## 3 Results
### Extraction of Dissolved Inorganic N and P  
Real initial concentrations of NH\({}_{4}\)-N were 1.76 \(\pm\) 0.12 mg N L\({}^{-1}\) (0.13 \(\pm\) 0.01 mM N), of NO\({}_{x}\)-N were 61.50 \(\pm\) 4.72 mg N L\({}^{-1}\) (4.39 \(\pm\) 0.34 mM N) and of DIN-N were 63.26 \(\pm\) 4.82 mg DIN-N L\({}^{-1}\) (4.52 \(\pm\) 0.34 mM N). Orthophosphate concentrations were 3.09 \(\pm\) 0.15 mg PO\({}_{4}\)-P L\({}^{-1}\) (0.10 \(\pm\) 0.01 mM P). For each extraction cycle (1 week), the extraction efficiencies were calculated based on the difference between the final and initial concentrations (Figure 3). Using a repeated measures ANOVA, a significant main effect of plant density (F\({}_{(1,16)}\) = 5.97, \(p\) = 0.027, generalized \(\eta^{2}\) = 0.11), week (F\({}_{(21.08,\ 337.24)}\) = 13.86, \(p\) = 5.92 \(\times\) 10\({}^{-8}\), generalized \(\eta^{2}\) = 0.366) and plant density-week interaction (F\({}_{(21.08,\ 337.24)}\) = 5.98, \(p\) = 4.67 \(\times\) 10\({}^{-4}\), generalized \(\eta^{2}\) = 0.20) were observed regarding DIN-N extraction efficiencies over time (Figure 3A). Regarding the total quantity of DIN-N extracted during the totality of the experiment (Figure 4A), a main effect of plant density (_p_ < 0.05) was detected: high-density units extracted a total of 875.3 \(\pm\) 187.7 mg and low-density units extracted in total 686.4 \(\pm\) 94.2 mg. Overall, high-density units extracted more DIN-N on average than low-density units and extraction efficiencies (%) were: F110 = 21.6 \(\pm\) 1.8%; F220 = 26.3 \(\pm\) 6.9%; L110 = 21.8 \(\pm\) 4.1%; L220 = 29.1 \(\pm\) 5.1%. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Unit** & **F110** & **F220** & **L110** & **L220** \\ \hline _Growth per hydroponic unit_ & & & & & \\ Final biomass & g FW & 150.8 \(\pm\) 25.2 ac & 246.9 \(\pm\) 44.9 b  & 142.2 \(\pm\) 24.3 c  & 237.6 \(\pm\) 36.4 ab  \\ Final aboveground biomass & g FW & 128.5 \(\pm\) 21.8 a  & 210.7 \(\pm\) 40.4 b  & 121.9 \(\pm\) 22.5 a  & 202.9 \(\pm\) 32.1 b  \\ Final belowground biomass & g FW & 22.3 \(\pm\) 3.4 a  & 36.2 \(\pm\) 5.3 b  & 20.3 \(\pm\) 2.0 a  & 34.7 \(\pm\) 4.6 b  \\ Leaves & n & 1215 \(\pm\) 178 a  & 2050 \(\pm\) 344 b  & 1305 \(\pm\) 167 a  & 2176 \(\pm\) 284 b  \\ Stems & mm & 276.0 \(\pm\) 35.2 a  & 412.0 \(\pm\) 54.9 b  & 251.5 \(\pm\) 41.4 a  & 409.2 \(\pm\) 38.4 b  \\ Root: shoot ratio & - & 0.17 \(\pm\) 0.01 & 0.17 \(\pm\) 0.02 & 0.17 \(\pm\) 0.02 & 0.17 \(\pm\) 0.01 \\ Relative growth rate & mg g\({}^{-1}\) day\({}^{-1}\) FW & 21.1 \(\pm\) 2.1 & 18.1 \(\pm\) 2.5 & 20.3 \(\pm\) 2.3 & 17.8 \(\pm\) 2.1 \\ Productivity & g m\({}^{-2}\) day\({}^{-1}\) FW & 37.1 \(\pm\) 7.8 ac  & 56.6 \(\pm\) 14.0 b  & 34.4 \(\pm\) 7.6 c  & 54.0 \(\pm\) 11.5 ab  \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 2: Individual cumulative weight gain (_n_ = 5). Error bars represent standard deviations. After normalizing the total quantity of DIN-N removed to the total biomass produced (Figure 4C), the main effects of plant density (\(p<0.001\)) and artificial lighting (\(p<0.05\)) were detected: low-density units and LED units resulted in higher DIN-N extraction per gram of biomass produced. Pairwise comparisons show that F220 removed significantly less (\(p<0.01\)) DIN-N per gram of biomass (4.7 \(\pm\) 0.2 mg g\({}^{-1}\)) than either F110 (6.0 \(\pm\) 0.9 mg g\({}^{-1}\)) or L110 (6.4 \(\pm\) 0.6 mg g\({}^{-1}\)), yet the L220 extraction rates (5.5 \(\pm\) 0.3 mg g\({}^{-1}\)) were not significantly different from those of low-density units. Regarding the results of DIP-P extraction efficiency over time (Figure 3B), the significant main effects were also detected fromplant density (F\({}_{(1,16)}\)= 14.25, \(p=0.002\), generalized \(\eta\)2 = 0.35), week (F\({}_{(30.2,\,483.2)}\)= 111.60, \(p=1.37\times 10^{-19}\), generalized \(\eta^{2}\) = 0.738) and the 'plant density-week' interaction (F\({}_{(0.2,\,483.2)}\)= 7.77, \(p=4.60\times 10^{-4}\), generalized \(\eta^{2}\) = 0.16).