## 3 Results
### Daily Cycles of Fluorescence
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Date**} & **PAR** & **Fs** & **Fm** & **ASP/687** & **ASF/760** \\  & **(umol-m\({}^{-2}\).s\({}^{-1}\))** & **(a.u.)** & **(a.u.)** & **(a.u.)** & **(mm\({}^{-1}\)**10\({}^{-4}\))** & **(mm\({}^{-1}\)**10\({}^{-4}\))** \\ \hline
2010/04/29 (DOY 119) & & (\(n=20\)) & (\(n=20\)) & (\(n=20\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1159 & 0.377 & 0.6 & 0.367 & 0.37 & 1.14 \\ Rel. var. non/morning & \(-14\%\) (**) & \(-25\%\) (**) & \(-25\%\) (**) & \(12\%\) (**) & \(-3\%\) (**) \\ \hline
2010/05/13 (DOY 133) & & (\(n=20\)) & (\(n=20\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1230 & 0.344 & 0.498 & 0.302 & 0.318 & 1.13 \\ Rel. var. noon/morning & & \(-12\%\) (*) & \(-16\%\) (n.s.) & \(-12\%\) (**) & \(11\%\) (**) & \(-11\%\) (**) \\ \hline
2010/05/17 (DOY 137) & & (\(n=19\)) & (\(n=19\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1257 & 0.359 & 0.534 & 0.328 & 0.325 & 1.08 \\ Rel. var. noon/morning & & \(-15\%\) (**) & \(-24\%\) (**) & \(-25\%\) (**) & \(15\%\) (**) & \(-3\%\) (*) \\ \hline
2010/05/20 (DOY 140) & & (\(n=20\)) & (\(n=20\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1288 & 0.347 & 0.513 & 0.321 & 0.341 & 1.12 \\ Rel. var. noon/morning & & \(-17\%\) (*) & \(-21\%\) (n.s.) & \(-11\%\) (**) & \(12\%\) (**) & \(-16\%\) (**) \\ \hline
2010/05/22 (DOY 142) & & (\(n=17\)) & (\(n=17\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1189 & 0.322 & 0.77 & 0.557 & 0.287 & 0.88 \\ Rel. var. noon/morning & & \(-7\%\) (n.s.) & \(-45\%\) (**) & \(-47\%\) (**) & \(4\%\) (**) & \(-10\%\) (**) \\ \hline
2010/05/29 (DOY 149) & & (\(n=32\)) & (\(n=32\)) & (\(n=32\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1327 & 0.194 & 0.387 & 0.474 & 0.345 & 1.04 \\ Rel. var. noon/morning & & \(-10\%\) (**) & \(-32\%\) (**) & \(-30\%\) (**) & \(6\%\) (**) & \(-5\%\) (**) \\ \hline
2010/06/02 (DOY 153) & & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1289 & 0.196 & 0.443 & 0.526 & 0.3\(\smallsetminus\)35 & 0.952 \\ Rel. var. noon/morning & & \(-4\%\) (n.s.) & \(-39\%\) (**) & \(-45\%\) (**) & \(27\%\) (**) & \(-4\%\) (**) \\ \hline
2010/06/04 (DOY 155) & & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1291 & 0.194 & 0.367 & 0.44 & 0.307 & 0.822 \\ Rel. var. noon/morning & & \(-13\%\) (**) & \(-37\%\) (**) & \(-44\%\) (**) & \(8\%\) (**) & \(-16\%\) (**) \\ \hline
2010/06/05 (DOY 156) & & (\(n=20\)) & (\(n=20\)) & (\(n=30\)) & (\(n=30\)) & (\(n=30\)) \\ morning & 1299 & 0.189 & 0.307 & 0.368 & 0.308 & 0.751 \\ Rel. var. noon/morning & & \(-20\%\) (**) & \(-40\%\) (**) & \(-52\%\) (**) & \(14\%\) (**) & \(-10\%\) (**) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Changes of fluorescence between morning ( 8:00 UTC) and noon ( 12:00 UTC) on sunny days. Fs: mean leaf fluorescence level measured with a PAM-2000; F\({}^{\prime}\)m: maximum fluorescence level of leaf upon a saturating pulse; \(\Phi_{P}\): leaf photochemical yield; number of samples as indicated; ASFY687 and ASFY760, apparent spectral fluorescence yield at 687 and 760 nm defined as the ratio between fluorescence radiance and incident PAR. Mean values between 8:00 and 8:30 (morning) and 12:00 and 12:30 (noon) are reported. Significance levels are indicated: n.s., \({}^{\prime}\)\(p<\) 0.05, \({}^{***}\)\(p<\) 0.01, \({}^{***}\)\(p<\) 0.001. The measuring distance on the leaf-clip was modified on DOY 149, so Fs and F\({}^{\prime}\)m measurements between DOYs 119–142 and DOYs 149–156 are not comparable. Figure 4: Relationship between PAR and sun-induced fluorescence (SIF) for different development stages and diffuse fractions of PAR (\(f_{diffPAR}\)). Two classes of LAI are represented: low—LAI ranges from approx. 0.8 to 6 (DOY from 62 to 119, blue and gray points); high—LAI is approx. 6 (DOY from 120 to 157, red and green points). Classes of diffuse fraction of PAR (\(f_{diffPAR}\)): low—clear sky days only, \(f_{diff/PAR}\) ranges from 0.15 to 0.5; high—\(f_{diffPAR}\geq\) 0.9.