Effects of soil P status on growth and P and N uptake of Carex species from fens differing in P-availability

We studied the effects of different soil P status (P-deficient, P-poor and P-rich fen soils) on growth, root allocation and P and N-uptake of Carex species from fens differing in P-availability. We carried out a 3-month pot experiment where the three species were grown in each soil. Carex acutiformis, a species from eutrophic fens, showed the highest production under all soil conditions and changes in biomass allocation to belowground parts, but not in specific root length (SRL) or root length/leaf area ratio (RLLA) in response to changes in the P-soil status. Carex lasiocarpa Ehrh., a species from P-limited areas, showed intermediate biomass production and low inherent root weight ratio (RWR). Carex diandra Schrank., a species from areas where the growth of the vegetation is limited by nitrogen, showed low biomass production in all three fen soils studied, and no changes in its high specific root length (SRL) or root weight ratio (RWR) with soil phosphorus status. All three Carex species showed the best growth under P-poor conditions and a very reduced growth on the P-limited soil. Phosphorus uptake by Carex species was affected by P-soil status being lowest under P-deficient conditions for all three Carex species. P-soil status also affected N-uptake which was lower under P-deficient conditions than in the other two soils. It can be concluded that the success of both small Carex species in nutrient poor sites cannot be explained by higher relative growth rate, biomass production or nutrient uptake than the species from eutrophic areas. Other factors (water and soil chemistry other than N and P richness, presence of a bryophyte layer, establishment of seedlings, clonal reproduction, competition ability) must play a role in determining the distinct distribution pattern of these species.