Availability of organic and inorganic phosphorus compounds as phosphorus sources for Carex species

Abstract

Inorganic phosphates (ferric phosphate, calcium phosphate and aluminium phosphate) and organic forms of phosphorus (inositol hexaphosphate and β-glycerophosphate) were tested as phosphorus (P) sources for the growth of three Carex species from fens differing in productivity and nutrient availability. Aluminium phosphate and β-glycerophosphate were equally effective sources of P for all three Carex species as KH2PO4, which was used as a control treatment. Phosphorus from ferric phosphate and calcium phosphate was also taken up by Carex acutiformis Ehrh., a species of high productivity from eutrophic fen areas, but not by the other two species. Only Carex lasiocarpa Ehrh., a species from P-limited fens, showed a higher P-uptake when grown with inositol phosphate than in the second control treatment without P. The P-source also affected, with differences between species, the biomass allocation to the below-ground plant parts and the area of absorption surface of the roots. The mobilization of organic sources of P by fen Carex species found in the present study might be an important factor in the P dynamics of fens because of the high contents of organic P in the fen peat soils where these species grow. In the same way, the utilization of inorganic sources of P can play a relevant role in the P-cycle in these systems where the discharge of ground water rich in ions can lead to the fixation of P into inorganic compounds. However, the differing abilities of the various Carex species to mobilize P from P-pools does not explain clearly their preferential presence in different fens in relation to the P-availability.