## 2 Results  
### Darkness Treatment Resulted in a Significant Decrease in Monoterpenoid Content in L. cubeba Fruits  
Light plays an important role in regulating the growth and development of plants. To investigate terpene content dynamics in _L. cubeba_ fruits under light and darkness, volatile organic compounds were analyzed by GC-MS. As shown in Figure 1A, no significant variation in terpenoid content was observed during light exposure (L1-L4), although terpenoid levels were marginally higher at the L3 stage (Light-12 h) than at the L1 stage (Light-0 h) (\(p>0.05\)). In contrast, darkness treatment resulted in a significant decline in terpene accumulation. Monoterpene levels declined from an initial 557 \(\mathrm{\mu g}\cdot\mathrm{g}^{-1}\) at D1 (Dark-0 h) to 498 \(\mathrm{\mu g}\cdot\mathrm{g}^{-1}\) at D2 (Dark-6 h), reaching a minimum of 372 \(\mathrm{\mu g}\cdot\mathrm{g}^{-1}\) at D3 (Dark-12 h). The monoterpene content at the D4 stage was 409 \(\mathrm{\mu g}\cdot\mathrm{g}^{-1}\). (Figure 1B). This demonstrates that light is necessary for terpenoid synthesis in _L. cubeba_. Studies have shown that over 90% of _L. cubeba_ essential oil consists of monoterpenoids, including \(\alpha\)-pinene, camphene, \(\beta\)-pinene, \(\beta\)-myrcene, D-limonene, eucalypttol, linalool, neral, and geraniad [11]. Here, we further analyzed the changes in the contents of these important monoterpenoids under light and darkness treatments. The retention times, chemical formulae, and changes in the contents of each compound in the L1 (Light-0 h) to L4 (Light-18 h) stages and the D1 (Dark-0 h) to D4 (Dark-18 h) stages are summarized in Tables S1 and S2, respectively. As shown in Figure 2, the content of each compound at the L2 (Light-6 h), L3 (Light-12 h), and L4 stages was compared with that at the L1 stage. Under light treatment, the contents of \(\alpha\)-pinene, camphene, and linalool were significantly increased in the L2 and L3 stages compared with those in the L1 stage. Specifically, the  
Figure 1: Changes of monoterpene content in _L. cubeba_ fruits under light and darkness treatments. (**A**) The monoterpenoid content of _L. cubeba_ fruits under light treatment (L1–L4). L2, L3, and L4 are compared with L1. (**B**) The monoterpenoid content of _L. cubeba_ fruits under darkness treatment (D1–D4). D2, D3, and D4 are compared with D1. All data are expressed as means \(\pm\) SD of three biological replicates (”_p_\(<0.05\), ***_p_\(<0.001\), Ns indicates that there is no significant difference.). \(\alpha\)-pinene content increased from 13.89 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L1 to 24.31 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L2 and 23.83 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L3. The content of camphene increased from 3.09 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L1 to 6.65 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L2, while that of \(\upmu\)g-pinene rose from 7.16 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L1 to 16.12 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L2, and then slightly decreased to 15.72 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at L3. Meanwhile, the contents of \(\upmu\)-myrrene, eucalypt, neral, and geranial showed no significant changes. We then investigated the changes in the contents of these monotereponids under darkness treatment (Figure 3). The content of each compound at the D2 (Dark-6 h), D3 (Dark-12 h), and D4 stages was compared with that at the D1 stage. The lowest content of \(\alpha\)-pinene was recorded at the D3 stage, decreasing from 18.15 \(\upmu\)g\(\cdot\)g\({}^{-1}\) (at D1) to 12.81 \(\upmu\)g\(\cdot\)g\({}^{-1}\), while that of \(\upmu\)-myrceene decreased from 48.53 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at D1 to 33.69 \(\upmu\)g\({}^{-1}\) at D3. The D-limonene content also decreased, dropping from an initial 96.01 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at D1 to 67.30 \(\upmu\)g\(\cdot\)g\({}^{-1}\) at D3. Additionally, citral content exhibited a significant reduction compared with D1.