## 3 Results and Discussion  
Magnesium is involved in many physiological and biochemical processes in plants, contributing mainly to photosynthesis and the transport of photo-assimilates [40; 41]. Mg deficiency can have a negative effect on plant biomass production, since the transport of sucrose from source leaves to sink organs is inhibited [42; 43]. On the contrary, the total fresh and dry weight of the sweet orange plants of the present study was not significantly affected by the concentration of Mg in the nutrient solution (Table 1). However, the plants irrigated with the solution containing 48 mg Mg L\({}^{-1}\) achieved the highest values of the total fresh and dry plant weight, while those treated with the highest Mg concentration presented the lowest ones (Table 1). Mg deficiency affects the uptake of nutrients and their concentrations in stems, leaves, and roots [20]. According to the results, the concentration of Mg in the nutrient solution was significantly and positively correlated [r = (+0.464, \(p<0.01\)) - (+0.802, \(p<0.001\))], with the concentration of Mg (leaves, scion's and rootstock's stems, roots), Ca (rootstock's stem), K (roots), and Fe (leaves, rootstock's stem), the total absorption of Mg, and the ability of plants to use Mn and Fe more efficiently (Table 2). However, the concentration of Mg in the nutrient solution was correlated significantly and negatively [r = (\(-0.371\), \(p<0.05\)) - (\(-0.808\), \(p<0.001\))], with the concentration of Mn (rootstock's stem, roots), Ca (leaves, scion's stems, roots), and Fe (roots), the total absorption of Mn, Fe, P, K, and  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline  & & & & & & & \\ \hline \multicolumn{2}{c}{**Mg Concentration of the Nutrient Solution (mg L\({}^{-1}\))**} \\ \multicolumn{2}{c}{**Parameter**} & **0** & **12** & **24** & **48** & **96** & **192** \\ \hline \multirow{4}{*}{Mg} & Leaves & 0.26 \(\pm\) 0.03 d 1 & 0.30 \(\pm\) 0.05 d & 0.33 \(\pm\) 0.03 bc & 0.36 \(\pm\) 0.02 b & 0.37 \(\pm\) 0.04 ab & 0.40 \(\pm\) 0.03 a \\  & Scion’s stems & 0.19 \(\pm\) 0.02 d & 0.21 \(\pm\) 0.02 bc & 0.21 \(\pm\) 0.01 bc & 0.23 \(\pm\) 0.02 b & 0.22 \(\pm\) 0.02 bc & 0.33 \(\pm\) 0.06 a \\  & Rootstock’s stem & 0.09 \(\pm\) 0.01 b & 0.09 \(\pm\) 0.01 b & 0.09 \(\pm\) 0.01 b & 0.10 \(\pm\) 0.01 a & 0.10 \(\pm\) 0.01 a & 0.11 \(\pm\) 0.01 a \\  & Roots & 0.28 \(\pm\) 0.03 bc & 0.27 \(\pm\) 0.03 c & 0.30 \(\pm\) 0.02 bc & 0.30 \(\pm\) 0.02 bc & 0.31 \(\pm\) 0.03 a & 0.34 \(\pm\) 0.04 a \\ \hline \multirow{4}{*}{Ca} & Leaves & 2.67 \(\pm\) 0.14 a & 2.27 \(\pm\) 0.13 a & 2.66 \(\pm\) 0.09 a & 2.44 \(\pm\) 0.14 b & 2.46 \(\pm\) 0.15 b & 2.19 \(\pm\) 0.08 c \\  & Scion’s stems & 1.52 \(\pm\) 0.19 ab & 1.65 \(\pm\) 0.19 a & 1.62 \(\pm\) 0.25 a & 1.37 \(\pm\) 0.09 bc & 1.50 \(\pm\) 0.13 a & 1.27 \(\pm\) 0.17 c \\  & Rootstock’s stem & 0.89 \(\pm\) 0.07 b & 0.53 \(\pm\) 0.04 b & 0.93 \(\pm\) 0.08 b & 0.97 \(\pm\) 0.12 b & 0.96 \(\pm\) 0.06 b & 1.06 \(\pm\) 0.04 a \\  & Roots & 1.25 \(\pm\) 0.09 a & 1.25 \(\pm\) 0.16 a & 1.22 \(\pm\) 0.09 a & 1.25 \(\pm\) 0.09 a & 1.23 \(\pm\) 0.09 Ca, and the ability of plants to use Mg more efficiently (Table 2). According to [PERSON] (1974) [44], increasing the availability of Mg also negatively affected the absorption of Ca and K uptake by peanut plants, whereas P absorption was not affected. Given the existence of significant negative interactions between the availability of Mg in the rhizosphere and the total absorption of some other nutrients (K, P, Ca, Mn, Fe), as well as their concentrations in the leaves (Ca), great attention is required regarding the applied doses of Mg fertilizers. Higher concentrations of Mg were recorded in the leaves of the plants, followed by the roots, the stems of the scion, and the stem of the rootstock (Table 1). In addition, concentrations of Mg in all plant parts were significantly higher when the plants were irrigated with the nutrient solution containing 192 mg Mg L\({}^{-1}\), compared to 0-48 mg Mg L\({}^{-1}\) (Table 1).