Molybdenum at Germany Norway spruce sites: Contents and mobility

• Published in: Canadian journal of forest research Vol. 30; no. 7; p. 1034
• Main Authors: Lang, Friederike, Kaupenjohann, Martin
• Format: Journal Article
• Language: English
• Published: Ottawa Canadian Science Publishing NRC Research Press 01.07.2000
• Subjects: Fluctuations; Forest ecosystems; Forest floor; Forest soils; Molybdenum; Pine needles; Pine trees; Plant extracts; Sandstone; Soil profiles; Soils; Spruce; Sulfates
• ISSN: 0045-5067; 1208-6037

Molybdenum plays an important role in the nitrogen turnover of ecosystems. However, very little is known about Mo availability in forest soils. We measured the oxalate-extractable Mo concentrations of acid forest soils, the Mo, nitrate, phosphate, and sulfate fluxes from the organic forest floor into the mineral soil using resin tubes and the Mo concentrations of the tree needles at 28 different Norway spruce (Picea abies (L.) Karst.) sites in southern Germany. The supply of oxalate-extractable Mo varied from 51 to 3400 g X ha^sup -1^ , with the lowest values occurring in sandstone-derived soils (370 +/- 212 g X ha^sup -1^; mean +/- SD). Molybdenum concentrations of current-year needles were in the range of 5 to 48 ng X g^sup -1^. The Mo needle concentrations and oxalate-extractable Mo of soils did not correlate. However, Mo fluxes (6-60 g X ha -1^ X a^sup -1^) from the organic forest floor into the mineral soils were correlated to needle concentrations and to the NO^sub 3^ fluxes. We conclude that Mo turnover within forest ecosystems is governed by Mo plant availability of mineral soils as well as by plant Mo uptake. In addition, Mo cycling strongly affects Mo distribution within soil profiles and Mo fluxes out of the organic layer. Resume : Le molyb&ne joue un role important dans le renouvellement de l'azote des ecosystemes. Toutefois, on connait peu de chosen au sujet de la disponibilite de Mo dans les sols forestiers. Nous avons mesure la concentration de Mo extractable a l'oxalate dans des sols forestiers acides, les flux de Mo, de nitrate, de phosphate et de sulfate, de la couverture morte organique vers le sol mineral, a l'aide de tubes de resines ainsi que la concentration de Mo dans les aiguilles d'6pic6a common (Picea abies (L.) Karst.) dans 28 sites differents du sud de l'Allemagne. L'apport de Mo extractable A Foxalate variait de 51 A 3400 g X ha^sup -1^ avec les plus faibles valeurs provenant des sols derives de gres (370 +/- 212 g X ha -1^; moyenne +/- ET). La concentration de Mo dans les aiguilles de l'annee courante variait de 5 a 48 ng X g^sup -1^. La concentration de Mo dans les aiguilles et le Mo extractable a l'oxalate dans les sols n'etaient pas correles. Toutefois, les flux de NO^sub 3^ (6-60 g X ha^sup -1^ X a^sup -1^) de la couverture morte organique vers le sol mineral etaient corr6l6s aux concentrations foliaires et aux flux de NO^sub 3^. Nous en concluons que le renouvellement de Mo dans les ecosyst@mes forestiers est gouverne par le Mo des sols mineraux disponible pour la plante autant que par le prelevement de Mo par la plante. De plus, le recyclage de Mo affecte fortement la distribution de Mo dans les profils de sol et le flux de Mo hors de la couche organique. At the sites we studied, Mo and N03 fluxes out of the organic layer were positively correlated (r = 0.51, p = 0.0197), suggesting that Mo uptake or at least Mo cycling is influenced by N03 availability. Consequently, to estimate Mo supply in trees at different sites not only Mo needle concentrations or Mo fluxes but also N03 availability should be taken into account. A high Mo/N03 flux ratio will be expected at high Mo availability, a low ratio at Mo deficiency sites. No correlation between oxalate-extractable Mo (concentrations, contents or soil number) and Mo/N03 ratio could be found. However, using Fe oxide impregnated filter paper extraction for determining Mo plant availability shows that Mo/N03 ratio may reflect Mo potential of the soils (results not shown here).