The gradient between pre‐dawn rhizoplane and bulk soil matric potentials, and its relation to the pre‐dawn root and leaf water potentials of four species

Abstract

Uptake of soil water by plants may result in significant gradients between bulk soil and soil in the vicinity of roots. Few experimental studies of water potential gradients in close proximity to roots, and no studies on the relationship of water potential gradients to the root and leaf water potentials, have been conducted. The occurrence and importance of pre-dawn gradients in the soil and their relation to the pre-dawn root and leaf water potentials were investigated with seedlings of four species. Pre-germinated seeds were grown without watering for 7 and ltd in a silt loam soil with initial soil matric potentials of-0-02, -0-t and -0-22 MPa. Significant gradients, independent of the species, were observed only at pre-dawn soil matric potentials lower than -0-25 MPa; the initial soil matric potentials were > -0-t MPa. At an initial bulk soil matric potential of -0-22 MPa, a steep gradient between bulk and rhizoplane soil was observed after 7 d for maize (Zea mays L. cv. Issa) and sunflower {Heliaiithus annuiis L. cv. Nanus), in contrast to barley {Hordeum vulgare L. cv. Athos) and wheat {Triticum aestivum L. cv. Kolibri). Predawn root water potentials were usually about the same as the bulk soil matric potential and were higher than the rhizoplane soil matric potential. Pre-dawn root and leaf water potentials tended to be much higher than rhizoplane soil matric potentials when the latter were lower than -()-5 MPa. It is concluded that plants tend to become equilibrated overnight with the wetter bulk soil or with wetter zones in the bulk soil. Plants can thus circumvent negative effects of localized steep pre-dawn soil matric potential gradients. This may be of considerable importance for water uptake and growth in drying soil.

Impacts of water stress, environment and rootstock on the diurnal behaviour of stem water potential and leaf conductance in pistachio (Pistacia vera L.)

“…PT compared to other Mediterranean plants was considered by Sakcali & Ozturk (2004) as a water spender and described it as a partially water-tolerant species which cannot sustain long in harsh conditions. These results differ from those reported by Germana (1997) and Gijón et al (2010) for potted pistachio plants, where PA is considered as a rootstock with little stomatal control compared to PT. In this study, PA maintained lower g l than PT and PI during stage II, but during stage…”

Assessing Water Stress of Desert Tamarugo Trees Using in situ Data and Very High Spatial Resolution Remote Sensing

“…Significant differences between mean values of the scenarios are indicated. Pre-dawn water potential was significantly lower for trees under long-term gradual depletion (Dep3-grad), implying that the water surrounding the root system was less available for these trees [43][44][45], and consequently, they were facing higher water stress than Dep1-null and Dep2-int. Additionally, the biochemical analysis showed that only trees with no groundwater depletion (Dep1-null) had higher values of EWT than trees under Dep2-int and Dep3-grad.…”

MAESPA: a model to study interactions between water limitation, environmental drivers and vegetation function at tree and stand levels, with an example application to [CO<sub>2</sub>] × drought interactions

“…The advantage of a multi-layer soil model is that the root density distribution can be specified, as well as vertical variation in soil texture. Furthermore, experiments have shown that plant water potential tends to equilibrate with the wettest zones in the soil, not the average soil water potential (Schmidhalter, 1997). Only a multi-layer soil model can reproduce this observation.…”