Osmotic adjustment and energy limitations to plant growth in saline soil.

Plant roots must exclude almost all of the Na and Cl in saline soil while taking up water, otherwise these ions would build up to high concentrations in leaves. Plants evaporate c. 50 times more water than they retain, so 98% exclusion would result in shoot NaCl concentrations equal to that of the external medium.

Hydraulic processes in roots and the rhizosphere pertinent to increasing yield of water-limited grain crops: a critical review.

A review of the role of roots in extracting water from the soil with regard to amount and timing leading to maximal grain yield, and of the various mechanisms underlying this.

Root hairs enable high transpiration rates in drying soils.

Do root hairs help roots take up water from the soil? Despite the well-documented role of root hairs in phosphate uptake, their role in water extraction is controversial. We grew barley (Hordeum vulgare cv Pallas) and its root-hairless mutant brb in a root pressure chamber, whereby the transpiration rate could be varied whilst monitoring the suction in the xylem. The method provides accurate measurements of the dynamic relationship between the transpiration rate and xylem suction.

Osmotic adjustment leads to anomalously low estimates of relative water content in wheat and barley.

Relative water content (RWC) is used extensively to determine the water status of plants relative to their fully turgid condition. However, plants often adjust osmotically to salinity or water deficit, which maintains turgor pressure and obscures the definition of 'full turgidity'. To explore this problem, turgor was measured by isopiestic psychrometry in mature leaf blades of barley (Hordeum vulgare) and durum wheat (Triticum turgidum ssp.

Viewpoint: The perils of pot experiments.

Experiments with plants in pots can be beset by several often-unrecognised artefacts. The soil or other medium at the bottom of a freshly watered and drained pot is inevitably saturated with water; if the pot is short the whole of the medium may have such little air-filled porosity that it becomes hypoxic. This is an especial problem with field soils used in pots, for these typically do not contain many pores large enough to be drained at the small water suctions that prevail.

The drought environment: physical, biological and agricultural perspectives.

'Drought' has many meanings in relation to crop production. These range from: statistical (say, the lowest decile of annual rainfall) to a meteorologist; through yield being limited by too little water to an agronomist; to sudden severe water deficits to many molecular biologists. To a farmer, the corresponding management issues, respectively, are risk management (how best to manage a meteorologically drought-prone farm over several years), how best to match cultivar and agronomic operations to the developing growing season, and how best to minimize possible major damage to (say) floral fertility induced by severe water deficits during flowering.

Rates of root and organism growth, soil conditions, and temporal and spatial development of the rhizosphere.

Background: Roots growing in soil encounter physical, chemical and biological environments that influence their rhizospheres and affect plant growth. Exudates from roots can stimulate or inhibit soil organisms that may release nutrients, infect the root, or modify plant growth via signals. These rhizosphere processes are poorly understood in field conditions.

Tissue stresses and resistance to water flow conspire to uncouple the water potential of the epidermis from that of the xylem in elongating plant stems.

Considerable evidence exists that, in elongating dicot stems such as soybean hypocotyls: (1) the elongation rate is controlled largely by the mechanical properties of the epidermal cell walls; (2) the inner tissue is under compression in the sense that the turgor pressure of the cells is not fully borne by their cell walls; (3) the surplus turgor pressure in this inner tissue generates a force that is transmitted to the epidermis, where it drives irreversible elongation of the cell walls; and (4) the radial flow of water from the xylem to the rest of the tissue, needed to fill the expanding cells, is driven by gradients in water potential. On the basis of these propositions, this paper develops a mathematical description of the biophysical control of elongation rate and the radial distribution of water potential in the growing plant stem. Additional simplifying assumptions are that the osmotic pressure of the cells and their elastic modulus are constant throughout, and that the proportion of the tensile force that is borne by the walls of the inner cells is also constant.

Review: Environmental biology and crop improvement.

The average yield of Australia's major grain crop, wheat, rose at its fastest rate ever during the last decade. The environmental biology behind this advance was predominantly ecological and nutritional - endemic root diseases were controlled through better management of inoculum levels, and the consequently healthier crops were more responsive to fertiliser, especially nitrogen. Applying nitrogen fertilisers became less risky; farmers used much more and thereby achieved much higher yields.