We hypothesized that for similar trunk circumferences and leaf masses, under similar climatic conditions, the canopy structure of Cupressus sempervirens L. influences transpiration rate such that the faster transpiring var. horizontalis exhausts the winter's allocation of rainfall earlier, to its own subsequent detriment.

To verify this assumption, heat pulse velocity measurements, by means of the heat pulse method, were done at eight periods during the year in the stem xylem of eight matched pairs of trees, each pair composed of a var. horizontalis and a var. pyramidalis tree of similar dimensions.

Results showed that during the daylight hours in winter and spring, midday sap flow velocity of var. horizontalis trees was greater than that of var. pyramidalis trees of similar trunk circumferences and foliage mass. Hence, the calculated average daily transpiration of var. horizontalis trees was nearly 50% greater than that of var. pyramidalis trees. During the wet period (November to May), mean daily transpiration of var. horizontalis exceeded, with 2.91 dm3 per tree, that of var. pyramidalis. This amount adds up to an additional water consumption of ~500 dm3 per tree during 170 clear-sky days within that period. This higher water consumption by var. horizontalis reduces the spatial soil-water storage and availability in the late spring and early summer, thereby prolonging the water stress period that might become critical under droughty winter conditions.

Thus, at afforestation sites under given soil and bedrock conditions, e.g., spatial and temporal water availability for each tree, the canopy structure will be the decisive factor influencing the development (time and amount) of the soil-water stress.

In: Israel Journal of Plant Sciences

Forest trees possess high genetic diversity and high heterozygosity which allow adaptation to changing environmental conditions. There is a tendency to propagate successful and unique genotypes, which are identified at their mature stage in the forests, for future improvement programs and conservation purposes. However, vegetative propagation of mature forest trees is still a challenge in many conifers. In this study, we focused on improving the rooting of cuttings of mature and old Pinus halepensis and its hybrids. We observed that storage of cuttings before rooting at 4°C for 4 weeks and prolong immersion of cuttings in a solution containing 400 mg/l of indole-3-butyric acid, 5 mg/l of the auxin conjugate 2-(2,4-dichlorophenoxy)propanoic acid-glycine methyl ester, and 0.01% of Amistar fungicide significantly improved rooting of mature cuttings. The active ingredient in Amistar is azoxystrobin, an uncoupler of respiration, which seems to directly promote rooting. Rooted cuttings of selected clones demonstrated unique and uniform growth performance, most likely delivering the intrinsic growth parameters of the mother trees. It was also observed that trees growing under drought stress possess improved rooting ability. By using rooted cuttings, it will be possible to study the relationship between growth rate and adaptation to semi-arid climate conditions. The ability to clonal propagate mature and old P. halepensis trees not only enables vegetative propagation of elite trees for improvement programs, but also provides an opportunity to preserve unique naturally occurring old P. halepensis genotypes.

In: Israel Journal of Plant Sciences