rather poor and
the adventitious roots contained only very little air space. A group o
f species occurring in regularly flooded grasslands (R. crispus, R. co
nglomeratus and R. obtusifolius) showed an intermediate response to so
il flooding. Two contrasting species, R. palustris and R. thyrsiflorus
, showed emergence of adventitious roots within 2 days after the onset
of waterlogging. Although the time of onset of adventitious rooting w
as similar in these two species, the primary lateral root system of R.
palustris was completely replaced by adventitious roots in 1 week, in
dependently of the age of the plants. In contrast, the biomass of adve
ntitious roots in R. thyrsiflorus after 1 week of flooding was never m
ore than one-third of the biomass of the primary lateral root system.
We concluded that the ability of species to form adventitious roots du
ring flooded soil conditions and the adaptive characteristics of these
roots were very closely related to the flooding frequency of these sp
ecies in their natural habitat. Differences in adventitious rooting be
tween species mainly occurred in the number, growth rate, morphology a
nd anatomy of the roots, and not in the timing of emergence.