ROOT AND LEAF ATTRIBUTES ACCOUNTING FOR THE PERFORMANCE OF FAST-GROWING AND SLOW-GROWING GRASSES AT DIFFERENT NUTRIENT SUPPLY

Despite their difference in potential growth rate, the slow-growing Br achypodium pinnatum and the fast-growing Dactylis glomerata co-occur i n many nutrient-poor calcareous grasslands. They are known to respond differently to increasing levels of N and P. An experiment was designe d to measure which characteristics are affected by nutrient supply and contribute to the ecological performance of these species. Nutrient a cquisition and root and shoot traits of these grasses were studied in a garden experiment with nine nutrient treatments in a factorial desig n of 3 N and 3 P levels each. D. glomerata was superior to B. pinnatum in nutrient acquisition and growth in all treatments. B. pinnatum was especially poor in P acquisition. Both species responded to increasin g N supply and to a lesser extent to increasing P supply by decreasing their root length and increasing their leaf area per total plant weig ht. D. glomerata showed a higher plasticity. In most treatments, the r oot length ratio (RLR) and the leaf area ratio (LAR) were higher for D . glomerata. A factorization of these parameters into components expre ssing biomass allocation, form (root fineness or leaf thickness) and d ensity (dry matter content) shows that the low density of the biomass of D. glomerata was the main cause for the higher RLR and LAR. The bio mass allocation to the roots showed a considerable plasticity but did not differ between the species. B. pinnatum had the highest leaf weigh t ratio. Root fineness was highly plastic in D. glomerata, the differe nce with B. pinnatum being mainly due to the thick roots of D. glomera ta at high nutrient supply. The leaf area/leaf fresh weight ratio did not show any plasticity and was slightly higher for B. pinnatum. It is concluded, that the low density of the biomass of D. glomerata is the pivotal trait responsible for its faster growth at all nutrient level s. It enables simultaneously a good nutrient acquisition capacity by t he roots as well as a superior carbon acquisition by the leaves. The h igh biomass density of B, pinnatum will then result in a lower nutrien t requirement due to a slower turnover, which in the long term is adva ntageous under nutrient-poor conditions.