Bohemian Knotweed Reynoutria × bohemica Chrtek et Chrtková Seems Not to Rely Heavily on Allelopathy for Its Persistence in Invaded Sites in the Southwest Part of the Zagreb, Croatia

Abstract

Notorious invasive Bohemian knotweed Reynoutria × bohemica Chrtek et Chrtková is a hybrid of two species, Reynoutria japonica Houtt. and Reynoutria sachalinensis (F. S. Petrop.) Nakai in T. Mori which spontaneously developed in Europe, outside the natural distribution of its parental species. Its success could potentially lie in its allelopathic activity, which was confirmed in a number of experiments conducted with the leaf and root exudates, testing their effect on the germination and growth of various test plants. Here, we tested its allelopathic potential using different concentrations of leaf exudates on two test plants, Triticum aestivum L. and Sinapis alba L., in Petri dishes and pots with soil and by growing test plants in the soil sampled in knotweed stands on the edges of stands and outside of stands. Tests in Petri dishes and pots with soil to which leaf exudates were added have shown a decrease in germination and growth in comparison to the control, hence confirming the allelopathic effect. However, this was not confirmed in a test with in situ soil samples, where no statistically significant differences were observed, neither in the growth of test plants nor in the chemical characteristics (pH, soil organic matter, humus content) of the soil. Therefore, the persistence of Bohemian knotweed at already invaded sites could be attributed to its efficient use of resources (light and nutrients) through which it outcompetes native plants.

Alelopatski učinek nekaterih invazivnih rastlin na kalivost in rast tatarske ajde (Fagopyrum tatricum)

“…Since Tartary buckwheat has high ecological adaptability and tolerance to nutrient-poor and other unfavourable conditions (Sofi et al, 2023;Zou et al, 2023), it is not surprising that its germination was not affected by the extract of F. japonica. On the other hand, the leaf extract of F. japonica significantly impaired the germination of common wheat (Triticum aestivum), especially at the highest concentration (0.05 g/mL), at which only one-third of the seeds germinated (Levačić et al, 2023).…”

Chemically Mediated Plant–Plant Interactions: Allelopathy and Allelobiosis

“…For example, spotted knapweed exhibited an allelopathic invasion in the western United States but not in eastern American grasslands [ 39 ]. Bohemian knotweed seems not to rely heavily on allelopathy for its persistence in invaded sites in the southwest part of Zagreb, Croatia [ 40 ].…”

“…In a compacted soil environment, ethylene accumulated in root tissues acts as a warning signal for roots to restrict root growth towards compacted soils [ 118 ]. Importantly, roots can chemically identify and respond to roots of conspecific and inter-specific neighbors and even self from non-self roots and kin from non-kin roots within a family [ 40 , 87 , 143 , 144 , 151 ], resulting in a series of root–root interactions that determine belowground ecological processes to a large extent. Any change in root–root interactions is likely to alter the soil resource availability, and subsequently, the plant fitness.…”