## 3 Results
### Responses to Recovery  
The SWC (Figure 3a) clearly recovered to the pre-drought (0-day drought level, namely, control treatment) condition in all drought treatments after five weeks of re-watering. They all reached identically high values, significantly higher than in the drought treatments from the 4-day drought level treatment onwards (\(p<0.001\)). \(A\) (Figure 3b) was higher and remained similar in the recovery treatment, particularly in the last three severe drought treatments. The mean of \(\mathrm{F_{V}/F_{M}}\) (Figure 3c) in the recovery treatment was significantly increased from the 7-day drought level treatment (\(p<0.001\)). Yield (Figure 3d) presented analogous changes with SWC, \(A\), and \(\mathrm{F_{V}/F_{M}}\) and increased from the 9-day drought level treatment (\(p<0.001\)). Both PRI (Figure 3e) and R690/R630 (Figure 3f) had no significant difference in the first four drought treatments with corresponding recovery treatments, but significantly increased from the recovery treatment of the 9-day drought level. The differential values of variables were calculated by subtracting nine drought levels treatments from corresponding recovery treatments to assess the changes of photosynthesis after one month of re-watering the plants of the drought treatment, and to evaluate the applicability of PRI and R690/R630 in detecting the recovery. The values of \(\Delta A_{\mathrm{recovery}}\), \(\mathrm{\Delta F_{V}/F_{Mrecovery}}\), and \(\mathrm{\Delta Yield_{recovery}}\) increased in conjunction with increasing \(\mathrm{\Delta SWC}\) and increasing drought levels (Figure 4). Both \(\mathrm{\Delta F_{V}/F_{Mrecovery}}\) and \(\mathrm{\Delta Yield_{recovery}}\) increased slowly in the last three drought levels. Changes in \(\mathrm{\Delta PRI_{recovery}}\) (Figure 4a) were consistent with \(\mathrm{\Delta A_{recovery}}\), \(\mathrm{\Delta F_{V}/F_{Mrecovery}}\), and \(\mathrm{\Delta Yield_{recovery}}\). \(\mathrm{\Delta R690/R630_{recovery}}\) (Figure 4b) also showed a gradual increase as with the other variables, with a high value in the 9-day drought level treatment. Figure 2: Relationships of \(A\) with PRI (**a**) and R690/R630 (**b**), and photochemical efficiency of PSII (\(\mathrm{\Phi PSI}\)) (\(\mathrm{F_{V}/F_{M}}\) and Yield) with PRI (**c**) and R690/R630 (**d**) for _Quercus__i__ex_. All the values are from Figure 1.  
Figure 4: Changes in differential \(A\) (\(\Delta A\)), \(\Delta\mathrm{F_{V}}/\mathrm{F_{M}}\), \(\Delta\mathrm{Yield}\), and \(\Delta\)SWC with \(\Delta\)PRI (**a**) and with \(\Delta\)R690/R630 (**b**) in response to nine different drought levels for _Quercus__ilex_. The differential values of variables calculated by subtracting the mean of nine drought levels treatment from corresponding mean of recovery treatments in Figure 3.  
Figure 3: Changes in SWC (**a**), \(A\) (**b**), \(\mathrm{F_{V}}/\mathrm{F_{M}}\) (**c**), Yield (**d**), PRI (**e**) and R690/R630 (**f**) in response to nine different drought levels and corresponding recovery treatments for _Quercus__ilex_. The significances were denoted as \({}^{+}\)\(p\)\(<\) 0.1, \({}^{*}\)\(p\)\(<\) 0.05, \({}^{**}\)\(p\)\(<\) 0.01 and \({}^{***}\)\(p\)\(<\) 0.001. Relationships of \(\Delta\)PRIrecovery and \(\Delta\)R690/R630 recovery with \(\Delta\)Arecovery, \(\Delta\)F\({}_{\mathrm{V}}\)/F\({}_{\mathrm{Mrecovery}}\), and \(\Delta\)Yieldrecovery  
Both \(\Delta\)PRIrecovery and \(\Delta\)R690/R630 recovery accounted for large proportions of the variability of \(\Delta\)Arecovery (\(R^{2}\geq 0.70\) and \(p<0.05\) for both, Figure 5a,b). \(\Delta\)PRIrecovery was highly significantly correlated with \(\Delta\)F\({}_{\mathrm{V}}\)/F\({}_{\mathrm{Mrecovery}}\) and \(\Delta\)Yieldrecovery (\(R^{2}\geq 0.85\) and \(p<0.001\) for both, Figure 5c).