Abstract By averaging in time and/or space, models predict less variable light patterns under tree canopies than in reality. We measured light every minute in 24 positions in a grid under different chestnut orchards, for several clear and overcast days. We also modelled this light with a purposely created 3D, spatially explicit, ray-tracing light interception model, where canopy porosity was calibrated to match measured daily light. Finally, we used both the measured and modeled light patterns transmitted under the tree canopies to estimate the daily net photosynthesis (An) and radiation use efficiency (RUE) of an understory wheat leaf. As expected, modeled light was more uniform than measured light, even at equal daily light. This resulted in large overestimation of daily An and RUE of the understory leaf. Averaging light in time increased the overestimations even further. A sensitivity analysis showed that this overestimation remained substantial over the range of realistic values for leaf photosynthetic parameters (i.e. Vc,max, Jmax, Rd) of the understory crop.

中文翻译：

---

通过在空间和时间上平均光，对树冠下的光进行建模会高估林下作物的净光合作用和辐射利用效率

摘要 通过对时间和/或空间进行平均，模型预测的树冠下的可变光模式比实际情况要少。在晴朗和阴天的几天里，我们每分钟测量不同栗园下网格中 24 个位置的光线。我们还使用特意创建的 3D、空间明确、光线追踪光拦截模型对这种光进行建模，其中校准冠层孔隙度以匹配测量的日常光。最后，我们使用测量的和模拟的树冠下传输的光模式来估计林下小麦叶子的每日净光合作用 (An) 和辐射利用效率 (RUE)。正如预期的那样，即使在相同的日光下，模拟光也比测量光更均匀。这导致林下叶的每日 An 和 RUE 大大高估。及时平均光进一步增加了高估。敏感性分析表明，这种高估在林下作物叶片光合参数（即 Vc,max, Jmax, Rd）的实际值范围内仍然很大。