Rhizospheric P and K in forest soil manipulated with ammonium sulfate and water

Abstract

Clegg, S., Gobran G. R. and Guan, X. 1997. Rhizosphere chemistry in an ammonium sulfate and water manipulated Norway spruce [Picea abies (L.) Karst.] forest. Can. J. Soil Sci. 77: 515-523. 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. éléments nutritifs observés dans les fractions de sol traduisaient le degré du stress, lequel à son tour était relié à l'absorption racinaire ou à la croissance de l'arbre. Étant donné le lien apparent entre croissance de l'arbre, absorption des nutriments et chimie de la rhizosphère, il découle que les sols doivent être étudiés au niveau de la rhizosphère plutôt qu'à celui du sol libre, si l'on veut comprendre plus en profondeur les effets des stress ambiantaux.

Rhizosphere effects on ion concentrations near different root zones of Norway spruce (Picea abies (L.) Karst.) and root types of Douglas-fir (Pseudotsuga menziesii L.) seedlings

“…This suggests that either (a) roots mobilised these ions from the solid phase, or (b) there was a root efflux of these elements, or (c) uptake rates of water by roots were higher than those of nutrients. Element mobilisation in the rhizosphere may be related to root or mycorrhiza-induced mineral weathering (Arocena et al 2004;Bakker et al 2004), organic matter decomposition (Clegg et al 1997;Turpault et al 2005), increased nutrient availability (in the present experiment), or to pH decrease (Wang et al 2001). Efflux of elements from roots can occur, but can significantly contribute to element accumulation in the rhizosphere only via substantial element uptake by other parts of the roots or by the leaves.…”

Rhizosphere: biophysics, biogeochemistry and ecological relevance

“…Nutrients that are abundant in the soil solution may thereby accumulate in the rhizosphere whenever their flow exceeds plant's demand. This typically occurs for Ca and Mg, and has been also reported to occur for K (Lorenz et al 1994;Barber 1995;Clegg and Gobran 1997;Vetterlein and Jahn 2004b;Turpault et al 2005). Precipitation of gypsum (Ca sulfate, Fig.…”

“…For example as K requirement is high for young plants but decreases with age, K depletion at the root surface can be observed in young plants (12 days old) while accumulation was found for older plants (29 days old) by Vetterlein and Jahn (2004b). Accumulation of easily available K in the rhizosphere as recorded in situ for field-grown plants such as forest trees can also result from the combination of uptake-driven depletion and weathering of K-bearing minerals or organic matter which over longer time scales may contribute a net increase in soil solution and exchangeable K in the rhizosphere (Clegg and Gobran 1997;Turpault et al 2005). If studies are conducted in soil and not in hydroponics, care should be taken in interpreting soil solution concentrations.…”

Communities of arbuscular mycorrhizal fungi and bacteria in the rhizosphere of Caragana korshinkii and Hippophae rhamnoides in Zhifanggou watershed

“…Soil sampling was then conducted in each plot, and rhizosphere soil (Clegg and Gobran 1997) from 5-25 cm depths was collected using five points sampling method. Irregular fields were sampled avoiding irregularities like foot or shoulder regions, roads or paths and ditches, power lines, oil wells, saline areas, etc.…”