Above-ground nutrient turnover and net primary production of an evergreen and a deciduous species in a heathland ecosystem.

(1) Above-ground nutrient turnover and net primary production (NPP) in adjacent wet heathland communities dominated by the evergreen dwarfshrub Erica tetralix and the deciduous perennial grass Molinia caerulea were studied for two years in The Netherlands. (2) The evergreen was able to achieve a high NPP in early spring (March-May), which accounted for 28% of total annual NPP. There was no NPP in winter (October-March). Secondary thickness growth accounted for 31-49% of NPP in the evergreen. (4) The growing season of the deciduous species lasted from April until September. The above-ground NPP was 2 1-2 6 times higher than that of the evergreen. (5) Leaf litter production by the evergreen only occurred during the summer. Leaf litter production of Molinia occurred in autumn. Life expectancy of the leaves was three times as high in the evergreen compared with the deciduous species. (6) The evergreen reduced nutrient losses mainly by leaf longevity, a relatively low allocation of nutrients to the leaves and low tissue nutrient concentrations. The deciduous species reduced nutrient losses mainly by a very efficient retranslocation of nutrients from senescing tissues. (7) Retention of nutrients was greater and NPP was smaller in the evergreen shrub than in the grass. It is suggested that there is a trade-off between these two plant characteristics. (8) It is shown that the differences in nutrient turnover and productivity between Erica and Molinia may explain the replacement of Erica by Molinia in wet heathlands when nutrient availability increases.

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