## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Dry Weight (kg)**} \\ \hline
**Substrate** & **Height (cm)** & **Aboveground** & **Belowground** & **Total** & **Shoot/ Root** & **DW/ FW** & **Leaf Area (m\({}^{2}\))** \\ \hline Control & \(128\pm 2.5\) a & \(0.46\pm 0.05\) a & \(0.14\pm 0.02\) a & \(0.60\pm 0.03\) a & \(3.31\pm 0.78\) ns & \(0.53\pm 0.01\) ns & \(0.92\pm 0.02\) a \\ A & \(104\pm 7.0\) b & \(0.31\pm 0.03\) b & \(0.08\pm 0.01\) b & \(0.39\pm 0.02\) b & \(3.57\pm 0.49\) ns & \(0.55\pm 0.02\) ns & \(0.61\pm 0.07\) b \\ B & \(113\pm 9.5\) ab & \(0.34\pm 0.03\) b & \(0.11\pm 0.01\) ab & \(0.45\pm 0.02\) b & \(3.24\pm 0.60\) ns & \(0.53\pm 0.02\) ns & \(0.66\pm 0.10\) b \\ C & \(110\pm 4.0\) b & \(0.33\pm 0.04\) b & \(0.09\pm 0.02\) b & \(0.42\pm 0.05\) b & \(3.60\pm 0.30\) ns & \(0.55\pm 0.01\) ns & \(0.76\pm 0.08\) ab \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average (\(\pm\)standard deviation) growth measures in _Photinia x/raseri_ plants (n = 4), growing on 3S:1 GW (A), 1S:1 GW (B), and 1S:3 GW (C)-based growing media. Different letters indicate statistically different values amongst substrates, according to the one-way ANOVA followed by [PERSON]’s test (\(p\leq 0.05\)). ns = not significant. into CO\({}_{2}\) by microbial metabolism [1] ([PERSON] 2018). However, such a decrease could be limited in co-compost with high S amount due to the low content of less degradable carbon sources in the S [17] ([PERSON] et al., 2023). In fact, the TOC significantly reduced only in pile C, while in the other piles, the TOC reduction was not statistically significant. However, the trend of the respiration rate better highlighted that the organic degradation occurred in all piles: in fact, after the first phase of the reduction in respiration rates, probably due to the microbial acclimatation to experimental conditions [51] ([PERSON] et al., 2015), the microbial respiration rate increased in all piles. The microbial respiration is positively correlated to the presence of the labile fraction of organic matter, stimulating the biological activities and the organic matter degradation [47; 51] ([PERSON] et al., 2015; [PERSON] 2023). Also, the reduction in TN occurred in pile C and it could be related to the release of ammonia, which could have phytotoxic effects [1] ([PERSON] et al., 2018). However, the germination test highlighted the absence of toxic effects in pile C, as well as in others, with values above 50%, thus the final co-compost resulted suitable for plant growth [18] ([PERSON] et al., 2020). This was also enforced by the metal concentrations below the legislation limits for the use of the co-compost as growing media [31] (D.Jgs. 75/2010). The eco-enzyme stoichiometry revealed the differences in microbial energy and nutrient limitation amongst piles. At the beginning of the process, in pile A, the microorganisms were N-limited as a result, showing an unbalance in the enzyme activities towards the N acquisition. This is also confirmed by the lower TN detected in A than in the other co-composts due to the high S content [14; 17] ([PERSON] et al., 2016; [PERSON] et al., 2023). The co-compost B in the starting phase showed P-limited conditions, in association with the higher abundance of bacteria and fungi than the other piles. The increasing percentage of GW in the co-compost (pile B) increased the presence of readily available compounds that could stimulate the microbial community, as the GW acted as an energy source increasing the microbial P demand [14; 17; 52] ([PERSON] et al., 2003; [PERSON] et al., 2017; [PERSON] et al., 2023). However, the high GW content (pile C) also led to microbial C and P limitations, probably due to the high amount of recalcitrant polymer (e.g., lignin) that reduce the accessibility to cellulose and hemicellulose. Because the lignin degradation is species-specific [4] ([PERSON] et al., 2021), the microbial abundance and growth reduced in pile C, thus the abundance of bacteria and fungi resulted similar to A.