ROOT-SHOOT HYDRAULIC CONDUCTANCES OF THREE Eucalyptus SPP. CLONES TO DIFFERENT WATERING REGIMES

The fast growth of Eucalyptus spp. commercially used for wood and woodproducts in the forestry industry in South Africa. On the other hand,Eucalyptus plantings, which are believed to reduce the underground watersupplies while, consume large quantities of water, perhaps the main factorlimiting forestry expansion too. South African forestry industries are concernfor improving silvicultural practices by selecting water use efficientEucalyptus clones that would not only restrict water utilization, but to beoptimum productive. Recently, three Eucalyptus spp. clones namelyEucalyptus grandis x camaldulensis (GC550), Eucalyptus grandis xurophylla (GU21O) and a pure Eucalyptus grandis (TAGI4) were introducedto study the responses to water availability. Three Eucalyptus clones ofGC550, GU210 and TAGI4, each with six replicates were randomized andgrown for 21 months in 85 I pots. Water availability of high and low as per arainfall simulation was assessed in terms of hydraulic architecture of root,shoot and whole plant hydraulic characteristics. Hydraulic conductance wasmeasured on roots and shoots using the high-pressure flow meter (HPFM).HPFM measures maximum root-shoot conductances by transient and steadystate methods. Root data were expressed per unit root dry mass (Kr/trdw) andper unit leaf areas (Kr/LA), shoot data expressed per unit shoot dry mass(KS/tsdw) and per unit leaf area (KSILA), and whole plant conductance wasexpressed per unit leaf area (KpILA). KrlLA was higher in high watered plantsthan those receiving low water, and clonal differences were observed inKr/trdw. There was no treatment effect in KSILA and KS/tsdw, but a clonal effectwas apparent. KplLA was significantly different between treatments, and wasreduced by low water in two clones of GC550 and GU210, and increased bythis in TAG 14. Reduced water availability increased root resistances e/KrILA) , except in TAG 14 where treatment had no effect. GU210 had thehighest root resistances under both treatments. Reduced water availabilityreduced biomass production, with a greater effect on roots than shoots, suchthat low watering reduced root: shoot ratios

Uniform Selection as a Primary Force Reducing Population Genetic Differentiation of Cavitation Resistance across a Species Range

Background: Cavitation resistance to water stress-induced embolism determines plant survival during drought. This adaptive trait has been described as highly variable in a wide range of tree species, but little is known about the extent of genetic and phenotypic variability within species. This information is essential to our understanding of the evolutionary forces that have shaped this trait, and for evaluation of its inclusion in breeding programs. Methodology: We assessed cavitation resistance (P 50), growth and carbon isotope composition in six Pinus pinaster populations in a provenance and progeny trial. We estimated the heritability of cavitation resistance and compared the distribution of neutral markers (FST) and quantitative genetic differentiation (QST), for retrospective identification of the evolutionary forces acting on these traits. Results/Discussion: In contrast to growth and carbon isotope composition, no population differentiation was found for cavitation resistance. Heritability was higher than for the other traits, with a low additive genetic variance (h 2 ns = 0.4360.18, CVA = 4.4%). QST was significantly lower than FST, indicating uniform selection for P50, rather than genetic drift. Putativ