Rhizosphere chemistry in an ammonium sulfate and water manipulated Norway spruce [Picea abies (L.) Karst.] forest

The purpose of this study was to examine how the treatments ammonium sulfate, drought and irrigation changed chemical characteristics of three soil fractions (bulk soil, rhizosphere and soil root interface (SRI)) from E, B-h and B-s horizons of Podzol in a Norway spruce stand in southwestern Sweden. Regardless of the treatment, the properties of the rhizosphere and SRI nearly always differed from the bulk soil due to the high quantity of organic and root material. Irrigation and ammonium sulfate raised water soluble cations and base saturation in the bulk soil. This was possibly due to leaching from the humus and exchange reactions. In the rhizosphere and SRI, irrigation and ammonium sulfate lowered soluble base cations (BC) and base saturation when compared with control; this is attributed to a combination of leaching and high nutrient demand by trees creating a zone of relative depletion. Drought accumulated more organic matter (OM), acidity and cations in the soil fractions suggesting that the lack of water limited transport and uptake of nutrients. Generally, the magnitude of accumulation/depletion of nutrients in the soil fractions reflected the degree of stress which was in turn linked to root uptake of nutrients or to tree growth. Due to the apparent linkage between tree growth, uptake of nutrients and rhizosphere chemistry, we emphasise that soils must be studied at the rhizospheric rather than the bulk soil scale to further understand the effects of environmental stresses.