Abstract. Root production and turnover were studied using sequential core sampling and observations in permanent minirhizotrons in the field in three dry heathland stands dominated by the evergreen dwarfshrub Calluna yr-' (Deschampsia) and 1.17-1.49 yr-' (Molinia), respectively. No resorption of N and P from senescing roots was observed in either species. Input of organic N into the soil due to root turnover, estimated using the core sampling data, amounted to 1.8 g N m-' yr-' (Calfuna), 1.7 g N mm2 yr-' (Deschampsia) and 19.7 g N rnw2 yr-' (Molinia), respectively. The organic P input was 0.05, 0.07 and 0.55 g P me2 yr-', respectively. Using the minirhizotron turnover estimates these values were 20-22% (Deschampsia) and ll- 30% (Molinia) lower. When the biomass turnover data were used, it appeared that in the Molinia stand root turnover contributed 67% to total litter production, 87% to total litter nitrogen loss and 84% to total litter phosphorus loss. For Calluna and Deschampsia these percentages were about three and two times lower, respectively.This study shows that (1) Root turnover is a key factor in ecosystem C, N, and P cycling; and that (2) The relative importance of root turnover differs between species.
Root biomass production, root length production and root turnover of Erica tetralix and Molinia caerulea were estimated by sequential core sampling and by observations in permanent minirhizotrons in the field. Root biomass production, estimated by core sampling, was 370 (Erica) and 1080 (Molinia) g m yr. This was for both species equal to aboveground production. Assuming steady-state conditions for the root system, root biomass turnover rates (yr), estimated by core sampling, were 1.72 (Erica) and 1.27 (Molinia). Root length production of both species, estimated by minirhizotron observations, varied significantly with observation depth. Root length turnover rate (yr) of both species did not vary significantly with observation depth and averaged 0.92 in Erica and 2.28 in Molinia. Reasons are given for the discrepancy between the results of the two types of turnover measurements. The data suggest that the replacement of Erica by Molinia in a wet heathland, which occurs when nutrient availability increases, leads to an increased flow of carbon and nutrients into the soil-system. Therefore, there may be a positive feedback between dominance of Molinia and nutrient availability.
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