Rhizospheric nutrient availability and tree root reactions in a changing environment.
1996
Clegg S.
A number of hypotheses have been tested in ecosystem experiments to further understand actual and potential threats to forests. Many of the studies have, however, not considered roots and the surroundig rhizosphere soil. This has lead to some criticism of forest ecosystem models, since tree roots are not passive receptors of nutrients from the soil but change their mode of nutrient uptake as an adaptation to changing environmental conditions. Due to close linkage between plants, microbes and soil, the study of rhizospheric processes will be a key to resoving problems related to understanding and predicting soil/plant interactions in a changing environment. Therefore, this study presents a conceptual model for nutrient availability in the mineral soil-root system. Soil and root samples were taken from a Norway spruce (Picea abies (L.) Karst.) stand at Skogaby, situated in SW Sweden. The samples were divided into three soil fractions (bulk soil, rhizosphere soil and soil-root interface) to investigate the effects of ammonium sulphate, drought and irrigation treatments on organic matter, nutrient availability and other chemical properties. In laboratory studies, uptake of mineral nutrients by birch (Betula pendula Roth.) and reactions to aluminium were examined under controlled conditions with steady-state nutrition technique. Growth response, phosphorus demand and cation exhange of roots were measured. The results generally indicated great differences between soil fractions, and that soil around roots had a more favourable nutritional condition than the bulk soil. The conceptual model, supported by these results, links soil chemistry with plant uptake and other biological processes. Therefore, this study can be used to develop models of nutrient availability and cycling. Moreover, it calls for a multidisciplinary approach to investigate such a complex system and its functionally related components.
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