## 4 Discussion  
The results showed that with the increase in PAR, the Pn and WUE of each growth period decreased and increased rapidly in the range of low light intensity 0-200 mmol-m\({}^{-2}\).s\({}^{-1}\) and even decreased slightly after the inflection point (light saturation point), which indicated that PAR was the main limiting factor of photosynthesis under low light intensity. When the light intensity exceeded a certain value, it began to decrease. With the emergence of strong light, the cotton leaves were unable to absorb and utilize the high light intensity. At the same time, the enzymatic reaction rate in the process of CO\({}_{2}\) assimilation limited the photosynthetic rate. The response curve of the CK treatment was the highest and that of CM3 was the lowest in each growth period, which was due to the shade created by the jujube trees. This is consistent with the results of [PERSON] et al. [4]. WUE is an index used to measure the ability of plants to adapt the environment under the same environmental conditions [34]. The WUE showed a rapid upward trend in the low light intensity range, indicating that the cotton supplemented the photosynthetic reaction substrate by rapidly increasing the WUE and Tr gas exchange rate to adapt to the weak light environment, which was consistent with the Pn results. The light-response curves of Gs and Tr showed a linear relationship, and CM2 obtained better results compared to the other two intercropping treatments. The trend in the Ci response curve was opposite to that of Pn, which decreased rapidly at first and then increased slowly. [PERSON] [35] obtained similar results. The Ci response curve of CM3 was higher than that of the other treatments, indicating that the CO\({}_{2}\) concentration of CM3 was high and the utilization rate of light energy was low. Thus, an appropriate intercropping configuration can improve the light-response curve of cotton. A number of studies [6; 36] have shown that the closer the distance to the jujube trees, the greater the competition and the smaller and thinner the leaves of edge cotton, as the intercepted light and light-use efficiency of the edge plants are impacted. The photosynthetic characteristic parameters calculated using the fitting curve can better reflect the utilization efficiency of cotton leaves to light energy. LSP and LCP reflect the adaptability of cotton leaves to strong light and weak light. High LSP and low LCP  
Figure 12: Principal component analysis for different configuration treatments. LSP: light saturation point; LCP: light compensation point; Pmax: the maximum net photosynthetic rate; AQE: apparent quantum efficiency; Rd: dark respiration rate; LER: the land equivalent ratio; Bw: single bell weight; Lp: lint percentage; Bpp: boll number per plant; Dwpp: dry weight per plant. mean that cotton leaves have strong adaptability to light intensity, and vice versa [37]. The results showed that the light saturation point LSP of the CK treatment was the highest in the cotton seedling period and budding period, and the LSP of the CM2 treatment was the highest in the flowering and boll development period and maturation period, indicating that the CK and CM2 treatments had strong adaptability to light intensity. With crop growth, the LCP gradually decreased with the CK and CM1 treatments while it decreased first and then increased with the CM2 treatment. Cotton was better able to use strong light at the flowering and boll development period and had the best adaptability to weak light at the seedling period (Table 1). Pmax represents the maximum photosynthetic capacity and the maximum assimilation capacity of leaves [38]. With the aging of the cotton leaves, the Pmax of each treatment was significantly reduced. The CK treatment generated the largest Pmax in each growth period, with the highest value of 33.6.