Mid Sweden University

This study investigated the influence of contrasting parent materials on tree chemical composition and growth rate under field conditions. On the island of Alno, Sweden, alkaline intrusions are interspersed into non-alkaline gneiss bedrock, which provides a unique opportunity to conduct this study with a minimum of confounding effects. Three plots with alkaline and three plots with non-alkaline parent material were established in a homogenous Norway spruce stand. The chemical composition of soil and soil solution was determined throughout the soil profiles. The chemical composition of bark, wood and needles was determined for each plot, and the latest 5 year basal area growth increment calculated. Concentrations of Ca in needles were correlated with the soil exchangeable Ca levels. Tree growth rate was significantly higher on the alkaline plots and positively correlated with soil concentrations of Ca, Mg, P, and Zn. The tree growth rate also tended to correlate with soil N concentrations, but levelled out for the highest soil N concentrations. Tree growth was enhanced on the alkaline plots and was correlated with several elements. However, none of these elements could be confirmed as the limiting one for tree growth at the current site.

Parent material greatly influences pedogenesis and soil nutrient availability and consequently we hypothesized that it would significantly affect the amount of organic solutes in soil, many of which have been implicated in rhizosphere processes linked to plant nutrient uptake. Consequently, we investigated the influence of two contrasting parent materials in which calcite was present or absent (alkaline and non-alkaline soils) on the concentrations of dissolved organic carbon (DOC), low-molecular weight organic acids (LMWOA) and glucose in soil solution. Both soils were under Norway spruce. The dynamics of LMWOAs in soil were also investigated using ¹⁴C-labelled citrate and oxalate. Some of the mineral horizons of the alkaline soils showed significantly higher concentrations of DOC, phenolics, and fumarate in soil solution and also a higher basal respiration. No major differences were seen in organic solute status in the organic horizons of the two soil types. LMWOAs were present at low concentrations in soil solution (< 1 to 25 µM). Their mineralization rate significantly decreased with soil depth, however, overall neither their concentration or half-life in soil was markedly affected by parent material. The alkaline soils had significantly higher CO₂-to-soil organic C (SOC) ratios, and consequently SOC in the alkaline soils did not seem more chemically stable against mineralization. Considering possible DOC and CO₂ efflux rates it was suggested that the equal or larger SOC stocks in alkaline mineral soils were most likely linked to a higher net primary productivity. In conclusion, our study found that parent material exerted only a small effect on the concentration and dynamics of organic solutes in soil solution. This suggests that in comparison to other factors (e.g. vegetation cover, climate etc) parent material may not be a major regulator of the organic solute pool in soil.

The gneiss bedrock at Alnö Island, (62o24N, 17o30E) in the middle of Sweden, has alkaline intrusions interspersed in narrow dikes. This gives an opportunity to study the impact of different parent material on soil solution in a homogeneous spruce stand. In this study, the alkaline parent materials gave rise to a soil solution with significantly (p 0.05) higher concentrations of DOC, SO4, NO3, Ca and Mg compared to the non-alkaline sites. For the deepest mineral horizons, 25-30cm, F and pH were also higher in the alkaline soil solutions. There were almost no differences between the organic horizons at alkaline and non-alkaline sites, probably explained by the influence of litter and recirculation of nutrients. The multivariate analyses emphasized the correlation between the parent material and the soil solution concentrations of Ca, Mg, PO4 and Al. The data were statistically evaluated by t-tests, ANOVA (Analysis of variances), PCA (Principal Component Analysis) and PLS (Partial Least Squares regression).

Centrifugation is a common technique to obtain soil solution. However, this method may disrupt living cells in the soil and release their contents into the soil solution. To examine this possibility, we compared leaching of low molecular mass organic acids (LMMOAs) and dissolved organic carbon (DOC) from the root of Scots pine (Pinus sylvestris) packed in quartz sand via extraction by centrifugation and milder procedures of water immersion and suction. Centrifugation enhanced leaching of shikimate appreciably; leaching of DOC, lactate, malate, and phosphate was also significantly enhanced. The concentration leached from the root was greater than 10 mu M for shikimate, and generally ranged between 0.5 and 5 mu M for the other acids. As for actual soil samples, this level of leaching could be appreciably large in upper mineral horizon(s) if the root density is as large as in our experiments and if the concentrations of LMMOAs in the soil matrix are relatively small.