Gro Wollebæk
OAP
Abstract
We conclude that the oxalate exuded constitutively by Picea abies / Laccaria bicolor may lead to rhizosphere oxalate concentrations that are relevant for Al resistance.
Abstract
Here we report on low molecular weight organic acids in root exudates and soil solutions of Norway spruce and silver birch grown in rhizoboxes, sterile microcosms and the field. Monocarboxylic acids dominated in all three experimental systems. Formic, shikimic and oxalic acids were found in both spruce and birch microcosms. Fumaric acid was exclusive for spruce, while lactic, malonic, butyric and phthalic acids were only found in the birch microcosms. In spruce rhizoboxes oxalic, lactic, formic, butyric and pthalic acids were found. In addition, citric, adipic, propionic, succinic and acetic acids were observed in the rhizosphere of birch. Behind root windows in the field, only oxalic and lactic acids were found in the rhizosphere of spruce fine roots, whereas also formic and phthalic were observed close to birch fine roots, all at low concentrations. The rhizosphere of mycorrhizal short roots of birch contained butyric acid along with the acids observed for birch fine roots. Our results emphasise that characteristics of both the trees e.g. species, developmental stage, root density, mycorrhizal status, and the experimental system, i.e. growth conditions are important for the composition and the amount of organic acids. We conclude that the rhizosphere of birch contains more organic acids at higher concentrations than spruce. (C) 2004 Elsevier Ltd. All rights reserved. Here we report on low molecular weight organic acids in root exudates and soil solutions of Norway spruce and silver birch grown in rhizoboxes, sterile microcosms and the field. Monocarboxylic acids dominated in all three experimental systems. Formic, shikimic and oxalic acids were found in both spruce and birch microcosms. Fumaric acid was exclusive for spruce, while lactic, malonic, butyric and phthalic acids were only found in the birch microcosms. In spruce rhizoboxes oxalic, lactic, formic, butyric and pthalic acids were found. In addition, citric, adipic, propionic, succinic and acetic acids were observed in the rhizosphere of birch. Behind root windows in the field, only oxalic and lactic acids were found in the rhizosphere of spruce fine roots, whereas also formic and phthalic were observed close to birch fine roots, all at low concentrations. The rhizosphere of mycorrhizal short roots of birch contained butyric acid along with the acids observed for birch fine roots. Our results emphasise that characteristics of both the trees e.g. species, developmental stage, root density, mycorrhizal status, and the experimental system, i.e. growth conditions are important for the composition and the amount of organic acids. We conclude that the rhizosphere of birch contains more organic acids at higher concentrations than spruce.
Authors
Toril Drabløs Eldhuset Holger Lange Nicholas Clarke Per Otto Flæte Erlend Ystrøm Haartveit Gro Wollebæk O. Janne KjønaasAbstract
Root and needle litter are the most important sources of organic carbon in forest soils. Their decomposition is thus important for the long-term storage of C in, and release of CO2 from, the soil. Different components in the organic matter will decompose with different speeds. NIRS (Near InfraRed Spectroscopy) is a relatively simple and promising way of analysing the composition of organic matter, but its use in forest soil and litter studies has been limited up to now. We will present preliminary results from litter decomposition studies in two forest ecosystems: Picea abies stands (30 and 120 years old) from Nordmoen, Norway, and uneven-aged P. abies stands with a mean age of 90 years and under different N treatments at Gårdsjön, Sweden. ags with litter collected from the stands have been buried in the soil for different time periods and have been analysed using a CHN-analyzer and NIRS. Two aspects will be discussed: a) model calibration and validation for C and N concentrations, and b) assessment of decomposability using NIRS.
Abstract
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Authors
Heleen A. de Wit Jan Mulder Per Holm Nygaard Dan Aamlid Magne Huse Egil Kortnes Gro Wollebæk Roald BreanAbstract
Aluminium (Al) is a key element in critical load calculations for forest. Here, we argue for re-evaluating the importance of Al. Effects of two levels of enhanced Al concentrations and lowered Ca:Al ratios in the soil solution in a field manipulation experiment in a mature spruce stand (1996-1999) on tree vitality parameters were tested. In addition, Al solubility controls were tested. Various loads of Al were added to forest plots by means of an irrigation system. Potentially toxic Al concentrations and critical ratios of Ca to inorganic Al were established.The ratio of Ca to total Al was not a suitable indicator for unfavourable conditions for plant growth. No significant effects on crown condition, tree growth and fine root production were observed after three years of treatment. In 1999, foliar Mg content in the highest Al addition treatment had declined significantly. This agreed with the known response to Al stress of seedlings in nutrient solution experiments. No support was found for using the chemical criterion Ca:Al ratio in soil solution, foliar and root tissue as an indicator for forest damage due to acidification. Al solubility was considerably lower than implied by the assumption of equilibrium with gibbsite, particularly in the root zone.The gibbsite equilibrium is commonly used in critical load models. Substitution of the gibbsite equilibrium with an Al-organic matter complexation model to describe Al solubility in soil water may have large consequences for calculation of critical loads. The results indicate that critical load maps for forests should be reconsidered.