SHORT-TERM ACCUMULATION OF ORGANIC-MATTER AND NUTRIENT CONTENTS IN 2 DRY SAND ECOSYSTEMS

Inland dunes in northwestern Europe support a number of dry vegetation types. These ecosystems are poor in nutrients and it has been suggest ed that accumulation of nutrients triggers succession in such systems. We studied the accumulation of organic matter and N and P over a 30 m onths period in two adjacent ecosystems, the Spergulo-Corynephoretum a nd the Genisto-Callunetum. Amounts of plant matter and soil organic ma tter significantly accumulated during the sampling period in the Genis to-Callunetum but not in the Spergulo-Corynephoretum. While nutrient c oncentrations of live and dead phytomass in the Spergulo-Corynephoretu m were significantly higher than in the Genisto-Callunetum, total nutr ient contents in the systems showed the opposite pattern. N and P conc entrations in litter were relatively high compared with the other frac tions of plant matter and the amount of N significantly increased in b oth ecosystems during the sampling period. Soil moisture contents show ed a seasonal pattern. It was highest in the top soil layer and higher in the Genisto-Callunetum than in the Spergulo-Corynephoretum. The es timated annual increase of total N in these two ecosystems was consist ent with rates of atmospheric N deposition (wet fall + dry fall) measu red in comparable Dutch sites.