Water Use and Drought Response in Cultivated and Wild Apples - Abiotic Stress: Plant Responses and Applications in Agriculture - page 251

by cDNA-AFLP analysis showed genotype-specific expression patterns related to the indige‐
nous environment (population). In another study populations of Encelia farinosa growing over
a broad rainfall gradient in the deserts of southwestern North America, were evaluated for
leaf characteristics. Leaf pubescence declined as mean water availability increased [19].
Variations among populations for both pubescence and carbon isotope discrimination
persisted when the plants were grown in common environments differing in water availability,
indicating a genetic basis for variation in these traits [20].
WUE in trees adapted to different environments has been documented in several forest species
[21-24]. For example, a study of four birch ( Betula pendula Roth) clones from environments with
different rainfall amounts indicated strong clonal differences in a number of water use and
photosynthetic traits, including leaf δ 13 C values [21]. A follow-up study correlated differences in
leaf and root morphological parameters and carbon partitioning with clones from the drier
environments [25]. Although individual leaf areas were smaller in drought-treated clones,
regardless of their region of origin, total leaf and specific leaf areas (leaf area/leaf weight) were
actually higher for the drought-treated clones from the drier environment. This is in contrast to
the often observed reduction in leaf surface area seen in plants exposed to water deficit (WD) [26].
Poplar species are differentially adapted to a variety of environments, and because poplar is
a rapidly growing tree with heavy water use, there is growing interest in developing lines that
are drought resistant. Links between productivity and Δ 13 C varied in a study comparing
different poplar genotypes, suggesting that genotypes displaying simultaneous high produc‐
tivity and improved water use efficiency could be selected [27]. To obtain more practical
information regarding productivity and WUE, a field study was conducted on the same
genotypes analyzed in the previous study. Significant clonal diversity was observed for several
traits related to productivity and for Δ which showed high heritability (H2 = 0.71) [28]. A lack
of correlation between above ground biomass and Δ was reflected in several clones where high
productivity was combined with improved WUE. This observation supports previous studies
with cereals indicating that WUE and yield can be inherited as separate traits.
Yield of deciduous tree fruit crops is not measured as total biomass yield in commercial produc‐
tion as are agronomic crops such as corn, wheat and rice or forest trees. In commercial orchards
it is common practice to reduce yield potential of fruit trees by as much as 50% to insure large fruit
size and high fruit quality [29]. Consequently, the paradigm that increased WUE is tied to reduced
yield potential is not necessarily valid for tree fruit production. For example, Glenn et al. [30] have
demonstrated the practicality of identifying peach cultivars with high WUE without compromis‐
ing productivity. This study, taken together with those cited previously, demonstrates the
feasibility of selecting for improved WUE without loss in productivity.
4. Adaptation, WUE and δ 18 O
Transpiration rate (E) affects water loss to the atmosphere and is negatively correlated with
WUE. Despite the fact that atmospheric 18 O is low (ca. 0.2% of total oxygen), plants tend to
accumulate 18 O and 2 H in leaf water due to the difference in vapor pressure between heavy