P-Niche: Parent material and land-use intensity as driver for niche complementarity in phosphorus mobilisation between plants and microbes

01/03/2026 to 28/02/2029

Phosphorus (P) supply is limited due to its reliance on finite mineral deposits. Additionally, the concentrations of dissolved P species in soil solution are low due to the retention by the soil matrix. Depending on initial parent material properties and land use intensity, plants and microbes might be forced to develop alternative P acquisition strategies and compete for scarce or difficult to access P resources. For example, P acquisition strategies include the solubilisation of inorganic P while mineralisation of organic P indicates P recycling strategies. Our overarching objectives are (i) to understand how land use intensity and its extensification, soil properties and plants determine P acquisition and recycling of microbes, (ii) to identify microbial keystone taxa for P mobilisation and their functional redundancy and (iii) to assess the degree to which a functional potential of the soil microbiome translates into real functioning in terms of P mobilisation in grasslands.
Our project is based on three work packages covering field campaigns in all 150 grassland plots, sample collection in the extensification “Land Use Experiment” (LUX) and controlled isotope labelling-experiments. We will test the following hypotheses:
H1: We will observe a gradient from P acquisition to P recycling strategies from high to low land use intensity (LUI) being more pronounced in regions with low inherent P contents.
H2: Extensification fosters P recycling strategies as well as microbiota with more versatile P mobilisation strategies.
H3: Plants rely more on P acquisition while soil microorganisms increase P recycling strategies in case of land-use extensification especially at sites with generally low P stocks. At sites with high P stocks additive effects of plants and soil microorganisms can be observed alternatively.
H4: During winter, P accumulates in microorganisms, but less so under low LUI because of the microbial use of alternative storage compounds that do not contain P. In spring, accumulated microbial P is turned over and uptake of P by plants starts, which is indicated by an increase of copiotrophic bacteria of versatile mineralisation capabilities. The P mobilisation from organic sources peaks in summer and this P recycling is most pronounced at low LUI and further reinforced by mowing.
With our project we will particularly contribute to the overall Biodiversity Exploratory aims to strengthen in-depth understanding of land use – biodiversity – ecosystem functioning relationships and how these are influenced by temporal dynamics and land use changes. Moreover, we close an important knowledge gap as the consequences of LUI and biodiversity on the P cycle have been barely investigated in the Biodiversity Exploratories in particular and for calcareous soils in general. In a potential second phase of the project, we envision to deepen our understanding about climate-change consequences and biodiversity loss on the identified plant-microbe-soil interactions.