## 4 Discussion  
### Plant Stress Indicators  
Although molecular methods are irreplaceable in discovering new traits, functions and other parameters [53], much cheaper and less time-consuming methods can be often  
Figure 8: \(Cy/pre\) PLFA stress indicators at the beginning and end of the vegetation periods (mean \(\pm\) SD, n = 4), the same letters above bars mark comparable groups according to Wilcoxon rank-sum test (\(p\) < 0.05) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**AGR**} & \multicolumn{2}{c}{**MIL**} & \multicolumn{2}{c}{**OIL**} \\ \cline{2-7}  & **Start** & **End** & **Start** & **End** & **Start** & **End** \\ \hline Respiration [mU/g dw] \({}^{\text{a}}\) & 3.63 \(\pm\) 0.55 a & 2.78 \(\pm\) 1.5 a & 3.17 \(\pm\) 0.55 a & 3.42 \(\pm\) 0.98 a & 6.35 \(\pm\) 1.30 b & 4.8 \(\pm\) 0.94 ab \\ Dehydrogenase [uU/g dw] \({}^{\text{a}}\) & 5.10 \(\pm\) 0.22 a & 0.82 \(\pm\) 0.5 b & 0.22 \(\pm\) 0.20 b & 0.69 \(\pm\) 0.26 b & 8.70 \(\pm\) 2.28 c & 0.71 \(\pm\) 0.64 b \\ Phosphatase [uU/g dw] \({}^{\text{b}}\) & 9.81 \(\pm\) 1.68 a & 25.30 \(\pm\) 2.63 b & 43.49 \(\pm\) 2.22 c & 14.95 \(\pm\) 2.45 a & 18.62 \(\pm\) 1.26 b & 21.93 \(\pm\) 4.12 b \\ Arylsulphatase [uU/g dw] \({}^{\text{b}}\) & 0.87 \(\pm\) 0.28 a & 1.15 \(\pm\) 0.16 a & 2.70 \(\pm\) 0.18 b & 0.39 \(\pm\) 0.09 c & 0.90 \(\pm\) 0.13 a & 0.66 \(\pm\) 0.24 ad \\ Protease [uU/g dw] \({}^{\text{b}}\) & 6.21 \(\pm\) 0.71 a & 9.63 \(\pm\) 1.04 b & 13.34 \(\pm\) 2.14 c & 8.47 \(\pm\) 1.71 ab & 13.99 \(\pm\) 0.64 c & 24.06 \(\pm\) 2.18 d \\ Glucosidase [uU/g dw] \({}^{\text{b}}\) & 2.41 \(\pm\) 0.47 a & 3.02 \(\pm\) 0.1 b & 5.03 \(\pm\) 0.24 c & 1.16 \(\pm\) 0.19 d & 1.45 \(\pm\) 0.06 d & 0.67 \(\pm\) 0.08 e \\ PLGA\({}_{\text{tot}}\) [mg/kg dw] \({}^{\text{b}}\) & 10.55 \(\pm\) 3.65 a & 14.56 \(\pm\) 3.76 a & 11.45 \(\pm\) 1.45 a & 16.13 \(\pm\) 3.17 a & 19.69 \(\pm\) 5.01 a & 22.64 \(\pm\) 7.34 ab \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Microbial and enzyme activities and microbial biomass (PLFAtot) (mean \(\pm\) SD, a = 8, b = 4), the same letters behind values mark comparable results (\(p\) < 0.05). used with satisfactory results for environmental studies like ours. In our case, even simple measuring of biomass parameters revealed differences in tested soils with the highest stress effect of OIL soil and mild effect of MIL soil, which led to decreased biomass production and changes in stem/leaf biomass ratio. Nevertheless, even if differences are not apparent at first sight, \(a\) plant can suffer from stress, which can be detected using more advanced methods [25; 30; 42; 54]. Measuring chlorophyll a fluorescence is one of the methods frequently used in plant studies because it is straightforward, inexpensive and fast. It also represents a sensitive tool for detecting changes in the photosynthesis process caused by different abiotic stress factors [54]. Generally, the values of indexes that were calculated in this study were similar to those measured for plants growing in non-contaminated compost with the same method [44]. That is consistent with previously published results showing that metal contamination does not affect _Mxg_ photosynthetic efficiency. In the study of [PERSON] et al. [55] miscanthus was grown on Pb, Cd, Zn contaminated soil with higher metals concentration than in our case with quantum yield value (Fv/Fm) close to 0.8, which is considered as a reference value for non-stress plants measured without using pre-illumination [56]. The same result was obtained by [PERSON] et al. [7] for miscanthus grown in mine tailing ponds with a high concentration of Zn, Cu and Pb. [PERSON] et al. [6] determined even slightly higher median values of Fv/Fm for miscanthus grown in post-mining mud waste soils highly contaminated by As, Pb and Sb compared to uncontaminated compost. On the other hand decrease of Fv/Fm was observed by [PERSON] et al.