Table 2 Mean plant water potential at Homeb for the different species.
Table 3 The mean plant water potential (±SD) of C. mopane recorded at Salambala in different seasons (dry season in August 2001, 'extreme' dry season in June 2002 and early rainy season in November 2002).
Mean minimum water potential Ψb50 has been found to vary among species [ 83], populations [ 84], and sites [ 41], whereas Tb is assumed mostly constant within species [ 85].
Soil water content mean β was 0.1 0.2 (range 0.03 0.31) in the clay and silty clay soils, increasing to 0.85 (range 0.50 1.04) on the sandy loam soil (Fig. 5A), which also had the highest mean soil water potential (Fig. 5A, inset).
The strong community change/productivity responses occurred on the two soils with high mean soil water potential (Fay et al. 2012), suggesting that the overall availability of soil water, not the increase in soil water content, determines community and productivity responses to CO2 enrichment.
V. erioloba indicates relatively low values: On average, this species indicates a mean pre-dawn water potential of around −1.78 ± 0.64 MPa (N = 7) and a mean midday water potential of −2.11 ± 0.55 MPa (N = 7).
Mean predawn leaf water potential reached −0.10, −0.49 and −0.75 MPa in the optimal, intermediate and low irrigation treatments respectively.
The water potentials assessed in August 2001 reflect a situation where all three stands indicate an overall mean pre-dawn water potential with low standard deviation (SD) of −1.60 (± 0.43) MPa and midday values of around −4.19 (± 0.32) MPa.
While the laboratory has now institutionalized weapons of mass destruction testing to be performed as part of routine surveillance (e.g., testing of drinking water), potential means and targets for future attacks cannot be perfectly forecast.
Following Mitlöhner (1995, 1998), the mean values of the pre-dawn water potential are understood reflecting the soil water availability within the rhizosphere, while the mean values of the plant water potential at midday are picturing the internal availability of water in the plant in the actual, least favourable situation.
