Question: What is the effect of nutrient addition on primary production, phytodiversity and succession of a very unproductive plant community (ca. 100 g.m−2.a−1)?
Location: A nutrient-poor, calcareous inland sand ecosystem in the northern upper Rhine valley, Germany.
Methods: Within a five-fold replicated randomized block design, 10-m2 plots were given six single or combined applications of nitrogen, phosphorus, potassium and other essential nutrients for four years. An organic carbon treatment was included as a measure to immobilize soil nitrogen. Data were analysed by mixed linear models.
Results: Productivity of above-ground vascular plant species doubled after nitrogen addition. Additional nutrient elements did not increase productivity further. The cover of ten species and the height of 15 (out of 19 examined) species were significantly enhanced by nutrient addition. Centaurea stoebe is nitrogen-limited and exhibits a decisive impact on total above-ground vascular species productivity. Nutrients did not affect phytodiversity. Low-dosage nitrogen addition (25 kg.ha−1a−1) and organic carbon treatment had no significant impact. However, long-term effects cannot be excluded.
Conclusions: The productivity of the examined plant community is responsive to nutrient addition. Although the response is actually more pronounced than in plant communities with higher initial productivity, productivity remained at a low level. Nutrient limitation (mostly phosphorus nitrogen co-limitation) of many individual species across all life forms is shown. Total above-ground vascular plant productivity is nitrogen-limited. No species were suppressed completely, nor has there yet been an encroachment of new species. However, high-dosage nitrogen addition resulted in accelerated succession.