Plant Functional Traits and Ecosystem Functions in Experimental Grassland Stands

151 In Experimental Grassland Stands on lysimeter facilities, herb contribution to grassland stands rather than functional diversity showed implications on ecosystem functions such as nutrient use, use efficiencies, yields and loss with seepage. Differences in ecosystem performance were due to the identity of functional group of dominant and co dominant species (grass/herb). Positive relations between higher nutrient availability and WUEbm of both grass and herb species were indicated for experimental grassland stands. Grassland stands with higher herb contribution favoured a higher nutrient sequestration in biomass and thus played an important role for safety net functions in grassland ecosystems. Slightly higher Nmin concentrations in soil solution likely reflected higher root-turnover rates of grass dominated stands in 2002. The investigated grass species showed higher base cation use efficiency and hence provided considerably growth under low cation supply. Grass dominated stands showed rather low performance in safety net functions for nutrients. Lower base cation yields in biomass of grass dominated stands were not automatically reflected by indicators for use of soil nutrients. In contrast to Nmin, base cation concentrations and losses with seepage did not reflect differences in base cation use by the grassland stands. In the Rhizodeposit Experiment P. lanceolata was identified as a species featuring lower competition ability in concern of biomass building up and Fe acquisition (Cab; WILSON, 1988) under Fe deficiency compared to H. lanatus. For swards containing P. lanceolata complementary was found in concern of individual biomass production and individual Fe stocks. P. lanceolata gained lower biomass than the accompanying species. Inverted patterns of Fe acquisition ability and the ability to build up individual biomass, hint at a trade-off between Fe demand and biomass build up for P. lanceolata. DOC release to rhizodeposit solution was enhanced after the 1 harvest. P. lanceolata showed the highest release of DOC, a higher diversity of carboxylic acids as well as a considerable release of potential Fe chelators (malic, citric and malonic acid) to 1.3 to 1.7 μM g shoot dm, while H. lanatus swards released only small amounts of carboxylic acids. Higher competition ability for species Fe contents after the 1 harvest indicated enhanced competition between P. lanceolata with A. odoratum. This finding was also reflected by higher DOC release and a release of potential Fe chelators amounting up to 2.3 μM g shoot dm in these swards. It was found that even transient grasslands species may show a high competition ability in concern of Fe-acquisition under Fe-deficiency. During the Root Mineralization Experiment, the basal respiration of the rhizosphere sand obtained from Rhizodeposit Experiment differed only tendentiously due to its origin (H. lanatus, R. acris, diculture rhizosphere or Ref sand). H. lanatus root tissues were identified to increase respiration rates significantly during a 236 h incubation period to a four-fold of basal respiration. The application of R. acris root tissues did not affect the respiration rates. Root tissue material was mineralised to the same extent as Corg material within the first 236 hrs. Since no differences of chemical parameters (eg. C/N-ratio) were found for roots of the two species, enhanced mineralization of H. lanatus roots in the initial phase are likely due to lower root diameters and higher root surface areas.