Allelopathic interactions of invasive black locust (Robinia pseudoacacia L.) with secondary aliens: the physiological background.
Despite of numerous benefits, black locust (Robinia pseudoacacia L.) is an invasive tree species in Slovakia and Hungary. Recently, secondary local invasions of black locust plantations by black cherry (Prunus serotina Ehrh.) and common hackberry (Celtis occidentalis L.) have been observed in these countries. In this study, we describe these unique tree-to-tree interactions directly in the field as well as simulated in the laboratory (1% water extracts from leaves and twigs applied on leaf and soil). In the field, we observed no effect on tree height and trunk diameter as well as leaf metabolic parameters caused by black cherry. However, the laboratory experiment showed a reduction in nodulation, and thus N fixation rate per plant, which did not mirror in the shoot and root dry matter (DM) production. On the other hand, common hackberry significantly affected tree height as well as leaf amino acid and total nitrogen concentration, but not the content of soluble sugars and hydrogen peroxide in the field. The laboratory experiment revealed significant reductions in nodulation, N fixation rate per plant, shoot and root DM and leaf hydrogen peroxide, nevertheless, a noticeable soluble protein accumulation. Thus, we can conclude that common hackberry, but not black cherry, can effectively suppress black locust N metabolism and growth.