Showing papers by "Ernst Detlef Schulze published in 1987"

Water Transport in Maize Roots: Measurement of Hydraulic Conductivity, Solute Permeability, and of Reflection Coefficients of Excised Roots Using the Root Pressure Probe

Abstract: A root pressure probe has been used to measure the root pressure (Pr) exerted by excised main roots of young maize plants (Zea Mays L.). Defined gradients of hydrostatic and osmotic pressure could be set up between root xylem and medium to induce radial water flows across the root cylinder in both directions. The hydraulic conductivity of the root (Lpr) was evaluated from root pressure relaxations. When permeating solutes were added to the medium, biphasic root pressure relaxations were observed with water and solute phases and root pressure minima (maxima) which allowed the estimation of permeability (PSr) and reflection coefficients (σsr) of roots. Reflection coefficients were: ethanol, 0.27; mannitol, 0.74; sucrose, 0.54; PEG 1000, 0.82; NaCl, 0.64; KNO3, 0.67, and permeability coefficients (in 10−8 meters per second): ethanol, 4.7; sucrose, 1.6; and NaCl, 5.7. Lpr was very different for osmotic and hydrostatic gradients. For hydrostatic gradients Lpr was 1·10−7 meters per second per megapascal, whereas in osmotic experiments the hydraulic conductivity was found to be an order of magnitude lower. For hydrostatic gradients, the exosmotic Lpr was about 15% larger than the endosmotic, whereas in osmotic experiments the polarity in the water movement was reversed. These results either suggest effects of unstirred layers at the osmotic barrier in the root, an asymmetrical barrier, and/or mechanical effects. Measurements of the hydraulic conductivity of individual root cortex cells revealed an Lp similar to Lpr (hydrostatic). It is concluded that, in the presence of external hydrostatic gradients, water moves primarily in the apoplast, whereas in the presence of osmotic gradients this component is much smaller in relation to the cell-to-cell component (symplasmic plus transcellular transport).

Plant Water Balance

Abstract: A lthough water is the earth's most abundant compound, lack of water is the major factor limiting terrestrial plant productivity on a global scale (Turner and Kramer 1980). Worldwide losses in crop yields from water deficits probably exceed the losses from all other causes combined (Kramer 1980). In natural plant communities, water deficits influence the distribution and abundance of many species. About half the earth's terrestrial communities, including dry tropical woodlands, savannahs, and grasslands, mediterranean woodlands and scrub, and temperate steppes, semideserts, and deserts, regularly experience extended periods of limited rainfall. Even very wet communities, such as lowland tropical rainforests, may experience moderate water deficits on a regular diurnal basis, with severe water deficits occurring every few

Plant Specialization to Environments of Different Resource Availability

Abstract: Plants exert a major control over ecosystem processes, because they are the organisms through which carbon and nutrients enter the biota, and because plant parameters strongly influence the fluxes through ecosystems. Plants operate under certain rules of cost and benefit under which they adjust their rates of resource acquisition and patterns of resource partitioning (Orians and Solbrig 1977; Schulze 1982; Bloom et al. 1985). Both acquisition and partitioning determine plant growth and biomass losses, which in turn influence the transfer of resources to other trophic levels of the ecosystem. Plants are specialized to the large variety of terrestrial habitat conditions by different plant life forms (Schulze 1982) or by variations in life histories, physiological specializations, and morphological or cytological modifications which determine the actual competition within the community (Grime 1977). Plants of a given species are capable only to a certain degree of using available resources, and, if resources are available beyond this range, the community shifts toward a different group of dominant species which in turn also alter the habitat by changing the availability of light, carbohydrates, and nutrients, and the fluxes of resources through the ecosystem.

Heterosis in hybrid larch (Larix decidua x leptolepis) I. The role of leaf characteristics

Abstract: Among 33-year-old forest trees ofLarix decidua, L. leptolepis andL. decidua x leptolepis, the hybrid possessed an above-ground biomass which was three times greater, although all larches displayed similar relative distributions of biomass. At a “relative growth rate” slightly lower than in the parent species, hybrid larch achieved twice the annual carbon gain, increment in stem length and above-ground production, and its foliage-related stem growth was higher than in European (L. decidua) but similar to Japanese (L. leptolepis) larch. A similar “relative growth efficiency” and foliage-related total above-ground production in all trees did reflect the similarity of photosynthetic capacity of the hybrid found at the leaf level. While the lengths of lateral twigs on hybrid branches were intermediate between the European larch with short, and the Japanese larch with large, twigs the hybrid possessed the longest branches with the highest needle biomass. This resulted in a crown structure of the hybrid crown similar to the Japanese larch together with a high needle density on branches as in the European larch. In total, the foliage biomass per crown length was about 30% higher in hybrid larch than in both of the parent species. Thus, the high carbon input for the stem heterosis was based on a “complementation principle” of advantageous parent features at the crown level. Similar slopes of foliage against sapwood area of stem and branches did not indicate a special need for a thick hybrid stem with respect to water transport.