Water Influx Characteristics and Hydraulic Conductivity for Roots ofAgave desertiEngelm.

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Abstract
Various plant and environmental factors influence the hydraulic properties for roots, which were examined using negative hydrostatic pressures applied to the proximal ends of individual excised roots of a common succulent perennial from the Sonoran Desert, Agave deserti Engelm. The root hydraulic conductivity, Lp, increased substantially with temperature, the approximately 4-fold increase from 0.5°C to 40°C representing a Q10 of 1.45. Such variations in Lp with temperature must be taken into account when modelling water uptake, as soil temperatures in the root zone of such a shallow-rooted species vary substantially both daily and seasonally. At 20°C, Lp was 2.3 × 10−7 m s¯1MPa¯1for 3-week-old roots, decreasing to about half this value at 10 weeks and then becoming approximately halved again at 6 months. For a given root age, Lp for rain roots that are induced by watering as lateral branches on the established roots (which arise from the stem base) was about the same as Lp for established roots. Hence, the conventional belief that rain roots have a higher Lp than do established roots is more a reflection of root age, as the rain roots tend to be shed following drought and thus on average are much younger than are established roots. Unlike previous measurements on root respiration, lowering the gas-phase oxygen concentration from 21% to 0% or raising the carbon dioxide concentration from 0.1% to 2% had no detectable effect on Lp for rain roots and established roots. Lp for rain roots and established roots was decreased by an average of 11% and 35% by lowering the soil water potential from wet conditions (ψsoil=0 kPa) to ¯40 kPa and ¯80 kPa, respectively. Such decreases in Lp may reflect reduced water contact between soil particles and the root surface and should be taken into account when predicting water uptake by A. deserti.