## 4 Discussion  
Currently, research on localized cooling techniques in greenhouses to mitigate heat stress has extensively explored crop physiological characteristics and stress damage mechanisms [4; 40]. A series of innovative root-zone cooling systems suitable for hydroponics or substrate-based cultivation have been developed [18; 41; 42], which are of significant importance in reducing costs and improving crop yields in climate-challenging regions. Previous studies have primarily emphasized the design and modification of system configurations, but the regulation methods have been relatively rudimentary. In this study, while refining the structural design of the system, emphasis was placed on precise management  
Figure 19: The overall appearance of plants from each area. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Group**} & **Root Fresh** & **Root Dry** & **Leaf Fresh** & **Leaf Dry** \\  & **Weight/g** & **Weight/g** & **Weight/g** & **Weight/g** \\ \hline Area A & 6.48 \(\pm\) 1.31c & 0.27 \(\pm\) 0.02c & 47.26 \(\pm\) 5.07b & 2.11 \(\pm\) 0.12c \\ Area B & 8.61 \(\pm\) 1.19b & 0.32 \(\pm\) 0.02b & 70.87 \(\pm\) 2.84a & 3.05 \(\pm\) 0.08b \\ Area C & 9.48 \(\pm\) 1.21a & 0.36 \(\pm\) 0.01a & 74.01 \(\pm\) 2.23a & 3.23 \(\pm\) 0.07a \\ \hline \end{tabular} Note: Means within each column followed by the same letters are not significantly different according to [PERSON]’s multiple range test at \(p<0.05\).  
\end{table} 
Table 5: Growth status of lettuce under different nutrient solution temperature treatments. of nutrient solution temperature. The NSTCS designed in this work achieved automatic temperature monitoring and operation of cooling devices. Under the control of the DBO-Fuzzy PID controller, the system demonstrated adaptive adjustment of the nutrient solution temperature. Compared to temperature control systems using conventional PID control, the proposed system exhibited more stable temperature regulation and enhanced adaptability to the high-temperature environment of greenhouses. This study focuses on the widely applied fuzzy PID control method and combines it with the novel DBO algorithm, achieving significant results. [PERSON] et al. optimized fuzzy PID parameters using the DBO algorithm [37], resulting in approximately a 40s reduction in stabilization time, a 7% decrease in overshoot, and the near elimination of steady-state error compared to standard fuzzy PID systems. Experimental validation demonstrated that this controller improved the overall temperature uniformity of four-bar targets and enhanced the detection accuracy of infrared thermography. Similarly, [PERSON] et al. integrated DBO with fuzzy PID control [43], revealing that the DBO-Fuzzy PID controller significantly reduced body acceleration under random disturbances compared to passive suspension systems. These findings collectively suggest that reasonable modifications to Fuzzy-PID algorithms can accelerate optimization of critical parameters, enhance control precision, and strengthen disturbance rejection capabilities-advantages that align closely with the results of the present study. When the nutrient solution temperature target was set at 22 \({}^{\circ}\)C, the system demonstrated superior cooling performance. Comparative analysis revealed 31.65% and 36.14% increases in root fresh weight and leaf fresh weight of lettuce, respectively, compared to non-cooled treatments. These results are consistent with findings from [PERSON] et al. [9], [PERSON] et al. [10], [PERSON] et al. [11], and [PERSON] et al. [15], who reported significant improvements in root and shoot biomass accumulation in lettuce through hydroponic nutrient solution cooling during high-temperature periods. As shown in Table 5, Area C exhibited greater biomass accumulation than Area B, a discrepancy potentially attributable to dissolved oxygen decline in Area B's nutrient solution during thermal elevation episodes, coupled with lettuce's high thermal sensitivity.