## 4 Discussion
Our laboratory study shows that benzaldehyde is the main component of VOCs emitted by fresh black cherry leaves and its content ranged from 99% of the fraction in spring to 97% at the end of summer. [PERSON] and coauthors [38] reported that benzaldehyde and/or its derivatives also predominate in the leaf essential oil compositions of other _Prunus_ species. The lower benzaldehyde emission from senescing leaves demonstrated by the authors mentioned is consistent with the results of our analyses. The allelochemical content may vary during the growing season, which is reflected by seasonal changes in plant phytotoxicity [39]. Benzaldehyde is formed following the enzymatic hydrolysis of prunasin, a cyanogenic glycoside present in _Prunus_ sp., which is a well-known defense compound produced as a chemical defense against herbivores [40; 41]. In the intact plant, prunasin is stored separately from hydrolytic enzymes. As a result of tissue disruption it is degraded to benzaldehyde, glucose and hydrogen cyanide (HCN) by the sequential action of the \(\beta\)-glucosidase prunasin hydrolase and mandelonitrile lyase [42]. Additionally, the research of [PERSON] [43] indicates that enzymatic hydrolysis of prunasin, with HCN emission, occurs not only in response to damage by external factors, but also as a result of naturally occurring processes controlling flower development. During the preparation of our experiment, separation of the petioles from black cherry twigs probably triggered the activation of several plant defense mechanisms simultaneously. This is evidenced by the noticeable presence in volatile compound profile of jasmone and green leaf volatiles (GLVs) such as 1-hexenol, 2-hexen-1-ol, 2-hexenal and 3-hexenal, which are emitted only in trace amounts in unstressed plants [44]. In addition, damage to the plant caused prunasin degradation, resulting ultimately in the simultaneous formation of benzaldehyde, present in the composition of VOCs and HCN, was not tested by us. Hydrogen cyanide impedes seed germination and the plant growth rate due to inhibition of respiratory functions in cells [45]. The negative effect of benzaldehyde, manifested in limiting the root growth, was previously observed in _Brassica campustis_ seedlings [46], which was associated with a disturbance in absorption of available nitrogen forms [47]. In the composition of _P. serotina_ volatile organic compounds, we also detected linalool and \(\beta\)-caryophyllene, two compounds with confirmed allebotathic effects that are emitted in low quantities from undamaged leaves [48]. The photovoltaic effect of \(\beta\)-caryophyllene has been observed in relation to seeds and seedlings of cultivated plants such as _Brassica rapa_ L., _Raphanus sativus L., _Solanum Iyopersicum_ L. [49; 50] and _Lactuca sativa_ L. [28]. Due to the confirmed presence of this compound, both in the sesquiterpene fraction from foliage of _P. serotina_[51] and _P. sylvestris_ needles [52; 53], it was not included in our study research. Linalool, one of the major compounds in essential oils of numerous spinc plants, is a monoterrene with significant phytotoxicity for several crop species (_Lactuca sativa_, _Allium cepa_ L., _Hordeum spontaneum_ [PERSON], _Secale cereale_ L.) and weeds (_Sinapis arrenesis_ L., _Amaranthus retroflexus_ L., _Chemopodium albun_ L., _Runex crispus_ L.) [27]. Detailed research by [PERSON] et al. [54] showed the possible mechanism of the negative effect of synthetic linalool on germination and growth of _Cassia occidentalis_ (L) Link seedlings. Treatment with this monoterpene causes a reduction in the chlorophyll content of the cotyledonary leaves and a weakening of the respiratory ability of growing seeds. Our results demonstrated that linalool adversely affects the germination and growth of _P. sylvestris_ seedlings and therefore could account for the observed phytotoxicity imparted by total leaf volatiles from _P. serotina_ leaves.