Soil acid phosphomonoesterase activity and phosphorus forms in ancient and post-agricultural black alder [Alnus glutinosa (L.) Gaertn.] woodlands

Black alder, an N-fixing tree is considered to accelerate the availability of phosphorus in soils due to the increased production of phosphatase enzymes, which are responsible for the P release from the litter. Acid phosphatase activity plays a pivotal role in organic P mineralization in forest soils and in making P available to plants. In order to check whether <em>Alnus glutinosa </em>stimulates acid phosphomonoesterase (PH_ACID) activity, we compared enzyme activities, total P concentration (P_TOT), plant-available P (P_AVAIL), organic P (P_ORG) and inorganic P (P_INORG), and organic matter content in 27 ancient and 27 post-agricultural alder woods (the latter ones representing different age classes: 11-20, 21-40 and 41-60 years) of soil samples taken from the litter and the mineral layers. Phosphomonoesterase activity, organic matter, P_TOT, P_INORG and P_ORG concentrations were significantly higher in ancient alder woods than in the soils of post-agricultural forests. Significant differences in the acid phosphatase activity, organic matter and P_AVAIL concentration were noted between the litter and mineral layers within the same forest type. In recent stands the amount of organic matter and phosphatase activity increased significantly with the age of alder stands, although only in the mineral layer of their soils. Phosphomonoesterase activity, organic matter and P_AVAIL content were higher in a litter layer and decreased significantly at a mineral depth of the soil. The acid phosphatase activity was significantly correlated with organic matter content in both ancient and recent stands. There was no significant relationship between PH_ACID activity and any P forms.