## 3 Results  
### Influence of Black Cherry Volatiles on Pine Seed Germination and Seedling Growth  
In the germination bioassays, the volatiles from _P. serotina_ fresh leaves did not cause any significant effect on _P. sylvestris_ germination (Table 1). The strongest phytotoxic effect on Scots pine seedlings was caused by volatiles emitted from leaves collected in April compared to the response of seedlings to VOCs from _P. serotina_ leaves collected in June and August (Figure 1). In addition, the growth of seedlings decreased with increasing April leaf biomass of the black cherry. With 40 g of _P. serotina_ leaves, the reduction of root length and stem height of _P. sylvestris_ young plants was 48.3% and 19.5%, respectively, compared to the same growth parameters for the control. Black cherry leaves collected in June showed a weaker but still significant inhibitory effect both on roots (20.4%-25.7%) and on stems (4.1%-9.5%) of Scots pine seedlings. In the case of volatiles emitted from August leaves only, a reduction of seedling root growth was observed (11.1%-12.6%).  
The growth response of the root of _P. sylvestris_ seedlings differed significantly depending on the month of _P. serotina_ leaf collection; it was the strongest in the presence of leaves collected in April and the weakest for August leaves (Figure 1). Moreover, root growth inhibition increased with leaf weight from 10 g and 20 g to 40 g. Differences in pine stem growth were found only for the 40 g weight of black cherry leaves. Volatiles from black cherry leaves collected in April caused more negative effect on seedling height than leaves from other collection dates.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Control**} & \multicolumn{2}{c}{**April**} \\ \cline{3-4}  & & **10 (g)** & **20 (g)** & **40 (g)** \\ \hline Germination capacity (\%) & 95.3 \(\pm\) 0.16 a & 90 \(\pm\) 0.26 a & 90.7 \(\pm\) 0.28 a & 88 \(\pm\) 0.22 a \\ Root length (mm) & 42.8 \(\pm\) 0.89 a & 28.3 \(\pm\) 0.81 b & 24.07 \(\pm\) 1.29 c & 22.13 \(\pm\) 1.16 c \\ Stem height (mm) & 50.9 \(\pm\) 0.80 a & 49.73 \(\pm\) 0.88 a & 44.73 \(\pm\) 1.28 b & 41 \(\pm\) 1.49 b \\ \hline \hline \end{tabular} \
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Control**} & \multicolumn{2}{c}{**June**} \\ \cline{3-4}  & & **10 (g)** & **20 (g)** & **40 (g)** \\ \hline Germination capacity (\%) & 95.3 \(\pm\) 0.16 a & 92.7 \(\pm\) 0.25 a & 90 \(\pm\) 0.24 a & 90 \(\pm\) 0.24 a \\ Root length (mm) & 42.8 \(\pm\) 0.89 a & 34.07 \(\pm\) 0.98 b & 32.8 \(\pm\) 0.95 b & 31.8 \(\pm\) 1.38 b \\ Stem height (mm) & 50.9 \(\pm\) 0.80 a & 48.8 \(\pm\) 0.55 ab & 46.07 \(\pm\) 0.97 b & 47.07 \(\pm\) 0.86 b \\ \hline \hline \end{tabular}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Control**} & \multicolumn{2}{c}{**April**} \\ \cline{3-4}  & & **10 (g)** & **20 (g)** & **40 (g)** \\ \hline Germination capacity (\%) & 95.3 \(\pm\) 0.16 a & 94 \(\pm\) 0.19 a & 92 \(\pm\) 0.24 a & 91.3 \(\pm\) 0.16 a \\ Root length (mm) & 42.8 \(\pm\) 0.89 a & 38.07 \(\pm\) 1.13 b & 40.73 \(\pm\) 1.13 b & 37.4 \(\pm\) 0.9 b \\ Stem height (mm) & 50.9 \(\pm\) 0.80 a & 49.2 \(\pm\) 0.54 a & 48.47 \(\pm\) 1.01 a & 47.2 \(\pm\) 1.4 a \\ \hline \hline \end{tabular}
\end{table}
Table 1: Effect of volatiles released by _Prunus serotina_ leaves (10, 20 and 40 g), collected in three months of the growing season (April, June and August), on germination and growth parameters of _Pinus sylvestris_ seedlings. Data are mean \(\pm\) SE. Different letters (a, b, c) following values in rows indicate significant differences for different weight of _P. serotina_ leaves determined in Tukey HSD or Kruskal-Wallis tests, with \(p\leq\) 0.05; n = 15.