Decreasing phosphorus (P) concentrations in leaves of beech ( Fagus sylvatica L.) across Europe raise the question about the implications for forest health. Considering the distribution of beech forests on soils encompassing a broad range of nutrient availability, we hypothesized that this tree species exhibits high phenotypic plasticity allowing it to alter mass, and nutrient allocation in response to local nutrient availability. To test this, we grew two groups of 12–15 year old beech saplings originating from sites with high and low soil P availability for 2 years in mineral soil from their own site and in soil from the other site. After two growing seasons, P concentrations in leaves and stem, as well as mass allocation to leaves and fine roots were affected by both soil and plant origin. By contrast, relative P allocation to leaves and fine roots, as well as P concentrations in fine roots, were determined almost entirely by the experimental soil. Independent of the P nutritional status defined as average concentration of P in the whole plant, which still clearly reflected the soil conditions at the site of plant origin, relative P allocation to leaves was a particularly good indicator of P availability in the experimental soil. Furthermore, a high plasticity of this plant trait was indicated by a large difference between plants growing in the two experimental soils. This suggests a strong ability of beech to alter resource allocation in response to specific soil conditions.

Forests dominated by beech (Fagus sylvatica L.) cover large parts of Europe where they occupy a broad ecological niche in terms of soil fertility. This indicates a large potential to adapt to different soil conditions over long time periods. Recent changes in tree mineral nutrition across Europe raise the question to what degree beech can acclimate to changing soil conditions in the short term. In this study, we aimed at assessing the plasticity of root traits and rhizosphere properties of young beech trees from populations that are adapted to either high or low nutrient supply, when growing in soils differing in their fertility. We sampled beech saplings from two forest sites of contrasting nutrient supply, most distinctly in terms of phosphorus. We grew them for 2 years in rhizoboxes in mineral soil either from their own site or from the other site. We assessed the influence of the factors "plant origin" and "current soil" on root traits and rhizosphere properties. Fine root traits related to growth (biomass, length), architecture (branching), and morphology (diameter) responded strongly to the factor "current soil." Provenance (factor "plant origin") modified the response. The modifying effect was consistent with an influence of the plant status in those nutrients, which were not in sufficient supply in the soil. An additional genotypic difference in the sensitivity of the beech saplings to different soil nutrient supply could not be excluded. Fine root parameters normalized for length, mass, or volume (root tip density and frequency, specific root length and area, and root tissue density) did not differ among the treatments. Differences in percentage of mycorrhizal root tips and rhizosphere parameters related to phosphorus mobilization potential (pH, abundance of organic acid anions, and phosphatase activity) were small and mainly determined by the "current soil." Provenance had only a minor modifying effect, possibly due to differences in the ability of the plants to transfer carbon compounds from the shoot to the root and the fungal partner. Our results indicate a high plasticity of young beech trees to adapt their root system to different soil nutrient supply, thereby also taking into account internal nutrient reserves.

<p>Soil enzymes catalyse the hydrolysis of various soil compounds leading to an increase in the availability of nutrients for plants and microorganisms, but the increase in mobility might also lead to losses by leaching. Sources of extracellular soil enzymes in soil include release by soil microorganisms such as bacteria and fungi and plant roots but also microbial necromass. Irrespective of their source, the released enzymes can accumulate in the soil by becoming stabilized on mineral and organic surfaces. It is generally assumed that 40 to 60% of measured enzyme activity originate from stabilized enzymes. As such they directly affect the ability of a soil to fulfil its numerous functions, including the provision of nutrients to plants, the cleaning of percolating water and climate regulation.</p><p>Although measurements of soil enzyme activity are increasingly recognised as sensitive indicators of soil health, variations and inconsistencies between existing methods make it difficult to compare the results of different studies. Most commonly, soil enzyme activities are assessed using destructive biochemical laboratory incubations, thus altering the natural soil conditions.</p><p>Therefore, based on the principle of soil zymography, a membrane based method to map the heterogeneity of enzymatic activity on exposed soil surfaces, we developed a portative, hand-held sensor allowing rapid measurement of the soil enzymatic activity in-situ (Digit Soil; https://www.digit-soil.com/). In this presentation, we will compare the performance of our sensor to laboratory incubations for the application on various types of soils differing in basic properties such as pH, texture and soil organic matter content at different moisture conditions.</p><p>Based on the results, we will discuss the prospects this new sensor offers for rapid in-situ evaluation of soil health in the framework of precision agriculture and sustainability labels.</p>

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