| Summary: | In northern Sweden, the clonal dwarf shrub Empetrum hermaphroditum Hagerup exerts strong inhibitory effects on other plant species. These inhibitory effects may, at least in part, be attributed to the high production of the secondary metabolite, batatasin-III, which is released from leaves and transported to the soil by rain (throughfall) and snowmelt. Considerable amounts of batatasin-III are also added to the soil by senescent leaves and litter. The quantification of batatasin-III in soil solution throughout one growing season showed that the concentration was high both in early spring and in August, coinciding with the periods of snowmelt, maximum litter fall, and with higher production of batatasin-III in E. hermaphroditum foliage. Under laboratory conditions, batatasin-III was found to interfere with physiological functions of birch, Betula pendula L. When the birch seedlings were exposed to batatasin-III for a short period (i.e. two hours), dry weights were reduced by more than 70 %, even ten weeks after the treatment. The growth inhibition may be explained by the findings that batatasin-III interfered with both the photosynthesis and ammonium uptake. The interference of batatasin-III with membrane processes and the presence of batatasin-III in soil solutions throughout the whole growing season suggest that batatasin-III not only has the potential to inhibit soil microorganisms, but also to exert phytotoxic effects in field. Reducing growth of surrounding plants would be advantageous for E. hermaphroditum, since it is shade intolerant and competes with difficulty under a closed canopy.
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