Phosphatverarmung des wurzelnahen Bodens und Phosphataufnahme von Mais und Raps

Abstract

Zusammenfassung -SummaryAus der Verteilung des isotopisch austauschbaren Phosphats wurde mit Hilfe der Phosphatdesorptionskurve festgestellt, daR die Phosphatkonzentration der Bodenlosung im Wurzelhaarbereich von 0,8 auf 0,03mg P/1, d. h. auf 4 % des Ausgangswertes, absinkt.Aus der Zunahme der Phosphatverarmungszone mit der Zeit wurde die Phosphataufnahme einzelner Maiswurzelabschnitte fur verschiedene Zeitintervalle errechnet. Danach erfolgt die P-Aufnahme 3-5 Tage lang in annahernd maximaler Rate, obwohl die P-Konzentration der Bodenlosung an der Oberflache des Wurzelzylinders schon nach 2 Tagen weit abgesunken war. Die Phosphataufnahmerate pro cm Wurzellange geht erst zuriick, nachdem der Boden des gesamten Wurzelhaarzylinders ausgeschopft ist. Phosphate depletion at the soil -root interface and the phosphate uptake of maize and rapeMaize and rape plants were grown in flat containers in a 33P-labelled sandy soil and the distribution of soil phosphate near roots was determined by using densitometric scans of autoradiographs. The concentration of isotopically exchangeable phosphate at the root surface decreased within a few days by 42 per cent with rape and by 50-65 per cent with maize. Initially the width of the depletion zone is very small. Within six days the depletion zone extended to the final distance from the surface of the root cylinders of about 2mm for maize and 2.6mm for rape. The soil within the range of the mean length of root hairs (0.7 mm for maize and 1.3 mm for rape) is almost equally depleted. This indicates that root hairs are very important for P-uptake from soil. This is further supported by higher P-uptake rates per cm root length of rape than of maize.The P-concentration of the soil solution was estimated by means of the phosphate desorption curve. Within the root hair cylinder the P-concentration of the soil solution decreased from 0.8 to 0.03mg P/I. 486-499 (1981) Phosphatverarmung 487 Changes of the P-depletion profile with time were used to calculate P-uptake rates for roots of different age. The results indicate that for the first 3-5 days P-uptake rates remained near maximum, even though the P-concentration of the soil solution at the root surface had strongly decreased within two days. Phosphate uptake rates per cm root length did not decrease unless the whole root hair cylinder had been depleted.

Development and replenishment of the P-depletion zone around the primary root of maize during the vegetation period

“…Even more markedly, the biphasic growth of the depletion zone became obvious when the time-course of the concentration of EP at the root surface was followed: While during the first phase EP was decreased by 70%, it increased again during phase two. The extent of the initial drop is quite in good agreement with data reported by Hendricks et al, (1981).…”

Phosphorus fractions depletion in the rhizosphere of young and adult maize and oilseed rape plants

“…The rhizosphere, i.e. the portion of soil influenced by the root concerning P, was in our experiment only 1 mm, which is close to values of Hendriks et al (1981) but smaller than 2-4 mm of Hedley et al (1994). The amount of soil volume within the range of the P depletion is much higher for cylindrical than for planar root surfaces.…”

“…This relatively low exploitation of the alkali-soluble P i , even though the ´planar` root causes a strong concentration decrease in soil solution (Claassen and Steingrobe, 1999;Hendriks et al, 1981), may be related to the following. For one, only part of the alkali-soluble P is isotopically exchangeable (Bühler et al, 2002) and thereby plant available and furthermore, 30-40% of this isotopically exchangeable P would not be plant available because its equilibrium P concentration in soil solution is below Figure 3 shows that maize only depleted the alkali soluble P i (NaHCO 3 -P i and NaOH-P i ) in both soils.…”

“…At each of the three harvests we obtained rhizosphere soil and measured the depletion of different P fractions as determined by a sequential P fractionation scheme as proposed by Hedley et al (1982). We obtained rhizosphere soil, because of its low mobility in soil P is only depleted in a narrow layer around the root of about 1 mm (Hendriks et al, 1981). To our knowledge, there is limited information about the use of different soil P fractions by oilseed rape and maize as affected by plant age and soil properties.…”

Root growth of <i>Lotus corniculatus</i> interacts with P distribution in young sandy soil

“…In apparent contrast to the notion that P becomes depleted with time in the rhizosphere (Hendriks et al, 1981;Hinsinger et al, 2011b;Wang et al, 2005), we observed elevated concentrations of labile P fractions in soil adjacent to roots as compared to soil farther away from the roots in the highdensity samplings. Likely reasons for this effect are P solubilization by root exudation and overriding P uptake by roots (Hinsinger et al, 2011b).…”