The Relationship between Biodiversity and Productivity in Permanent Grasslands and in Ley System

To investigate the effect of plant diversity on productivity, two experiments have been conducted. The first experiments aimed to study the biodiversity-productivity relationship in permanent grasslands at within- and across-sites scale in semi-natural and natural dry acidic grasslands. The hypothesis tested was whether there is a consistent relationship between biodiversity and productivity or this relationship is influenced by the existing environmental conditions. The second experiment studied the effect of increasing the functional diversity of the ryegrass-white clover mixture by introducing a naturally growing forb (dandelion, Taraxacum officinale Web.) into the mixture under two nitrogen (N) fertilization levels (0 and 200 kg ha-1) on herbage yield, weed infestation and herbage mineral yields of N, calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), and sodium (Na). In the first experiment, our results indicate that there is no general relationship between plant diversity and productivity that is consistent for all sites, therefore the type of the diversity-productivity relationship might be influenced by the existing environmental conditions. The relationship between diversity and productivity varied according to the used diversity measure. Productivity of the studied permanent grasslands is better explained by species evenness and plant community composition than by species richness. Our analysis also showed that the productivity of the semi-natural grasslands is positively correlated with evenness, but no significant relationship between species richness and productivity was observed. In dry acidic grasslands, increasing species number was accompanied by higher productivity.In the second experiment, our results indicated that the herbage yield of the three-species mixture was not significantly different from the binary mixture of ryegrass and white clover but significantly higher than the monocultures and the other binary mixtures. Niche differentiation (RYT >1; relative yield total) among the sown species was more evident in the three-species mixture compared to the other mixtures. In respect to the yield stability of the sown pastures over years, our results gives an indication that the presence of dandelion in mixtures led to a better pasture stability across time, where the lower temperature and precipitations in the second and third years compared to the first year might be responsible for the reduction in herbage yields of ryegrass and white clover. The biomass of the unsown species was significantly lower in the three-species mixture compared to white clover and dandelion monocultures as well as compared to ryegrass-dandelion and white clover-dandelion mixtures. Regarding the mineral contents of the herbage, our results showed that dandelion contains the highest concentrations (g kg-1 DM) of Mg, K and P, followed by white clover and ryegrass, respectively. On the other hand, white clover monoculture produced the highest herbage mineral yield (kg ha-1) for the most tested minerals, followed by dandelion and ryegrass, respectively.