Yearly variation in allelopathic compound production along a climatic gradient. A case of study of Empetrum nigrum

Empetrum nigrum is a plant common in northern ecosystems with capacity to produce allelopathic compounds, which among other effects inhibit seed establishment and germination of other plants. Some of the most studied compounds regarding this effect are batatasin-III and phenolic acids, among them caffeic acid, which account for a large proportion of the leaf’s biomass. 5 random sites were established following a climatic gradient, and first year shoots were collected during 7 years. The plant’s antioxidant effect was studied as proxy of allelopathy, and shoot length was measured for the possible trade-offs between production of secondary metabolites and growth. The effect of climatic variables on the production of batatasin-III and caffeic acid was assessed, and the plant’s antioxidant activity and shoot growth were studied in accordance to the metabolite production and the weather conditions. Plants had higher concentration of batatasin-III in sites with low temperature, high number of freezing days during winter or both. Nevertheless, a positive relation between temperature and production of batatasin-III was found at the site level. Caffeic acid and antioxidant activity were positively related, however neither the weather variables studied explained their pattern. Shoot length was related to the year air temperature, but not to the production of batatasin-III or caffeic acid. In conclusion, this study shows that an increase of yearly temperature is likely to lead to an increase in batatasin-III production at the site level, but that no effect would happen to the growth of first year shoots. We were not able to find any impact of weather conditions on concentration of caffeic acid and on antioxidant activity