PRELIMINARY RESULTS ON ENZYMATIC ACTIVITIES IN TWO SALT MARSH SOILS DIFFERING IN HYDROMORPHIC CHARACTERISTICS AND VEGETATION COVER

Salt marsh soils are characterized by temporary hydric saturation and by vegetation cover that is dominated by different salt-tolerant plant species depending on factors such as duration of submersion. The composition of microbial communities is an essential component of trophic dynamics and biogeochemical processes in salt marshes and determines the activities of enzymes that catalyze the conversion of complex molecules into simpler ones. However, enzymatic activities have not yet been investigated in salt marsh soils. The aim of this study was to analyze the activities of some oxidoreductase and hydrolase enzymes in two salt marsh soils affected by different levels of water saturation and covered by vegetation dominated by different plant species [Juncus maritimus Lam and Spartina maritima (Curtis) Fernald]. The enzyme activities were measured both in air-dried (only) and in air-dried, re-moistened soil samples. The activities in soils under both types of vegetation were much lower than usually found in terrestrial ecosystems. However, in the air-dried samples, the enzyme activities were higher in the soil under Juncus than in the soil under Spartina and tended to decrease with depth, particularly in the former. The activities of all enzymes considered tended to be higher, throughout the whole soil profile, in the re-moistened than in the air-dried soils, especially in the soil under Spartina. Hydrolase activity was strongly and positively related to organic matter content in both air-dried and re-moistened soil samples, particularly in the latter. By contrast, oxidoreductase activity was generally only related to organic matter content in the re-moistened soil samples. Further studies, preferably with freshly collected soil samples, are required to clarify the relationship between enzymatic activities and environmental conditions.