Agriculture Reference
In-Depth Information
potential of young leaves before they are offset by increasing costs associated with
salt excretion. In this instance, the shift from leaf to whole-plant level in resolving
the stress arises not in limits to tissue repair but in competing foliar functions.
Abiotic Stressors: Flooding
Flooding can impair leaf function in terrestrial plants through two effects: submer-
sion, which cuts off access to atmospheric CO
2
, and anaerobic conditions in the root
zone that impair root function and reduce the transpirational stream to emergent
leaves (Mommer et al. 2006; Parolin 2009). Depending on their degree of flood
tolerance, species differ in the impact of flooding on leaf longevity (Terazawa and
Kikuzawa 1994).
Alnus japonica
, a flood-tolerant riparian species, responds to
flooding by developing adventitious roots near the surface and lenticels on the stem
for air exchange; leaf longevity is prolonged under relatively short or shallow flood-
ing conditions but shortened by deeper or long flooding. The response of leaf lon-
gevity is reversed in the upland, flood-intolerant
Betula platyphylla
var.
japonica
(Terazawa and Kikuzawa 1994). Similarly, in herbaceous species from wetlands,
submergence in water through which light can penetrate prolongs leaf longevity,
but in species from terrestrial habitats leaf longevity is shortened by submergence
(Mommer et al. 2006). Most trees species submerged by the muddy floodwaters of
the Amazon River immediately lose all their leaves, but others retain leaves
throughout floods that can persist up to 9 months of the year; in some cases the
retained leaves may actually carry on photosynthesis during submergence and in
others only resume aerial photosynthesis as the flood recedes (Parolin 2009). For
most of these Amazonian trees, flooding is an unfavorable period for photosynthe-
sis, more akin to winter or prolonged drought than to an abiotic stress in which a
dose-response relationship determines shifts in leaf longevity.
