## 3 Results and Discussion
### Average Photosynthesis Rate at Plant Level  
In the same way, Figure 8a-h presents the evolution of average photosynthesis rate in a line 10 cm above the plants during the day, for eight indicative days of the year. Again, in each graph, five lines are given corresponding to (i) \(\tau_{\text{n,PAR}}\) = 30% (green line continuous), (ii) \(\tau_{\text{n,PAR}}\) = 45% (red dashed line), (iii) \(\tau_{\text{n,PAR}}\) = 60% (brown dot-dashed line), (iv) \(\tau_{\text{n,PAR}}\) = 89%--bare cover (black dotted line), and (v) photosynthesis rate in open field (blue continuous line with blue circles). It should be noted that in the current simulation the side walls are considered opaque and the radiation enters the domain only through the arched roof. Figure 8: _Cont._  
The daily photosynthesis rate at the plant level is given for the examined days and for the examined cover/PV combinations is given in Table 10.  
The year-round mean values of the daily average photosynthesis rate simulated for the cases of OPV/cover combinations with normal PAR transmission of 30%, 45%, 60%, and 89% were 18.1, 21.3, 23.7, and 27.1, respectively. Based on the above findings, it could be seen that the reduction observed in the mean daily average photosynthesis rate (Table 10) due to the presence of the OPVs for the cases with normal PAR transmittance of 30%, 45%, and 60% in relation to the bare PE was 33%, 21%, and 12%, respectively. Similar results were also observed in the reduction of the cumulative daily photosynthesis rate. The results of a literature survey [33] showed that a 1% radiation reduction results in a 0.6% to 1.1% yield reduction in tomato crop, whereas interviews held with growers indicated values between \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Day**} & \multicolumn{3}{c}{**Daily Average [in \(\mu\)mol m\({}^{-2}\)d\({}^{-1}\)] and Cumulative [in Parenthesis,**} \\  & \multicolumn{3}{c}{**in 10\({}^{3}\)\(\mu\)mol m\({}^{-2}\)d\({}^{-1}\)] Photosynthesis Rate Values**} \\  & \(\tau_{\text{n,PAR}}\) = 30\% & \(\tau_{\text{n,PAR}}\) = 45\% & \(\tau_{\text{n,PAR}}\) = 60\% & \(\tau_{\text{n,PAR}}\) = 89\% \\ \hline
6 February & 17.71 (580) & 21.45 (713) & 24.04 (851) & 26.74 (962) \\
21 March & 19.41 (717) & 22.95 (870) & 25.15 (977) & 27.83 (1122) \\
6 May & 23.20 (996) & 25.63 (1073) & 27.02 (1178) & 28.64 (1358) \\
21 June & 24.29 (1071) & 26.30 (1197) & 27.43 (1275) & 28.80 (1373) \\
6 August & 24.06 (1045) & 26.10 (1174) & 27.28 (1256) & 28.70 (1363) \\
21 September & 23.09 (877) & 25.41 (990) & 26.78 (1062) & 28.46 (1157) \\
6 November & 16.04 (523) & 19.85 (655) & 22.63 (756) & 26.53 (910) \\
21 December & 13.09 (399) & 17.97 (549) & 21.05 (647) & 25.74 (801) \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Daily photosynthesis rate at plant level. Figure 8: Photosynthesis rate at plant level during the solar day for 8 indicative days of the year. (i) \(\tau_{\text{n,PAR}}\) = 30% (green line continuous), (ii) \(\tau_{\text{n,PAR}}\) = 45% (red dashed line), (iii) \(\tau_{\text{n,PAR}}\) = 60% (brown dot-dashed line), (iv) \(\tau_{\text{n,PAR}}\) = 89%—bare cover (black dotted line), and (v) photosynthesis rate in open field (blue continuous line with blue circles). 0.7% and 1.0%. It is difficult to survey the growth and yield reduction. Shading of a crop at high light intensities only slightly reduces photosynthesis of the upper leaves in the light saturation range. On the other hand, shading at low light intensities may change the net photosynthesis from positive to negative values, especially for the lower leaves. Accordingly, it could be also stated that photosynthesis is significantly affected by shading mainly in regions or periods with low radiation levels. [PERSON] and [PERSON] (2013) [34] studied the response of tomato to constraining the intensity of solar radiation. They found that although they reduced the PAR radiation by 57% and 34%, the measured plant dry matter increment decreased only by 31% and 19%, respectively, that is, light use efficiency increased markedly.