Agriculture Reference
In-Depth Information
There is good intraspecific evidence for prolonged leaf longevity in response
to aridity. For example,
Encelia farinosa
is a drought-tolerant shrub distributed
along a precipitation gradient in Arizona and California. Its leaves become more
tomentose under drier conditions, decreasing rates of transpiration but also
increasing the cost of leaf construction as well as reducing photosynthetic capacity.
Hence, the payback period on leaf construction is extended and leaves survive
longer in the drier regions (Sandquist and Ehleringer 1998). Similar results were
found when the effect of drought on leaf longevity was investigated experimen-
tally in
Cryptantha flava
, a desert shrub in Utah (Casper et al. 2001). Leaf
longevity was compared between plants receiving half versus all natural precipi-
tation. Stomatal conductance and photosynthetic rates were lower in the plants
receiving less precipitation, and as expected leaf longevity became longer:
leaves present at the initial census persisted 49.2 days in the dry plot versus 22.6
days in the control (Fig.
8.3
). Similar trends occur in the dioecious shrub
Pistacia lentiscus
in southern Spain where precipitation ranges from 350 to
1,000 mm year
−1
in a Mediterranean climate regime (Jonasson et al. 1997). Leaf
longevity in male plants of
P. lentiscus
was shorter under more-arid conditions;
the relationship in female plants was the same, but it was not statistically signifi-
cant because of confounding effects from variation in fruit production (Jonasson
et al. 1997). A severe drought extended leaf longevity in five species of decidu-
ous trees in a Swiss forest, mostly because of later leaffall (Leuzinger et al.
2005). In general, we can expect drought to extend leaf longevity within species
but not always among species.
12
Drought
Control
10
8
6
4
2
0
140
145
150
155
160
165
170
175
Julian date
Fig. 8.3
Effect of drought treatment on leaf longevity in the desert plant
Cryptantha flava
. Leaf
longevity was prolonged by drought. (From Casper et al. 2001)
