# Upscaling Gross Primary Production from Leaf to Canopy for Potato Crop (_Solanum tuberosum_ L.)
## 3 Results
### Photosynthetic Behavior through the Canopy  
The response of the net assimilation rate to the incident photosynthetic photon flux density (PPFD) varied with canopy depth and leaf age. The leaves of the upper stratum presented the highest carbon assimilation (\(An\)) responses to PPFD. The largest \(An\) response to an incident PPFD was observed between 71 and 91 DPP. Maximum values around 23 \(\upmu\)mol (CO\({}_{2}\)) m\({}^{-2}\) s\({}^{-1}\) were obtained with PPFD higher than 900 \(\upmu\)mol (photon) m\({}^{-2}\) s\({}^{-1}\) (Figure 4a). The middle leaves had a lower response of net photosynthetic rate (\(An\)) to photosynthetic photon flux density than the upper stratum leaves. The highest responses of \(An\) to PPFD were observed between 71 and 77 DPP. In this canopy position, \(An\) leaf values of around 20 \(\upmu\)mol (CO\({}_{2}\)) m\({}^{-2}\) s\({}^{-1}\) were obtained with a PPFD greater than 800 \(\upmu\)mol (photon) m\({}^{-2}\) s\({}^{-1}\) (Figure 4b). The bottom leaves presented a limited (maximum average 9.7 \(\upmu\)mol (CO\({}_{2}\)) m\({}^{-2}\) s\({}^{-1}\)) net photosynthetic rate response to PPFD in all evaluated dates. Although the highest response to PPFD was observed between 77 and 105 DPP, the highest possible assimilation values (\(An\) < 15 \(\upmu\)mol (CO\({}_{2}\)) m\({}^{-2}\) s\({}^{-1}\)) were obtained at low PPFD values (500 \(\upmu\)mol (photon) m\({}^{-2}\) s\({}^{-1}\)) (Figure 4c). The declining tendency in net photosynthetic responses to PPFD was observed with leaf aging and canopy depth. The measured light response of \(An\) declined from the top (young and unshaded leaves) to the basal (old and most shaded leaves) within the potato canopy. Likewise, the net photosynthetic responses to PPFD were lower when canopy age was greater than 117 DPP in all canopy strata, revealing the impact of leaf age on potato leaf photosynthetic traits (Figure 4).  
The three models represented the variation of the photosynthetic traits with leaf aging and canopy depth well. The measured light-saturated net photosynthetic rate (\(A_{gmax}\)) and quantum yield of assimilation (\(\Phi\)) reached their maximum at full canopy development, around the maximum LAI stage (60-90 DPP), and then declined gradually as leaves senesced (Figure 5). Regarding canopy leaf position, the three models showed an \(A_{gmax}\) declination from the top to the bottom of the canopy, where the lowest carbon assimilation rates at light saturation were observed. In contrast, by comparison with upper canopy leaves, values for \(\Phi\) in the lower canopy were higher. The parameters \(A_{gmax}\) and \(\Phi\) calculated throughout [PERSON] ([PERSON]) [47] and Mitscherlich ([PERSON]) [49] models showed a similar trend and values for the three canopy strata. The values of \(A_{gmax}\) and \(\Phi\) obtained from [PERSON] ([PERSON]) [46] were higher and varied over a wider range. In  
Figure 4: Measured response of net photosynthetic rate (An) for potato (_Solanum Tuberosum_ L. Var. Diacol capiro) to photosynthetic photon flux density (PPFD) at different days post planting (DPP) on the bottommost shaded leaves (**left**), middle leaves (**center**), and the topmost unshaded leaves (**right**) of potatoes (_Solanum Tuberosum_ L. Var. Diacol capiro).  
addition, they presented variations in their behavior, easily observed in the leaves of the middle and lower canopy strata (Figure 5).