The water status of Terminalia brownie seedlings was assessed in relation to incident microclimate and initial irrigation treatments, during establishment at Olorgesailie in the Rift Valley of Kenya. Experimental treatments involved incorporation of a water-absorbing polymer with the root systems of the plants during establishment, and repeated irrigation, in a factorial design. The maximum photosynthetically active radiation of over 2500 μmol/m<sup>2</sup>/s recorded during the first 9 days after outplanting was associated with air temperatures of up to 47•4°C, and leaf-to-air vapour pressure deficits (VPDs) of up to 8•04 kPa. Water potentials declined to a minimum of -3•7 MPa, 9 days after out-planting, indicating severe water deficits. Stomatal conductances were generally below 0•2 cm/s, reflecting a high degree of stomatal closure. However, conductances of over 1•3 cm/s were observed on the 6th day after out-planting, associated with VPDs below 1•5 kPa. These relatively high conductances were restricted to plants which had received irrigation; overall, irrigation was found to significantly increase stomatal conductance on three of the four measurement days. Although the application of synthetic polymers increased stomatal conductances on two of the measurement days, the effects were very slight (treated means 0•02-0•03 cm/s higher than controls). These results indicate the severity of the transplant shock in semi-arid sites for seedling water status, and imply that initial irrigation treatments are more likely to increase establishment rates of tree seedlings than application of synthetic polymers.
Journal of Arid Environments (1993) 25 (4) 363-374 [DOI: 10.1006/jare.1993.1069]