No abstract

A 34.5 m borehole, which was drilled near the Dead Sea coast (altitude -394 m) in the southern part of the fan delta of Wadi Zeelim, reveals the geological history of that area from the latest Pleistocene to present. The depositional time frame is based on six 14C dates and two U-Th dates. An erosional (or nondepositional) period is implied by the hiatus between 21,100 yr B.P. (U-Th age, depth 33 m) and 11,315 yr B.P. (14C age, depth 32 m). A subsequent arid phase is recorded by a 6.5-m-thick layer of halite; based on 14C dates this phase relates to the abrupt Younger Dryas cold period reported in temperate to polar regions. The fragility of the environment in this region is indicated by the fact that the region experienced such a severe, short aridification phase (less than 1000 yr), evidence of which is found widely in the desert fringes of the Middle East and North Africa. The aragonite found in most of the Holocene section indicates that the well site was covered by the lake for most of the Holocene. Exceptions are the intervals at 0-3 and 10-14 m depths which represent low stands of the lake.

SUMMARYRecovery from water stress was studied on similarly sized VA mycorrhizal and non-mycorrhizal rough lemon seedlings {Citrus jambhiri Lush). VA mycorrhiza affected stom.atal conductance, photosynthesis and proline accumulation, but not leaf water potential, suggesting that most of the effect of the mycorrhizal association is on stomatal regulation rather than on root resistance.

Summary Infection of rough lemon seedlings (Citrusjambhiri Lush) by the vesicular–arbuscular mycorrhizal (VAM) fungus, Glomus intraradices (Schenck and Smith), increased root growth and transpiration rate and reduced leaf water potentials relative to non‐infected control plants. Half of the VAM and control plants were subjected to three drying cycles each of 5 to 7 days. The hydraulic conductivity of previously drought stressed root systems was lower than that of the well‐watered plants and VAM infection further reduced root conductivity. These data suggest that the higher root densities and higher transpiration rates of VAM infected plants may have depleted soil water more quickly than the non‐infected seedlings and resulted in more severe water stress conditions during drought cycles.