The P cycle in grassland and forest ecosystems of different biodiversity and land-use intensity
With increasing diversity, the content of plant-available nutrients in the soil decreases due to more effective resource use by the plants. This relationship has already been shown several times for nitrogen. Such studies are lacking for other nutrients that may also limit plant growth, such as phosphorus. Since diversity and land-use intensity or history are closely related in managed systems, the influence of these factors on the phosphorus cycle in the grassland and forest of the biodiversity exploratories is being investigated in the DYNPHOS sub-project in order to determine the control variables for soil nutrient levels.
Our aim is to separate the effects of diversity and land-use on:
- the phosphorus fractions in the soil
- the phosphorus cycle in the soil
- the phosphorus stocks in plants
We also plan to determine the influence of past land-use via innovative isotope methods (?18O in PO4).
1. More intensive land-use, which is usually linked to higher nutrient availability in the soil due to fertilisation, leads to a reduction in the negative influence of plant diversity on phosphorus availability (organic and inorganic) in the soil.
- a reduction in the negative influence of plant diversity on phosphorus availability (organic and inorganic) in the soil and correspondingly
- a reduction in the positive influence of plant diversity on phosphorus stocks in the above-ground biomass.
2. Among the main sources of phosphate in the soil solution (dissolution of P-containing minerals, desorption, mineralisation of organic matter), the share of phosphorus in the above-ground biomass
- is with more intensive land-use, the proportion of easily soluble, fertiliser-borne P-containing minerals is increased and thus the influence of plant diversity – according to hypothesis 1a –
- is reduced and within a land-use intensity (with the same nutrient supply), the proportion of mineralised phosphate increases with increasing plant diversity due to the stimulation of the mineralisation of organic matter.
3. The oxygen isotope signal of phosphate can be used to distinguish between different phosphorus sources (solution of P minerals, desorption, mineralisation).
To prove these hypotheses, we determine the phosphorus stocks in soils and plants, the phosphorus release by solution, desorption and mineralisation, and ?18O in PO4 from these three sources.