Gaseous exchange of Simmondsia chinensis [(Link) Schneider] (a desert shrub which may provide a substitute for sperm whale oil) was studied by exposing leaves simultaneously to radioisotopes of water (3HHO) and CO2 (14CO2) to determine conductances to water vapor and total conductances to CO2 assimilation, respectively. Fixation rates of CO2 and mesophyll conductances to CO2 were calculated. Leaf conductance to water vapor and CO2 fixation rates decreased markedly only at very low values of soil‐water and leaf‐xylem pressure potentials and recovered to maximum values after having been subjected to soil water potentials below ‐‐40 bars, indicating the extreme drought tolerance of S. chinensis. The ratios of increased as water stress became more intense, suggesting that transpiration was reduced relatively more than photosynthesis, which could have considerable value under drought stress. Plants under intense water stress generally had little or no reduction in mesophyll conductance to CO2.There was no significant decrease in conductance to water vapor, CO2 fixation rate, or mesophyll conductance to CO2 with increasing salinity down to root medium osmotic potentials as low as —9 bars. This is consistent with the reported high salt tolerance of S. chinensis. Nitrogen‐deficient plants had significant reductions in CO2 fixation rate and mesophyll conductance to CO2 but not in conductance to water vapor.

Amounts of soil boron extracted from six Canterbury, New Zealand soils by hot water (HWS), hot 0.02 M CaCl2, 0.01 M CaCl2 + 0.05 M mannitol, and a boron specific resin were significantly (P < 0.01) correlated with each other. The soils are all formed from greywacke alluvium and/or loess but cover a range of organic matter and clay contents. Hot water and hot 0.02 M CaCl2 yielded higher levels of extractable boron than did 0.01 M CaCl2 + 0.05 M mannitol and the resin. Amounts of boron extracted by all four reagents were significantly correlated with soil organic carbon contents (and to a lesser extent clay contents), but not with soil pH. Dry matter yield and boron uptake by radishes (Raphanussativus L.) over two harvests increased with increasing extractable soil boron for all four extractants showing that all were suitable for assessing the boron available to radishes. Decreased yields occurred in soils with HWS or hot 0.02 M CaCl2 extractable boron levels less than 1.1 �g g-1 and were associated with a progressively lower allocation of dry matter to roots. For analytical purposes, the hot 0.02 M CaCl2 reagent provided the most convenient measure of available soil boron.

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Jo]oba (Simmondsia chinensis (Link) Schneider) is desert shrub which can provide a much needed substitute for sperm whale oil. Because of the absence of soil‐plant‐water data for jojoba and the limited amount of such information for desert plants in general, selected plants were water‐ and salt‐stressed in greenhouse soil and sand culture experiments. Responses of leaf water, osmotic, and turgor potentials to stress and associated stomatal behavior were studied. Leaf water potentials of well watered jojoba plants (measured with thermocouple psychrometers) averaged —20 bars in the daytime and were generally below —10 bars at night, very low in comparison to most mesophytic plants. The recovery of plants which were water stressed to leaf water potentials below —50 bars (soil water potentials below —40 bars) indicates great drought tolerance. Turgor potential decreased linearly with decreasing leaf water potential, showing a lack of osmotic adjustment as leaf water potentials fall below about —30 bars. Turgot potential reached zero at a leaf water potential of about —35 bars, and dropped as low as —10 bars under the most severe water stress without wilting of mature leaves. Plants in the salinity experiment showed osmotic adjustment down to a root medium osmotic potential of —9 bars. Values of leaf conductance decreased markedly only at very low xylem pressure potentials (pressure chamber measurements) and soil water potentials (—40 bars and —20 bars, respectively), corresponding to about the same values at which turgor potential reached zero. Stomatal closure was continuous with increasing water stress, rather than occurring abruptly at a threshold. There was no significant decrease in leaf conductance at root medium osmotic potentials as low as —9 bars in the salinity experiment. Conductances of well watered plants to water vapor on lower leaf surfaces were typically similar or greater in value than those of upper leaf surfaces, whereas plants under water stress showed significantly higher conductances on their upper leaf surfaces rather than lower leaf surfaces. Leaf xylem pressure potentials decreased with increasing transpiration rate under non‐limiting soil water conditions and decreased below values predicted for well watered plants at the same transpiration rate as soil water potentials decreased. Thus it was possible to make an estimate of edaphic limitations of water absorption based on leaf xylem pressure potentials despite variation in the pressure potentials in response to microclimatic changes.

The nature and extent of textural layering was investigated in 367 profiles described during a 30 by 30 m grid survey of an area of Ochrepts developed on a Holocene floodplain in the South Island of New Zealand. The typical profile texture form (to 1 m) consists of a uniform textured layer of varying thickness (but less than 60 cm), underlain by a texturally layered portion in the B horizon and below. Textures in the layered portion ranged from heavy silt loams to sands. The number of layers ranged from one to thirteen with six to eight being the most usual. The pattern of textural layering is random and hence unpredictable, and is the result of sedimentary depositional processes forming the parent material of these alluvial soils. Continuous (short range) lateral variability in textural layering was similar to that identified during the 30 by 30 m grid survey.